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International Conference on Chemical, Environmental Science and Engineering (ICEEBS'2012) July 28-29, 2012 Pattaya (Thailand)

Biological denitrification of wastewater-A Mini Review on Carbon Source

Srinu Naik. S and Y. Pydi Setty

cancer [1-4], and blue baby syndrome [5-6]. Denitrifiers may Abstract—A comparative study on the use of carbon sources as play an important part in the breakdown of various supplementary source to enhance denitrification in primary and hydrocarbon compounds. In agricultural areas denitrification secondary anoxic zones is reported. Denitrification is a process in leads to a loss of effiency [7], and incomplete which the oxidized substances, i.e. and are denitrification can lead to the release of NO and /or N2O, both reduced to nitrogen gas, such as N2O and N2, when a proton donor (energy source) is available. contamination is one of the of which are known to be involved in the formation of acid major problems in , which is increasingly becoming a rain, and global warming. threat to groundwater supplies. Nitrate in drinking water for animal To address this problem, specific rules have been and human consumption is not recommended for health reasons. The established globally. The European and the USA World Health Organization has set a limit of 10 mg/L NO3- for - Environmental Protection Agency, set 5.6 mg (NO3-N)/L and human consumption and 100 mg/L NO3 for animals. Nitrogen in 10 mg (NO3-N)/L) respectively [8-10]. Therefore, the nitrates groundwater results from human excreta, ground garbage and industrial effluents, particularly from food processing plants. The removal is essential to successful wastewater treatment. addition of external carbon source helps in increasing denitrification Biological denitrification is an attractive treatment option, in rates and enhances the nitrogen removal. Nitrates cause cancer, which the denitrifying converts nitrate to inert methemoglobinemia (blue baby syndrome), hypertension and thyroid nitrogen gas and the waster product usually contains only hypertrophy and in plants. In most biological biological solids. Biological removal of nitrate is widely used denitrification systems, the nitrate polluted wastewater (e.g. domestic in the treatment of domestic and complex industrial ) contains sufficient carbon source to provide the energy source for the conversion of nitrate to nitrogen gas by the wastewaters [11-17]. . The groundwater, in which the nitrate contents Organic carbon is often the limiting substrate for biological may be as high as 100 mg/L with low dissolved carbon content, an denitrification and many wastewater treatment plants add additional proton acceptor is required. The review addresses the state extra carbon for denitrification to balance the processes [18]. of the art of each electron donor candidate for its potential Among the various process techniques available for nitrate application to the treatment of industrial wastewater containing removal like ion exchange ion exchange [19], reverse osmosis nitrate. [20], electro dialysis [21], chemical and catalytic Keywords—Biological treatment, Carbon source, denitrification [22]. Ion exchange and adsorption processes Denitrification, Wastewater. have been developed mainly for the production of high purity water and generate concentrated brine that needs additional I. INTRODUCTION treatment, often involving adsorption resins whose capacity is rapidly reached by these concentrates, thus requiring frequent EMOVAL of nitrate from wastewater through biological R treatment in enforced in most developed countries to replacement or regeneration. Membrane technology is a protect local waterways from eutrophication. In biological concentrating method which needs a post-treatment of the denitrification the nitrate reduction reactions involve the brine before discharging out of the process, and chemical following pathway, in this process microorganisms first treatment is inefficient in treating the low nitrate reduce nitrates to nitrites and then produce , concentrations of wastewater and requires a continuous and and nitrogen gas. large supply of chemicals [23-26]. Each of them has its own advantages and disadvantages, →→→→ 3 2 2 NONNONONO 2 from which biological method is found to be the most The beneficial aspects of denitrification include control or commonly used and effective method as shown in Table 1, of NO3-contaminated waters, which can cause biological denitrification is a well developed and widely used eutrophication. However, it has also been linked to stomach method, one technically and economically superior compared to other competing methods [27] and involves a microbial Sapavatu Srinu Naik is with the National Institute of Technology, respiration which uses nitrate as a final electron acceptor Warangal, Andhra Pradesh-506 004, INDIA (phone: 09885 165 333 under anoxic conditions. ; fax: 0091-870-2459547; e-mail: [email protected]). Several studies has been carried on denitrification [28-36] Yelamarthi Pydi Setty is with National Institute of Technology, Warangal, Andhra Pradesh- 506 004, INDIA.(e-mail: [email protected]).

47 International Conference on Chemical, Environmental Science and Engineering (ICEEBS'2012) July 28-29, 2012 Pattaya (Thailand)

A source of organic carbon is an important component of Wilawan et al. (2010) made a comparison report on the denitrification process; generally most of wastewater biological nitrate removal using three different carbon sources treatment plants use as external carbon source due like acetate, and hydrolyzed rice. The results to economic reasons in denitrification process. Other suggested that acetate is the most appropriate carbon source compounds can be used in denitrification process includes for nitrogen removal and hydrolyzed rice is a satisfactory acetate, ethanol, methane, glucose, peptone, saw dust, alternative carbon source [37]. , lactic acid, molasses, etc. A number of Sunil et al. (2010) has been also compared with acetate, investigations are reported in the literature on the nitrate methanol and ethanol as supplementary carbon sources in the removal from wastewater using carbon sources. denitrification process using bio-granules as shown in Fig. 1, 2, and 3. The bio-granules degraded 200 mg/L and Carbon source studies suggested that the capacity of supplementary carbon source on enhancing nitrate removal enzyme activity is TABLE I methanol>acetate>ethanol on molar basis or COMPARISON OF DENITRIFICATION PROCESSESS acetate>ethanol>methanol on an added weight basis [38]. Process Merits Demerits Biological Economically superior Electron donor is required, Jae Yeon Park et al. (2009) made a review on biological method process among available Shedding suspended solid. nitrate removal in industrial wastewater treatment and processes, transformation of compared the estimated costs of substrates for nitrate removal. nitrate into harmless nitrogen gas, stable and continuous Denitrification rate of different electron donors like methanol, removal of nitrate, No need ethanol, acetic acid, acetate, cotton, sulfur and hydrogen was for intermittent pause of compared. According to the review methanol has the low reactor for maintenance and price 0.7 $/kg substrate and nitrate removal rate nearly 1000- repairing. -3 -1 27,000 g-N m day compared to other sources [39]. Reverse Used for high concentration High capital, operation and Guven Didem (2009) have reported an overview on the Osmosis of nitrate, insensitive to maintenance costs due to effect of carbon sources (acetate, propionate, ethanol and temperatures variations, No power consumption, post treatment required, Requires pre-treatment of glucose) on denitrification efficiency associated with culture Relatively easy to operate, water to remove organic adaptation and C/N ratio and suggested that methanol has Removes virtually all matter, suspended and shown to select for a denitrifying population consisting of contaminants, Producing the colloidal particles and other highest quality of water. contaminants, Sensitive to Paracoccus and Hyphomicrobium vulgare genera, when used PH and pressure variation as only external carbon source [40]. and chlorine content. Ginige et al. (2009) made a comparative study on methanol

Ion High efficiency when other Disposal of spent regenerate as carbon source using three lab-scale sequencing batch exchange ions do not exist, effluent brine solution, Sensitive to reactors (SBR) as shown in Fig. 4. The experiments were concentration can be lowered high levels of TDS, Large conducted by adding more to the first reactor, a under very low level, can teat volumes of salt required for small amount of methanol to the second and no methanol was high concentration of nitrate, regeneration, Water may relatively insensitive to flow require pre-treatment due to added to the third reactor. The addition of methanol stimulates and temperature variations, suspended solids, organic the growth of specific methanol-utilizing denitrifiers, which low capital cost. matter, iron and other improves the capability of sludge to use methanol and ethanol oxidizing agents, to prevent anion resin fouling, Requires for denitrification, but reduces its capability to use wastewater post treatment due to COD for denitrification [41]. corrosive to product water, Shao et al. (2008) reported on water denitrification using Does not completely remove nitrate from water. rice husk as carbon source and also as biofilm carrier. The experimental was conducted for a flow rate of 41.4 L/d and Ultra High removal efficiency Membrane is easy to be nitrate concentration of 25.0 mg/L and achieved a highest filtration contaminated denitrification rate of 0.096 kg/m3d [42]. Tatsuki Ueda et al. (2006) studied on biological Electro Does not require extensive High capital, operation and dialysis pretreatment compared to maintenance costs due to denitrification using sugar industry wastes namely final RO, Insensitive to scaling or power consumption, molasses as a carbon source with charcoal pellets as fouling compared to RO, Sensitive to iron, manganese, supporting media for denitrifying bacteria. The study Removal of nitrate, hydrogen sulfide (H2S), demonstrated that final molasses could be used as a carbon accomplished without the use chlorine, and hardness. of additional chemicals, Can source for biological denitrification. At least an influent C/N operate at higher TDS levels, ratio of 2 and HRT of 0.8-1.0 h were required to achieve relatively insensitive to PH enough denitrification [43]. and temperature variations.

48 International Conference on Chemical, Environmental Science and Engineering (ICEEBS'2012) July 28-29, 2012 Pattaya (Thailand)

TABLE 237 NITROGEN REMOVAL EFFICIENCY AND C/N RATIO REQUIREMENT OBSERVED USING VARIOUS CARBON SOURCES Nitrogen References Carbon C/N ratio removal source (mg-C/mg-N) efficiency (%) Acetate 1.5 90-100 Methanol 1.5 90-100 [51] Acetate 5.0 100 Glucose 5.0 100 [52]

Acetic acid 1.1 100 [53] Ethanol 0.6 100 Acetic acid 4.3 98 Ethanol 2.35 91 [54] Methanol 2.9 93 Ethanol 2.5 100 Succinate 2.5 100 [55] Molasses 6a 92 [56] Fig. 1. Effect of addition of acetate on denitrification by Corncobs 1.5a 90 [57] aerobic sludge granules

Savia Gavazza et al. (2004) have carried out their extensive study on comparison of methanol, ethanol and methane as electron donors for denitrification and compared the same efficiency achievement with three sources based on the hydraulic retention time. Results suggested that the most effective electron donor was ethanol, which completely removes nitrite and nitrate in 50 min, the same efficiency was achieved by feeding the reactors with methanol and methane for 120 and 315 min respectively [44]. Greben et al. (2004) have also conducted an experiment on biological denitrification of wastewater using saw dust as the carbon and energy source, which is a common waste product of the forestry industry and it is available readily. The results reported for a HRT of 24 h and wastewater containing nitrate concentration of 100 mg/L and thereafter 200 mg/L with a removal of 100% efficiency. But according to their report Fig. 2. Effect of addition of ethanol on denitrification by when the HRT decreased to 12 h, the denitrification process aerobic sludge granules was ceased and removal efficiency was decreased [45].

Peter Kesseru et al. (2002), directed their investigation on denitrification activity of immobilized Pseudomonas butanovora cell in the presence of three different carbon

sources, succinic acid, ethanol and acetic acid and reported highest denitrification activity was observed with ethanol - -3 -1 about 1.63 kg NO3 N m d followed by acetic acid about - -3 -1 1.53 kg NO3 N m d [46]. Nogueira et al. (1998) studied on Elimination of nitrate in an Inverse Fluidized-bed bio-film reactor using acetate as an external carbon source and suggested that the maximum -3 -1 nitrate removal rate is 2.98 kgN-NO3- m d [47]. Constantin et al. (1997) has investigated on denitrification of industrial wastewater with two different carbon sources such as ethanol and acetic acid with Pseudomonas sp. microorganism using two stirred anaerobic reactors in a continuous flow culture mode. The experiments have shown that the development of the microorganism was higher on Fig. 3. Effect of addition of methanol on denitrification by ethanol, but on acetic acid, the specific denitrification rate was aerobic sludge granules higher [48].

49 International Conference on Chemical, Environmental Science and Engineering (ICEEBS'2012) July 28-29, 2012 Pattaya (Thailand)

TABLE 3 municipal waste and waste disposal site drainage is oxidized ESTIMATED COSTS OF SUBSTRATES FOR NITRATE REMOVAL 39 to nitrate that also contributes to nitrate contamination of Substrate Price of Consumption Substrate cost Nitrate groundwater. Nitrate is harmful to both mankind and animal substrate of substrate of denitri- removal rateb -3 and also to the environment. Hence drinking water ($/kg (kg sub/kg fication (g-N m - - -1 substrate) N-NO3 ) ($/kg N-NO3 ) day ) regulations are required to strictly implement in order to limit human risks and environmental pollution. Because of 58 Methanol 0.92 2.08-3.98 1.8-3.6 1,000-27,000 globally increasing concern for nitrate in the environment, the 59 Methanol 0.7 1.9 1.33 regulations for nitrate release are being strengthened. Ethanol 58 1.10 2 2.2 400- 1,200 Biological denitrification to treat these waters in considered Acetic Acid 58 2.21 3.5 7.36 Acetate 59 1.67 2.7 4.37 600-1,000 being the most economic process available and among these Giant reed 60 0.65 0.94 0.61 4.23 biological processes using carbon source as an electron donor, Cotton 59 0.53 2.8 1.48 360 has proven feasible for wastewater treatment if there are Sulfur 0.1 2.5 0.25a 50-560 readily usable internal or external carbon sources. However Hydrogen 2.2-3.1 0.43 0.95-1.3a 500-2,400 the high operating costs of wastewater treatment which does 58Boley et al. 2000,59Soares et al. 2000, 60Ovez et al. 2006, a not contain carbon sources and the related secondary Calculation based on the stoichiometric usage of each substrate contamination problems resulting from the residual carbon bValues were extracted from Table 3 of reference 39. content have raised the need of research utilizing autotrophic

Michal et al. (1996) used cotton as energy source for denitrification. From the review it is clearly shows that carbon denitrification of groundwater and compared the source is plays an important role for the biological denitrification rate by changing the temperature levels. The 0 denitrification of wastewater. There are different types of denitrification rates at 14 C is approximately half of the rates 0 carbon sources used like ethanol, methanol, acetic acid, observed at 30 C [49] . acetate, methane, propionate, glucose, saw dust, succinic acid,

hydrolysed rice, news paper, cotton, rice husk, and molasses. Among these, most of the biological denitrification of wastewater was carried out using ethanol, methanol and

acetate as carbon source and most of the work suggested these are the best and suitable carbon sources (From Table 2 and Table 3) for the nitrate removal due to their low price and more denitrification rate.

REFERENCES

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50 International Conference on Chemical, Environmental Science and Engineering (ICEEBS'2012) July 28-29, 2012 Pattaya (Thailand)

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