Production of Bioflocculant Using the Effluent from a Hydrogen-Producing Bioreactor and Its Capacity of Wastewater Treatment

J. Water Resource and Protection. 2008. 1: 1-65. Published Online June 2008 in SciRes (http://www.SRPublishing.org/Journal/jwarp/).

Production of bioflocculant using the effluent from a hydrogen-producing bioreactor and its capacity of wastewater treatment

Shuangshi DONG1, Nanqi REN1, Aijie WANG1, Fang MA1, Dandan ZHOU2 1School of Municipal and Environmental Engineering, Harbin Institute of Technology,Harbin, China 2School of Water Resource and Environment, China University of Geosciences, Beijing, China

Abstract

In this study, compound bioflocculant-producing bacteria, named F2-F6, were adopted as bioflocculant (BF) producer. In order to domesticate the strains of F2-F6 to utilize the effluent from a hydrogen-producing bioreactor as solely carbon resource, a method of poor-rich alternative nutrition was developed. After acclimation, the optimum fermentation conditions were investigated using only the effluent as culture substrate. The optimum fermentation conditions were to be initial pH of 7.0, fermentation time of 21 h, rotation speed of 140 rpm, temperature of 30 ℃ and no sterilization of the culture. Under these conditions, the maximum flocculation rate of the BF produced was over 93.0%. The molecular weight of BF was more than 106 g/mol according to the result of molecular exclusion chromatography. It was also found that the bioflocculant has high capacity of turbidity-removal, color-removal and organic-removal up to 98.7%, 90.3% and 62.6% respectively when it was used to treat domestic wastewater, black ink wastewater and Chinese medicine wastewater. Keywords: Bioflocculant-producing bacteria; Bioflocculant; Bioflocculant production; Bio-hydrogen effluent; Wastewater treatment

1. Introduction 3000 mg/l, which has the reuse potential. In this study, the acclimation and its fermentation conditions of Bioflocculant is one kind of microbial metabolic compound bioflocculant-producing bacteria, named F2- products. Its ingredients carry high contents of F6, were investigated, as well as the efficiency of glucoprotein [1,2,3], polyoses [4,5,6,7], protein [1,4,8], bioflocculant produced on several kinds of typical etc. In recent years, bioflocculant has attracted great wastewater. Furthermore, the organic components of attention due to its bio-degradability and the harmlessness bioflocculant were analyzed in chemical method. of their degradation intermediates toward the ecosystem [9]. Several bioflocculant produced from different 2. Materials and methods microorganisms have been reported recently which mainly focused on the bacteria such as paecilomyces 2.1. Microorganism variot [8], Aspergillus sojae [10], Rhodococcus erythropolis [11]. However, the high cost of culture In this study, the compound bioflocculant- producing medium is an obstacle in their commercial application bacteria, named F2-F6, were obtained from the [12]. In order to reduce the cost, the effluent from a Environmental Biotechnology key laboratory of Heilongjiang, China. Flocculation fraction (FF) of 93.1% hydrogen-producing bioreactor was used as substrate in [15] this study. Bio-hydrogen production technology was obtained in former study . developed by Nanqi REN [13,14] achieves wastewater 2.2. Culture medium treatment and hydrogen production simultaneously under ethanol-type fermentation, which was discovered in a Seed culture medium: It was used to incubate the F2-F6 continuous-flow reactor operated at a low pH value of and consist of distilled water 1000 mL, glucose 10g, 4.0–4.5 generates ethanol, acetate, H2 and CO2. But if K2HPO4 0.4 g, MgSO4·7H2O 0.2 g, carbamide 0.5 g, the effluent was discharged directly, it would do harm to KH2PO4 0.4 g, NaCl 0.1 g, yeast extract 0.5 g, at pH the environment. Furthermore, the COD of effluent from value 7.5 with sterilization for 30min under 112 ℃. hydrogen-producing bioreactor is usually higher than Culture medium foracclimation: It is the 150 mL mixture

2 S. DONG ET AL. of seed culture medium and effluent from bio-hydrogen 2.6. Analysis of bioflocculant component producing reactor with different ratio as follow: 9:1, 6.5:1, 4:1, 2:1, 1:1, 1:2, 1:4, 1:6.5 and 1:9. The content of Separation and purification of bioflocculant: 200 ml fermetation solution was placed in the centrifuge under K HPO and KH PO was maintained at 0.2% and 0.08%. 2 4 2 4 the speed of 10000 r/min for 12 mins to remove the Culture medium for fermentation: It was used to incubate bacteria. The sample was kept under the condition of 4℃ the F2-F6 and consists of distilled water 1000 mL, glucose for 12 h followed by double washing with 80% ethanol. 10 g, K2HPO4 0.4 g, MgSO4·7H2O 0.2 g, carbamide 0.5 g, Butanol and chloroform were used to remove the free protein. The sample was dissolved in double distilled KH2PO4 0.4 g, NaCl 0.1 g, yeast extract 0.5 g, at pH value 7.5 with sterilization for 30 min under 112 ℃. water after vacuous drying and then used for component analysis. 2.3. Flocculation test Items and methods of component analysis: Since Since The flocculation fraction was determined by performing protein, polyoses and nucleic acid were mostly found by bench-scale beaker tests. The experiments were carried other researchers, the items analysed were focused on out by an initial 30 s rapid mix (at 160 rpm) after the these three materials. Methods used in this research for addition of fermentation solution of 10 ml and 10% wt the component analysis of polyoses, protein and nucleic [17] [18] CaCl2 solution of 1.5 ml to 5 g/l Kaolin clay solution, in acid were phenol–sulfuric acid , Bradford , and which pH value was adjusted to 7.5, followed by 280 s ultraviolet spectro-photometry. slow mixing period at 35 rpm. The mixing speed was the Analysis by molecular exclusion chromatography (MEC): rotation speed of the stirrer paddle controlled by motor. After fermentation, the samples were diluted by 100 times Subsequently, the flocs were allowed to settle down for and then filtered by membrane (0.2μm). At last, the 20 min. Sample from the supernatant was collected and samples were injected into the sample bottles. The control optical density was determined at 550 nm with a samples were the effluent before fermentation. Samples spectrophotometer. A system with adding culture medium were analyzed using a Shimadzu LC-10A HPLC with a solution instead of fermentation solution was also R1D-10A differential detector (Shimadzu, Kyoto, Japan). prepared as the control simultaneously. Flocculation The compounds were separated on a μBONDAGEL E- fraction was calculated by Eq. (1): 125 column at 30℃. Sample volume of 20 μL was A − B FF= ×100% (1) injected throughout the study. The mobile phase used was A ultrapure water with a flow rate of 0.5 μl/min. Where A and B are optical densities of the control and 2.7. Wastewater treatment test sample, respectively, at 550nm 2.4. Acclimation procedure Bioflocculant produced was applied to deal with three kinds of wastewater. Domestic wastewater was from The method of poor-rich alternative nutrition was adopted resident area of Harbin Institute of Technology with pH to acclimatize the compound bioflocculant-producing of 6.6 and optical density at 550 nm (OD550) of 0.392. bacteria F2-F6 in order to improve the capacity of Black ink wastewater was made of pure black ink and tap bioflocculant production. In the first round, 15 ml water with OD550 of 0.193; its color was 310 PCU after degradation solution of F2-F6 with seed culture medium dilution with same volume water. Chinese traditional was added to culture medium for acclimation that its ratio medicine wastewater was from the 2nd Chinese was 9:1. 15 ml of fermentation solution from the first traditional medicine factory with pH of 4.4; its COD was flask was transferred to next ratio (6.5:1) culture medium 15800 mg/l. The experimental conditions were similar after 48 h fermentation. Analogy, they were transferred with those in flocculation test, but calcium chloride was from higher ratio to lower one every 48 h and then to the substituted by 0.2 mol/l aluminium chloride and the pH last ratio (1:9) culture medium, followed by back to value of the wastewater was as received. Color or COD of higher ratio (9:1) culture medium in the second round. supernatant was determined and then their removal Like the first round, the solution was transferred to lowest fractions were calculated as the way of Eq. (1). ratio (1:9) in the third round and was transferred to 100% 2.8. Items analyzed and their measurement effluent after three rounds acclimation. All the samples were in 250 ml flasks with cover of bacteria filters. All The absorbency of sample was determined at wavelength the transfers were operated in the aseptic cabinet. of 550 nm with a type 721 spectrophotometer. Color was Flocculation fraction of the fermentation solution in every measured by color meter (HANNA HI93727) and pH flask was determined every 12h, and the highest one for value was determined by pH meter (METTLER every flask was used to plot. TOLEDO 320). COD was measured with CTL-12 rapid response COD meter. 2.5. Identification of fermentation condition The optimum initial pH value of culture medium for 3. Results and discussion fermentation, fermentation time, temperature and rotation speed were determined by flocculation test. 3.1. Results of acclimation

The flocculation fraction of different ratio culture at rotation speed was turned out to be around 140 rpm. medium for acclimation was evaluated. Fig.1 illustrated Rotation speed of the shaker affects the dissolved oxygen flocculation fraction variation curves with three rounds concentration in the fermentation solution. Relative acclimation. At the first round acclimation, flocculation higher rotation speed will inhibite the formation of fraction descent from 84.6% to 11.4% along with decline bacterium aggregates and then conduct to flocculant of ratio of seed culture medium to the effluent. The production simultaneously [16]. Meanwhile, lower speed primary reason was that F2-F6 did not accommodate the cannot supply enough dissolved oxygen for bacteria change of environment so as to their multiplication rate growth and bioflocculant production. and producing bioflocculant ability lowered. At the same ratio of seed culture medium to the effluent between the 3.3. Results of component analysis and MEC first and the second round acclimation, flocculation After the component analysis to bioflocculant, the fraction increased obviously in the second round because nucleic acid matter was not detected because there was no F2-F6 gradually accommodated the environment and absorption peak at wavelength of 265 nm. It was also produced more bioflocculant. The flocculation fraction of found that the main components of bioflocculant were the third round acclimation did not increased much than protein and polyoses, and the content for them was 1.47% that of the second because of limited nutrition. The wt and 6.12% wt respectively. production of bioflocculant was almost the maximum and the flocculation fraction reached 50.3% at the rate of 1:9. Fig.3 showed the result of MEC. As can be seen, there was one more peak at 2.5 min in the after-fermentation

10 0 curve and no peak at 6 min which is in the before-

n fermentation curve. It showed that the bacteria utilized 80 the compound which formed the peak at 6 min to produce 60 the compound which formed the peak at 2.5 min and it 1s t was calculated that the molecular weight of former 40 2nd compound was between 180 g/mol and 386 g/mol and the

Flocculation fractio Flocculation (%) 3rd 6 20 latter compound was larger than 10 g/mol which benefit

0 capturing fine particles and other pollutants in wastewater. 9 ∶ 6.5∶ 41∶ 2 ∶ 1∶ 1∶ 1∶ 1∶1 1 According to the component of the effluent of the hydrogen-producing bioreactor, the molecular weight of Ratio of culture medium to the effluent sucrose is 342 g/mol and can be easily used by bacteria. Figure 1. Change of flocculation fraction to the Kaolin So sucrose was the main material that formed the peak at clay suspension in three rounds acclimation, applying 6 min and the large molecular weight material gave the bioflocculant with calcium chloride. peak at 2.5 min was bioflocculant.

3.2. Fermentation conditions 3.4. Results of wastewater treatment In Fig.2, optimum fermentation conditions were The optimal dosage of BF and aluminum chloride was examined, under the different initial pH value, time, and determined repetitively, during the experiments, while the temperature and rotation speed. During these experiments, pH value of wastewater treated was left unchanged. 5 ml fermented sample was added to the Kaolin clay solution, followed by the addition of 0.2 mol/l aluminum In particular, the respective optimal dosage to chloride. The optimal pH value and temperature for domestic wastewater for bioflocculant and aluminum flocculation of Kaolin clay solution were found to be chloride was 8 ml/l and 2.4 ml/l corresponding to flocculation fraction of 98.7%. However, the highest around 7.0 and 30 ℃. Under these conditions, the growth flocculation fraction of 91.3% was obtained when the of bacteria and production of bioflocculant were much aluminum chloride of 4 ml/l was used solely. This dosage better, especially for pH value. When the pH value was was much higher than that used with bioflocculant. For lower than 6.5, there was even no flocculation found for the treatment of black ink wastewater, it was similar with pH affects the activity of enzyme, nutrition utilization rate that of treatment of domestic wastewater. The respective and cell structure. Minus flocculation fraction is because optimal dosage for bioflocculant and aluminum chloride there were still some bacteria in the fermentation solution was 2 ml/l and 0.8 ml/l corresponding to color removal with no bioflocculant which increased the optical density rate of 90.3%. However, the highest color removal rate of of the kaolin suspension solution. 83.9% was obtained when the aluminum chloride of 1.4 It can be also observed in Fig. 2 that the optimum ml/l was used solely. But the dissimilarity was that the fermentation time was about 21 h, after that, the positive color removal rate was showed in aluminum flocculation fraction did not change much because of the chloride dosage of 1.6~2.4 ml/l. Because the limited nutrition, while, the highest flocculation fraction bioflocculant used here was fermentation solution which

Copyright © 2008 SciRes. J. Water Resource and Protection. 2008; 1:1-65 4 S. DONG ET AL. bacteria and culture meadium were also included, the medicine wastewater, the optimal dosage for dosage lower or higher than optimal one would induce bioflocculant was 8 ml/l corresponding to removal rate of the increasing of color. So, it was important to confirm 62.6%, when the dosage of aluminum chloride was 5 ml/l. the optimal dosage. During the treatment of Chinese

0.0015 0.0015 Before fermentation

0.0010

0.0005 Voltage(V) 0.0005

0.0000 Voltage (V) 0.0000

After fermentation -0.0005

-0.0005

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Time/min Figure 2. Molecular weight distribution of effluent before & after fermentation by means of molecular exclusion chromatography 100 100 80 80 60 60 40 FR( %) 20 40 FR( %) FR( 0 20 -20 Origin 5.0 6.0 6.5 7.0 7.5 Flocculation fraction (%) 3 6 9 12151821243648 Flocculation fraction (%) -40 (a) Initial pH (b) Time (h)

100 100 95 90 90

85 80 FR(%)

80 FR(%) 70 75

70 60 Flocculation fraction (%) Flocculation fraction (%) 24 27 30 33 36 100 120 140 160 180 (c) Temperature (℃) (d) Rotation speed (rpm)

Figure 3. Fermentation conditions of F2-F6 with the effluent from the biohydrogen-producing reactor: effect of different (a) pH value, (b) time, (c) temperature and (d) rotation speed.

100 100

80 80

0mL BF 3mL BF 60 60 40 0mL BF 2mL BF 4mL BF 5mL BF 40 flocculatin rate(%) flocculatin 20 4mL BF 6mL BF chroma removal rate(%) Flocculation fraction (%) 20 Flocculation fraction (%) 0 0 0.4 0.8 1.2 1.6 2 2.4 2.8 3.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 20 (a) Aluminum chloride dosage (ml) (b) Aluminum chloride dosage (ml)

60 Figure 4. Effect of bioflocculant and aluminum chloride dosage to the three 40 kinds of typical wastewater without adjustment of pH value: (a) domestic 20 wastewater, (b) black ink wastewater COD removal rate(%) and (c) Chinese medicine wastewater COD removal fraction (%) 0 1.0 2.0 3.0 4.0 5.0 6.0

black ink wastewater and 62.6% COD removal rate for Chinese medicine wastewater could be achieved. 4. Conclusion 5. Acknowledgment The following conclusion can be drawn from the present study: The authors thank the members of Environmental Biotechnology key laboratory of Heilongjiang, China for The bioflocculant-producing bacteria, F2-F6, could utilize the effluent of hydrogen production bioreactor. kind help and support. We acknowledge the fund of The results of three rounds acclimation show that the Department of Science & Technology of Heilongjiang bioflocculant produced had higher flocculation fraction province for financial support, under which this study from 11.4% to 50.3% on kaolin clay solution. was conducted. After acclimation, the optimum fermentation condition of F2-F6 using the original effluent of hydrogen 6. References production bioreactor as substrate was to be initial pH of 7.0, fermentation time of 21h, rotation speed of 140 rpm, [1] C. Choi, S. Yoo, I. Oh and and S. Park, temperature of 30℃. “Characterization of an extracellular flocculating substance produced by a plank tonic cyanobacterium, The component analysis show that the bioflocclant in Anabaena sp.,” Biotechnology Letters, vol. 20, pp. 643- this study contained protein (1.47%) and polyoses 646, July 1998. (6.12%). The results of molecular exclusion chromatography illustrated that its molecule was 106 [2] Z. Wang, K. Wang, Y. Xie and Y. Yao, “Studies on g/mol magnitude which helped to capture more fine bioflocculant-preducing micro-organisms, ” Acta particles in the water. Microbiologica Sinica, vol. 35, pp. 121~129, Feb. 1995. The efficiency of bioflocculant was examined in the [3] H. Yokoi, T. Yoshida, J. Hirose, S. Hayashi and Y. treatment of three kinds of typical wastewater, when Takasaki, “Biopolymer flocculant produced by an applied with aluminum chloride. With the optimal dosage Pseudomonas sp. ,” Biotechnology Techniques, vol. 12, and no adjustment of pH value, 98.7% flocculation rate pp. 511-514, July 1998. for domestic wastewater, 96.9% color removal rate for

[4] B. Xin, Y. Zhuang, T. Li, S. Dai, “Basic research on [12] F. Ma, S. Li, W. Jin, J. Yang, “Present Conditions & and application of bioflocculant,” Technigues and Trend of Studies on Microbial Flocculant,” Industrial Equipment For Enviro.poll.cont, Vol. 6, pp. 57-61, May Water & Wastewater, vol. 33, pp. 7-9, Jan. 2002. 1998. [13] N. Ren, B. Wang, and F. Ma, “Hydrogen [5] K. Nakata, R.Kurane, “Production of an extracellular bioproduction of carbohydrate fermentation by anaerobic polysaccharide bioflocculant by Klebsiella pneumoniae,” activated sludge process,” In Proceedings of Water Bioscience Biotechnol. Biochem. (JAPAN), vol. 63, pp. Environmental Federation. 68th Annual Conference and 2064-2068, Dec. 1999. Expo. Miami Beach, FL, USA, 21–25 October 1995, pp. 145–153. [6] G. S. Kwon, S. H. Moon, S. D. Hong, H. M. Lee, H. S. Kim, H. M. Oh and B. D. Yoon, “A novel flocculant [14] N. Ren, B. Wang, and J. Huang, Ethanol-type biopolymer produced by Pestalotiopsis sp. KCTC fermentation form carbohydrate in high rate acidogenic 8637P,” Biotechnology Letters, vol. 18, pp. 1459-1464, reactor. Biotechnol Bioeng vol. 54, 1997, pp. 428–433. Dec. 1996. [15] F. Ma，J. Liu，S. Li, J. Yang, L. Zhang, B. Wu and [7] K. Toeda, R. Kurane, “Microbial flocculant from Y. Zhu, “Development of Complex Microbial Alcaligenes cupidus T201,” Agri. Biol. Chem, vol. 55, pp. Flocculant,” China Water & Wastewater, vol. 19, pp. 1-4, 2793-2799, Nov 1991. 2003. [8] R. Kurane, K. Hatamochi, T. Kakuno, M. Kiyohara, [16] X. Chai, J. Chen. “Culture condition for production M. Hirano, Y. Taniguchi, “Production of a bioflocculant of microbial flocculant by Azomonas sp,” Environment by Rhodococcus erythropolis S-1 grown on alcohols, ” Pollution & Prevention, vol. 23, pp. 61-62, Feb 2001. Bioscience, biotechnology, and biochemistry, PPM, pp. 44-51, Oct. 1992. [17] G. Cuesta, N. Suarez, M. Bessio, “Quantitative determination of pneumococcal capsular polysaccharide [9] H. Li, Z. Zheng, Z. Zhu, H. Zheng. “Microbial serotype 14 using a modification of phenol–sulfuric acid Flocculant, ” Chongqing Environment Science, vol. 22, method, ” J Microbiol. Meth., vol. 52, pp. 69-73, Jan. pp. 18-21, Feb. 2000. 2003. [10] J. Nakamula, S. Miyashiro, Y. Hirose, “Screening, [18] M. Bradford, “A rapid and sensitive method for the isolation and some properties of microbial cell quantitation of microgram quantities of protein utilizing flocculants,” “Agric. Biol. Chem, ” vol. 40, pp. 377-383, the principle of protein-dye binding, ” Anal. Biochem., Feb 1976. vol. 72, pp. 248-254, 1979. [11] H. Takagi, K. Kadowaki, “Flocculant production by Paecilomyces sp. taxonomic studies and culture condition,” Agric. Biol. Chem, vol. 49, pp. 3151-3157, Nov. 1985.

Copyright © 2008 SciRes. J. Water Resource and Protection. 2008; 1:1-65 J. Water Resource and Protection. 2008. 1: 1-65. Published Online June 2008 in SciRes (http://www.SRPublishing.org/Journal/jwarp/).

Risk-based water quality management in river system

Pengcheng SUN, Jining CHEN, Siyu ZENG Department of Environmental Science and Engineering, Tsinghua University, Beijing, China E-mail: [email protected]

Abstract

Presence of uncertainties and varieties in the model input variables and parameters is one major challenge in the river water quality management practice. A risk-based framework is developed to address the problems derived from uncertainties and varieties in the river water quality management work and assess the performance risk of waste load allocation strategies in compliance with the water quality management goal. Monte Carlo simulation technique is applied to take the different uncertainties into account. Regional sensitivity analysis using a task-based Hornberger- Spear-Young (HSY) algorithm is conducted to identify the sensitive point sources, sort them according to their sensitivities and produce available strategies of waste load allocation for the pollution sources. Keywords: Water quality model; Regional sensitivity analysis

1. Introduction classify pollution sources according to their contributions to the water quality risk. Within the framework waste Water quality models have been broadly applied in the load allocation scenarios for point sources could be river water quality management such as carrying capacity obtained with the consideration of risk. calculation and waste load allocation process [1-4]. Presence of various types of uncertainties has been 2. Framework of the risk-based water quality recognized as one of the major challenges in water quality modeling. Both uncertainties in model inputs and management approach parameters lead to the uncertainties in the model outputs, especially for the river systems lack of monitor data and 2.1. Framework of the risk-based water quality insufficient information of pollution sources. If we have management approach not taken the uncertainties into account when the water As shown in Fig.1, the risk-based water quality quality management was made with the help of water management framework consists of two steps, i.e. an quality models, risk of failure in achievement of the water inner cycle for risk analysis and an outer cycle for water quality management goal could be brought in. quality management applications. In recent years, uncertainties and risk are being The inner cycle is conducted just as a normal model focused in the river water quality management. Tung and application within a framework of Monte Carlo Hathhoun considered uncertainties in a stochastic waste simulation. Pollution sources inputs and parameters of the load allocation model in a chance-constrained format [5]. water quality model are regarded as random variables Cardwell and Ellis present dynamic programming with given distributions. For each run of the model, the formulations for addressing model and parameter inputs and parameters are randomly sampled according to uncertainty in environmental management problems [4]. their distributions and then substituted into the model for Fuzzy set, probability theory and other methods are simulation. The performance risk of the water quality in applied to address the water quality risk in rivers, which compliance with the water quality management goal, becomes an important factor in the river water quality subject to variability of water quality and flow of head management process [1, 6-9]. water and waste loads as well as the parameters’ uncertainties, could be predicted within the inner cycle. This paper presents a framework to address uncertainties in the water quality management problems The risk-based water quality management approach, with Monte Carlo simulation technique. Regional the outer cycle, is performed as a regional sensitivity sensitivity analysis [10] is conducted to screen and analysis [10], using a task-based Hornberger-Spear-

Young (HSY) algorithm [11]. Under most of the dx/ dt= −+ C21 x s conditions the river water quality management problems (1) could be treated as the management of pollution sources. Where x is the concentration of NH4_N in the tank; C21 In the outer cycle, series of waste load allocation represents the coefficient of the removal rate of NH_4 in scenarios of pollution sources are randomly generated and the tank (day-1), s is the source and sink term which is then each scenario is put into the inner cycle to assess its calculated as equation（2）. risk level. After that all the generated scenarios will be sQx= ()//(1)−− xV C screened with the task-based Hornberger-Spear-Young iIinii,16 (2) (HSY) algorithm, and available scenarios will be distinguished to satisfy the requirement of risk Where QI is the inflow of the tank; x is the same as in management. Decision-makers could use the available (1); C16 is the dead zone coefficient which represents the scenarios to make water quality management strategies mixture level in the tank. with consideration of other factors such as economy and The HSY algorithm [11] was applied for model equity, which can be done with the risk-based waste load identification, in which the behavior-giving simulation allocation model too. A K-S test approach is contained in was defined. All the simulations and thus the parameters the regional sensitivity analysis, and contribution rank of accordingly fell into a ‘behavior-giving’ and a ‘nonpoint sources to the water quality risk of the river system behavior-giving’ set. For each parameter, the empirical could be carried out which could help the decision- probability distributions of the two sets were then makers with further management tasks. compared with the Kolmogorov-Smirnov (K-S) test to determine whether they were statistically different at a certain significance level. A significant difference indicated that the model output was sensitive to the parameter. The behavior-giving parameter set, which characterize the parameters’ uncertainties, was saved for further analysis. 2.3. Risk analysis The performance risk of the river water quality in compliance with the management goal could be expressed as the probability that the simulated concentration of the water quality indicators violates the management control level. To assess the performance risk of each waste load allocation scenario, the water quality model is applied within a risk analysis framework through the Monte Carlo simulation to account for the uncertainty of model parameters and the variability of water quality and flow for both head water and point loads. The model parameters’ uncertainties are assumed to be represented by the behavior-giving set obtained in the identification process, and the variability of head water and point loads is obtained with an analysis of the historical data. Figure 1. Framework of the risk-based water quality Parameters are sampled independently and correlations management appr. among different parameters are not considered. Each run 2.2. Water quality model produces a water quality simulation result for all the tanks along the river and risk is calculated based a statistical All models could be used in the developed framework work with all the results. but the heavy computation task and the characteristics of In this paper we pay attention to two types of risk: one the river would influence the model selection. The river is the water quality risk at certain location which is water quality model based on Continuously Stirred Tank mentioned as checkpoint and the other is the water quality Reactor (CSTR) conception is used in this study. The risk for the whole river system. Checkpoints would be CSTR model has been widely applied in the river water those important locations that water quality is crucial such quality simulation studies [12-14]. River is considered to as in the drinking water sources or is sensitive such as be made up of a series of tanks, and water in each tank is where the point sources discharged in. completely mixed. For each tank, biodegradation and Hence, two simple types of performance risk are impacts of sinks and sources are integrated in the model. defined as follows: For example the transport and transform equation for The performance risk for checkpoint NH4_N is shown in (1) risk= n/100% N × ii (3)

The performance risk for the whole system by the local government and the water quality model has risk=× n/ N 100% been calibrated with the monitor data. whole (4) The varieties of the head water and point loads are not Where riski is the performance risk at checkpoint i; N is considered in the existed plan. Therefore there would be the total run number in the Monte Carlo simulation and ni risk introduced by the varieties and uncertainties of the is the number that the water quality violates the river system. A risk analysis study is conducted for the management control level at checkpoint i, and n is the existed water quality management plan and the stability number that the water quality violates the management of the Monte Carlo simulation is also investigated. The control level in the whole river, and the riskwhole represents head water is pumped from the Yangtz river, with a the performance risk for the whole system. According to variety between 10% assumed to the flow, and the the risk definition, the risk could not be smaller than whole concentration of NH4_N is assumed to be a triangle riski. distribution according to the historical monitor data. A Astringency speed and stability of the Monte Carlo variety between 10% is also assumed to the point loads. method is very important because it decides the time spent Because the river network is mainly worked in the dry on computation. The risk analysis process will run many season and the pollution in the system is mainly caused times in the waste load allocation period. An experiment by point loads, impacts of diffuse sources are not should be conducted to investigate the convergence speed considered. and then risk analysis could be carried out with the suitable run time. 4. Risk analysis 2.4. Regional sensitivity analysis and waste load allocation 4.1. Astringency and stability of the risk With the different waste load allocation scenarios and quantification method their water quality risk values obtained in the Monte Carlo Before the risk analysis is conducted, an experiment simulation step, a screening analysis is conducted to find was done to investigate the astringency of the risk the available scenarios according to the risk management quantification algorithm. A wastewater discharge scenario goal. The screening analysis is carried out using a of point sources was randomly generated and then its risk Regional Sensitivity analysis approach based on task- was simulated within the Monte Carlo framework of based HSY method as mentioned before and the behavior- different run times. As shown in Fig.2, increase of the run giving scenarios are those which can satisfy the risk times of the Monte Carlo simulation could also increase management goal. K-S test is included in the analysis to the stability of the performance risk assessment algorithm. rank contributions of pollution sources. The performance risk value remains stable when the run Based on the behavior-giving scenarios the decision- number exceeds 2000 times approximately. When the run makers could make the water management plan. Economy times is more than 5000, the stability increases quite and equity could be considered in the model to help the slowly and it means that to run the Monte Carlo simulation decision-makers in the final step. If economy factor such 5000 times for a risk assessment process is a reasonable as the removal costs is chosen as the main limitation we choice. can rank the strategies according to their costs and choose the one which spends least money. If equity is considered we can firstly make all the point sources achieve the same removal rates or removal quantity and then do the Monte Carlo simulation job. Also the costs and equity factors could be considered together in the model.

3. Case and source data

The developed approach is applied into a case study of a river system in eastern China. The river supplies water for urban and agricultural use and the water quality is not good enough due to the heavy pollution. The river Figure 2. Results of the astringency experiment of the risk receives the waste loads from 38 major effluent outlets analysis approach which consist of both industrial effluents and municipal effluents. NH4_N is a major pollutant in the river. 4.2. Risk analysis According to the Environmental quality standards for Risk of water quality is checked at a series of surface water of China, the concentration of NH _N 4 checkpoints, which are chosen for every point load at the needs to be kept under 1 mg/L in order to comply with location that 1 kilometer after the point sources. Fig.2 the water quality of class III. All the data are supported

Copyright © 2008 SciRes. J. Water Resource and Protection. 2008; 1:1-65 10 P. SUN ET AL. gives an example of the risk assessment result at one checkpoint. It’s obvious that waste load allocation scenario in Fig.2 has a very high risk level of about 30%. Fig.3 shows the results of the performance risk assessment of a zero-emission scenario and a scenario representing the actual condition of pollution sources. As shown in the figure, if the pollution level keeps at the actual condition, the risk that NH4_N concentration violates the water quality criteria will be very high at the downstream river where point loads discharge a lot into the river. The performance risk of NH4_N violation will be reduced to a very low level if point loads are controlled as the zero- emission scenario, and a very low risk appears only at the start of the river because of the variety of headwater. Figure 4. The K-S test results for point loads at a risk Because the zero-emission scenario is too strict that all of control level of 10% the point loads are not permitted to discharge NH _N, 4 Decision-makers can screen the available scenarios considering both the environmental and economic impacts, with other indices such as economic cost and social it’s better to make the pollution reduction work more equity to make a final waste load allocation plan. For efficient and control the water quality risk under a certain example, a final result of the waste load allocation level according to the decision-makers’ choice. designed from the result set in terms of the minimization

of the total treatment cost could be obtained, and the total waste load permitted to be discharged from all the point sources is 31895.5 kg/day, which is more economically feasible than the zero-emission scenario

6. Conclusions

Risk derived from varieties of model inputs and uncertainties of model parameters are considered as random distributions and risk-based waste load allocation method is conducted within a task-based HSY framework. The model is developed to help decision-makers to make waste load allocation policies to control the risk of low water quality under an acceptable level, especially for Figure 3. Risk analysis of water quality under the actual data-lacked conditions. With different definitions of the pollution level and the zero-emission level behavioral function, other objects as economic cost and equity in the water resource management could be considered as well as the risk of water quality. The model 5. Regional senstitivity analysis and waste could also be applied to identify key point loads in the river or rank them according to their contributions to the load allocation risk, and then different scenarios for water quality management could be made for them. The K-S test result of the ‘behavior-giving’ and ‘non- behavior-giving’ waste load allocation scenario sets could 7. References give us a quantitative analysis and rank point pollution sources according to their pollution contributions. Fig.4 [1] Y.S.R. Murty, S. Murty Bhallamudi, and K. shows results of the K-S test of the waste load allocation Srinivasan, “Non-Uniform Flow Effect on Optimal Waste process when the risk control level is 10%. The columns Load Allocation in Rivers”, Water Resources in the figure indicates the dstatistic value (the maximal Management, 2006, 20: 509-530. difference between the cumulative curve of ‘behavior- [2] M. Saadatpour1 and A. Afshar2, “Waste load giving’ and ‘non-behavior-giving’ sets) of the removal allocation modeling with fuzzy goals: simulation- rate for each point load, while the line represents the optimization approach”, Water Resources Management, critical K-S value (0.048 in this analysis) at a significance 2007, 21(7): 1207-1224. level of 0.01. As shown in the figure, the achievement of the water quality management goal is sensitive to most of [3] Gu, R. and M. Dong, “Water quality modeling in the the point sources and the importance of the point sources watershed-based approach for waste load allocations”, Water Science and Technology, 1998, 38(10): 165-172. could be ranked by the dstatistic value.

[4] Cardwell, H. and H. Ellis, “Model uncertainty and [10] Beck, M.B., “Water quality modeling: A review of model aggregation in environmental management”, the analysis of uncertainty”, Water Resour. Res, 1987, Applied Mathematical Modelling, 1996, 20(2): 121-134. 23(8): 1393-1442. [5] Tung, Y.-K. and W.E. Hathhorn, “Stochastic waste [11] Chen, J. and Beck, M. B., Quality assurance of multi- load allocation”, Ecological Modelling, 1990, 51(1-2): media model for predictive screening tasks. Washington 29-46. DC, USA: Office of Research and Development, EPA, 1999. [6] Subimal Ghosh and P.P.M., “Risk minimization in water quality control problems of a river system”, [12] Paul Whitehead, P.Y., and George Hornberger, “A Advances in Water Resources, 2006, (29): 458-470. system model of stream flow and water quality in the Bedford-Ouse river-1 stream flow modeling”, Wat. Res.,

[7] Mujumdar, P.P. and V.R.S. Vemula, “Fuzzy waste 1979, 13: 1155-1169. load allocation model: Simulation-optimization approach”, Journal of Computing in Civil Engineering, 2004, 18(2): [13] Peng, J., “Hydraulic residence time of CSTRs under 120-131. unsteady-state condition”, J. of Envir. Eng, 1994, 120: 1446-1458. [8] Sasikumar, K. and P.P. Mujumdar, “Fuzzy optimization model for water quality management of a [14] Reda A.L.L.; Beck M.B., “Simulation model for real- river system”, Journal of Water Resources Planning and time decision support in controlling the impacts of storm Management-Asce, 1998, 124(2): 79-88. sewage discharges”, Wat. Sci. Tech, 1999, 39(9): 225- 233 [9] Karmakar, S. and P.P. Mujumdar, “Grey fuzzy optimization model for water quality management of a river system”, Advances in Water Resources, 2006, 29(7): 1088-1105.

Degradation of quinoline in aqueous solution by the light of 185 nm/254 nm

Dazhang ZHU1, Dongmei SUN2, Shilong WANG2, Xiaoyu SUN2, Yaming NI2, Side YAO2 1Department of Chemistry, Tongji University, Shanghai, P.R.China 2School of Life Science & Technology, Tongji University, Shanghai, P.R.China E-mail: [email protected]

Abstract

The degradation of quinoline in aqueous solution by the radiation of low-pressure quartz mercury light which could emit the light of 185 nm and 254 nm and the influence factors were studied. It showed that quinoline could be degraded effectively by this process. In the irradiation lights of the two main wavelengths, 185 nm was the main effective one to degrade the substrate. The degradation rate became faster with the increasing of the temperature and the electric power of the mercury light. O2 played an important role in the degradation progress. However, the initial pH of the solution did not impact the degradation rate obviously. Keywords: Quinoline; Advanced oxidation process; Vacuum ultraviolet; N-heterocyclic compounds

1. Introduction decompose to produce hydroxyl radical[14]. Degradation of pollutants by vacuum ultraviolet light has obviously Quinoline and its derivatives are widely used as raw excellent feature of no reagent adding to the material and as solvent in the manufacture of medicines, wastewater[15]. Actually, it was reported that the * dyes, paints, herbicides, insecticides and rubbers. The pollutants were degraded by Xe 2 excimer light which wastewater of these industries contains amounts of radiates the light of 172nm in some literatures[16-19]. quinoline. Meanwhile, quinoline occurs naturally in coal But because of low luminous efficiency, expensive tar, so it is also a typical pollutant in the wastewater of apparatus and high working temperature, it is difficult to coking industry. Structurally, Quinoline is a typical use in real system. Low pressure quartz mercury lights simple N-heterocyclic compound in which a benzene ring could emit the light of 185nm and 254nm. While, 185nm is fused to a pyridine ring. Since many of N- was located in the range of vacuum ultraviolet. But the heteroaromatics are considered toxic and/or mutagenic price was much cheaper. When the light of 185nm and carcinogenic[1-4], the contamination of surface and radiated the solution in the existence of air, a series of groundwater by them is a major environmental elementary reactions might happen to produce a series of concern[5,6]. Biodegradation[7], UV/O process[8], transient species as follows[14]: 3 • • UV/H O process[9], photo-catalytic oxidation[10], H2O + hν (< 190 nm) → H + HO (1) 2 2 + − • electro-catalytic oxidation[11], wet oxidation[12] and H2O + hν (< 190 nm) → H +eaq +HO (2) + − • super critical water oxidation[13] were reported as main H +eaq →H (3) • • methods of degradation of quinoline. However, since the H + O2 → HO2 (4) • • conditions of biodegradation were very severe, the H + HO2 →H2O2 (5) • research of biodegradation was limited in laboratory and H2O2 + hν (254 nm) → 2 HO (6) − •− had not been applied in real system yet. The other eaq + O2 → O2 (7) − • − processes were advanced oxidation processes based on eaq +HO →HO (8) hydroxyl radical. Since some of them require adding Among the transient species, hydroxyl radicals reagents, which would make second pollution and some produced in the reactions could oxide quinoline very of them require very expensive apparatus, their easily. Meanwhile, the lights of 185nm and 254nm could application in real system was also limited. The energy of also photolyze quinoline directly. Therefore, irradiation vacuum ultraviolet light was high enough to make water by low pressure quartz mercury light might be a very

Copyright © 2008 SciRes. J. Water Resource and Protection. 2008; 1:1-65 DEGRADATION OF QUINOLINE IN AQUEOUS SOLUTION BY THE LIGHT OF 185 NM/254 NM 13 effective process to remove quinoline in wastewater. In serviced (Context Transfer Unit). The user context this paper, the degradation of quinoline by low pressure comprises all the information necessary to continue the quartz mercury light and the influence factors were active services to the user in the other band. This transfer studied. occurs in real time, and is transparent to the end user. During the context transfer, control parameters essential 2. Multiband scheduling for the transmission are transferred. Adaptation and prioritization of the user data flows may be needed, since the new band might not be able to accommodate all traffic The general framework in which the MBS operates is from the band that is no longer available. The timing of presented in Figure 1. Higher-layer protocol data units the transfer is an important issue; rapid changes when a (PDU) arriving at the IP convergence layer (IPCL) are band becomes unavailable are supported, as well as converted into Radio Link Control (RLC) service data preparation of context transfers when information is units (SDU) after header compression and ciphering. In obtained that the availability of a band will change in the accordance with the decision of the scheduler, a certain (near) future. This is done by the so-called Band amount of data is selected from the RLC SDU buffer and Monitoring functionality in the MBS. segmented and/or concatenated, depending on the size of the SDU. A user terminal (UT) identification code, a In the multiband architecture considered here, many transmission sequence number, and optionally a CRC common functions for the operation in the different bands code are added. If RLC acknowledged operational mode can be identified. These functions may be shared between is used, then an outer end-to-end ARQ is performed at the the different bands. For example, the same flow ID, UT RLC level. The multiband scheduler schedules the RLC ID, etc. can be used in both bands, which simplifies the PDUs for transmission in the correct band. The resource context transfer between the bands. However, some scheduler (RS) of each band fetches the RLC PDUs from problems related to ARQ and synchronization remain, the buffer and constructs from them transport blocks (TB), and need to be solved in order to allow fast switching. which are scheduled for transmission. Hybrid ARQ These will be addressed in the following sections. In the (HARQ) can be used for improving the transmission of conceptual discussion above we spoke of switching the TBs. The MAC adds a retransmission sequence between two spectrum bands, but a more generalized number to TBs that use HARQ. The RS of each band approach can also be used in the case of a spectrum that is operates independently and the coordination of the more fragmented. different bands is done exclusively by the MBS. The operation of the different ARQ schemes is depicted in 2.1. Handovers for MBS and non-MBS cases Figure 2. We assume that the network supports mobility via normal inter- and intra-frequency handovers, and that the Higher layer PDU Higher layer PDU Hi gher layer PDU handover mechanism is hard handover (meaning that IPCL Header com pressi on & there is always a short break in the connection when a ciphering RLC SDU RLC SDU RLC SDU handover is done). Further, we assume that handover RLC Segmentation & decisions are done by the network and that only UTs RLC RLC RLC Concatenation Header Header Header perform measurements and that the UTs keep the serving RLC PDU BS informed of the measured values and of triggered Multi-band Scheduler events (such when the signal of a neighbor BS has become stronger than that of the serving BS).

MAC A UT performs periodical measurements, both for Multiplexing TB TB TB identifying neighboring BSs and for measuring the signal B B B Band B level of the identified BSs. A measurement report, TB TB TB A A A Band A containing filtered measurement results, is then sent to the serving BS, either periodically or when a network- Figure 1. Illustration of the Multi Band Scheduler and the configured event occurs. Based on the measurement data unit it is working on. reports, the serving BS decides whether a handover Different Hybrid ARQ protocols exist and two should be performed. possible approaches can be used: chase combining (retransmission of the whole TB and combining these at After a handover from the serving BS to a target BS is the receiver), or incremental redundancy (retransmission triggered, the serving BS sends a request to the target BS of additional redundancy bits, providing the receiver with to confirm that the UT is allowed to do the handover. If more information about the TB). the target BS allows the handover, the serving BS sends a handover command to the UT, identifying when and to In the case that a certain band is no longer available, which BS the handover should be done. Finally, the UT the MBS provides a mechanism for transferring the user responds to the handover command by sending an context from that band to any other band that is still being acknowledgement to the serving BS, and then breaks the

Copyright © 2008 SciRes. J. Water Resource and Protection. 2008; 1:1-65 14 D. ZHU ET AL. connection to the serving BS at the agreed time and 2) After the switch, the arriving data is directed to connects to the target BS. the scheduling queue of the new band and any data remaining in a buffer is transferred to the In the non-MBS case a UT needs to perform a queue of the other band. handover when switching between the B and E bands. This means that there is always a break in the connection Lo g ical ch an n el: when moving from the B band to the E band, which Flow address + term inal class causes the user throughput to drop to zero for a while. Traffic Scheduler Multi-band scheduler Co n t e x t The overall delay caused by the handover is of the order Tran sfer Un it Band Monitoring of tens of milliseconds. In our simulations the delay has been assumed to be 20 ms. Qu eu e E- Qu e u e B-Queue Monitoring

Scheduler state, E2 E ARQ In contrast, when an MBS is used the biggest delay is HARQ HARQ e.g. current band HARQ scheduling delay, which is only of the order or few of a flow etc transfer milliseconds. A small additional delay arises from the RS RS Band time needed by the UT for switching bands. This allows sw it ch for more seamless switching between resources and thus UT for better load balancing and higher user throughput. A

3. Hybrid ARQ context transfer Figure 2. Main functions and operation of the Multband Scheduler. Fast context transfer during a switch to another band during an ongoing HARQ process. The design of the automatic repeat request (ARQ) mechanism is very important with regard to the speed of Next to the HARQ buffer, the number of performed context transfers between bands. If ARQ retransmissions retransmissions and information specific to the utilized have to be finished before switching to another band is HARQ scheme is exchanged. allowed, then, depending on the ARQ design, switching 3.3. Preparation for band switch delays of up to 20 ms are possible. In order to make fast In many situations the timing of the band switch is context transfer possible, we propose the use of an ARQ known beforehand and preparations can be made before mechanism that consists of an outer ARQ for RLC SDUs the switch. For example, if the BS knows that the E band and an inner HARQ for retransmissions of transport will not be available any more after 5 ms, then it can blocks [8]. command the UT to synchronize with the B band. The BS 3.1. E2E ARQ (outer ARQ) can assist the synchronization by sending, for example, the time shift to the beginning of the next frame on the B The E2E ARQ is situated on a higher protocol plane band, the frequency shift between the two bands, and than the MBS, and thus context transfers from one band other system information, such as the position of the to another do not affect the E2E ARQ process (Figure 2 resource allocation table. Furthermore, the UT can illustrates this). After a context transfer the new band is estimate the pathloss or an initial channel quality briefly not in use, and the multiband scheduler takes this indicator and report it to the BS well before switching to into account in its scheduling decisions. the B band. When the UT switches bands, this 3.2. HARQ (inner ARQ) information is forwarded from the E band to the B band scheduler. The anticipation of the band switch allows for Each band has an independent HARQ process, and a seamless handover, because contexts can be exchanged thus a fast context transfer is required for these processes. before the connection on the band is actually lost. In order to allow the HARQ process to continue uninterrupted, we propose a mechanism in which the 4. Use of MBS for flexible spectrum sharing HARQ buffer is transferred between the two bands, as illustrated in Figure 2. The Context transfer Unit of the The ITU-R studies [10][11] show that a considerable MBS coordinates the exchange of the HARQ data and amount of new spectrum will be needed to provide the parameters. total capacity that is needed for delivering the predicted When a UT switches for example from the extension services and traffic in the future. However, spectrum for (E) band to the basic (B) band, also the HARQ buffer is wireless networks is already a scarce resource and will transferred, and as a result, the HARQ retransmissions become even scarcer in the future. Therefore sharing the can be continued on the B band. This requires the spectrum with other radio systems is a possibility to following: access additional spectrum. It is based on the assumption 1) The HARQ processes in the B queue and the E that when one network operator or radio system is in queue use a common numbering scheme. demand of spectrum, another network operator might have spectrum available. Thereby the exploitation of available unused spectrum or sharing of spectrum

Copyright © 2008 SciRes. J. Water Resource and Protection. 2008; 1:1-65 DEGRADATION OF QUINOLINE IN AQUEOUS SOLUTION BY THE LIGHT OF 185 NM/254 NM 15 between technologies leads to a better utilization of 4.1. Case study spectrum throughout a multi-operator or a multi-radio- network environment. Figure 4 depicts a simulation scenario for which we study a band transfer of a UT with and without MBS at In the preparation phase towards WRC-07 several IMT the BS. The circle in the center marks a transmission candidate bands have been identified [12] and parts of exclusion zone, where UTs are not allowed to use the E these bands have been allocated as IMT bands for band and have to switch to the B band. communication systems at WRC07. The newly identified spectrum comprises the following spectrum bands: 450- In our simulations we use an event driven dynamic 470 MHz was identified globally, 698-802 MHz was system simulator that simulates UL and DL directions identified in the Americas and some Asian countries, 790- simultaneously with OFDMA symbol resolution and uses 862 MHz was identified in Europe, Africa and most an Exponential Effective SINR Mapping (EESM) link to Asian countries, 2300 - 2400 MHz has been identified system mapping [13]. globally, and 3400 - 3600 MHz was identified in most We use the handover procedures described in section countries in Europe and Africa, and in several countries 2.1 to model BSs that are/are not equipped with an MBS. in Asia. Figure 5 illustrates the instantaneous throughput of a UT Fixed Satellite Service (FSS) is the primary service when entering and leaving the exclusion zone and deployed in large portions of the candidate bands. In the changing to the B band for the MBS and the non-MBS allocated C-band (3.4 to 3.6 GHz) dedicated spectrum case. It clearly shows that the MBS and the anticipation will be available for IMT systems, but not world wide. To of the band switch avoids periods with zero throughput enable further deployment in the C-band sharing with when entering the exclusion zone. Nevertheless, in both FSS will be required. When bands are available on a cases the UT will experience lower throughput because of sharing basis their availability cannot always be the lower capacity of the B band. guaranteed. For example transmission exclusion zones around technologies with which the spectum is shared, 4 13 22 might be defined. On the one hand the shared new bands should be accessible to guarantee high capacity, but on 5 14 23 the other hand, dedicated and guaranteed bands are 6 15 24 required to offer guaranteed network access. Therefore, the UTs have to operate in a multi band environment. A 7 16 25 possible spectrum allocation for a system deploying one 0 8 17 dedicated band between 3.4GHz and 3.6GHz and a shared band at higher frequency in the same band is 9 18 26 illustrated in Figure 3. 1 10 19

2 11 20 Basic (B) Extension (E) 3 12 21 Basic band with limited Extension band with larger f bandwidth in 3.4-3.6 GHz band bandwidth at alternative location in (guaranteed access) the C-band (shared access) Figure 4. Macro-cellular simulation scenario with 27 sectors. Figure 3. Possible spectrum allocation for IMT-Advanced in Results are presented for the 6 sectors in the center. The a multi band deployment. circle in the center marks an exclusion zone. UTs in this zone are not allowed to use the E band. Flexible Spectrum Use (FSU) between operators using If the B band is congested the MBS can relocate traffic the same technology is another possibility of dynamic from the B band to the E band or decide to drop or reduce spectrum use, enabling flexible deployments with a the bandwidth of less important flows in the B band. limited amount of available spectrum. Also in this case a When leaving the exclusion zone, the UT can shared band for enhanced capacity and a dedicated band immediately receive data on the E band and benefit from with guaranteed access can be defined [13]. the increased capacity. However, without an MBS the UT A fast context transfer is required when a user terminal has to go through a handover procedure, which typically served on the shared extension band moves into an area involves some time to trigger the handover, pending where it would interfere with the other system’s HARQ transmissions are lost and the initial throughput is transmissions, e.g. when it enters the transmission lower because the serving RAP does not have CQI exclusion zone around a satellite earth station. The fast information from the UT. transfer to the basic band can be provided by the MBS, assuming that one BS handles both B and E band.

5 x 10 2 500m and the other 4 are on a circle with a radius of

1.8 1000m as illustrated in Figure 7. We assume a line-of-

1.6 sight (LOS) link between RN and BS and for the BS-UT

1.4 and RN-UT links we assume a non-LOS link. The corresponding channel and pathloss models can be found 1.2 in [16]. The BS transmit power is 43dBm per sector and 1 UT enters UT is in UT leaves the RN transmit power is 37dBm. 2000 UTs move in the 0.8 exclusion exclusion exclusion zone zone zone area at a speed of 3km/h and the scenario contains no 0.6

Throughput in bits/sec in Throughput exclusion zone. 0.4 0.2 MBS Table 1 compares the average cell throughput of the No MBS 0 0 100 200 300 400 500 600 700 800 900 two center cells. Adding the E band to the B band at the Time in ms BS increases the cell throughput seven fold. However, the high capacity E band is not available for most of the users Figure 5. Instantaneous User Throughput averaged over in the cell and the increase does not fully scale with the 5ms with and without MBS when entering an exclusion zone. increase in bandwidth. When using RNs to extend the E 5. Application of MBS to relaying band coverage the throughput almost doubles. Further, the high capacity E band is available to most of the users in the cell. In a multiband operation, Relay nodes (RN) can be used to extend the coverage of the band with worse Table 1. Cell throughput comparison with/without E band propagation characteristics. For the example spectrum and RN. allocation in Figure 6 a radio access point (RAP) is able Scenario Average cell throughput to provide wide area coverage on the basic (B) band at [Mbps] 860MHz. However it cannot cover the same area with the Only B band BS 22 shared extension (E) band at 3.4GHz because of the BS with both bands 150 differences in the propagation loss due to the different BS with both bands 270 carrier frequencies. and RN with E band

Basic (B) Extension (E)

Extension band with 90MHz bandwidth at 3.4GHz in the C-band RN (shared access)

Figure 6. Possible spectrum allocation for IMT-Advanced in RN RN a multi band deployment.

In such a scenario RNs can extend the E band RN RN coverage to the areas of interest. The RNs do not require a backhaul connection and an E band radio interface is RN sufficient. Thus the RNs are less complex and cheaper than adding additional BSs. The RNs in the E band do not have to provide ubiquitous coverage but they should Figure 7. Each sector of Figure 4 is augmented with 6 RN. cover most of the area to make the high capacity E band The BSs transmit on both B band and E band, whereas the available for most of the UT. RNs only transmit on the E band. The BS uses the MBS for load balancing between the For quality-of-service support the BS has to take bands. additional criteria into account in the presence of relays, when deciding which data packets should be sent on the 5.1. Case study basic band and which packets on the extension band: We study the performance difference with and without • Services with low delay requirements should be RN in the E band for the scenario presented in Figure 4. scheduled on the band/link that requires fewer hops The BSs are equipped with both B band and E band radio (this will mainly be the B band as it has the better interface. The Inter-Site Distance is 3km, and the BS can propagation conditions and therefore a wider provide the basic coverage for the B band at 860MHz coverage area). using the pathloss model in [15]. • High speed users with an E band served by RNs Each BS sector has 6 RN to extend the coverage area should be transferred to the basic band (RN will of the E band at 3.4GHz, two of them are evenly have smaller coverage area and this policy will distributed on a circle around the BS with a radius of

reduce the number of missed packets, because the gain, whereas the RN is equipped with an omni- UT has left the coverage area of the RN). directional antenna and an antenna gain of 7dBi, following the assumptions in [17].

5.2. Relays with MBS So far we have presented the multi-band operation in RECs for RNs that operate only in the E band. However some of the RNs might be equipped with both a B band and an E band radio interface. Figure 8 illustrates the case where the RN closest to the BS is equipped with an MBS and therefore packets that should be transmitted on the B band to the UT by the RN can be received on the E band. Typically the E band offers higher capacity than the B band. Thus, it is beneficial to use the E band on the BS-RN link, even if the RN serves the UT on the B band. Here the MBS allows balancing the load of the two bands on the link between the BS and the RN. To investigate the potential benefits of RNs equipped with an MBS and a B band radio interface for the spectrum allocation in Figure 6 we study the coverage for indoor users in the scenario presented in Figure 9. Each BS is equipped with two sectors and they form together with 3 RN in the same street a REC. The sectors to the right and down have 2 RNs wheras the RN closer to the Figure 9. Relay based deployment in the Manhattan grid. BS is equipped with an MBS. The other RNs have only The closest RN right of the BS in horizontal streets and an E band radio interface. down from the BS in vertical streets is equipped with a B and E band radio interface and an MBS.

The E band can only provide a spectral efficiency of more than 1b/s/Hz in 60% of the area even though every RAP is equipped with an E band interface. In contrary, the BS alone can already provide this spectral efficiency for the same area on the B band. The coverage area can be further increased to 83% by equipping one third of the RNs with a B band interface. The coverage for the B band in the center area of the scenario in Figure 9 is illustrated in Figure 10 and Figure Figure 8. Relay enhanced cell with B band at lower 11 for the case when only BS have a B band radio frequency and E band at higher frequency. BS/RN with interface and for the case where additionally one third of MBS can decide on which band to transmit packets. RN the RNs are equipped with a B band radio interface, without MBS receive and forward packets only on extension respectively. This comparison clearly shows that the B band. band should be available at the RN as well to provide Table 2 compares the coverage area of the different coverage. However, due to the lower bandwidth of the B bands for this scenario. The coverage area has been band, the B band should only be used to serve UT that calculated using the pathloss models in [16]. In particular cannot be served on the E band but not for forwarding we applied the B1 LOS model for points in the same data to the RN. Therefore, the RN should be equipped street than the RAP (BS or RN) and the B1 NLOS model with an MBS to be able to receive data on the E band and for points in different streets. Inside the building blocks forward it on the B band to UTs that it serves on the B we use the B4 outdoor-to-indoor model, whereas we band. assume an indoor pathloss of 0.5dB/m for the E band (as Table 2. Area with a spectral efficiency higher than 1bps/Hz. specified by the model) and 0.3dB/m for the B band to take into account the lower indoor propagation losses at E-band 60% 860MHz than at 3.4GHz. In both cases the BS and RN B band without RN 68% use a transmit power of 30dBm and the BS is equipped B band with RN 83% with a 120 degree sector antenna having 11dBi antenna

detailed description of the ARQ handling in RECs can be found in [8]. For relay deployments with more than two hops, an MBS offers additional degrees of freedom. Even though the BS initiates a handover to a RN in the E band, the BS or another RN with MBS might still be able to serve the UT on the B Band. In this case, outer ARQ retransmissions of delay sensitive traffic can be performed on the B band by these nodes. 5.4. MBS and cooperative relaying Next to single path relaying, cooperative relaying can be integrated as an add-on to single path relaying as proposed for example in [8]. A receiving node combines signals from more than one transmitting node. Figure 10. Coverage of B band with BS and part of the Cooperative relaying and intelligent deployment reduce RN having an B band interface. the total cost of a multi-hop network by reducing the number of relays needed for a given performance [8].

Thus, it is important to show, that the MBS concept fits

well with cooperative relaying. In particular we discuss it using the cooperative relaying concept in [8]. Multi-hop diversity is one example, in which a receiving node combines the signals received from previous nodes in the path. In a 2-hop DL path, the UT combines the signal from a RN with the signal from the BS that can be received on different resources. MIMO cooperative relaying is another example, where the BS first transmits the data to be forwarded in a cooperative transmission to the RN. Then the BS and the RN antennas form a virtual antenna array and perform a joint MIMO transmission on the same resources. In both cases the BS allocates the resources for all the cooperative transmissions, i.e. even in a case where the RN is equipped with an MBS, the BS also decides on Figure 11. Coverage of the B band with only BS having a B which band and resources the cooperative transmissions band interface. will take place. On the other hand, for relay deployments with more For the multi-hop diversity case, cooperative than two hops the BS might be able to reach RNs via one transmissions could in principle be scheduled on two hop on the B band and via multiple hops on the E band. different bands requiring the UT to be associated with In this case, it will be beneficial for delay sensitive traffic two bands at the same time which increases the UT to send data on the B band to the RN, which forwards it complexity and power consumption. Thus, cooperative then to the UT. transmissions on different bands should be avoided and the BS has to balance the gain from utilizing cooperative 5.3. ARQ in relay network with MBS relaying and from using different bands on the first and Another important aspect of a REC is the handling of second hop. However, as described above, by using the the outer ARQ (E2E ARQ) between BS and UT, HARQ context transfer, retransmissions can be performed sometimes also referred to as relay ARQ [8]. Without an on another band and additional diversity gain can be outer ARQ between BS and UT, the BS does not know obtained without requiring the UT to operate whether data sent to the RN is successfully transmitted to simultaneously on two bands. the UTs. Thus, in case of handovers, data that is still in This is not an issue in the MIMO cooperative relaying the buffer of RNs might be lost, even if the handover case, where the BS can send for example data on the E destination is within the REC. Additionally, an outer band and then perform a joint MIMO transmission on the ARQ (E2E ARQ) process is used on each hop to recover B band, whereas the UT only receives on the B band. from residual inner ARQ (HARQ) errors, caused for example by a NACK that is misinterpreted as an ACK. A 6. Conclusion

A new concept called Multi-Band Scheduler (MBS) S. Pfletschinger, “Flexible Spectrum Use between for future communication systems was introduced. This WINNER Radio Access networks”, IST Mobile Summit, scheduler allows for operation on multiple bands in a Greece, June 2006. delay constrained environment. The proposed tight [3] K. Doppler, He Xiaoben, C. Wijting, A. Sorri, integration between multiple bands enables a fast and “Adaptive Soft Reuse for Relay Enhanced Cells”, IEEE seamless switch between different bands. The Multi-Band Vehicular Technology Conference 2007 spring, April scheduler also ensures that the PHY and MAC layer 2007, pp 758-762. operation is abstracted from the higher layers. This means that the higher layers are not aware of the actual resources [4] https://www.ist-winner.org used, but only of the available capacity. The fast switch [5] M. Sternard, T. Svensson, G. Klang, “The WINNER between multiple bands adds additional degrees of B3G System MAC Concept”, IEEE Vehicular freedom for optimizing the network operation. Moreover, Technology Conference 2006 fall, Sept 2006. the MBS can be utilized to efficiently balance the load of the bands in the network or to provide required quality of [6] IST-WINNER II, “D6.11.2 Key Scenarios and service levels to the UTs. Implications for WINNER II”, Sept. 2006, available at https://www.ist-winner.org/deliverables.html The operation of the MBS was discussed in detail for two scenarios: Spectrum sharing and relays. [7] 3GPP TR 25.913 V7.3.0 (2006-03) Requirements for Evolved UTRA (E-UTRA) (Release 7). The spectrum sharing case comprises a multiband operation with a smaller band dedicated to the [8] IST-WINNER II, “D3.5.2 Assessment of relay communication system and an extension band that is based deployment concepts and detailed description of shared with another system but offers higher capacity. In multi-hop capable RAN protocols as input for the concept this scenario the MBS can be applied in two ways, on the group work”, June 2007, available at https://www.ist- one hand the MBS enables simultaneous access to a winner.org/deliverables.html guaranteed basic band and the band shared with another [9] K. Doppler, C. Wijting, J-P. Kermoal, “Multi-Band technology. On the other hand the MBS can be used for Scheduler for Future Communication Systems”, WiCom sharing spectrum between different operators of the same 2007, P.R: China, Sept. 2007, pp 6738-6742. technology where a part of the band is dedicated to each operator and the rest of the band is shared between the [10] Recommendation ITU-R M.1768, “Methodology for operators. Our simulation results show that using the calculation of spectrum requirements for the future MBS, a seamless switch can be made if the shared band is development of the terrestrial component of IMT-2000 no longer available. and systems beyond IMT-2000”, 2006. The relay case illustrates a scenario with different [11] Report ITU-R M.2078, “Spectrum requirements for propagation properties and thus different coverage area of the future development of IMT-2000 and IMT- the used bands. In this scenario RNs are used to extend Advanced”, 2006. the coverage of the high capacity extension band that has a higher propagation loss than the basic band. Our [12] Report ITU-R M.2079, “Technical and operational simulation results show that RNs are an effective way to information for identifying spectrum for the terrestrial balance the coverage of the bands. Thereby they greatly component of future development of IMT-2000 and IMT- increase the overall capacity of the network and the high Advanced”, 2006. capacity band is available to most of the user terminals. [13] M. Bennis, J. -P. Kermoal, P. Ojanen, J. Lara, S. Further, the MBS at both the BS and the RN enables to Abedi, R. Pintenet, S. Thilakawardana and R. Tafazolli, balance the network load on each hop by utilizing “Advanced spectrum functionalities for 4G WINNER different bands. radio network”, Wireless Personal Communications journal, Springer 2007 (accepted for publication). 7. Acknowledgement [14] K. Brueninghaus, D. Astely, T. Saelzer, et al. “Link The authors would like to thank Kennett Aschan for performance models for system level simulations for his valuable support and fruitful discussions during the broadband radio access systems”, Proceedings of the preparation of this article. PIMRC 2005, Berlin, September 2005 8. References [15] “Universal Mobile Telecommunications System (UMTS); Selection procedures for the choice of radio transmission technologies of the UMTS”, TR 101 112 [1] Recommendation ITU-R M.1645, “Framework and v3.2.0 (1997-11), UMTS30.03 overall objectives of the future development of IMT-2000 and systems beyond IMT-2000”, 2003. [16] IST WINNER II “D1.1.2 WINNER II Channel Models Part I Channel Models”, September 2007 [2] K. Hooli, S. Thilakawardana, J. Lara, J-P. Kermoal,

Copyright © 2008 SciRes. J. Water Resource and Protection. 2008; 1:1-65 20 D. ZHU ET AL. available at https://www.ist-winner.org/deliverables. html Concept and assessment of key technologies”, October 2007 available at https://www.ist-winner.org/ [17] IST WINNER II “D6.13.11 Final CG “metropolitan deliverables.html area” description for integration into overall System

Study on the flow-pollutant of the Kuncheng lake

Qin YI1, Ruijie LI1, Wenjin ZHU2, Jingjing CAO2 1Key Laboratory of Coastal Disaster and Defence, Ministry of Education(Hohai University) Xikang Rd. Nanjing, China 2Laboratory of Marine Environment, Hohai University, Xikang Rd. Nanjing, China E-mail: [email protected]

Abstract

It is based on the calculating results of the flow field of the Kuncheng Lake to simulate the diffusion of the chemical oxygen demand (COD) in the lake. And utilize the observed data and the calculating results of the water quality concentration field of the lake to achieve the water environmental capacity in the dry season. From the results, it is shown that the velocity of the lake is small and the direction is from the northwest to the southeast as the topographic form is the northwest higher than the southeast. Both the observed and the computed results of the COD concentration show that they are smaller than the standard limit value of COD emission concentration. The results will provide the advice to improve the water environmental quality of the lake in Changshu City, the ecological regime and scientific management of the lake. Keywords: Flow field; The chemical oxygen demand; Concentration field; diffusion; The environmental capacity

1. Introduction

The Kuncheng Lake, also named as the East Lake, the mathematic model largest lake in Changshu City and the seventh largest lake around the Taihu Lake area, has the reservoir capacity of 2.1. The basic equations of fluid model 45 million m3. The Kuncheng Lake, whose water quality maintains the Ⅲ–Ⅳ Standard of the surface water, can be The two-dimension fluid equations by depth integral: used for navigation, aquiculture, modulation the flood, ∂d ∂∂ irrigation and junketing in Shajiabang. In the 1970th the + ()ud⋅+() vd ⋅=0 (1) float grass was exuberant, the lake was limpid, the ∂∂tx ∂ y benthic animals were various and the distribution was ∂∂∂uuu ∂ d∂z ++=−−uv g gb +2sin vωφ + uniform, and the business of fishery was extensive. Since ∂∂∂txy ∂ x ∂ x 1/2 the 1990th, a great deal of industrial and sanitary sewage 1 ⎡ ∂∂∂∂⎛⎞uu⎛⎞222 gu⎤ ⎢ ⎜⎟εεςψddWuv++−+cos ⎥ has been dumping into the lake directly or indirectly, as ρdx∂∂∂∂xx x y⎜⎟ xy y 2 ( ) ⎣⎢ ⎝⎠⎝⎠ Cdz ⎦⎥ the economy around the lake area is developing rapidly; (2) and aquiculture has been developed and utilized in excess ∂∂∂vvv ∂ d∂z ++=−−uv g gb −2sin uωφ + as the extensive business of fisher becoming intensive. So ∂∂∂txy ∂ y ∂ y 1/2 it causes the ecological condition changing, such as the 1 ⎡ ∂∂∂∂⎛⎞vv⎛⎞222 gv⎤ ⎢ ⎜⎟εεςψyxddWuv++−+⎜⎟ yy sin ⎥ water grass has almost been disappeared and the ρ dx∂∂∂∂⎝⎠ x y y 2 ( ) ⎣⎢ ⎝⎠ Cdz ⎦⎥ (3) eutrophia of the lake has been rapidly. It should protect the lake as the water quality has been declined year after Where, d is the depth of flow; g is the gravity year. z ρ acceleration; b is the bed elevation; is the water The hydrodynamic and environmental model of lake density; ς is the experiential coefficient of wind stress; has been used to simulate the variational trend of the W is the wind speed; ψ is the angle between the wind current, the water level and the environmental impact direction and the positive X axis; Cz is the Chezy factors (take the chemical oxygen demand (COD) for ε example). coefficient; ij is the eddy viscosity, determined by the fluid character and the fluid turbulent intensity; ω is the 2. The basic equations of two-dimension fluid

Copyright © 2008 SciRes. J. Water Resource and Protection. 2008; 1:1-65 22 Q. YI ET AL. earth rotational speed; φ is the local latitude; from 180.05 m2 to 26362.05 m2. There are 3410 2sinvω φ 、 2sinuω φ represent the Coriolis force. triangular mesh elements and 7245 nodes in the model. Grid distribution is shown in Fig.2. Two main intakes are 2.2. The basic equations of environmental model fetched nearby the Zhangjiagang Bridge and the Mochenghe Bridge, and the boundary conditions are The substance transport equation by the depth integral: controlled by the flux. Two main vents are fetched nearby ∂∂∂∂∂∂∂ccc c c Rc( ) the Sujiaweng Bridge and the Laotang Bridge, and the ++=uv Dxy + D +−−σ kc (4) boundary conditions are controlled by the water level. ∂∂∂∂∂∂∂txyxxyy h The wind velocity on the measurement day in December Where, h is the water depth; c is the concentration of was 1-3 scale, and in June it was 2-3 scale. the contamination; t is temporal hour; u, v represent the 3.1. The verification of the water level speed of the x, y axes respectively; DD, represent x y Fig.3-Fig.6 are shown the comparison of the computed the diffusion coefficient; σ is the source-sink item; and the observed water level results nearby the Rc() is the capacity of rainfall or evaporation; k is the Zhangjiagang Bridge and the Mochenghe Bridge in first-order decay coefficient, and could be represented as December and June respectively. The dots represent the follows: observed results, and the continuous lines represent the computed results. It can be seen that the graph of the i Ct() −kit()− t0 water level computed is in good agreement with the = e (5) Cti ()0 observed results. The amplitude of the water level fluctuation is small. The water level of the lake in the Where, Cti () is the current concentration of the north is higher than the south, and in the east is higher than the west. contamination; Cti ()0 is the previous concentration. 3.2. The verification of the velocity 2.3. Boundary condition

The boundary condition of the normal zero flux was 3500000 Changshu City the Zhangjiagang Bridge the Luoxinggang used to the land boundary of the hydrodynamic and Bridge environmental model. The tangential sliding boundary 3499000 the Xinjiang Bridge

the Tangjialou condition, which allowed the current to flow Bridge parallellingly the boundary, was used in the 3498000 hydrodynamic model. Although these forcing conditions the Ni Bridge do not represent the lateral velocity of viscous fluid in the 3497000 flow field exactly, the application of the boundary the Center of the lake condition, under the practical situation, has reduced the 3496000 element numbers of the model system. The water level relation and flux relation are adopted to control the open the Dajishuigang 3495000 Bridge the reconditeness boundary. bridge 2＃

the Shajiabang 3494000 Bridge 5＃ the Ludangshizheng 3. The flow-pollutant calculate-ion Bridge the Xinantang Bridge the Linjiahe the Laotang Bridge Middle Bridge the Zhangjing Middle 3493000 Bridge the Zhoujing Middle The finite-element method is adopted to the Bridge hydrodynamic and environmental calculation of the 568000 569000 570000 571000 572000 573000 Kuncheng Lake. Simulate the diffusion of COD in the lake under the simulation of the flow field. Figure 1. The schematic plan of the Kuncheng Lake Fig.1 is the schematic plan of the hydrologic basin of The graphs of the computed and the observed the Kuncheng Lake. The shape of the whole lake appears velocity data nearby the Laotang Bridge, the a trapezium. As there are many rivers disemboguing into Zhangjiagang Bridge, and the Sujiaweng Bridge, the the lake, some of whose flux is small and even little, only center of the Kuncheng Lake in December and June some main ports(two main intakes: the Zhangjiagang are shown in Fig.7-Fig.12. The dots represent the Bridge, the Mochenghe Bridge; two main vents: the observed results, and the continuous lines represent the Sujiaweng Bridge, the Laotang Bridge) are considered in computed results in the figures. order to simplify the calculation and shorten the calculating time. Encrypt the grids of the entrance of the The hydrographic and water quality measurements ports and some narrow areas in the model, and the were observed for two phases, from 07:00 on 18th in variational depth of the central hydrologic basin is not December in 2005 to 17:00 on 19th in December, and obvious and the velocity of flow is slow, so the grids of from 07:00 on 4th in June in 2006 to 17:00 on 5th in June. the model are great in the central lake are large, the areas It can be seen from the verification that most of the rivers

Copyright © 2008 SciRes. J. Water Resource and Protection. 2008; 1:1-65 STUDY ON THE FLOW-POLLUTANT OF THE KUNCHENG LAKE 23 upstream disembogue themselves into the lake from the 3.50 3.40 the observed data west and the northwest, venting from the east and the 3.30 the computed data 3.20 southeast, and the main intake is near the Zhangjiagang 3.10

3.00 Bridge and the velocity there is fast. The computed results Z(m) 2.90 can describe the hydrodynamic characteristic of the lake 2.80 2.70 primarily. 2.60 2.50 0 1020304050 t(h)

Figure 5. The verification of the water level nearby the

3499000 Mochenghe Bridge in December

3.50 3.40 the observed data 3.30 the computed data 3.20 3498000 3.10

3.00 Z(m) 2.90 2.80 3497000 2.70 2.60 2.50 0 1020304050 t(h) 3496000

Figure 6. The verification of the water level nearby the

3495000 Mochenghe Bridge in June

0.50 the observed data 3494000 0.40 the computed data

0.30 569000 570000 571000 572000 573000

V(m/s) 0.20

Figure 2. The grid plan of the Kuncheng Lake 0.10

0.00 3.50 0 1020304050 the observed data t (h) 3.40 the computed data 3.30 3.20 Figure 7. The verification of the velocity nearby the 3.10 3.00 Zhangjiagang Bridge in December Z(m) 2.90 2.80 0.50 2.70 the observed data 2.60 0.40 the computed data 2.50 0.30 0 1020304050 t (h) V(m/s) 0.20 0.10 Figure 3. The verification of the water level nearby the 0.00 Zhangjiagang Bridge in December 0 1020304050 t (h) 3.50 the observed data 3.40 the computed data 3.30 Figure 8. The verification of the velocity nearby the 3.20 Zhangjiagang Bridge in June 3.10 3.00

Z(m) 0.30 2.90 2.80 the observed data the computed data 2.70 0.20 2.60 2.50 V(m/s) 0 1020304050 0.10 t (h)

0.00 Figure 4. The verification of the water level nearby the 0 1020304050 Zhangjiagang Bridge in June t (h)

Figure 9. The verification of the velocity nearby the Sujiaweng Bridge in December

0.50 quality and the evolvement trend of the city and materialize the relationship between the intensity of the 0.40 the observed data human activity and environmental protect in the city. the computed data 0.30

V(m/s) 0.20

0.10

0.001m/s 0.00 3499000 0 1020304050 t (h) 3498000 Figure 10. The verification of the velocity nearby the Sujiaweng Bridge in December the Sujiaweng Bridge in June 3497000

0.50 the observed data 3496000 0.40 the computed data

0.30 3495000

V(m/s) 0.20

0.10 3494000 0.00 0 1020304050 569000 570000 571000 572000 573000 t (h) Figure 13. The flow field in December Figure 11. the verification of the velocity nearby the center of the lake in June

0.001m/s 3499000 1.00

0.80 the observed data the computed data 3498000 0.60

V(m/s) 0.40

3497000 0.20

0.00 0 1020304050 3496000 t (h)

Figure 12. The verification of the velocity nearby the center 3495000 of the lake in December

3.3. The flow field of the Kuncheng lake 3494000 The flow field diagrams of the lake in December and 569000 570000 571000 572000 573000 June are shown in the Fig.13 and Fig.14, respectively. In Figure 14. The flow field in June order to display the flow field of the lake obviously, the velocity fast than 0.001m/s is just considered 0.001m/s. It 3.4. The COD concentration diffusion diagram of can be seen that the flow field reflect the hydrodynamic field. It could be shown, from the figures, that the the Kuncheng lake distribution of the velocity is non-homogeneous, and the The chemical oxygen demand (COD) is defined as the velocity in some areas in December is larger than in June dosage of the used oxidant, under the definitive condition, as the observed flux data of two main intakes of the when adopting the definitive strong oxidant to dispose the Zhangjiagang Bridge and the Mochenghe Bridge in water sample. It is the index of the reductive material, December are greater than in June, while the observed such as the various organic substances, the nitrite, the water level data of two main vents of the Laotang Bridge ferrite and the sulfide in the water sample. The reductive and the Sujiaweng Bridge in December are less than in material is the organic substances mainly except the June. specific water sample. Some organic substances, the The water quality condition and the eutrophia potential elements of which will become more various when the of the lake in the city, could indicate the environmental water quality is polluted, are contained in the native water

Copyright © 2008 SciRes. J. Water Resource and Protection. 2008; 1:1-65 STUDY ON THE FLOW-POLLUTANT OF THE KUNCHENG LAKE 25 at any degrees. The organic substances are mainly In December, the average value of the observed data of composed by the humus and the non-humus in the COD concentration in the center of the lake is 7.55 mg/L, commonly native water. Use the strong oxidant to draw and the average value of the computed data is 7.71 mg/L; away the carbon and hydrogen of the some oxidatively in June, the average value of the observed data of COD organic substances, so it is also using the chemical concentration in the center of the lake is 6.68 mg/L, and oxygen demand as the index of ineasuring the relative the average value of the computed data is 7.75 mg/L. As content of the organic substances. The oxygen demand is the observed flux data in the intakes in June are smaller one of the indexes to estimate the drinking water, the than in December, and the same as the vents are, and at industry water, the water treatment and the corrodibility, the same time, the computed velocity data in some area in and is very important to evaluate the extent of the water the lake are smaller in June. Therefore, the COD diffusing pollution. Then simulate the concentration distribution of to the vents is slow, and the computed data of the COD the environmental impact factors COD. concentration in June are higher than the observed data. Figure 15. and Figure 16. are the contour charts of the 4. The calculation of the water environmental CODMn. capacity of the lake It is the important link and the technical key problem of the amount manipulation in the study of the water

7 .32 26 environmental capacity. Only do find out and master the water environmental capacity of the lake, and then 232 7.3 confirm the waste load allocation of the water basin, the

7.3236 distribution of the water basin payload to the each emission source, the relationship between the

240 environmental goal and the input of the emission source, 7.3 7.3240 and the objective to control the water pollution.

7.3242 4.1. The water environmental capacity model of the organic substances According to some literatures, lakes (reservoirs) could 7 .3244 be divided into two sorts: the completely mixed type and the non-completely mixed type. To some medium and small-sized lakes (the area not more than 50km2), their areas are small and the closeness is strong. When the contamination is dumping into the lake, under the effect of the lake flow and wind wave, there may emerge the Figure 15. The contour chart of the CODMn in the lake in phenomenon that the water will intermix uniformly, so December the lake of the completely mixed type will intermix uniformly, that is to say the coefficient of the asymmetry is near 1.0. So the Kuncheng Lake here is sorted as the lake of the completely mixed type. Therefore use the uniform mixture and easy degradation water quality model to simulate the organic substances of the water

7.6 000 environmental capacity calculation.

7. 64 00 It is shown that there is a relationship between the

7 .7 0 water environmental capacity calculation of the lake or 0 0

0 0 the reservoir and is impoundment (the volume of the 0 .6 7 water capacity). So it must have a determinate reservoir capacity of safety to project the water from the pollution.

0 0 4 .6 And it can make the lake or the reservoir exert its 7 deactivating function, and control the contamination

0 0 0 00 0 .5 6 7 under the safe level. Usually the reservoir capacity of . 7 safety, the payload of the lake or the reservoir equaling to the impoundment of the lake or the reservoir when the water achieves its permissible maximum payload, is called the critical reservoir capacity of contamination control. Another way, the environmental capacity also Figure 16. The contour chart of the CODMn in the lake in could calculate by the total amount of the contamination June dumping under the standard of maintaining the water

Copyright © 2008 SciRes. J. Water Resource and Protection. 2008; 1:1-65 26 Q. YI ET AL. environmental quality. Taking the lake capacity in the dry capacity was 8231.421t/a. season as the safe capacity, the formula for the environmental capacity of COD in the paper can be 4.3. The water ecosystem construction in the lake expressed as: Because of the natural disaster and the human elements inducing the some affection to the ecological 1 WCCVKCVCq=−++()No N N (6) environment, it is found that, in the field survey of the Δt lake, there were a lot of hyacinth and alternanthera Where, W is the water environmental capacity of the philoxeroides, while the vascular plants were little. On the lake, g/d. △t is the temporal hour of dry season, other hand, in the 1980th and in the early 1990th, there determining by the variation of the water level in the year; were too much the crabs and the fishes lived by the water if the amplitude of the variation is large, △t adopts 60~90 grass, and the water grass was used excessively. days; and if the amplitude is stabilization, △t adopts It is emphasized by the multiple stable states theory in 90~150 days. CN is the standard concentration for the the shallow lakes that, the water vegetation will be relived water environmental quality of the contamination, mg/l. and the ecological environment of the fishery will be C0 is the original concentration of the contamination in rebuilt by adjusting the fishery configuration, eliminating the lake, mg/l. V is the safe capacity, m3. q is the flux the environmental factor of endangering the submerged discharging from the lake during the safe capacity period, plant, and controlling the input of the nutrition outside m3/d. K is the natural attenuation coefficient of the and the water level. Therefore it could be regulating the contamination in the lake, 1/d; and can be reversely lake by the navigation management and the sewage ascertained by the observed data and expressed as prevention, by growing the vascular plants, creating the follows: condition for the submerged plant living, and improving the fishery capability, to achieve the goal that optimize PtΔ +− Mo M K = (7) the water environment and realize the sustainable and ΔtM· o harmonious development. Where, P is the quality of the contamination dumping 5. Conclusion into the lake daily, kg/d. P△t is the total quality of the contamination dumping into the water at the time of △t, It can be seen from the hydrodynamic calculation, the kg. MO is the total quality of the contamination at the current velocity is little, and the direction is from the initializing period, kg. M is the total quality of the northwest to the southeast as the result of the runoff of the contamination at the end of the period, kg. Yangtze River and the landform character that is the northwest higher than the southeast. And the lake is the 4.2. The calculation of the water environmental small velocity lake. capacity of the lake at the present state The oxygen demand substances are rooted in the As the water level of the lake rises slow and falls slow, industrial sewage, the sanitary wastewater and the various and the amplitude of the variation is little, the dry season humus. Not only will the apparent mass of the water be from October in year to February in next year and the wet changed, but also the existence of the biologic will be season from June to September in year, the paper imperiled, if the chemical oxygen demand is overproved. considers that the dry season will last 150 days during the So according to the goal of achieving the Ⅲ category calculation of the water environmental capacity of the water standard, the environmental capacity of CODMn in lake. The main function of the lake is modulation the the lake is8231.42t/a. impoundage, navigation and aquiculture, according to the Environmental Quality Standards for Surface Water of The paper is proceed based on the data observed on the People’s Republic of China (GB3838-2002), so the two days (twice a day) during in December and June. And lake is assorting normally as the Ⅲ category and the advise to enhance the hydrographic and water-quality standard boundary value of the chemical oxygen demand monitor, as it is a complexly physical, chemical and biotic (COD) is 20 mg/L. Seen from the observed data, the process for the contamination in the lake and the concentration of COD in the lake is smaller than the parameters are various, and the limitation of the observed standard boundary value of the water quality. data will lead to the errors. Adopt the data observed in the dry season in 6. Acknowledgement December in 2005 as the designedly hydrographic condition. Obtain the environmental capacity in the dry This study was supported by the National Nature season from the results of the concentration field Science Foundation of China (Grant No. 50339010). calculation of the water quality. During the calculating of the COD, the natural attenuation coefficient could be 7. References obtained by the formula (7). Finally, the natural [1] Gu Jun-ming. Study on Water Resource of Changshu. attenuation coefficient of the chemical oxygen demand Journal of Changshu College. Vol.17, No.2, pp. 81-83, COD in the lake is 0.006/d, and the environmental

Mar.2003 Wind-driven Current in Lake. Journal of Hydraulic Engineering. Vol.12, (2004) 34-38 [2] Li Rui-jie, Yan Yi-xin, Song Zhi-yao. Calculation of Suspended Sediment Transport in Taiping Waterway. [5] Peng Qin-wen. Research on Stochastic Diffusion Journal of Sediment Research. No.4, pp. 46-51, 2003 Water Quality Model. Advances in Water Science. Vol.17, No.1, pp. 113-115, 2006 [3] Wang Wei-lun, Chen Long-xing. Soil-Water Protection and Environmental Construction of Changshu [6] Chong Jia-rong, LING Qu-fei, YANG Cai-gen. City. Resource Development and Market. Vol.11, No.4, pp. Investigation and Fishery Utilization of the Plankton in 176-178 , 1995 Kuncheng Lake. Journal of Xinyang Normal University (Natural Science Edition). Vol.16, No.4, pp. 444-446, [4] Zhang Fa-bing, Hu Wei-ping, Qin Bo-qiang. Oct.2003 Numerical Analysis on Influence of Topography on

Purification of river flowing into Dian-lake by ecological floating-bed system

Yangjun GAO, Congjun SUN Water Research Dept. Shanghai Academy of Environmental Science, Shanghai, China E-mail: [email protected]

Abstract

The aim of the study was to examine the nutrient removal efficiency by floating-bed system grown aquatic plants and filled with spherical elastic porous stuffing materials for improving water quality of the river flowing into Dian-lake. The floating-bed system consisted of an aquatic plant unit, three groups of elastic stuffing units and an aquatic plant unit. The results showed that the whole ecological floating-bed system had good performance to purify the wastewater by plant nutrient uptake, nitrification activity of root-associated and bio-membrane bacteria, filtration and sedimentation. The concentration of CODCr, NH4+-N decreased 65.4%, 52.5% in routine aeration condition respectively and the numbers were 46.8%, 17.51% in low intensity aeration condition. The removal of CODCr, NH4+-N, TN and TP in routine aeration condition floating-bed system were better than those in the low intensity aeration condition system and had significant difference. There was high nitrate concentration accumulation in both two kinds of intensity aeration conditions. The higher nitrate and orthophosphates removal in the floating-bed system have to be depended on aquatic plant uptake. Further research will be done to identify the nutrient uptake by large amount of aquatic plants in the whole system.

Keywords: Eutrpphication; Floating beds; Aquatic plant; Elastic stuffing; Nitrogen; Phosphous; Dian-lake essential cornerstone of eutrophication control. Both of N 1. Introduction and P are considered to be the limiting elements of Dian-lake is the biggest fresh water lake in Yunnan primary productivity in most freshwater ecosystems, and plateau in China. Its water quality has been becoming therefore to be the control targets for the restoration of poor since 1980’s with the .population growth, industrial freshwater ecosystems [4].Efforts to restrict fluxes of N improvement and agriculture fertilizer heavily application. and P in streams and rivers will be necessary to improve The degradation of Dian-lake water resources by the eutrophication-related water quality of flowing water. eutrophication result in losses of component species, as [5] well as losses of the amenities and service that its system N and P removal by means of the cultivation of provides. [1] According to the Environmental Quality aquatic macrophytes is desirable for the restoration of Report of Kunming municipality Yunnan Province 2006, eutrophic water bodies such as lakes, streams, reservoirs, the water quality of Dian-lake is very poor, belonging to ponds and marshes. [6]. Harvesting aquatic plants with low quality of VI which has been hypertrophic. [2]Dian- assimilated and stored N and P is effective for controlling lake has 29 main streams and rivers flowing into it. The freshwater eutrophication, and the utilization of harvested quantity of flowing rivers is the main water source of aquatic plants can provide economic returns and generate Dian-lake. Especially, the amount of Da-qing river flux valuable products, e.g., biogas, biofertilizer, biomaterial, accounts for 18%. In recent study, it found 95% of 19 and even animal food. [7]The floating bed systems are monitoring rivers water quality monitoring data failed to effective measures to eliminate the dissolved forms of N meet the widely accepted surface water standard. A great and P in wastewater. [8]Spherical elastic porous stuffing deal of untreated waste effluent directly discharged to material is also a good medium basing on the these streams and rivers flowing into Dian-lake.[3]These comprehensive function of the bio-membrane formed on data suggest that the water quality in a majority of Dian- the surface of bio-medium to control water pollution. It is lake streams and rivers is poor from the standpoint of effective to improve the eutrophication water quality of eutrophication. scenic water bodies. [9] Eutrophication is the process by which water bodies However, the utilization of floating bed has never are made more eutrophic through an increase in their been used in Dian-lake eutrophication control although it nutrient supplies. Nutrient loading restriction is the has been widely used in Japan, Germany and European

countries to control water eutrophication.[10]In this paper, From July. 10 to Nov. 4, 2007, influent, effluent the main objective was to evaluate the attempt to remove water of each unit of system were sampled approximately nutrients and improve the river water quality flowing into every four days under normal conditions to evaluate the Dian-lake by floating-bed systems grown aquatic plants system treatment performances. Water samples were and filled with spherical elastic stuffing in different analyzed for chemical oxygen demand (CODCr), aeration intensity conditions. The nutrient removal ammonium-nitrogen (NH4+-N), nitrate-nitrogen (NO3-- efficiency was examined, and the potential application of N), total nitrogen (TN) and total phosphorus (TP). All the floating bed in Dian-lake valley streams and rivers was parameters mentioned above were determined according explored. to the method as described in the Standard Method for Examination of Water and Wastewater (Standard Method 2. Material and Methods for the Examination of Water and Wastewater Editorial Board, 2002) 2.1. Floating-bed system design 2.4. Statistical analysis The floating-bed system was shown in Fig 1. It The treatment efficiency was calculated as the percent consisted of five treatment units ranking as aquatic plants removal R for each parameter, which was calculated by floating bed unit, three elastic stuffing floating bed units R=(1-Ce/Ci)×100,where Ce and Ci were the effluent and and aquatic plants floating bed unit. Each planted floating bed was made of polyethylene foam had a size of influent concentrations in mg per liter. Mean influent 39.5×27×3 cm(in length× width× height ). On the value of the system was used to calculated removal rate floating beds, there were two kinds of young aquatic for each parameter to eliminate the difference. All plants canna (Canna generalis Bailey) and typha (Typha statistical analysis was performed using the SPSS angustifolia) obtained in Dian-lake local area. The elastic software package, including analysis of variance stuffing was put into Da-qing river wastewater (ANOVA). beforehand, and had a good performance of biomembrane formed on the surface, then it was put into 3. Results and discussion the elastic stuffing floating bed provided with different oxygen concentration. DO was from 4 to 6 mg/L in 3.1. Purification process routine aeration condition and 0.5 to 1 mg/L in low intensity aeration condition. The elastic stuffing material The whole purification process included several parameters were shown in talbe1.The floating beds were phases shown in Fig. 2. The aquatic plants adopted in the then placed into plastic tanks which had a size of floating bed which had well-developed root system 40.5×28×24 cm(in length× width× height )and filled with offered the expanded adhesive base for microorganism eutrophic water from Da-qing river flowing into Dian- and resulted in the formation of mutual beneficial sub- lake. The tank had an effective volume of 20 liter. system basing on the coordinated and additive effects. Some metabolite secreted by aquatic plants roots during its growing process offered nutrition and protection for all kinds of heterotrophs. The elastic stuffing floating bed was kept a suitable oxygen condition. Under these condition, nitrogen and phosphorus removal microorganism started to work. Their purification mechanisms Figure. 1 Ecological floating-bed system for were described as follows. Nitrogen removal process wastewater treatment included nitrification and denitrification. Phosphorus Talbe 1. Parameters of elastic stuffing material removal process was that under the aerobic condition, the bacteria used the energy released from the oxidation Diameter wire diameter Mass specific surface void ratio decomposition reaction of the organic matter in the cell to (mm) (mm) (kg/m3) area(m2/m3) (%) 140 0.5 2.65-3.06 265-305 >99 absorb the phosphorus existing outside the cell. The difference between the absorbing and releasing speed caused the excessive absorption of phosphorus. 2.2. Operation and monitoring 3.2. Improvement of water quality and removal The Eutrophic water of Da-qing river flowing into performance Dian-lake was continuously pumped into the floating-bed The removal mechanism of the floating bed system is treatment system. The influent rate was adjusted to activate the purification capability of the whole manually and checked regularly to achieve a mean treatment by aquatic plants growth and elastic stuffing hydraulic residence time of 7.14hr which was the actual biomembrane. During the system running process, COD average residence time of Da-qing river. The operation and TN influent concentration were not significantly and monitoring of the treatment system was conducted different in routine aeration and low aeration condition between July to December 2007. but not with TP (Table 2). The main reason was the influent quality fluctuation which was directly affected 2.3. Water sampling and chemical analysis

30 Y. GAO ET AL. by the upriver. Upriver area was distributed with high mineral phosphorus that could be assimilated by the density population, small industry. Most amount of the plants. Removal of phosphorus occurred by sorption, wastewater was discharged into the river flowing into complexation, precipitation and assimilation by microbial Dian-lake without treatment, especially in rainfall season. and plant biomass. The removals for COD decreased by filtration and adsorption in routine aeration and low aeration were TN summed the nitrogen in ammonium, oxidized 65.42% and 46.8% respectively. The aquatic plant roots forms and aggregate organic forms. Ammonium provide a large area for microbial growth and allow for concentration was reduced. Most ammonium was biofilm formation. The solids cling in the root systems converted to nitrate nitrogen. Paralled to the NH4+-N were then decomposed and mineralized by bacteria. The decreased 52.5% and 17.51% respectively in routine floating bed system showed good performance in aeration and low aeration condition, the nitrate nitrogen degradation COD in both routine aeration and low concentration increased from 0.02 to 5.90mg per liter and aeration condition. 0.21 to 1.96 mg per liter. The total nitrogen concentration decreased not significantly. The removals for TN were TP decreased in the treatment system, but was not 12.64%, 8.13% in routine aeration and low aeration completely eliminated by the system. It decreased by 17.31% and 8.09% in routine aeration and low aeration condition. The main reason was possibly that the respectively. Phosphorus compounds were commonly denitrified condition had not been formed. classified into orthophosphates, acid-hydrolyzable The differences in removal efficiencies of COD, TP phosphates and organic phosphates. Acid-hydrolyzable and TN between the different aeration intensity conditions phosphates were negligible in wastewater. Organic were significant. phosphorus was converted by the bacterial activity into Figure.2 Diagram of purification process of ecological floating bed system

Aquatic Aquatic plant growth uptake plant Bacteria metabolism uptake

Phosphorus Precipitating Influent removal bacteria Phosphorus removal wastewater Bacteria Photosynthesis Organic matter decomposition bacteria + Elastic NH4 Organic nitrogen Ammonitication stuffing degradation Nitrification NO - NO - bacteria 2 3 Denitrification

3.3. Purification performance for floating- bed Table 2. Influent parameters and removal efficiencies units Aeration Mean+ Parameters Min Max The floating bed units were ranked as shown in Fig.1. intensity Std.Deviation When wastewater pass through the treatment units, the 103.87 routine aeration +22.19a 78.20 135.70 degradable organic pollutant and the suspended solids COD was oxidated by microorganisms clinging on the aquatic influent low aeration 87.80 +8.78a 76.50 99.60 plants root and elastic stuffing biomembrance. In the first routine aeration 65.42 +3.03a 59.77 68.15 aquatic plant floating-bed unit, most pollutants were COD removed by filtration, adsorption and sedimentation. removal low aeration 46.80 +3.91b 40.56 50.90 Root released oxygen by plant photosynthesis. Dissolved routine aeration 0.95 +0.17a 0.76 1.26 oxygen in the water was improved thus enhanced the pollutants degradation. The plant roots provide a large TP influent low aeration 0.67 +0.20b 0.30 0.86 surface area for microbial growth and allow for biofilm routine aeration 17.31+1.36a 15.84 19.15 formation. The root heterotrophic bacteria decomposed the organic pollutants in aeration condition. On the other TP removal low aeration 8.09+1.69b 5.49 9.64 hand, some nutrients were used for plant growth. In routine aeration 13.22 +2.00a 10.29 14.88 aquatic plant floating-bed unit, organic loading decreased much. TN influent low aeration 12.32 +1.80a 10.52 15.34 routine aeration 12.64 +1.58a 10.47 14.78 After wastewater flowing to elastic stuffing floating- bed unit, the microorganism on the elastic stuffing TN removal low aeration 8.13 +0.45b 7.46 8.64 biomembrane began to work.

4. Conclusion 160 routine aeration

120 low intensity aeraton It was clear from the research that floating bed system with aquatic plant and elastic stuffing material was an 80 effective way in treating eutrophic river flowing into the Dian-lake water body. Compared with low aeration COD (mg/L) COD 40 condition system, routine aeration condition system had a higher potential for nutrient removal. Especially most 0 ammonium nitrogen was converted to nitrate nitrogen influnet aquatic plant elastic elastic elastic aquatic plant effluent and they were easy to be used by plants. The oxygen stuffing stuffing stuffing condition and floating bed units decided the removal floating bed unit efficiency of the treatment system. However, it was impossible for the system to achieve high removal of nitrate nitrogen since it could not provide both aerobic 1.6 and anaerobic conditions at the same time. In the whole system, because of no recirculation of wastewater and 1.2 solid in different oxygen condition, the total phosphorus and nitrate nitrogen removal were not as high as 0.8 expectation. The high removal efficiency could be

TP (mg/L) TP achieved by large number of plants growth utilization. 0.4 The application of floating-bed treatment system in Dian- 0 lake valley streams and river had been done and the i n f l u net a q u a t ic p lant e l a s t ic elastic elastic a q u a t ic p lant e f f l u ent performance of the engineering was in examination. stuffing stuffing stuffing Further research is still needed for enhancing the nitrate floating bed unit and orthophosphates removal by plant utilization in the whole system and the quantitative examination of the 16 plants growth utilization nutrient performance will be explored. 12

8 5. Acknowledgement

TN (mg/L) TN 4 The authors would like to thank Prof. Xiaoping LI and Manman Chen for their constructive suggestion. This 0 influnet aquatic elastic elastic elastic aquatic effluent work was supported by state high tech research develop- plant stuffing stuffing stuffing plant ment Plan, China. (Grant No. 2005AA6010100411 ). floating bed unit

6. References 16 [1] GUO Huai-cheng, SUN Yan-feng. Characteristic 12 Analysis and Control Strategies for the Eutrophicated Problem of the Lake Dianchi. Progress in Geography. 8 Vol. 21, No. 5, Sep., 2002 [2] Environmental Quality Report of Kunming City, 4 Yunnan Province 2006, Yunnan Kunming Municipality. NH4-N (mg/L) NH4-N 2007. 0 influnet aquatic elastic elastic elastic aquatic effluent [3] http://env.people.com.cn/GB/5424286.html plant stuffing stuffing stuffing plant floating bed unit [4] J.l. Garland, L.H.Levine, N.C. Yorio, M.E. Hummerick. Response of graywater recycling systems based on hydroponic plant growth to three classes of 8 surfactants Water Res. 38(8),1952-1962,2004 6 [5] Quinn,J.M. Guidelines for the control of Undesireable Biological Growths in Water(Consultancy 4 Report No.6213/2) Water Quality Centre, Hamilton, New 2 Zealand. 1991.

NO3-N (mg/L) NO3-N 0 [6] Forni, C., Chen,J., Tancionil, L., Caiola, M.G. influnet aquatic elastic elastic elastic aquatic effluent Evaluation of the fern Azolla for growth, nitrogen and plant stuffing stuffing stuffing plant phosphorus removal from wastewater. Water floating bed unit Res.35(6),1592-1598, 2001.

[7] Singhal and Rai, J.P.N. Biogas production from Figure.3 Purification performance of CODCr, TP, TN, water hyacinth and channel grass used for NH4+-N and NO3--N of the floating bed units phytoremediation of industrial effluents. Bioresource. Technol. 86,221-225, 2003 .

32 Y. GAO ET AL.

[8] Abe, K., Ozaki, Y. Comparison of useful terrestrial floating beds. J Xi’an Univ of Arch ＆ Tech. (Natural and aquatic plant species for removal of nitrogen and Science Editon) Vol.39, No.1, Feb. 2007 phosphorus from domestic wastewater Soil Sci. Plant Nutr. 44(4),599-607, 1998. [10] Vollenweider. R.A., Elemental and biochemical composition of plankton biomass, some comments and [9] Huang Ting-lin, Song Li-tong, Zhong Jian- explorations. J Arch Hydrobiol. 105: 11-29,1985. hong.Study on the urban scenic water purification by

Applications of electrochemical technique for organic wastewater treatment

Zucheng WU1, Xiangjuan MA1, Feng YU1, Fan LUO1, Xiangjuan MA2, Yanqing CONG2 1Department of Environmental Engineering, Zhejiang University, Hangzhou, China 2College of Environmental Science & Engineering, Zhejiang Gongshang University, Hangzhou, China

Abstract

This paper summarized the application of electrochemical technique for wastewater treatment, including wastewater disinfection and degradation of organic pollutants, especially for toxic and biorefractory organic pollutants, such as phenolic pollutants.

Keywords: Electrochemical technique; Application; Disinfection; Phenolic pollutant

1. Introduction versatility, energy efficiency, amenability to automation and cost effectiveness [3]. Applications of electrochemical technique for treatment of organic With the development of industry, more and more pollutants, removal of toxic metal ions, recycling of pollutants are discharged into environment and lead to valuable material and disinfection of wastewater have serious environment pollution. The demand for new already been the hot topic of several literatures. technology to remove or to detoxify organics especially those are toxic to biological treatment processes from Electrochemical reaction includes electrochemical aqueous effluents is widely recognized. As typical oxidation and electrochemical reduction. The former is contaminants, phenolic pollutants are found in many using an anode to generate hydroxyl radicals to degrade industries, such as oil refineries, coke plants, chemical the organic pollutant to small molecules or carbon dioxide and plastic plants [1]. Because of their resistance to and water. A model described in [3] for the course of the common microorganisms, they cannot be easily treated by anodic oxidation of an organic molecule assumes three common biological action. Therefore, the treatment major steps: should be of considerable importance in environmental Discharge of water forming an adsorbed hydroxyl protection. species: Electrochemical technique offers promising S[ ] + H2O = S[OH ] + H+ + e- (1) approaches for the prevention of pollution problems in the process industry [2] and has attracted a great deal of The adsorbed OH is the ‘activated state’ of water in attention for the treatment of such kinds of wastewater, O-transfer reactions to the organic molecule R: mainly because of its amenability to automation, high efficiency and environmental compatibility [2]. In S[OH] + R = S[ ] + RO + H+ + e- (2) electrochemical process, the main reagent, the electron, is Co-evolution of O2 by oxidation of water diminishing a ‘clean reagent’. Electron transfer is occurred on the the current efficiency: surface of electrode and an ion conducting medium at the action of electric field, then lead to a series of reactions. S[OH] + H2O = S[ ] + O2 +3 H+ + 3 e- (3) This implies that the performance of electrochemical Hydroxly radical is a very powerful oxidant (E0, processes may suffer from limitations of mass transfer 2.80V vs. SHE) which leads to a very effective oxidation and the size of specific electrode area. process. In our previous work, the direct evidence for •OH Removal and destruction of pollutant species can be formation was obtained by electron spin resonance (ESR) carried out directly or indirectly by electrochemical method [4]. oxidation /reduction processes in an electrochemical cell For the direct oxidation two main properties are without continuous feed of redox chemicals. In addition, required for a suitable anode: high oxygen overpotential the high selectivity of many electrochemical processes and corrosion stability. Thus, the choice of optimum helps to prevent the production of unwanted by-products, electrode material is extremely important. Some research which in many cases have to be treated as waste. results showed that Pt, PbO2 and SnO2 are good Attractive advantages of electrochemical processes are

Copyright © 2008 SciRes. J. Water Resource and Protection. 2008; 1:1-65. 34 Z. WU ET AL. electrocatalytic electrodes [5-8]. until 100 min. The value of fmix changes very slowly and insignificantly after 120 min treatment. As shown in Fig. In indirect oxidation, the most used oxidant 1, when phenol is almost completely removed at 120 min, electrochemically generated belonging to this category is the fmix is about 0.06 Lmg-1, which has reached the level chlorine or hypochlorite. Besides peroxide, Fenton’s for biological process. Consequently, it may be applicable reagent and peroxidisulphate, ozone is the other to degrade phenol when it is completely removed. This prominent oxidant which can be produced indicates that partial degradation of phenol followed by a electrochemically. biological process would be feasible. Partial degradation Electrochemical reduction is using an appropriate of phenol would be an alternative for wastewater electrode to generate active agents to destruct organic pretreatment. pollutant indirectly, such as H2O2 [9], Fenton’s reagent 1.0 5 f mix and so on. phenol 0.8 benezoquinone 4 Where Mred and M ox represent the reduction and organic acids ) 1 oxidation state of metal catalyst, respectively. Thus 0.6 3 ) - organic pollutants can be degraded quickly in the -1 presence of hydroxyl radicals in the electrochemical 0.4 2 (L mg (L mix system. c (mmolL 0.2 1 f 2．Treatment of wastewater by electro- 0.0 0 0 40 80 120 160 200 chemical approach time (min)

Figure 1. The variation of main products and toxicity in the 2.1. Improving the biodegradation ability of degradation of phenol. Operational conditions: initial wastewater phenol concentration 100mg L-1; circulated rate 1800mL Mentioned as above, electrochemical oxidation can min-1; temperature 25°C; K2SO4 1.0g L-1; current density use the hydroxyl radicals generated on the surface of 7.5mA cm-2; pH 5.6. anode to degrade organic pollutants, especially for some easily oxidized substances, such as phenol, aldehyde etc. Direct electrochemical oxidation is appropriate to treat the In practical use, it may be more worthwhile to treat high concentration and solubility organic wastewater. phenol to the biodegradable stage-aliphatic carboxylic acids followed by an economical biological process. As is The partial degradation of phenol by advanced well-known that, for a biological process, EC50 of electrochemical oxidation processes (AEOPs) was benzoquinone should not be lower than 3 mgL-1, i.e., f = conducted in our previous work [8], β-PbO2 modified 0.33 Lmg-1. Therefore it would be conservative to with fluorine resin and Ni-Cr-Ti alloy grid were used as conclude that the wastewater will be suitable for the anode and cathode, respectively. The main products biological treatment when the EC50 of the wastewater is formed during the electrochemical oxidation are below 3 mgL-1. Partial degradation of phenol improved benzoquinone (BQ), fumaric acid, and oxalic acid (Fig. 1). biodegradation ability of wastewater, combined by the It can be seen that phenol and BQ are vanished almost at followed biodegradation to treat organic wastewater the same time in 2 h. The concentration of organic acids offers a new way to degrade toxic and biorefractory increases at the first 40 min and then begins to decrease wastewater. till complete removal within 4 h. Hydroquinone, catechol, and maleic acid were also detected in very small 2.2. Disinfection of wastewater quantities in the degradation of higher initial Chlorine is a widely utilized disinfectant and used to concentration of phenol. Hydroquinone is the first product disinfect grey water prior to reuse [10], but some formed by oxidation of the phenol molecule. The literatures reported that this method would produce oxidation of BQ, after ring opening, leads to the formation carcinogen. Electrochemical disinfection by in-situ of aliphatic carboxylic acids such as fumaric acid and generated radical species exhibited perfect bactericidal oxalic acid. The final products are carbon dioxide and capability and can make up the disadvantage of Cl2 water. The experimental results show that the main disinfection. Fig. 2 shows the electrochemical mechanism of electrochemical oxidation can be classified disinfection efficiency at different current density and as (a) complete oxidation of the contaminants to CO2, disinfection time. Germicidal efficiency was increased water, and other inorganic products, (b) modification or with the increasing of current density and treating time. alteration of the chemical structures of the organic Germicidal efficiency of 100% was achieved with contact molecules to make the separation well or easier, and (c) time of 5 min and current density of 7 mA cm-2 [4]. The partial destruction of the molecules to make it less toxic or main mechanism of electrochemical disinfection is as more biodegradable [8]. follows: at the action of electron field, bacteria was Fig. 1 also shows the variation of the toxicity (fmix) adsorbed on the surface of electrode and reacted with the during phenol degradation. The value of EC50 reaches the hydroxyl radicals generated in the electrochemical peak in no more than 10 min and then sharply decreases process, and then the cellularity was destroyed and

Copyright © 2008 SciRes. J. Water Resource and Protection. 2008; 1:1-65. APPLICATIONS OF ELECTROCHEMICAL TECHNIQUE FOR ORGANIC WASTEWATER TREATMENT 35 attained the aim of disinfection. HO⋅ + RH →HORH⋅ (12) 100 HORH⋅ + O2 → ROH + HO2⋅ (13) 90 80 Obviously, in the FACEC, the side reactions at the 70 electrode or the bulk of the solution would compete with 60 the main reaction or consume the oxidants generated. 50

40 Therefore it is very important to choose suitable

30 5 min conditions as well as electrode materials to ensure the 20 10 min main reactions both at the electrode and the bulk of the 15 min Bacteria removal rate (%) rate removal Bacteria 10 30 min electrolyte could be strengthened in harmony. Firstly, it 0 01234567 was the current that should ensure the electrode voltage in Current density (mA cm -2) a reasonable range. Thus the oxidation of ferrous ion would be depressed and not to affect the anodic reaction Figure 2. Bacteria removal rate of electrochemical that generated hydroxyl radicals, simultaneously, there disinfection at different contact time and current density. generation of ferrous ion could also be fulfilled. Secondly, it is the suitable ratio of the concentration of ferrous ion to the rate of air sparged. Therefore there would be not many 2.3.Synergetic effects of anodic-cathodic residual ferrous ions affecting the anodic reaction and the hydrogen peroxide formed by the reduction of oxygen electrocatalysis for phenol degradation could be continuously catalyzed by the ferrous ion. In Although electrochemical oxidation has some such conditions, the beneficial effects would be achieved; advantages, such as amenability to automation, high therefore the rate of phenol degradation would be greatly efficiency and environmental compatibility, but the improved [11]. reaction mechanism and effecting parameters are need to further study. In recent years, it has been a trend to develop combined processes with one or more kinds of AOPs such as UV / H2O2, UV / Fe3+, UV / Fe2+ (Fe3+) /H2O2 which have been found existing synergetic effects. The role of cathode has not been paid enough attention to for a long time; at present, the trend has been towards electrogenerated reagents such as hydrogen peroxide, which leaves no inorganic residue after reaction with the organics. The Synergetic effect of anodic-cathodic electrocatalysis in the presence of ferrous ion (FACEC) was studied [11]. Fig. 3 shows the possible principal mechanism of phenol degradation by FACEC. Obviously, Figure 3. The schematic diagram of the main mechanism of the extent of the reaction would depend on the catalytic the phenol degradation by FACEC characteristic of the electrode and the operation conditions. The hydroxyl radicals were generated from 3. Conclusion the water molecule which was adsorbed on the surface of lead dioxide under anodic polarization. Equation (9) is the Applications of electrochemical technique for main reaction: wastewater treatment are still in developing stage, to explore a high efficiency and cost-effective technology PbO2(h+) + H2Oads → PbO2(⋅OH)ads + H+ (9) has been an active research scope. Although some At the anode, there also existed side reaction: electrochemical processes are in small scale, but with the development of new electrode materials and the union H2Oads → 1/2 O2 + 2H++ 2e- (10) technique of some other approaches, electrochemistry At the cathode, dioxygen was reduced to hydrogen technology will exhibit its particular superiority in dioxide. The hydroxyl radical was formed from the environmental fields. hydrogen dioxide under catalysis of Fe(II). There existed side reaction of hydrogen generation: 4. References 2H+ + e- → H2 (11) [1] V.S. DeSucre, and A.P. Watkinson. “Anodic oxidation By stirring, the reactive substances such as hydroxyl of phenol for waste water treatment,” Can. J. Chem. Eng., radicals and hydrogen peroxide would be transported to vol. 59, pp. 52–59, 1981. the bulk of the electrolyte where reactions that are similar to Fenton reaction would take place. In the presence of [2] K. Rajeshwar, J.G. Ibanex, and G.M. Swain, hydroxyl radical, the contaminants would be easily “Electrochemistry and the environment,” J. Appl. oxidized and finally into carbon dioxide after a series of Electrochem. vol. 24, pp. 1077-1091, 1994. chain reactions:

[3] K. Jüttner, U. Galla, and H. Schmieder. oxidation of phenol for wasterwater treatment using SnO2 “Electrochemical approaches to environmental problems anode,” J. Appl. Electrochem. vol. 23, pp. 108-112, 1993. in the process industry,” Electrochim. Acta, vol. 45, pp. [8] Z.C. Wu and M.H. Zhou, “Partial degradation of 2575–2594, 2000. phenol by advanced electrochemical oxidation process,” [4] Y. Q. Cong, Z.C Wu, and Y.Q. Li. “Hydroxyl Radical Environ. Sci. Technol., vol. 35, pp. 2698-2703, 2001. Electrochemically Generated with Water as the Complete [9] M.A.Oturan, N. Oturan, C. Lahitte, and S. Trevin, Atom Source and its Environmental Application,” Chin. “Production of hydroxyl radicals by electrochemically Sci. Bull., vol. 52, pp. 1346-1348, 2007. assisted Fenton’s reagent application to the mineralization [5] R.A. Torres, W. Torres, P. Peringer, and C. Pulgarin, of an organic micropollutant, pentachlorophenol,” J. “Electrochemical degradation of p-substituted phenols of Electroanal. Chem., vol. 507, pp. 96-102, 2001. industrial interest on Pt electrodes: Attempt of a [10] G. P. Winward, L.M. Avery, T. Stephenson, B. structure-reactivity relationship assessment,” Jefferson. “Chlorine disinfection of grey water for reuse: Chemosphere, vol. 50, pp. 97-104, 2003. Effect of organics and particles,” Water Res., vol 42, pp [6] X. Quan, S. Chen, J. Su, J.W. Chen, and G.H. Chen, 483-491, 2008 “Synergetic degradation of 2,4-D by integrated photo- [11] Z.C. Wu, M.H. Zhou, and D.H. Wang, “Synergetic and electrochemical catalysis on a Pt doped TiO2/Ti effects of anodic-cathodic electrocatalysis for phenol electrode,” Sep. and Purif. Technol. vol. 34, pp. 73-79, degradation in presence of iron (II),” Chemosphere, vol. 2004. 48, pp.1089-1096, 2002B. [7] Ch. Comminellis, C. Pulgarin, “Electrochemical

Copyright © 2008 SciRes. J. Water Resource and Protection. 2008; 1:1-65. J. Water Resource and Protection. 2008. 1: 1-65. Published Online June 2008 in SciRes (http://www.SRPublishing.org/Journal/jwarp/).

Enhanced degradation of nitrobenzene by ozone/zeolite process

Ke LIU, Qingdong QIN, Jun MA School of Municipal and Environmental Engineering, Harbin Institute of Technology, Harbin, China E-mail: [email protected]

Abstract

Degradation of nitrobenzene by ozone/zeolite process was investigated under different experimental conditions. The results showed that the removal efficiency of nitrobenzene was significantly promoted in the presence of zeolite compared with the case of ozonation alone. By investigating the effect of tert-butyl alcohol on nitrobenzene removal, it was concluded that nitrobenzene was mainly degraded by hydroxyl radicals in solution. The degradation rate of ozone/zeolite process was inhibited significantly by increasing ionic strength. When the ionic strength concentration increased from 0 to 1×10-3mol/L, the removal of nitrobenzene by ozone/zeolite process decreased from 81.2% to 31.6% correspondingly. The pH mainly affected the decomposition rate of ozone. As pH decreased, the degradation rate of nitrobenzene by ozone/zeolite process decreased. Finally, the adsorption of ozone on H-form zeolite was investigated. The results showed that ozone can be adsorbed on H-form zeolite, and finally decomposed. Keywords: Zeolite; Nitrobenzene; Hydroxyl radical; Adsorption

1. Introduction 6. Additionally, sufficient decomposition of MIB by ozone in the presence of high silica zeolites was achieved, The application of ozonation in water treatment is preventing the formation bromate. Nevertheless, there are widespread throughout the worldwide due to its high very limited reports on the use of ozone in the presence of oxidation potential [1, 2]. With the increase of chemically zeolite for pollutants removal from water and more effort very different refractory micropollutants in a broad range is required in this area in order for such process to be of water matrices, much more attentions have been paid practically applied. to enhance ozone decomposition to generate hydroxyl In the present study, nitrobenzene was selected as radical (·OH), the species of a known powerful oxidant target compound due to its low oxidation rate by ozone. (Ε0=2.8V), and that react with organics in an unselective Artificial zeolite was selected as solid catalyst and way in water. It has been found that ozone can be catalyzed ozone to remove nitrobenzene. The objective of 2+ decomposed effectively by Mn and H2O2 to this work is to investigate the efficiency of nitrobenzene produce ·OH to remove refractory pollutants. However, removal by ozone/zeolite process. Then influencing the residual metal ions and H2O2 need to be further parameters such as tert-butyl alcohol, ionic strength and removed as they may be harmful for humans. Therefore, pH are evaluated. Finally, adsorption and decomposition solid catalyst has been widely researched, such as characteristics of ozone in the zeolite are discussed in the activated carbon, TiO2，MnO2 and Al2O3. present experiment. Zeolite has been widely applied in water treatment for removing heavy metal, ammonia nitrogen and organic 2. Experimental section compounds due to its adsorption and ion exchange property [3, 4, 5]. Recently, it has been reported that 2.1. Materials zeolite can adsorb ozone to improve organic compound Artificial zeolite with SiO /Al O ratio of 1.5 was removal from water [6, 7, 8]. The results showed that the 2 2 3 rinsed well with 2mol/L NH Cl solution at room larger the SiO /Al O ratio the highest adsorption 4 2 2 3 temperature to remove residual OH- ions. Then, the capacity of water-dissolved ozone. The ozone sample was dried and calcined for 4 hours at 350℃ to decomposition rate was independent of SiO2/Al2O3 ratios in the range of 30-3000 or a solution pH in the range of 4- obtain H-zeolite. The specific surface area of zeolite was 70.35m2/g. The Ca2+ exchange capacity was not less than

38 K. LIU ET AL.

15mg/g. Nitrobenzene was purchased from Tianjin third removal factory (Analytical Grade) without further purification. The initial concentration of nitrobenzene used in the Fig.2 illustrates the effect of tert-butyl alcohol on the experiment was 240.4μg/L. The pH was adjusted with oxidation of nitrobenzene by ozone/zeolite process. perchloric acid. The ionic strength (I) was adjusted by Before ozonation experiment, the adsorption of tert-butyl alcohol on zeolite was carried out. It was found that no NaClO4 solution. The tert-butyl alcohol was used as radical scavengers. Other reagents in this study were all tert-butyl alcohol was adsorbed by zeolite. From Fig.2, it of analytical grades and were used without further can be seen that the presence of tert-butyl alcohol purification. significantly decreased the nitrobenzene removal by ozone and ozone/zeolite process. The nitrobenzene 2.2. Ozonation procedure and analytical method removal by ozone/zeolite process at 15min in the presence of tert-butyl alcohol of 5mg/L and 80mg/L was The ozonation process was carried out in a 350ml glass 81.2% and 18.8%, respectively. However, the inhibition cylinder equipped with a circle device to provide a of tert-butyl alcohol on ozone/zeolite process was lower homogeneous mixture. Ozone gas was produced with than that on ozone process. It was assumed that the high purity of oxygen (>99.99%) by ozone generator at nitrobenzene oxidation in ozone/zeolite process followed concentration of 5.9mol/min, and was fed into the reactor hydroxyl radical oxidation mechanism. On the other hand, through a porous glass diffuser located at the bottom of it was concluded that the concentration of hydroxyl the reactor cylinder. During the experiments, samples radical generated by ozone/zeolite process was higher were withdrawn regularly for analysis. than that by ozone alone.

The adsorption apparatus of ozone consists basically of 1.0 three parts: an ozone solution tank, a packed bed of zeolite and analytical systems. Ozone was introduced into 0.8 1 L of distilled water contained in a glass vessel. Saturated ozone solution was introduced into a packed 0.6 0 bed of zeolite. The ozone concentrations at the inlet and 0.4 outlet of the packed bed were measured by a UV C/C spectrophotometer at a wavelength of 258 nm. 0.2

2.3. Analytical methods 0.0 012345678 Nitrobenzene was extracted by hexane at a volume ratio Time (min) of 1:1 and was measured by a SP-580 gas chromatograph Figure 1. Nitrobenzene removal by ozone/zeolite process: (■) with electron capture detector (Lu Nan Instrumental Ozone alone, (▲) Ozone/zeolite, (▼) Adsorption. Ozone dose Factory, Shandong, China). The chromatographic 5.9mg/min, C0=240.4μg/L, zeolite dose 8g/L and pH5.5. conditions were set as follows: column temperature 160 1.0 ℃, detector temperature 220℃, injector temperature 200 ℃, and the carrier gas was nitrogen. The dissolved ozone 0.8 was determined by indigo method. 0.6 0

3. Results and discussion 0.4 C/C

3.1. Efficiency of nitrobenzene removal by 0.2 ozone/zeolite process 0.0 0246810121416 Nitrobenzene evolution of remaining concentrations in Time (min) dimensionless with time during the course of nitrobenzene ozonation at concentration of 240.4μg/L, Figure 2. Effect of tert-butanol alcohol on nitrobenzene removal by ozone/zeolite process: (□) (■) ozone alone with pH5.5 is shown in Fig.1. The result indicated that 5mg/L and 80mg/L tert-butanol alcohol, (▲) (▼) nitrobenzene in solution could be completely degraded by ozone/zeolite process with 5mg/L and 80mg/L tert-butanol ％ ozone/zeolite process within 7 min, and an 89.1 alcohol. Ozone dose 5.9mg/min, C0=240.4μg/L, zeolite dose nitrobenzene removal could be obtained by ozone alone. 8g/L and pH5.5. Additionally, nitrobenzene can not be adsorbed by zeolite. The effect of ionic strength on the degradation of It was assumed that ozone can be adsorbed by zeolite and nitrobenzene by ozone/zeolite has been determined and the nitrobenzene degradation mainly took place in the results are presented in Fig.3. It indicated that the solution. removal of nitrobenzene by ozone/zeolite process 3.2. Influencing parameters on nitrobenzene significantly decreased with the increase of NaClO4 concentration of the solution. When the NaClO4

Copyright © 2008 SciRes. J. Water Resource and Protection. 2008; 1:1-65. ENHANCED DEGRADATION OF NITROBENZENE BY OZONE/ZEOLITE PROCESS 39 concentrations were 0, 0.5×10-3mol/L and 1×10-3 mol/L, Fig.5 shows the ozone breakthrough curves for H-zeolite. the removal of nitrobenzene were 81.2%, 42.8% and The residence time of ozone in distilled water in the 31.6%, respectively. As zeolite has a exchange capacity, packed bed of H-zeolite was much longer than that of a the H+ will be exchanged by Na+, then, ozone can not blank bed, which means that a certain amount of ozone diffuse into the pore of zeolite because of the salt out. was adsorbed on H-zeolite. It was noted that the effluent Finally, the degradation of nitrobenzene by ozone/zeolite concentration after equilibrium did not reach the influent process was inhibited significantly by the increasing ionic concentration. The influent concentration of dissolved strength. ozone was approximately 0.85mg/L. The effluent

1.0 concentration of ozone in the packed bed of H-zeolite 0.9 after equilibrium was 0.32mg/L. This is because the 0.8 adsorption and decomposition of ozone occurred in the 0.7 packed bed. When the concentration of Na+ in distilled 0.6 water was 1×10-3mol/L in the solution, it should be noted 0 0.5 0.4 that the effluent concentration of dissolved ozone after C/C 0.3 equilibrium was almost the same as that of the influent + 0.2 concentration 0.83mg/L. This means that Na may 0.1 prevent the adsorption and decomposition capacity of 0.0 0246810121416 water-dissolved ozone in the zeolite. The results verified + Time (min) that Na inhibited ozone diffuse into the pore of zeolite and decreased the nitrobenzene degradation by Figure 3. Effect of ionic strength on nitrobenzene removal ozone/zeolite process. by ozone/zeolite process: (□) I=0 in ozone alone, (▼) I=0, (▲) I=0.5×10-3mol/L, (■) I=1.0×10-3 mol/L. Ozone dose 5.9mg/min, C0=240.4μg/L, zeolite dose 8g/L, tert-butanol 4. Conclusion alcohol 5mg/L and pH5.5. In order to determine the effect of pH on the removal Ozonation of nitrobenzene in the presence of zeolite can of nitrobenzene by ozone/zeolite process, solution pH be readily accomplished with ozone in less than 7 min at was adjusted by HClO4. The result is shown in Fig.4. It is 5.9mg/min ozone feed rate. The presence of tert-butyl well known that ozone decomposes into hydroxyl radical alcohol had a negative effect on nitrobenzene ozonation. more easily in basic solution than neutral or acid The experimental results confirmed the proposition that circumstances because hydroxide ions play a role of the degradation of nitrobenzene by ozone in the presence initiator of the chain reaction. Hence, more nitrobenzene of zeolite followed a radical-type mechanism. The molecules can be oxidized in a high pH solution since the increase of ionic strength inhibited the nitrobenzene concentration of hydroxyl radical is much higher than that degradation by ozone significantly. The decrease of pH in low pH. Obviously, the removal of nitrobenzene by also decreased the degradation rate of nitrobenzene by ozone/zeolite process decreased with the decrease of pH. ozone/zeolite process due to the decrease of ozone The removal of nitrobenzene by ozone/zeolite process decomposition at low pH. By investigating the adsorption within 15 min at pH 5.5 and pH 3.0 was 100% and 80.6% of ozone on H-form zeolite, ozone can be adsorbed on H- respectively. At pH3.0, the removal of nitrobenzene by form zeolite and finally decomposed. Cation mainly ozone/zeolite process was a little higher than that by affected ozone diffuse into the pore of zeolite and then ozone alone at 15 min. self-decomposition due to the salt out. 0.9 1.0 0.8 0.7 0.8 0.6 0.5 0.6 0.4 0 0.3 0.4 C (mg/L) C/C 0.2 0.1 0.2 0.0 0 20406080100120 0.0 Flow volume (ml) 0246810121416 Time (min) Figure 5. Breakthrough curves of ozone: (■) ozone dissolved -3 Figure 4. Effect of pH on nitrobenzene removal by in distilled water, (▲) ozone dissolved in I=1.0×10 mol/L ozone/zeolite process: (□) (▲) ozone alone with pH3.0 and distilled water, solid line was ozone dissolved in distilled pH5.5, (■) (▼) ozone/zeolite process with pH3.0 and pH5.5. water under saturation and dash line was ozone dissolved in I=1.0×10-3mol/L distilled water under saturation Ozone dose 5.9mg/min, C0=240.4μg/L and zeolite dose 8g/L. 3.3. Adsorption and decomposition of ozone

5. Acknowledgment [4] U. Wingenfelder, C. Hansen, G. Furrer, R. Schulin, Removal of heavy metals from mine waters by natural The author would like to thank Dr. Yixin Yang for zeolites, Environ. Sci. Technol. vol. 39, 2005, pp. 4606- discussing and reviewing the manuscript. 4613. The authors are grateful for the financial support [5] M. Ötker, I. Akmehmet-Balcloğlu, Adsorption and provided by the National 863 High Technology degradation of enrofloxacin, a veterinary antibiotic on Development Scheme (Project 2006AA06Z306). natural zeolite, J. Hazard. Mater. vol. 122, 2005, pp. 251- 258.

6. References [6] H. Fujita, J. Izumi, M. Sagehashi, T. Fujii, A. Sakoda, Adsorption and decomposition of water- dissolved ozone on high silica zeolites, Water Res. vol. [1] B. Kasprzyk-Hordern ， M. Ziólek, J. Nawrocki, 38, 2004, pp. 159-165. Catalytic ozonation and methods of enhancing molecular ozone reactions in water treatment, Appl. Catal. B: [7] H. Fujita, J. Izumi, M. Sagehashi, T. Fujii, A. Environ. vol. 46, 2003, pp. 639-669. Sakoda, Decomposition of trichloroethene on ozone- adsorbed high silica zeolites, Water Res. vol. 38, 2004, pp. [2] U. Von Gunten, Ozonation of drinking water: PartⅡ. 166-172. Disinfection and by-product formation in presence of bromide, iodide or chlorine, Water Res. vol. 37, 2003, pp. [8] M. Sagehashi, K. Shiraishi, H. Fujita, T. Fujii, A. 1469-1487. Sakoda, Ozone decomposition of 2-methylisoborneol (MIB) in adsorption phase on high silica zeolites with [3] S. Li, V. Tuan, R. Noble, J. Falconer, MTBE preventing bromate formation, Water Res. vol. 39, 2005, adsorption on all-silica β zeolite, Environ. Sci. Technol. pp. 2926-2934 vol. 37, 2003, pp. 4007-4010.

Study on the adsorption of nitrite in water with crosslinked chitosan

Jing LIU1, Kaixuan TAN2, Zhipan GU1 1School of Urban Construction, University of South China, Heangyang, China 2School of Nuclear Resource and Safety Engineering, University of South china, SNRCE, Hengyang, China

Abstract

Crosslinked chitosan（CCTS）was prepared with crude macromolecule compound chitosan as a matrix material and epichlorohydrin as crosslinked reagent under alkaline conditions. The adsorption behavior of nitrite from water by CCTS was studied. Then the effects of the CCTS amount, adsorption time, pH, temperature, initial nitrite concentration, on its adsorption performance were discussed. The optimum experimental condition was determined, under which the maximum removal rate can reach 92.5%. Finally, the adsorption mechanisms were summarized.

Keywords: Crosslinked chitosan; Adsorption; Nitrite

1. Introduction Whereas acylation reaction, carboxy methylation reaction, etherification, grafting copolymerization, N- alkylation Treatment of nitrite in water has become a subject of reaction and esterification reaction all can occur on great concern due to its toxic effect on human health and chitosans owing to multiplicate functional group with environment. In 1971, Stoelvsand proposed that long- strong reactivity in the chitosan structure and they form term eating nitrite-containing foods could cause struma, chitosan derivatives with different property[6][7]. cancer and other diseases[1]. Therefore, reducing the Crosslinking is one of modified methods which can content and controlling the pollution of nitrite have change the structure of chitosan. The cross-link effect can became the spotlight of researchers[2]. The traditional limit the activity and undermine the regularity of the denitrification approaches which can remove the nitrite polymer molecular, and those changes leaded to the are ion exchange, biological denitrification and reverse network structure formation, porosity significant increase, osmosis. But the cost of investing and operation is so adsorption surface area augment and polymer high. Removal technology based on adsorption is chosen crystallization decline. Consequently, the CCTS mainly because of the high elimination efficiency as well demonstrates a nicer adsorption property. as economical advantages such as cheap adsorbent[3]. In The main objectives of this work were to state the this case material like chitosan becomes of interest, impact of influencing factors on its adsorption and however, continuous efforts have been focused on the determinating the best experimental condition. The adsorption of chitosan, the study on the CCTS were less. experimental results could provide the theoretical basis Hence this paper aimed at the adsorption of nitrite from for the application of wastewater treatment, drinking water by CCTS. water purification, and food industry infuture. Chitosan, a natural mucopolysaccharide, is widely 2. Experiments and methods existed in the Arthropod shell such as crab, clobster, shrimp as well as the cell wall of fungi, algae and other unicellular lower eukaryote. New chitosan-based 2.1. Experimental instruments and reagents a materials have been applied in the agricultural, paper Template industry, pharmaceutical industry, chemical industry, Experimental instruments membrane material, absorbent, water treatment agent, 101A-2Electric blast drying oven(Shanghai textile auxiliaries, and other fields. The hydroxyl and experimental instrument factory); SHB-III cycle water amino group in the chitosan molecule forming the multiple vacuum pump(Zhengzhou GreatWall Scientific intramolecular hydrogen bond and CCTS–NH2 being Industry and Trading Co.,Ltd); JJ-1Precision timing protonated into soluble CCTS–NH3 under acidic electric agitator(Jintan Ronghua Instrument manufacture condition can lower the adsorption property of CCTS. Co.,Ltd); 752 UV-VIS spectrophotometer(Shanghai

Spectrum Instruments Co.,Ltd); AL-104Electronic C0 is the nitrite concentration before adsorption, (g/L) Balance(Shanghai Mettler Toledo Instrument Co.,Ltd); C is the nitrite concentration after adsorption,(g/L) 98-1Magnetic Stirrer(Zhengzhou GreatWall Scientific V is the volume of the adsorption solution,(L) Industry and Trading Co.,Ltd). m is the amount of CCTS.（g） Experimental Reagents Chitosan (CTS, Chengdu Kelong Chemical Reagent 3. Results and discussion Factory, Degree of deacetylation 85%, Powdery, relative molecular weight 1×105 ～ 3×105); Sodium Nitrite 3.1. Effect of CCTS amount on adsorption (Analytically Pure 99.0%, Tianjin University Reagent performance Factory); Acetic Acid(Analytically Pure 99.8%, Tianjin The effect of adsorbent amount on the nitrite Reagent Third Factory); Anhydrous Sulfanilic adsorption behavior at room temperature (25℃) and pH Acid(Analytically Pure 99.5%, Tianjin Resent 6.0 was shown in Fig. 1. It can be seen from this figure Chemicaais Co.,Ltd); 8-Hydroxyquinoline (Analytically that the adsorption rate increased from 15% to 90.5% Pure 99.8%, Xiangzhong Geological and Experimental with increasing CCTS amount and this increase tendency Institute); Epichlorohydrin(Analytically Pure, Tianjin was significant when CCTS dosage was below 0.1g. This Resent Chemicaais Co.,Ltd). result can be interpreted that the CCTS amount in the 2.2. Preparation of CCTS[6] nitrite solution was relatively lower which led to 15g CCTS were immersed in 960mL 1% acetic acid incomplete adsorption without competition. It was also solution and 18ml epichlorohydrin were added slowly found that when the CCTS amount was above 0.375g per into the solution with intense agitation of electric agitator. 100mL solution, the adsorption rate was conversely Then 150mL 5%sodium hydroxide were gradually decreased with increasing CCTS amount. This dropped into the reaction solution and the reaction was phenomenon can be explained that more CCTS molecule maintained for 18 hours until the white solid appeared. competitively adsorb nitrite resulting in an unstable Subsequently, the white solid washed with water, rinsed absorption of nitrite by CCTS. Besides, the hindrance of excessive CCTS weakened its contact with adsorbent. with little acetone, dried in oven under 100℃, milled and The above results suggested the optimal addition amount sieved with sample sieve of pore size (0.088mm),then of CCTS was 3.75g/L under which complete adsorption stored for use. was achieved. 2.3. Experimental methods 100% Adsorption experiment and determination The adsorption were carried out in bunsen beaker where a certain quantity of CCTS and a certain 80% concentration of nitrite were added first. Then the nitrite 60% solution was adsorbed for a period under magnetic stirring and constant temperature, filtrated the adsorbed 40% solution with vacuum pump. Finally, a certain amount 20% filtrate was diluted to the linear ranges of 0~1.4×10-3g/L Adsorption rate X which could make the absorbance and nitrite 0 concentration in agreement with the formula as follow: 0 1 2345 Amounts of CCTS (g/L） Α=0.028723Χ+0.001779 （1）

Where is the absorbance, and is the microgram Figure 1. Effect Curve of CCTS mass on adsorption. amounts of nitrite. The detail information on the Experimental variables：temperature=25℃, pH=6. determination of nitrite concentration changed before and after adsorption can get in the reference[8]. 3.2. Effect of adsorption time 1) Adsorption capacity and Adsorption rate[9][10] The change of adsorption rate with time at a optimal The adsorption capacity and adsorption rate were CCTS addition was shown in Fig.2. It is obvious that the calculated through the formula as follow: nitrite concentration was reduced gradually at the first 10min and then increased rapidly during the period from （） × （） X= C0-C /C0 100% 2 20min to 30min. However, it sharply declined after 30min untill adsorption time reach 1.5h. Interestingly, the adsorption rate increases again. Lastly, the adsorption Q=（C0-C）×V/m （3） rate almost unchanged after 2.0 hours. The above phenomenon can be explained as follows: the swelling of Where X is the adsorption rate,(%) CCTS is insignificant at the beginning of 30 minutes and Q is the CCTS adsorption capacity,(mg/g) the physical adsorption process occurred during this

Copyright © 2008 SciRes. J. Water Resource and Protection. 2008; 1:1-65. STUDY ON THE ADSORPTION OF NITRITE IN WATER WITH CROSSLINKED CHITOSAN 43 period. And the surface physical adsorption quickly but exhibited negative correlation after reaching reached saturation with an adsorption rate of 91.16% at adsorption saturation. 30min. The swelling of CCTS was evident subsequently 3.4. Effect of temperature on adsorption after 30min, which was a dominant factor leading to the adsorption on solvent water [9]. Our observed results was Fig.4 displayed the profiles of the nitrite adsorption in agreement with Zhu’s[11]. Meanwhile, the physical rate versus the temperature. It can be clearly seen from desorption took place on the surface of CCTS, and the Fig.4 that the adsorption rate differed at various desorption rate slowed down at 1h (Fig.2). The possible temperatures and achieved a maximum value of 92.5% at reason is that diffusion resistance of water increased 22ºC. The changes of adsorption rate against temperature through the CCTS owing to the water molecule subject to relate to the activation energy and Gibbs free energy of the flabby stress from gel network. As a result, the the adsorption reaction system[12]. The higher the desorption rate slowed as the CCTS swelling slacked. temperature, the greater the energy of the reaction system When the CCTS molecule swelled completely, the and the less the Gibbs free energy, which help to the CCTS—NH2 was protonated into CCTS—NH3+, then adsorption in some degree. Whereas, for the exothermic the electrostatic attraction between the nitrite and CCTS adsorption, the excessively high temperature will reduce became the dominant factor causing another increase of interfacial tension and weaken the attractive force adsorption rate. The adsorption reached a dynamic between CCTS and nitrite. Furthermore, the nitrite equilibrium and the adsorption rate kept unchanged with adsorbed to the CCTS may fall off with the strenuous further lengthening of time. movement at relatively high temperature, resulting in a decrease of adsorption rate. To sum up, we should choose 100% the optimal temperature 22℃.

80%

60% 93%

40% 92% 91% Adsorption rate20% X 90%

0 89% 0 100 200 300 400 500 600 700 800 900 10001100 1200 88% Adsorption time (min) 87% 0 0.01 0.02 0.03 0.04 0.05 Figure 2. Effect curve of time on adsorption. Experimental Initial concentration of nitrite （g/L） variables: mass of adsorbent=3.75g/L, temperature=25℃, pH=6.0. Figure 3. Effect curve of initial concentration of nitrite on 3.3. Effect of nitrite initial concentration on adsorption. Experimental variables: mass of CCTS=3.75g/L, adsorption temperature=25℃, adsorption time=30mins, pH=6.0. Fig.3 reflects the effect of initial nitrite level on its adsorption performance by CCTS at different initial nitrite concentrations. An increase of adsorption rate was 100% observed with increasing initial nitrite concentration 80% when the concentration was lower than 0.03g/L. The maximum adsorption rate can reach up to 92.5%. This is 60% because the probability of collision between nitrite and 40% CCTS is not very high at early stage when the initial nitrite concentration was relatively lower and the CCTS 20% surface was comparatively unpolluted. Then it is clearly Adsorption rate X 0% observed that the status was opposite to the former as the 0 1020304050 nitrite concentration increased above 0.03g/L. This can Temperature (℃) be attributed to the saturation of nitrite adsorption process when the initial nitrite concentration was 0.03g/L. The CCTS had no redundant available surface to adsorb Figure 4. Effect of temperature on adsorption. nitrite. So the adsorption rate never incresed but Experimental variables: mass of CCTS=3.75g/L, decreased even though the nitrite concentration was temperature=25℃, adsorption time=30mins, pH=6.0, initial increased. Zhu[11] studied the adsorption of the protein concentration of nitrite=0.03g/L onto chitosan. It was also shown that the adsorption rate increased with the initial protein concentration rising and

3.5. Effect of pH on adsorption NH2 can be protonated into CCTS-NH3+, and CCTS- NH3+ with forms of coordination or amino group forms The effect of pH on the nitrite removal by CCTS was the charge transfer complex with nitrite in the acidic shown in Fig.5. Obviously, the maximum adsorption rate condition. The adsorption is influenced by the external of nitrite (92.5%) was achieved at pH 6.0 (near neutral conditions, for example, pH, temperature, etc. pH), and but decreased at pH below or above 6.0. The In summary, the competition existed in different lower adsorption rate at low pH observed is probably due adsorption action, so it is difficult to define what is the to the presence of excess H+ which can combine with uppermost action in adsorption process. It is also not nitrite and further form nitrous acid. Yet the nitrous acid simple to expound a certain adsorption mechanism is a weak electrolyte unfavorable for the negative among the complex and competitive adsorption mode. electrostatic adsorption between protonated CCTS Further in-depth research may be required to clarify the (CCTS-NH3+) and nitrite ion. The adsorption rate of fact. nitrite decreased with further increasing pH (above 7.0), since the positive charges in CCTS were neutralized by 4. Conclusion the hydroxide ion (OH-) under basic conditions, leading to the weakening of the electrostatic nitrite adsorption by z The adsorption of nitrite by CCTS was greatly protonated CCTS (CCTS-NH3+). Ding[13] has discussed influenced by the following factors: the CCTS the effect on CCTS using a equilibrium reaction equation. amount, adsorption time, initial nitrite concentration, The positive reaction is CCTS-NH2 combining with H+ temperature and pH value. and forming CCTS-NH3+ , and the reverse reaction is z The optimal adsorption effect achieved when the opposite.This equilibrium reaction equation forwarded CCTS amount is up to 3.75g/L, the adsorption time right with increasing pH at the beginning of adsorption 30min, the temperature 22℃ and the pH 6.0. Under and the protonation of CCTS is favorable to the this condition, a maximum of nitrite adsorption rate adsorption of nitrite because of the strong electrostatic (92.5%) was obtained. attraction. The phenomenon in basic solution with z Surface physical adsorption and electrostatic increased pH over 6 was just contrary to the former pH attraction adsorption are two dominant mechanisms below 6. Their studies was verified our experimental on nitrite adsorption by CCTS, accompanied by results and interpretation on the effect on adsorption. other adsorption mechanisms. In this paper, the maximum of equilibrium adsorption capacity achieved 7.4mg/g. This value is not very high, 100% which may relate to the lower deacetylation degree, the 80% higher crystallinity and the purity of the CCTS. The deacetylation degree affect both the hydrogen bond, the 60% protonation and the crystallinity affect the infiltrate of 40% nitrite into CCTS. This study is of great significance to control the nitrite level in drinking water as well as to 20% solve the problem of the nitrite pollution in groundwater.

Adsorption rate X 0% 0246810 pH 5. Acknowledgment

R. B. G. thanks Doctor Yi Zhengji’s help and my Figure 5. Effect of pH on the adsorption. Experimental parents’ supports. variables: mass of CCTS=3.75g/L, temperature=25 ℃ , adsorption time=30mins, pH=6.0, initial concentration of 6. References nitrite=0.03g/L, temperature=22℃. 3.6. Proposed adsorption mechanism of CCTS [1] K. Takatsuki, and T. Kikuchi, Gas chromatographic determination and mass spectrometric confirmation of N- Physical adsorption is the dominant mechanism on nitrosodimethylamine in fish meal, Journal of Chromatography A, vol.111, pp. 416- nitrite adsorption by CCTS since it is a porous solid with 419.september,1975. a high surface area[14]. The physical adsorption is [2] Z. E. Ding, Roles and effect mechanisms of nitrites intermolecular adsorption caused by van der waals force, in food, Journal of Anhui Agricultural University, vol. 21, which includes dispersion force, induction force and pp. 199-205, May, 1994. orientation force. The adsorption of nitrite by CCTS was attributed to the synergistic effect of three above- [3] G. McKay and M. J. Bino, Adsorption of pollutants mentioned forces. from wastewater onto activated carbon based on external But the CCTS has some unique adsorption mass transfer and pore diffusion, Water Research, vol.22, mechanisms besides the simple electrostatic attraction pp.279-286, March, 1988. adsorption belonging to physical adsorption. The CCTS-

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Pinch technology reduces wastewater at a paper mill

Jidong LIANG, Yanling HE, Xudong ZHAO, Guodong WANG Department of Environmental science and engineering, Xi’an Jiaotong University, Xi’an, China E-mail: { [email protected] , [email protected]}

Abstract

The pulp and paper industry is under regulatory pressure to reduce the volume of its water consumption and wastewater discharge. A systematic methodology for analyzing the ways to reduce wastewater amount and consequently reduce the freshwater consumption is called Mass Exchange Integration (MEI) or Pinch technology. The pinch technology establishes the minimum water flow rate required for the plant and thus sets the target for minimizing water consumption. In this paper an example is illustrated to show how pinch technology is effectively used for minimizing the wastewater in a paper mill. The result shows that this method is effectively used for minimizing freshwater consumption and wastewater discharge in the paper mill. Keywords: Pinch technology; Wastewater minimizatio; Paper mill

1. Introduction the internal recycles [2~4]. Internal recycles may require some treatment or no treatment at all, to make them Water scarcity and more stringent environmental suitable for reuse [4]. regulations on paper industrial effluents demands The pinch technology presented above was usually responsible freshwater saving and wastewater applied in petrochemical and chemical complex but few minimization in the paper industry [1]. in other fields，such as pulp and paper industry [2~4]. In A systematic methodology for analyzing the ways to 1996, Tripathi, Paul applied pinch technology in a paper reduce the amount of wastewater and consequently mill and showed that pinch technology was effectively reduce the freshwater consumption is called Mass useful for minimizing the waste water in a pulp and paper Exchange Integration (MEI) or Pinch Technology [2]. mill [1]. It was developed the water-using system based The pinch technology is a modern descendant of pinch on TSS as the contaminant in the paper mill. But TSS was calculations in heat transfer [2]. Its history is short. The no more harmful than CS affecting on the produce first report addressing the similarity between heat and process. So it was important to develop the water-using mass transfer pinch was published in 1989 by El-Halwagi system based on CS in paper mill to enhance the optimal and Manousiouthakis of the University of California Los design of water-using networks in paper industry. In this Angeles [3]. Remarkable work was done by Wang and paper, we involved pinch technology to design the Smith by introducing the important concepts of “Water networks of one paper mill with consideration of CS. pinch” and “limiting water profile” [2~4]. Subsequently, this concept has been accepted by other researchers in 2. Pinch technology water system integration. A number of papers have been published since extend the Pinch technology to Pinch technology uses water purity and flow rate as wastewater application [2~4]. the process parameter. We apply a graphical procedure to The pinch technology establishes the pinch point that draw a graph with purity as its vertical axis and water determines the minimum water flow rate required for the flow rate as its horizontal axis. The output water streams plant and thus sets the target for minimizing water of all operations can be plotted to construct the source of consumption [2]. The basic strategy to reduce water supply of water for the plant. So the source curve consumption is to use the outlet water from one operation represents effluent water of sufficient purity available for to satisfy the water requirement of another, or even the somewhere in the plant. The water demands in terms of same operation [2]. Pinch technology provides better required input purities for the individual streams for the understanding of process needs and thus helps establish overall plant. In that the demand curve represents water

Copyright © 2008 SciRes. J. Water Resource and Protection. 2008; 1:1-65. PINCH TECHNOLOGY REDUCES WASTEWATER AT A PAPER MILL 47 needed by the process units. Match the curve lines till the under vacuum on its way back to the slice. This suction demand curve line no higher than the source line leads to roll draws more water out of the wet sheet, increasing its calculation of input and output (Figure 1). consistency to about 20% and making it strong enough to be transferred onto an endless porous-fabric blanket (felt). Fresh Water Supported on this felt, which absorbs water, the wet paper 0 1 sink sheet passes through a series of press rolls that squeeze as 20 much water out of the sheet as possible. recycle water 40 1 source The remaining water (more than half the wet weight of 2 sink Water source curve line Water demand curve line 60 3sink the sheet) is removed, either by pressing alternate sides of the continuous sheet against the surface of a large number 80 of steam-heated drums or by supporting the sheets on a

Water purity C (mg/l) 2 source 100 series of jets of hot air as it passes through the drier. recycle water pinch Usually the sheet leaving the dryer passes through a 120 3source fresh water pinch waste Water calendar stack. Normally, the mill will wind the 0 102030405060708090100 continuous web of paper into jumbo rolls. These are Flow rate Q (m3/d) either rewound or cut into sheets on a separate machine and packaged for shipment. Winding and cutting Figure 1. Example of Limiting composite curve for pinch technology. consume no water. The water network before optimal design is shown in Figure2. If the demand exceeds the supply, fresh water is needed. Excess waste water is routed to the treatment area. 3.2. Synthesis of the water pinch There are three fields in the graph from right to left. They The plant is located in a semi-dry climate. Before water are fresh water, recycled water and wastewater integration, its fresh water consumption was 1370~1710 respectively. The borderlines are defined pinch points. m3 per air-dry ton paper production, and the volume of The borderline between fresh water and recycle water wastewater it discharged was 1000~1400m3. Because fields is defined fresh water pinch. The borderline freshwater consumption and wastewater discharge is between recycle water and wastewater fields is defined restricted by the local government, it is important to recycled water pinch. Then we can design the water using further reduce the freshwater consumption and quantity of networks according to the pinch analysis. wastewater. Fresh water 3. A real mill analysis 289t/h

1. Hydraulics beating 3.1. Current water-usage scheme 77.9 40.38 The paper mill regenerates paperboard，of which the Reused water mass quantity is 180g • m-2 ， from waste box and 2. Separating paperboard bought from neighboring cities. The 210.87 Waste water production steps for paper manufacture from waste paper 3. Cleaning and concentrating material include pulp making and paper production. 196.65 36.25 399.8 Firstly, the waste paper material and water is mixed 4. Modulating and made into stock (a dilute water-suspension of fibers) by hydraulics beater. Then a considerable portion of the 468.35 flake of plastic, sand and impurities are removed in the 5. Screening Waste water screening by separator. After that, the stock is cleaned, 82.74 refined and concentrated to a certain concentration after 1.5 1.5 passing the disk refiner and concentrator. Finally, the 6. Felt washing stock is transferred into the pool for pulp reservation to be 17.74 modulated by adding water and other wet-end additives. 7. Pressing and drying 3 Paper manufacture is to extrude a uniform continuous Evaporated water stream of a dilute pulp, of a specified low concentration 8. Winding and cutting or consistency, through a long narrow slot (the slice) onto an endless belt of wire screen traveling at the same speed Figure 2. Current water network in the stock and paper as the pulp. Most of the water drains rapidly through the making screen as it moves over a series of table rolls and suction boxes that support the traveling screen and remove water z Determintion of Contaminants from the sheet. The screen passes around a perforated roll

When synthesizing the initial water network, the source line (seeing in figure 4). Then we find the fresh contaminants must be identified first. As an initial practice, water pinch and the recycled water pinch. The demand only those contaminants that have the most obvious effect exceeds the source in the right is the quanlity of fresh on the processes should be taken into consideration. In this water required. Excess source in the left is the quantity of way, the initial synthesis problem is simplified. For the wastewater produced. It will be the theoretical minimum paper mill, colloidal Substance (CS) is the most obvious water requirement and the corresponding minimum harmful contaminants to the produce. wastewater discharge. Table 2 shows the amount of fresh z Determination of Water Sources and Water Sinks water required after analyzing the problem and selecting In addition to freshwater, the effluent water streams the streams that can be the recycled water. Some streams from certain water-using processes may be potential changed entirely to the recycled water. sources for other water consuming processes, provided that the used water meets the inlet contaminant The area between the fresh and recycled pinch concentration requirements. As shown in Figure 3, indicates the potential for water reuse. Water processes 3, 5, 6 and 7 are possible sources. Water minimization (using less freshwater and discharging less discharged from processes 1, 2 and 4 can be reused in the used water) obviously causes the concentration of paper pulp process, and water discharged from processes 8 contaminants (CS) in a system to increase. The dirty in the paperboard production. We should be aware that the water presents a challenge to keep the paper machines water evaporated into the environment is no longer a water clean. Fresh water will be required at certain critical source. positions in the paper- forming units, such as modulation Water sinks are those processes that consume freshwater and felt washing. or water containing contaminant, that is, so-called reuse water. By viewing the current water-using system in This study can be extended to any process plant. CS has Figure3， processes 1, 2, 3, 4, and 6 are water sinks. The been considered as the only impurity in this example. But, inlet water to processes 5, 7 and 8 forms a paper pulp with in reality the water could also be contaminated by other the solid fiber. Hence, these processes, consuming water chemicals that may make water hard to reuse without any with solid product, are not considered to be water sinks. pretreatment. So further research should be done in the Processes 3 and 6 are both sources and sinks. near future. z Determination of Limiting Concentrations

By experience and field investigatation, the limiting 200 inlet and outlet concentrations of CS for the processes are 6sink estimated, as given in table1. The limiting concentrations, 400 7 source for some of the processes, are determined as follows. 600

800 Water demand curve line Table1 Limiting data of CS for water-using processes of 6source the paper mill 1000 5source - 4sink No Water-using Source Water flow rate (t h Limit concentration of 3 source 3sink . process or sink 1) contaminant (mg l-1) 1200 Water source curve line in out inlet outlet Limit centration of CS (mg/kg) 1400 2sink 1 Hydraulics sink 77.9 — 1500 — beater 1sink 1600 2 Separator sink 40.38 —- 1300 — 0 100 200 300 400 500 600 700 800 Flow rate of water (t/h) 3 Cleaning & Source 210.87 274.55 1050 1200 concentration & sink 4 Modulation sink 436.05 — 1050 — Figure3. Limiting composite curve for water source and sink 5 Screening source — 468.35 — 1050

6 Felt washing Source 1.5 1.5 270 950 & sink 200 fresh water 7 Pressing and source — 17.74 — 560 6sink Drying 400 Water sink curve line 7source 600 3.3. Water pinch analysis Water source curve line 800 Table1 shows the paper machine water requirements waste water 6source along with the water quality. CS was used as the measure 1000 5source 3sink 3source 4 sink of purity. According to Figure3, we can draw a plot of 1200 tabulated information after completion of analysis. The 2sink Fresh water pinch

Limit centration of CS of CS (mg/kg) centration Limit 1400 recycle water pinch numbers on the vertical axis decrease, the amount of 1sink contaminants represents lower purity on the graph. 1600 0 200 400 600 800 1000 The demand curve extension over the source curve Flow rate of water (t/h) (overhang) shows the amount of excess wastewater. In order to analysis, we move the water demand curve line Figure4. Limiting composite curve for pinch analysis to right on level till the line is no higher than the water Table2 Water consumption in each process unit

process unit Fresh water flow rate t·h-1 material in the waste water. The removal rate of CS is Before optimal design After optimal design about 95%. The concentration of this contaminant in the 1.Hydraulics beater 0 0 regenerated water was below the limit concentration of

2.Separator 40.38 0 them as enumerated in Table1. So the regenerated water can retake the fresh water as was shown in Figure 4. 3.clean & concentration 210.87 0 Finally the mill successfully achieved zero effluent 4.Modulation 36.25 158.88 discharge. Till now, the paper mill has no waste water 5.Screener 0 0 discharge for about 2 years and the treated water can be 6.Felt washing 1.5 1.5 reused without harmful effect on production and 7Pressing and Drying 0 0 paperboard quality. Water consumption rate decreased 3 3 Total consumption 289 160.38 from 90~110m to 1.6 m per ton paper production. Water saving（%） 44.5 Anaerobic bio-treatment system

3.4. System of optimal water-using networks Fiber Modulate UASB The system contains 7 process units. According to figure 4, Inflow reclaiming pond reactor we can establish the optimal network for this case shown in Figure5. The Total fresh water consumption of this water network is 160.38t·h-1. Treated Sand Sett- AS Fresh water water filtr- ling reac- 160.38t/h pond ation pond tor Outflow 1. Hydraulics pu 77.9 dl Reused water Aerobic bio-treatment system 2. Separating 40.38 Figure6. Flow chart of waste water bio- regeneration Wastewater 3. Cleaning and concentration 4. Conclusions 156.27 210.879 Pinch technology is effectively used for minimizing 4. Modulation 376.72 the fresh water using and wastewater discharge in the paper mill. The pinch technology establishes the 158.88 468.35 minimum water flow rate required for the plant and thus 5. Screening sets the target for minimizing water usage. Then the minimized wastewater flowing into a bio-treatment 1.5 1.5 system can be regenerated and then reused for 6. Felt washing papermaking. As a result we successfully achieved zero discharge of wastewater. At the same time, the produce 17.74 and quality of paper is not affected. Water consumption 7. Pressing and drying 3 rate decreased from 90~110m3 to 1.6 m3 per ton paper Evaporated water production.

8. Winding and cutting 5. Acknowledgement

Figure5. Current water network in the stock and paper This paper was sponsored byNational Natural Science making Foundation of China under Grant No.20376066 and

20436040 and National Key Basic Research Development Program of China (No. 2003CB214500). 3.5. Water Regeneration We also thank Professor Feng Xiao and Professor The wastewater from the networks described above flows Charles Chou for their kind advice in the writing of this into a bio-treatment system to regenerate. The bio- paper. treatment system contains anaerobic and aerobic bio- treatment system, which is shown in figure6. The result 6. References shows that the treatment capacity of the anaerobic and aerobic treatment system increases with the organic

[1] Tripathi, Paul. 1996. Pinch Technology Reduces use of graphical method to determine the targets of Wastewater; Mass exchange integration maximizes water single-contaminant regeneration recycling water systems. recycling at a paper mill. Chemical Engineering 103, 87- Chem. Eng. Sci., 62, 2127-2138 98 [4] Castro, P., Matos, H., Fernandes, M. C. & Nunes, C. [2] Wan, Y., P., & Smith, R. 1994a. Wastewater P. 1999. Improvements for mass-exchange networks minimization. Chem. Eng. Sci., 49, 981-1006 design. Chem. Eng. Sci.,54, 1649-1665 [3] XiaoFeng, Jie Bai, Xuesong Zheng. 2007. On the

Simulation of organic matter loss in area around Taihu lake

Xiangyang XU 1, Tianyi XU 2 1University State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Hohai UniversityNanjing, China. 2 College of Water Conservancy and Hydropower Engineering, Hohai University, Nanjing, China

Abstract

The agriculture around Taihu Lake is highly developed, but a large amount of sand and organic matter is directly brought into Taihu Lake from farmland in rainy season and is seriously polluting the water quality of the lake. In order to make a quantitative analysis for the influence of organic matter to the water body of Taihu Lake, the area around Taihu Lake is divided into two land area of paddy farm and dry land to set up a mathematical model of organic matter loss from farmland. Runoff generation, water drainage, soil erosion and organic matter loss are stimulated in different typical periods of high-flow, normal-flow and low-flow by the model. The modeling result shows the soil erosion and organic matter loss increase in an exponential form with the increase of surface runoff intensity. The sand and organic matter in the surface runoff are pollutants in themselves and also carrier of other toxic substances, which are seriously influencing the water quality of Taihu Lake. Effective measures attached with importance must be taken in the water quality program and treatment for the Lake. Keywords: Taihu Lake; simulation; water quality; organic matter

1. Introduction Taihu Lake District is the area around Taihu Lake which occupies a land area of 889km2 within the lake Taihu Lake lies in the downstream area of the belt highway in which 607km2 are farmlands and others Changjiang River with an area of 2,338km2 and a storage are hills and non-farmlands. The sediment and organic capacity of 44.3×108m3, and it is one of the main water matter in the area can be directly discharged in to the sources for industry, agriculture and living in Taihu basin. water body of the lake with storm water which will bring In recent years with the highly development of economics a distinct pollution to the water quality. The pollution of in the basin, the organic pollutants discharged into the the organic matter is from non-point sources and factors lake have been increasing year by year and seriously of influence is very complicated, so it is difficult to polluting the water quality of the Lake. The monitored calculate the total amount of discharge and stimulate the result from the local environmental protection institution process only through surveying the pollution source and has shown that the water quality of most rivers in the monitoring the water quality. This study will take an plain region around Taihu Lake can only reach Grade IV analysis for the land usage, soil erosion, or Grade V Standard for surface water, and most of the hydrometeorological process and farmland drainage in rivers are being degraded to Grade V below. The central Taihu Lake District to stimulate the loss of organic matter water body of Taihu Lake is still maintained in Grade II, with surface runoff and the process of soil erosion by a but the water quality in the river mouth to the Lake is mathematical model. being seriously degraded[1],[2]. As the requirement for economic development in Taihu basin, the recent and 2. Mathematical model prospective program for the water quality of the Lake is to maintain in Grade II for surface water. And in order to 2.1. Simulation of paddy farm drainage realize this program, a survey and evaluation must be taken to the source of organic pollution to the water On the assumption that the suitable water depth for quality of Taihu Lake so as to work out some effective paddy growing is H1~H2, and thus the average applicable measures for controlling and treatment. water depth of the paddy farm in the Lake District H =

(H1+H2)/2 in consideration area of the Lake Districts very 2.2. Simulation of runoff generation from dry large and irrigation happens asynchronously. In normal land situations, the irrigation and drainage mode of the paddy farm is: drawing water to compensate the evaporated and Taihu Lake basin is located at humid region with infiltrated water at non-raining days so as to maintain the abundant groundwater, loose soil and thick vegetation, H thus the amount of runoff generation in dry farm is average water depth H of the whole paddy farm at ; calculated in the natural storage model[3]. In terms of draining water in the maximum drainage ability He when the principle of the natural storage mode, the residual H is higher than the allowable water depth H3; neither amount after the precipitation has met the storage drawing nor draining when H ≤H≤H3 so as to reduce the capacity of the basin is the amount of runoff yield. In consumption of power and water resource. Thus, the which, the net precipitation above the surface gravimetric water amount discharged from the paddy farm in the infiltration rate is the surface runoff, and the infiltrated whole irrigation area to the river and lake can be gravimetric water is underground runoff. represented by the following equation: The inhomogeneity of the unsaturated zone above the groundwater level can be represented by the curve of 0 H ≤ H 3 basin water storage, and the common equation is (1) Rs = H − H 3 0 < H − H 3 < H e

H e H − H 3 ≥ H e b (4) α =1−(1− S / Sm ) The initial water depth of the paddy farm at the t+1 day can be represented by the recursion equation of water in which α is the area proportion of runoff generation in amount balance the basin, S is the soil moisture storage capacity (mm) of each point in the basin, Sm is the maximum storage

Ht+1 = Ht +Pt −Et −It −Rst (2) capacity (mm) of a point in the basin, and b is the index of soil moisture storage capacity curve in the basin. in which Ht, Pt, Et, It, and Rst respectively represent the initial water depth (mm), rainfall amount (mm), According to equation (4) and the concept of runoff evaporation amount (mm), infiltration amount (mm) and generation after full storage of water, main equations for surface runoff amount (mm) at the t day. calculating the runoff generation can be obtained, as follows The evaporation amount E in the paddy farm has correlations to the growing season, meteorological S = (1 + b )W condition, soil condition and species of the paddy. m m (5) Generally for a concrete area, it has a correlation to the water surface evaporation amount E varying with the A = S [1 − (1 − W / W )1/(1+b ) ] 0 m m (6) paddy growing season or month 1+b (7) R = P−E+W −Wm +Wm[1−(P−E+ A)/Sm] ] P−E+A f cα Δ t the paper mill

Month H 1(mm) H2 (mm) H3 (mm) K I (mm/d) 4 10 30 50 1.01 2 R = R − R (10) 5 20 40 70 1.19 2 g s 6 20 40 70 1.23 2 7 20 40 70 1.28 2 8 20 40 80 1.35 2 The soil moisture content at the t+1 day, Wt+1, can be 9 15 30 70 1.35 2 calculated by a recursion equation, as below 10 10 20 50 1.20 2

SIMULATION OF ORGANIC MATTER LOSS IN AREA AROUND TAIHU LAKE 53

Wt+1 = Wt + Pt − Et − Rst (11) an integrated analysis. 2.4. Estimation of organic matter loss in which the evaporation amount E in the farmland can be calculated by the 1-layer evaporation model[4] Most of the organic matter in soil exists in the form of organic matters closely combined with the soil particles, and the others are undecomposed plant and animal W (12) residues[6]. The organic matter is brought into the water E = Em Wm body in sediment with surface runoffs, and forms the organic pollutants in the water body[7]. In the runoffs, the in which the evaporation ability of soil can be calculated organic matter has the following correlation to the by a value surveyed upon water surface evaporation sediment

E = βE m 0 (13) D = Ed ScCs (17)

The estimated value for each parameter is obtained in which D is the wash load of organic matter (kg/km2), through a calculation upon water amount balance on basis Ed is the concentration ratio of organic matter in surface 2 of local hydrographic data and infiltration tests. The runoffs (kg/km ), and Cs is the ratio of organic matter in values of the parameters are: Wm＝80mm; b＝0.3; β＝ soil. 1.05; fc＝5mm/h (in dry land); fc＝2mm/h (in hills). If it is lack of data on the ratio of organic matter in 2.3. Simulation of soil erosion surface runoffs and in sediments, Ed can be calculated by an empirical formula[8] Because of erosion from heavy rains, the sediments in the catchment area are brought into the water body with surface runoffs[5]. Analyzing according to the surveyed 0 .003 (18) E d = + 1 .08 data on sediment transport in Taihu Lake basin, assume C s 2 the erosion modulus in the catchment area Sf (t/km ) has an exponential correlation to the intensity of surface Analyzed the surveyed data on soil, the average ratio of runoff rs (mm/h). organic matter in soil of Taihu Lake Districts is 2.7% and Ed is 1.19. a The organic elements in soil are mainly carbon, oxygen, S f = crs (14) nitrogen, and hydrogen, etc. with stable composition, and the average percentages are about: carbon α ＝ 55%, If the catchment area occupies a land area of F, the C ＝ % ＝ % ＝ % amount of soil erosion at a time period is oxygen αO 32 , nitrogen αN 5.5 , hydrogen αH 5 and others 2.5%[7]. According to the theoretical oxygen consumption formula a Sc = crs F (15) 32 16 in which the parameter c and a can be calculated by the aTOC = a C + a N − a O (19) least square method based on the sediment yield in the 12 2 area. It can be calculated that the weight ratio of theoretical The survey on soil erosion is very difficult while the data oxygen consumption to the weight of organic matter is on sediment transport in rivers is sufficient. If the rate of α ＝1.547. The molecular weight of organic groups in sediment transport in river course is E , the amount of soil TOD 5 soil is relatively large, and most of the organic matter is erosion can be calculated by the amount of sediment products from micro-biological degradation, so the transport S in river course. s biochemistry is very poor. On basis of related studies, and the biochemical oxygen consumption is about 9% of the theoretical oxygen consumption. In this way, the S c = S s / E s (16) corresponded total oxygen consumption and biochemical oxygen consumption can be calculated from the runoff Taihu Lake District lacks of surveyed data on sediment amount of organic matter. transport of itself. According to the actually measured flow rate and data on sediment transport in three catchment areas of Liuhe, Zhangjiagang and Nandu, 3. Results and analysis results of c=0.117 and a=1.3 can be obtained on basis of

Based on the above models and parameters, the process themselves and also carrier of other various toxic of annual rainfall in Taihu Lake District differently in substances, thus the amount of runoff is seriously high-flow, normal-flow and low-flow periods of a typical influencing the water quality of Taihu Lake, and effective year is modeled day by day, and the annual statistics of measures attached with importance must be taken in the rainfall precipitation Rs, infiltration I, sediment yield Sc, water quality program and treatment for the Lake. At erosion modulus Sf, organic matter D, oxygen present the most important measures should be enhancing consumption TOD, and biochemical oxygen consumption the conservation of water, soil and fertilizer, such as BOD are listed in Table 2. building some water retaining works and stagnant belts to decrease the total amount of surface runoffs and limit the The modeled result shows that the generation of runoffs flow rate on slopes, perfecting the fertilizing time and and sediments as well as the loss of organic matter in the mode, and expanding and thickening the vegetation on farmland and hills in Taihu Lake Districts has the hills and slopes so as to reduce the discharge of pollutants following characteristics: from farmland and hills, increase the environmental [9] (1) The annual total amount and index of surface runoffs capacity of the water body , and protect the water has a trend of rising with the increasing of rainfall quality of Taihu Lake and other rivers fundamentally. precipitation year by year, and the influence of rainfall intensity is also distinct. 4 References (2) The sediment yield in the basin and the loss of organic matter appears with an exponential rising with the [1] B. Cheng and Z. Zhang, “Eutrophication of Taihu increase of surface runoffs. Lake and Pollution from Agricultural Non-point Sources (3) The total sediment yield and loss of organic matter in Lake Taihu Basin”, Journal of Agro-environmental have a distinct difference between in a high-flow year and Science, 2005, 24: pp. 120-124. a low flow year, and the analysis on a typical year shows [2] F. Han, Y. Chen, Z.Liu, “Advance in the that the ratio can be more than 7 times. Eutrophication Models for Lakes and Reservoirs”, (4) In typical years, the average contents of TOD and Advances In Water Science, 2003, 14(6): pp. 785-789. BOD in surface runoffs in a high-flow year are obviously [3] L. Tang, “Effect of Agricultural Non-Point Source higher than those in a low-flow year, and the ratio of Pollution on Water Environment”, Environmental high-flow year to low-flow year is 1.6, and it will be 3.2 Protection, 2003(3): pp. 18-20. if calculated as per the total amount of runoffs in the lake area. [4] D. Zhan, “Engineering Hydrology”, Beijing: China Water Power Press, 2003, pp. 22-29 (5) Either in a high-flow year, normal-flow year or a low- flow year, the contents of sediments and organic matter in [5] R. Zhao, “Drainage Basin Hydrographic runoffs are both distinctly higher than the annual average Stimulation”, Beijing: China Water Power Press, 1984, values. pp. 87-10 The above result shows that the contents of organic [6] N. Vladimir and C. Gordon, “Handbook of pollutants from soil in low-flow years is relatively small, Nonpoint Pollution”, New York: CRC Press Inc., 1981, and industrial sewerage may be the main pollution source, pp. 212-230. but the agricultural organic pollutants during Heavy [7] Q. Wu and T. Gao, “Water Pollution from Rainfall period can not be neglected. In high-flow years, Agriculture and Its Control measures” , Ecologic Science, the organic pollutants from soil distinctly increases, the 2003, 22(4): pp. 371-375. average concentrations of TOD and BOD in the runoffs to the water body are respectively 12.0mg/L and 1.1mg/L, [8] T. Yu, and Z. Wang, “Chemistry of Soil Analysis”, and the maximum daily average concentrations are Beijing: Science Press, 1988, pp.115-123 17.8mg/L and 16.0mg/L which will bring a serious [9] J. Wang, “Study on Control Measures of the Non- degradation to the water quality of the lake. The sand and point Source Pollution of Taihu Lake Region ”, organic matter in the surface runoff are pollutants in Environmental Protection Science, 2003, 29: pp. 16-17.

Table2. Modeled result of runoffs, sediments, and organic matter in Taihu Lake of a typical year 8 3 8 3 4 2 Typical year P (mm) Rs (10 m ) I (10 m ) Sc(10 t) Sf (t/km ) D (t) TOD (t) BOD (t)

1978 617 1.30 3.30 2.09 23.5 672 1040 93.5

1982 1034 3.67 3.96 8.19 92.2 2630 4070 366

1983 1325 5.89 4.45 15.2 170.6 4880 7560 680

J. Water Resource and Protection. 2008. 1: 1-65. Published Online June 2008 in SciRes (http://www.SRPublishing.org/Journal/jwarp/).

Bioaugmentation combined with biofilim process in the treatment of petrochemical wastewater at low temperatures

Jingbo GUO, Fang MA, Kan JIANG, Di CUI School of Municipal and Environmental Engineering & State Laboratory of Urban Water Resources and Environment Harbin Institute of Technology,Harbin,China E-mail: [email protected]

Abstract

Three sets of lab-scale reactors, which applied activated sludge process, bioaugmented activated sludge process and bioagumented biofilm process, respectively, were operated parallel to explore the optimum process for the treatment of petrochemical wastewater at low temperatures (13-15℃). Though being inoculated twice with enriched specialized bacteria, the bioaugmented activated sludge reactor (R2) didn’t show significant overall improvement on effluent quality when compared with the unbioaugmented reactor (R1) (average removal efficiency, COD: R1=65.02%, R2=70.39%; NH4+-N: R1=42.07%, R2=52.49%), except for increased levels of enzyme activity as described by dehydrogenase activity (DHA) and slightly better performance at the early stage of inoculation. Microscopic observation indicated that free-living cells were scarce in R2 and the main explanation was the grazing of protozoa to the bioaugmented cells. However, the application of porous polyurethane foam as carrier in the bioaugmented biofilm reactor (R3) could retain sufficient biomass within the reactor, and the COD (75.80%) and NH4+-N (70.13%) removal efficiencies were enhanced with more stable performances. In conclusion, massive inoculation couldn’t always warrant successful bioaugmentation due to predation to the inoculated specialized bacteria, and biofilm process was promising when combined with bioaugmentation technology in the treatment of petrochemical wastewater at low temperatures. Keywords: Bioaugmentaion; Low temperature; Activated sludge; Bioflim; Specialized bacteria

1. Introduction allochthonous wild-type or genetically modified organisms to polluted hazardous waste sites or bioreactors Traditionally, activated sludge process is widely used in in order to accelerate the removal of undesired pollutants dealing with industrial wastewater owing to its simplicity [6]. It had been widely used in enhancing the removal and relatively low cost. Petrochemical wastewater is ability of biological system to nitrogen [7] and heterogeneous organic compound mixtures, which phosphorous [8] as well as various organic refractory contains quantity of organic compounds that possess chemicals contained in industrial wastewater [9,10]. some degree of either toxicity or activity inhibition to the Although bioaugmentation of activated sludge system microorganisms in the biological unit [1]. Moreover, the with the introduction of specialized bacteria was microbial activity would be further inhibited under low successful in some cases with significant improvement to temperature conditions [2-4], when the adsorption and the removal of target compounds[11,12], it is not yet settling ability of the activated sludge would be widely applied due to several factors concerning influenced. Thus, microorganisms in the activated sludge unfavorable environmental conditions and the system, even well acclimatized, are inefficient in dealing competition between the inoculums and other with petrochemical wastewater containing relatively high microorganisms existed in the system[5,11]. However, concentration of organic compounds due primarily to low these limitations can be solved by replacing the biodegradability and inhibitory effects of these organic suspending biomass system by attached biomass process compounds [5], especially under low temperature [13]. Immobilization of mixed populations of conditions. microorganisms, predominantly bacteria, on or within inert supports has the following advantages [14,15]: (1) Bioaugmentation is the application of indigenous or high reactor biomass concentrations, (2) strong capacity

Copyright © 2008 SciRes. J. Water Resource and Protection. 2008; 1:1-65. 56 J. GUO ET AL. to handle shock loadings, and (3) low excess sludge production. 2.2. Bioaugmentation method The objective of this research is to investigate the effectiveness of bioaugmentation technology and to Specialized bacteria previously isolated from various explore an optimum bioaugmentation strategy for the environments, which mainly consisted of Pseudomonas, treatment of petrochemical wastewater under low Bacillus, Acinetobacter, Flavobacterium and Micrococcus, were functioned as COD degrading bacteria (mainly temperatures (13-15 ℃ ). Therefore, three lab-scale consist of oil and grease, phenol and aniline degrading reactors, which applied activated sludge process (R1), bacteria), bioflocculant-producing bacteria and denitrifier. bioaugmented activated sludge process (R2) and They were primarily acclimated with petrochemical bioagumented biofilm process (R3), respectively, were wastewater after being taken from the refrigerating operated parallel under low temperatures to compare their chamber and then inoculated into R2 and R3 with a total performances in treating petrochemical wastewater. dry mass 150 mg/L 4 days after steady-state was achieved. The second bioaugmentation in R2 was performed 13 2. Materials and methods days later in the same way while the addition amount rising up to 700mg/L. Systems were hermetically isolated 2.1. Stand-up and operation of the A/O process from each other to avoid cross-contamination.

Three identical plexiglass anoxic-oxic (A/O) set-ups (shown in Fig.1), with effective volumes of anoxic tank, 2.3. Immobilization on polyurethane foams oxic tank and clarifier were 1.5L, 3.5L and 1.25L, Polyurethane foam is considered as a suitable carrier respectively, were adopted. Each aerobic tank was for cell immobilization for its easy control of the pore size, inoculated with the same amount (0.5L) of activated stable maintenance of quantity of cells and large-scale sludge (MLSS=4000mg/L) taken from the aerobic tank of application at low price. It was widely used as a carrier in the petrochemical wastewater treatment plant (WWTP). the biodegradation of organic compounds [17,18]. Polyurentane foams were added as carrier in R3. Under Spontaneous adhesion immobilization strategy was steady-state, specialized bacteria were bioaugmened into adopted in the present study as it is simple, cheap and the oxic tank of R2 and R3, while R1 was operated under allows significant biomass immobilization [13]. Physical the similar condition without bioaugmentation. characteristics of the polyurethane foam are summarized Wastewater collected from the primary settling basin of in Table2. Strip polyurethane foams were stuffed in petrochemical WWTP (Table1 shows its quality) was fed spherical polythene plastic (D=80mm) frame to protect into these systems with flow rate increased stepwise to the carrier from being washed out from the system. The 0.5m3/h. The activated sludge was recycled at a 100% carrier hold-up was 30% in R3. ratio and the excess sludge was discharge at a 10% ratio per day from R1 and R2. The hydraulic retention time Table 2. Physical characteristics of the polyurethane (HRT) for anoxic stage and oxic stage was 3h and 7h, foam respectively. The dissolved oxygen (DO) in oxic tank was Items Values 4.0-6.0 mg/L. The wastewater was 13-15℃ during the Pore size 150-500μm Specific densiy 0.2-0.95 whole process. Specific area 2.0×104m2/m3 ≦ ≦ Acid and alkali resistence ability 5 pH 11 Sludge return Service life 10 years

P M Effluent 2.4. Analytical methods

Daily composite samples of influent and effluent were Influent A noxic tank O xic tank Clarifier obtained by mixing samples collected every 6 hours. COD, NH4+-N were analyzed according to standard Figure 1. The schematic diagram of the experimental A/O methods [19]. Biomass attached on the polyurethane foam process was removed by microwave agitation, while the biomass Table 1. Influent quality of the biological systems of the activated sludge process was collected directly. a Parameters Value Level Ⅰ Criteria Biomass concentration was determined by filtering the COD 400~600 100 μ 200~300 30 samples through 0.45 m millipore filter and then drying + NH4 -N 30-50 15 at 105℃ until constant weight. The free-living bacteria SS 70-200 70 were counted as colony forming unit (CFU) using culture Oil and grease ≤80 10 method. Protozoa was observed by electronic microscope. pH 7-9 6-9 For dehydrogenase activity (DHA) quantification, TTC- a.Integrated wastewater discharge standard of China [16]; Values are in mg/L except for pH. DHA method [20] was used. Polyurethane foam with

Copyright © 2008 SciRes. J. Water Resource and Protection. 2008; 1:1-65. BIOAUGMENTATION COMBINED WITH BIOFILIM PROCESS IN THE TREATMENT OF PETROCHEMICAL WASTEWATER AT LOW TEMPERATURES 57 biofilm for scanning electron microscope (SEM) system with inert support performed better than both the observation was fixed in 4% glutaraldehyde buffer (2.5%, conventional and the bioaugmented activated sludge pH=6.8) for 1.5h at 4℃, then rinsed three times in 0.1M system. The environment created by polyurethane foam phosphate buffer (pH=6.8), dehydrated using an ethanol provided a favorable condition for the growth and series (50%, 70%, 80%, 90% once for 10-15min and proliferation of the inoculums, i.e, the degrading 100% thrice for 10-15min), died overnight in the capability of microorganisms had a better chances to desiccator and then were fixed on metal supports and display with their immobilization on polyurethane foams. sputter coated with gold (10nm) (k550x, EMITECH, Moreover, compared to R2, since high concentration of England). Finally, biofilm samples were observed with a biomass and high cellular retention time were achieved by Philips XL30 SEM (Quanta 200, FEI, the Netherlands) biofilm, only one inoculation was conducted.. and photographed. Influent Effluent of R1 Effluent of R2 Effluent of R3 600 3. Resluts and disscusions ) 500 400 300 3.1. Performances of each reactor 200 COD(mg/L 100 The daily influent and effluent COD and NH4+-N of 0 60 1 6 11 16 21 26 each reactor were shown in Fig.2. When the influent Time(d) COD and NH4+-N were 309.00-548.71mg/L and 32.08- 50 40 49.26mg/L, respectively, the performances of R2 were 30 -N(mg/L) slightly better than that of R1 (average removal efficiency, + 20 4

COD: R1=65.02%, R2=70.39%; NH4+-N: R1=42.07%, NH 10 R2=52.49%). However, the average effluent COD and 0 NH4+-N of R2 was up to 133.97mg/L and 20.52mg/L 1 6 11 16 21 26 Time(d) respectively, and the improvement on pollutants removal efficiency only lasted for about 2 days after Figure 2. Influent and effluent characteristics of each bioaugmentation. The nitrification behavior of R1 was reactor even better than R2 before the second inoculation, while 3.2. Biomass Concentrations and Enzyme slightly better performance was detected in R2 after the Activities second bioaugmentation. Thus, even R2 was inoculated twice with the specialized consortia, improvment induced The average DHA and biomass in each reactor during by bioaugmentation was still unfavorable. one month operation were detected The DHA of the Therefore, under low temperatures, by inoculating activated sludge in R2 (1.83mgTF/gMLSS.h) was much specialized bacteria into the activated sludge set-up, higher than that of the R1 (0.99mgTF/gMLSS.h), while bioaugmentation technology failed for the treatment of the average concentration of MLSS in R1 (1100mg/L) petrochemical wastewater as the effluent quality couldn’t was slightly higher than that of R2 (900mg/L), which meet the national wastewater discharge standards [16]. demonstrated that with the addition of specialized The previous literatures indicated that bioaugmentation bacteria, the activity of the activated sludge increased would be a useful tool for the removal of recalcitrant compared to the unbioaugmented one, however, the organic compounds and the enhancement of the inoculums failed to exhibit their capability to decompose wastewater treatment systems’ stability under extreme the target pollutants and there was no notable correlation environments [21], such as low and high temperatures, between pollutants removal efficiency and enzyme saline environments, acidic and alkaline environments as activity, which differed from the conventional concept well as deep-sea environments. Results herein may due to that the higher the enzyme activity, the lower organics the difficulty in the ecological control of the added remaining in the effluent[20]. This phenomenon may be specialized strains and the other microorganisms involved particular to low temperature as the microorganisms in the activated sludge system, thus the availability of the needs long period for its lag phase until the degradation specialized consortia added was reduced. began to display. For biofilm reactor, sufficient biomass With the application of polyurethane foam as carrier, (2000mg/L) was retained with even higher activity the average effluent COD and NH4+-N of R3 were (2.08mgTF/gMLSS.h), which performed best with the 91.69mg/L and 20.52 mg/L, and it’s quite promising microorganisms bioaugmented in the system. These since the average removing efficiency to COD and results indicated that massive inoculation didn’t always NH4+-N reached to 75.80% and 70.13% respectively. coupled with favorable performances, and the availability Meanwhile, in the later period, the effluent concentration of inoculums was crucial for successful bioaugmentation. COD and NH4+-N were below 90mg/L and 12 mg/L, respectively. The results suggested that bioaugmented 3.3. Microscope observations

Obvious proliferation of protozoa after the inoculation biofilm process performed effectively in pollutants of specialized consortia was observed in R2, while free- removal with high microbial activity. Thus, living bacteria were scare. In order to determine whether bioaugmentation was optimal when combined with the lack of free bacteria was mainly caused by washout or biofilm process. by protozoa, average free-living bacteria in aeration tank and secondary tank was counted as colony forming unit (CFU). Under the same operational conditions, free-living bacteria in R1 was higher than that of the R2, while the proportion of free-living cells that lost along with the effluent were 75% and 30% for R1 and R2, respectively. It could be inferred that the main reason for the rapid disappearance of the numerous bacteria inoculated in R2 (a) (b) was not washout but the grazing of the protozoa which overgrew with the addition of large amount of specialized bacteria. Conventionally, the proliferation of protozoa was considered to be an indication for favorable water quality, however, it was not the case after bioaugmentation with massive specialized bacteria in the system, where the ecosystem equilibrium was disturbed. (c) (d) Thus, it would be advisable to take measures to prevent Figure3. SEM images of the biofim the inoculated bacteria from being phagocytized by overgrowing protozoa.

4. Conclusion 3.4. SEM observation of biofilm Microorganisms immobilized on polyurethane foam Under low temperatures, compared to bioaugmened were observed by SEM. Images are showed in Fig.3. activated sludge process, since it could retain sufficient There were three kinds of immobilization forms for the biomass, bioaugmentation combined with biofilm process bacteria on polyurethane foam, that is: (a) cells entrapped performed more effectively in removing pollutants in the pores; (b) individual cells distributed randomly on contained in petrochemical wastewater with high the on the surface of polyurethane foam; (c) and (d) Cells microbial activity, while bacterial species were congregated together on the surface or in the pores of disappeared due to the strong increase in the grazing polyurethane The numerous microorganisms immobilized pressure exerted on the inoculums in the activated sludge on the porous carrier performed well in the pollution system. Thus, the application of polyurethane foam as degradation and were against from the predation of carrier in the bioaugmentation practice is promising for protozoa and the washing out along with the effluent. the retention of sufficient biomass and prevention Many previous study pointed out that compared to mechanisms to the immobilization cells. Further conventional free cell systems, the bioreactors with researches on the ecological relationships in immobilized cells showed better results including greatly bioaugmented system by adopting advanced molecular improved reactor productivity and enhanced withstand microbial techniques are necessary for better ability to extreme environment such as low temperature understanding to the bioaugmentation mechanism. due to its high cell density and optimum microbial community structure [13,18,19]. 5. Acknowledgment However, from Fig.3(a), it was obvious that there was large percentage polyurethane foam hadn’t been utilized We gratefully acknowledge the National Basic Research both for the pores and the surface, possible reasons are Program of China (973 Program) (Granted No. the relatively short operational time or the washing force 2004CB418505) and Heilongjiang Provincial Science and of the flow or the unfavorable condition for cells’ Technology Development Program (Granted No. immobilization. Thus, certain modification may be CC05S301) for their financial supports. required for the wide application of porous polyurethane foam s as a carrier. 6. References The results obtained above demonstrated that under [1] L. Castillo, H. El Khorassani, P. Trebuchon and O. low temperatures, bioaugmentation of the activated Thomas, “UV treatability test for chemical and sludge process with domesticated specialized bacteria petrochemical wastewater,” Wat. Sci.Tech., Vol. 39, No. induced a slightly better performance in treating 10-11, pp. 17-23, 1999. petrochemical wastewater than the system without [2] G. C. Banik and R. R Daugue, “ASBR treatment of bioaugmentation, while bioaugmentation combined with low strength industrial wastewater at psychrophilic

Copyright © 2008 SciRes. J. Water Resource and Protection. 2008; 1:1-65. BIOAUGMENTATION COMBINED WITH BIOFILIM PROCESS IN THE TREATMENT OF PETROCHEMICAL WASTEWATER AT LOW TEMPERATURES 59 temperatures,” Wat. Sci. Tech., Vol. 36, pp. 337- tesrosteroni strain, I2gfp,” Applied Environmental 334,1997. Miceobiology, Vol. 36, No. 7, pp. 2006-2913, 2000. [3] R. W. M. Jr., C. R. Baillod and J. R. Mihelcic, “Low- [13] D. Hadjiev, D. Dimitrov, M. Martinov and O. Sire, temperature inhibition of the activated sludge process by “Enhancement of the biofilm formation on polymeric an industrial discharge containing the azo dye acid supports by surface conditioning,” Enzyme and Microbial black,” Water Research, Vol. 39, pp.17–28, 2005. Technology ,Vol. 40, pp. 840-848, 2007. [4] D.B. Nedwell, “Effect of low temperature on [14] M. Zielińska and I. Wojnowska-Baryła, “Removal of microbial growth: lowered affinity for substrates limits organic compounds from municipal wastewater by growth at low temperature,” FEMS Microbiology immobilized biomass,” Polish Journal of Environmental Ecology, Vol. 30, pp. 101-111, 1999. Studies, Vol. 13, No. 5, pp.573-577, 2004. [5] H. Van Limbergen, E. M. Top and W. Verstraete, [15] D. Georgiou, J. Hatiras and A. Aivasidis, “Microbial “Bioaugmentation in activated sludge: current features immobilization in a two-stage fixed-bed-reactor pilot and future perspectives,” Appl Microbiol Biotechnol, Vol. plant for on-site anaerobic decolorization of textile 50, pp. 16-23,1998. wastewater,” Enzyme and Microbial Technology,Vol. 37, pp. 597–605, 2005. [6] S. EI Fantroussi and S. N Agathos, “Is bioaugmentation a feasible strategy for pollutant removal [16] State Standard Bureau, “Integrated wastewater and site remediation,” Current Opinion in discharge standard(GB8978-1996)”, China Microbiology,Vol. 8, pp. 268-275, 2005. Environmental Press, Beijing, China, 1997. [7] M. A. Head and J. A.Oleszkiewicz, [17] S. Manohar, C. K. Kim and T. B. Karegoudar, “Bioaugmentation for nitrification at cold temperatures,” “Enhanced degradation of naphthalene by immobilization Water Research, Vol. 38, pp. 523-530, 2004. of Pseudomonas sp. Strain NGK1 in Polyurethane Foam,” Appl Microbiol Biotechnol, Vol. 55, No. 3, pp. 311-316, [8] E. Belia and P. G. Smith, “The bioaugmentation of 2001. sequencing batch reactor sludges for biological phosphorous removal,” Wat. Sci. Tech., Vol. 35, No. 1, [18] C. Guimarães, P. Porto, R. Oliveira and M. Mota, pp.19-26, 1997. “Continuous decolourization of a sugar refinery wastewater in a modified rotating biological contactor [9] D. Park , D. S. Lee, Y. M. Kim and J. M. Park, with phanerochaete chrysosporium immobilized on “ Bioaugmentation of cyanide-degrading polyurethane foam disks,” Process Biochemistry, Vol.40, microorganisms in a full-scale cokes wastewater pp. 535-540, 2005 treatment facility,” Bioresource Technology, 2007，in press. [19] State Environmental Protection Administration of China, “Water and wastewater analytical methods [10] S. C. Chen, S. L. Chen and H. Y. Fang, “Study on (Edition 4),” China Environmental Press, Beijing, 2002. EDTA-degrading bacterium Burkholderia cepacia YL-6 for bioaugmentation,” Bioresource Technology,Vol. 96, [20] Q. Tian , J. Chen, H. Zhang and Y. Xiao, “Study on pp. 1782–1787, 2005. the modified triphenyl tetrazolium chloride– dehydrogenase activity (TTC-DHA) method in [11] F. Kardi, S. Eker and A. Uygur, “Biological determination of bioactivity in the up-flow aerated bio- treatment of synthetic wastewater containing 2,4- activated carbon filter,” African Journal of Biotechnology, dichlorophenol(DCP) in an activated sludge unit,” Vol. 5, No. 2, pp. 181-188, 2006. Journal of Environmental Management,Vol. 76, pp. 191- 196, 2005. [21] R. Margesin and F. Schinner, “Biodegradation and bioremediation of hydrocarbons in extreme [12] N. Boon, J. Goris, P. De Vos, W. Verstraete and E. environments,” Appl Microbiol Biotechnol, Vol. 56, pp. M. Top, “Bioaugmentation of activated sludge by an 650–663, 2001. indigenous 3-chloroaniline-degrading Comanmonas

Trihalomethane occurrence in chlorinated hospital wastewater

Yingxue SUN1, Hongying HU1, Ping GU2 1Department of Environmental Science and Engineering, Tsinghua University, Beijing 100084, China 2School of Environmental Science and Engineering, Tianjin University, Tianjin 300072, China

Abstract

Chlorination as a disinfection process is often used for disinfecting hospital wastewater in order to prevent the spread of pathogenic microorganisms and causal agents of nosocomial infectious diseases, but harmful byproducts might be formed and cause adverse ecological and health effects. In this study, the generation of trihalomethane (THMs) in the effluent of hospital wastewater during chlorine disinfection process was evaluated. The results showed the formation of THMs increased gently along the increasing chlorine dosages at beginning of the chlorine disinfection, but increased significantly after the chlorine dosages over 20 mg/L. Chloroform was the most abundant THM species and occupied above 40% of the total concentration. The second-order model interpretation of the long-term formation of THMs showed a good linearity and a second-order rate constant of 0.8857 (mg/L)-1s-1 in this experiments. Additionally, THM formations in these water samples well correlated with SUVA with generally exponential (R2=0.9987).

Keywords: Chlorination; Hospital wastewater; Trihalomethane

potential (THMFP) of various treated industrial 1. Introduction wastewaters [11], and evaluated the effect of hydraulic retention time and mixed liquor suspended solids (MLSS) Hospital wastes could be dangerous to the ecological on THMs precursor removal in the activated sludge balance and public health. Pathological, radioactive, process with synthetic domestic wastewater [12], chemical, infectious, and pharmaceutical wastes, if left respectively. Sirivedhin and Gray compared the DBPs untreated, could lead to outbreaks of communicable formation potential among samples of a wastewater diseases, diarrhea epidemics, water contamination, and effluent and surface waters, and found the effluent-derived radioactive pollution [1]. To prevent the spread of organic matter (EfOM) were less reactive with chlorine on pathogenic microorganisms and causal agents of a per DOC concentration basis. Yet, EfOM had higher nosocomial infectious diseases, chlorination as a proportions of brominated DBP [13]. Marhaba et al. disinfection process is widely used for disinfecting analyzed the THMFP for all shrimp farm effluents in the hospital wastewater. However, the chlorination process range of 810-3100 μg/L, and obtained that the hydrophilic results in the formation of mutagenic/carcinogenic organic fraction was a more active precursor of THMs [14]. disinfection by-products (DBPs) deriving from the In studies of Matamoros et al. for three chlorinated reaction of the chlorine with organic compounds in effluents (i.e. secondary and tertiary) from full-scale hospital wastewater, which are dangerous to the aquatic wastewater treatment plants, chlorine disinfection of environment and source of drinking water [2]. reclaimed water used for agricultural and landscape Trihalomethanes (THMs), as a major class of DBPs, were irrigation results in lower TTHM concentrations than those discovered in drinking water [3,4], and their carcinogenic observed in conventional drinking water supplies [15]. Up effects were observed in laboratory animals a few years to now, The ultrasonic process and coagulation method has later [5]. applied to investigate its effect on the reduction of organic Many researches about THMs have focused on the matter and THMFP during chlorination in wastewater samples of raw and treated drinking water since the past effluent, and respectively got good effects in some degree several decades [7-10], but only recently, a few studies [16,17]. As disinfection of wastewater is a complex have investigated THMs in the chlorinated effluents from process for the multi-components in water, complicated wastewater treatment. Galapate et al. had determined the chemical reactions and various operational conditions, all influence of some chemical functional groups (COOH, of which will influence the formation of DBPs, Wang et al. phenolic-OH and organic nitrogen) and bulk parameters used photobacterium bioassay test and umu test (UV 260 and DOC) on the trihalomethane formation repectively investigated the toxicity and genotoxicity of

Copyright © 2008 SciRes. J. Water Resource and Protection. 2008; 1:1-65. TRIHALOMETHANE OCCURRENCE IN CHLORINATED HOSPITAL WASTEWATER 61 wastewater effluent during chlorine disinfection [18,19]. ultraviolet absorbance (SUVA) in the hospital wastewater Compared with domestic watewater, there are more were to be established. kinds of pathogens and chemicals in hospital wastewater. In China, One of the main environmental problems caused 2. Materials and methods by hospital effluents is due to their discharge in urban sewerage systems without preliminary treatment only 2.1. Water samples and analytical methods followed by disinfection. In addition, chlorination has been Wastewater samples were collected from a general the main strategy for disinfecting hospital wastewater due hospital before disinfection, which were immediately to its very broad-spectrum of biocide activity against delivered to the laboratory in an ice cooler and stored at bacteria, virus and fungi, and its low cost. So the pollution 4℃ to minimize changes in the constituents. of DBPs in effluent of hospital wastewater is self-evident. The principal conventional qualities of these water Some researchers applied adsorbable organic halogens to samples were analyzed in accordance with standard demonstrated the DBPs in chlorinated effluent of hospital methods [22], and the results are shown in Table 1. wastewater [20,21], but few have paid attention to THMs Concentration of ammonia nitrogen (CNH3–N) was in that of hospital wastewater. Although THMs are not determined by colorimetry by using the Nesslerizatin mentioned in the ‘Discharge Standard of Water Pollutants method. Concentration of dissolved organic carbon for Medical Organization of China’, their negative impacts (CDOC) was detected with a TOC analyzer (Model: on aquatic environment ought to be concerned. TOC-5000A, Shimadzu, Japan). UV absorbance at 254 nm The aim of this study was to evaluate the generation of (UV254) was measured with a photospectrometer THMs in the effluent of hospital wastewater during (Model:UV-2401, Shimadzu, Japan). The concentrations chlorine disinfection process, including to investigate the of THMs (including CHCl3, CHCl2Br, CHClBr2 and formation of THMs and its sepecies along the breakpoint CHBr3) were determined using a gas chromatograph curves during chlorination and to determine the (Agilent Trace GC) with an electron capture detector (ECD) relationship of THMFP and dosages of chlorine. Also the by USEPA method 551.1 [23]. correlations between the formation of THMs and specific

Table 1 Water quality characteristics of hospital wastewater samples used in this study Total bacteria Fecal coliform Sample C (mg/L) C (mg/L) UV (cm-1) NH3-N DOC 254 (CFU/mL) (MPN/L) Wastewater 24.29~19.80(22.82) 62.53~125.00 (86.72) 0.64~1.11 (0.77) 105~107 105~108

Note: average data are in parenthesis. procedure described in Standard Methods of 5710B [22]. 2.2. Chlorine disinfection The method involved buffering samples with phosphate Chlorine disinfection was conducted within 24 h after buffer at pH value of 7.0, chlorinating samples with sampling. A series of 600 mL glass bottles with Teflon excess free chlorine and storing the sample at 25 °C for inner plugs were prepared, and each bottle was filled with several days to allow the reaction to approach completion. about 580 mL of wastewater sample. Chlorination The chlorinated samples were placed into 125 mL amber experiments adopted sodium hypochlorite as the glass bottles with polypropylene screw caps and disinfectant. A series of different concentrations of TFE-faced septa. The vials were carefully filled for available chlorine was added into corresponding reaction preventing the trapping of air bubbles inside. Then they bottles by using sodium hypochlorite solution with a were incubated at 25 °C until seven days. Then, residual concentration of 3 g available chlorine per liter. The chlorine was determined according to the DPD bottles were sealed and kept in a dark isotherm chamber colorimetric method [22], and the quenching agent of (20℃) for special time, and then total residual chlorine sodium sulfite was added for depletion of residual was measured according to the standard method [22]. chlorine. Based on the concentration of residual chlorine, different sodium sulfit was added to each bottle to remove residual 3. Results and discussions chlorine. All of the chemical reagents used in this study were of analytical purity. Chlorination experiments were 3.1. Breakpoint chlorination and the speciation of carried out in a well mixed batch reactor at pH 7. Each THMs test run was initiated by adding a preset chlorine dosage The chlorine dosages to achieve 1-hour breakpoint to the test solution. chlorination of hospital wastewater samples were found to 2.3. THMFP test be 35 mg/L (counted as Cl2) and the corresponding residual chlorine was 7.45 mg/L (as shown in Fig. 1). The THMFP test was conducted according to the results showed that concentration of THMs increased

Copyright © 2008 SciRes. J. Water Resource and Protection. 2008; 1:1-65. 62 Y. SUN ET AL. gently along the increasing chlorine dosages at beginning concentration of residual chlorine and contact time). The of the experiment, but increased sharply after the dosages THMs species including CHCl3, CHCl2Br, CHClBr2 and of chlorine exceeded 20 mg/L, which is somewhat similar CHBr3 were both observed before and after the with the study of Yang et al. [24]. For the wastewater breakpoint, where the CRT value was 7.45 (mg·h)/L. with highly concentration of dissolved organic carbon Among these, CHCl3 was the most abundant THM (DOC) (as shown in Table 1), there were many types of species and occupied above 40% of the total components in the wastewater could react with NaClO, concentration and its concentration elevated gradually which existed discrepancy in structures and activities with an increase in the chlorine dosage before the among each others. The NaClO will reacte firstly with breakpoint. CHCl3 concentration slightly decreased and precursors having higher activity, but for the lower activty the CHCl2Br elevated gradually with the increasing of precursors, the reactive degree depend on the dosage of chlorine dosage after the breakpoint. CHBr3 disinfectant. So the THMs concentration increased concentrations decreased to lower levels with the increase significantly along the increasing of chlorine after the of chlorine dosage. The total concentration of dosages of 20 mg/L. Meanwhile, for the wastewater trihalomethanes and the individual THM species in samples containing much suspended solids posed as chlorinated water strongly depended on the composition masks for the pathogens, NaClO could not reached the of the raw water, on operational parameters and chlorine excellent effect of disinfection. The fecal coliform (FC) in dosage. this wastewater samples decreased lower than 500 4500 MPN/L after disinfection with the concentration of 4000 (a) available chlorine is 20 mg/L, but could not been completely inactivated even until the available chlorine 3500 THMFPf

3000 reached 50 mg/L with 1.0 h contact time (under 30 times ）

µg/L 2500 experiments). mg/L （ 2000 THMFP 150 35 THM 1500 FC ≤ 500 (MPN/L) 30 1000 THMFPi 25 100 500 g/L)

μ 20 0 15 0 50 100 150 200 50 10 Time时间（ (h)h ） THMs ( THMs 5 200 80 breakpoint 0 0 (mg/L) chlorine residual 175 70 0 5 10 15 20 25 30 35 40 45 50 150 60 chlorine dosage (mg/L) 125 (b) 50 100 40 (mg/L) Figure. 1. 1-hour breakpoint chlorination curves and the concentration of THMs. (FC: the count of fecal coliform) 75 30 耗氯量 50 y = 0.8857x 20 2

R = 0.9424 (mg/L) demands Chlorine 100% 25 10

80% 0 0 0 50 100 150 200 60% Time时间（ (h)h）

40% Figure. 3.Formation of THM from chlorination of hospital 20% wastewater (pH 7, DOC 80.2 mg/L, UV254 0.859 cm-1

0% [THMFPf]= 3450 µg/L, [THMFPi]= 795 µg/L, k=0.8857 distributions of THMsdistributions species 0.64 2.98 5.5 9.17 16.7 13.2 7.45 10.4 16 24 (mg/L)-1s-1)

CRT (mg.h/L) CHCl3 CHCl2Br CHClBr2 CHBr3

Figure. 2. The distribution of THMs species at different 3.2. Relationship of the THMFP and Cl2 CRT value with 1 h contact time. (CRT is the arithmetic product of concentration of residual chlorine and contact THMFP is often the term employed to indicate the time) amount of THMs that could be produced during the Fig. 2 illustrates the distribution of each THM species chlorination process. We employed the analytical after 1 h chlorination of wastewater samples at various methods in the study of Gallard and Gunten [25] for this CRT value (CRT is the arithmetic product of investigation. Fig. 3a shows that after 3 h of reaction time

Copyright © 2008 SciRes. J. Water Resource and Protection. 2008; 1:1-65. TRIHALOMETHANE OCCURRENCE IN CHLORINATED HOSPITAL WASTEWATER 63 the concentration of THMs was 795 μg/L, but there were corresponds to the nature of organic matter in the water little change until 24 h. Thereafter, THMs were slowly source, samples with an SUVA≥4 L/mg.m have a produced during 6 days until a plateau was reached relatively high content of hydrophobic organic 3357.13 μg/L. Therefore, and as depicted in Fig. 3a, the compounds, while samples with an SUVA≤3 L/mg.m are initial THM formation potential (THMFPi) corresponds largely hydrophilic [27]. The SUVA of these samples was to the fast reacting THM precursors formed within the lower than 3 L/mg m, which may have led to the first hours of reaction time (t

⎛⎞g/L) 1 [][]THMFP× Cl2 ×=ln ⎜⎟T kt μ ⎜⎟ 150 ()[][Cl22−− THMFP ] [][ Cl() THMFP ][ THM ] iTiT⎝⎠ (1) 100

where [Cl2]i is the concentration of chlorine after the ( THMs y=13exp(2.671x) initial chlorine consumption (t=ti and [THM]=[THMFPi]) 50 R2=0.9887 and [THMFP]T is the total concentration of slowly 0 reacting THM precursors ([THMFP]T=[THMFPf]- 0.7 0.8 0.9 1.0 1.1 [THMFPi]). The plot of the left-hand side of Eq. (1) SUVA (L/mg.m) versus time should result in a straight line with a slope of k. Figure 4. Relationships between SUVA with For the hospital wastewater sample, the second-order THMs. model interpretation of the long-term formation of THMs (Fig. 3b) showed a good linearity and a second-order rate constant of 0.8857 (mg/L)-1s-1(the correlation coefficient was 0.9424). An exponential relationship between contact 4. Conclusions time and chlorine demand also was showed in Fig. 3b. The results were in agreement with the proposed kinetic For hospital wastewater samples containing much model for natural organic matter in nature waters [25], but suspended solids posed as masks for the pathogens, the rate constant was higher than that of nature fecal coliform in the water samples could not been waters(which was 0.1417 (mg/L)-1s-1). completely inactivated even until the available chlorine reached 50 mg/L with 1.0 h contact time in the 3.3. Relationship of the THM and SUVA disinfection process. The results showed concentration Because the tests for THMFP is quite tedious and of THMs increased gently along the increasing time-consuming, attempts have been made to examine the chlorine dosages at beginning of the chlorine relationships between various potential surrogates and disinfection, but increased sharply when the dosages of THMFP [25]. THMFP was found to be influenced mainly chlorine up to the breakpoint. Chloroform was the most by the types of organic matters in the water sample. abundant THM species and occupied above 40% of the Generally the type of organic matters is identified by total concentration. For this hospital wastewater several parameters such as dissolved organic carbon sample, the second-order model interpretation of the (DOC), ultraviolet absorption at a wavelength of 254 nm long-term formation of THMs showed a good linearity (UV254), and specific ultraviolet absorbance (SUVA), and a second-order rate constant of 0.8857 (mg/L)-1s-1. which is the ratio between UV254 and DOC [26]. Also, THM formations well correlated with SUVA However, the relationship between each surrogate and THMFP was often specific to each particular water source, with generally exponential (R2=0.9987). As the relationship at one water source might not be suitable disinfection of hospital wastewater is a complex for the others [25]. The relationships between SUVA with process for the multi-components in water, THM levels in studied wastewaters are shown in Fig. 4. complicated chemical reactions and various operational We found that THM formations well correlated with conditions, the formation of DBPs required more SUVA with generally exponential, and get high deeply researches. regression coefficients. This can be attributed to the 5. Acknowledgements influence of aromaticity on THMs, the more aromaticity existed in the wastewater samples, the more THMs produced. As it is generally accepted that the SUVA This work was financially supported by the National High Technology Research and Development Program of

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