Development and Application of Some Renovated Technologies for Municipal Wastewater Treatment in China

Front. Environ. Sci. Engin. China 2007, 1(1): 1–12 DOI 10.1007/s11783-007-0001-9 REVIEW ARTICLE

Development and application of some renovated technologies for municipal wastewater treatment in China

QIAN Yi (), WEN Xianghua, HUANG Xia

Department of Environmental Science and Engineering, Tsinghua University, Beijing 100084, China

Abstract China has been experiencing fast economic To control water pollution in the country, thousands of sci- development in recent decades at the cost of serious environ- entists and engineers in this field have made great efforts in mental deterioration. Wastewater discharge, especially developing appropriate technologies of water and wastewater municipal wastewater discharge, and non-point pollution treatment. Preliminary progress has been obtained. sources are becoming the major water pollution source and This paper reviews the development and application of research focus. Great efforts have been made on water pollu- the appropriate technologies, including natural treatment tion control and a number of renovated technologies and pro- systems, anaerobic biological treatment and wastewater cesses for municipal wastewater treatment and reclamation as reclamation technologies, for water pollution control in China. well as non-point pollution control have been developed and applied in China. This paper discusses the development and application of the appropriate technologies, including natural 2 Appropriate process and technology for treatment systems, anaerobic biological treatment, biofilm wastewater treatment in China reactors and wastewater reclamation technologies, for water pollution control in the country. China is a big developing country with many environmental problems. Developing and applying appropriate wastewater Keywords China, water pollution, natural treatment treatment processes and technologies characterized by high technology, anaerobic biological treatment, biofilm reactor, efficiency and low cost, is an urgent need for water pollution wastewater reclamation control in the country. The characteristics of appropriate process or technology for wastewater treatment in China are as follows: 1 Introduction High system efficiency and stability in producing high quality effluent to be reused; With the rapid development of the industry and urbanization Lower energy consumption and operational cost; as well as the population growth , China is facing an increas- Easy operation and maintenance; ingly serious water crisis in terms of water shortage and Accommodating to local conditions; pollution. The annual average precipitation in the country Lower specific footprint to reduce the occupied land area is 648 mm and the water resource available per capita is and the investment cost. 3 2 220 m /a, which is only 1/4 of that of the world. The low In the following paragraphs, some examples of appropri- treatment rate of municipal wastewater, illegal discharge of ate processes and technologies for municipal wastewater industrial wastewater, and non-point pollution sources have treatment and non-point water pollution control developed resulted in severe water pollution, expressed by the deteriora- and renovated by Chinese scientists and engineers are tion of surface water, the eutrophication of lakes, the increase discussed. of nitrate in groundwater, etc. Persistence organic pollutants (POPs) have been monitored in some water bodies. 3 Natural wastewater purification systems

Received October 10, 2006; accepted December 15, 2006 In ancient China, people used excrement and urine to E-mail: [email protected] manure the fields, which can be considered as crude natural 2 wastewater disposal schemes. Nowadays, there is an expand- Province. The designed treatment capacity is 5000 m3/d and ing worldwide interest in the application of natural purifica- the actual influent flow is in the range of 2000 to 10 000 m3/d. tion systems as a low-cost, effective wastewater treatment Under normal operational conditions, the final effluent process to purify wastewater and recycle valuable organics quality meets the National Integrated Wastewater Discharge and nutrients. Standard (GB 8978–1996) very well. Seven species of plants The natural purification processes, including land treat- were selected and grow in the wetland. It is noticed that ment systems and stabilization ponds, had been intensively the plants growing in the wetland are vulnerable to lower studied during the 1980s to the 1990s [1–3] in China. The temperature in winter [23]. major research focus was the design, performance, cost anal- In the past few years, the Chinese government has paid ysis and mechanisms of pollutant removal in natural treat- great attention to lake eutrophication caused by non-point ment systems. More attention to the natural treatment system and point source pollution. Many investigators have been has been obtained since the late 1990s in the country when engaged in researching and developing natural systems for non-point source pollution control was introduced. The major rural sewage treatment. There is a considerable body of processes studied and applied include: rapid infiltration [4–6], literature on nitrogen and phosphorus removal efficiencies slow rate filtration [7–8], overland flow [1,9], subsurface and mechanisms by natural purification systems [11,21,22, infiltration [10,11], constructed wetland [12–32], anaerobic, 56–64]. facultative, aerobic (aerated), high rate pond, etc. [33–43]. Figures 3 and 4 show two sets of natural systems in Dian Various unit processes may be arranged in sequence to create an integrated treatment system [44–51]. Lake area, Yunnan Province, which have been successfully Since 1990, large scale natural systems have been applied used for rural sewage treatment and achieved high nitrogen in many areas in China to treat municipal wastewater and phosphorus removal [65,66]. One is a subsurface infiltra- [8,13,23,28,36,42,47,48] and industrial wastewater [20,30,30]. tion system (Fig. 3). The other is a combination treatment Some demonstration treatment systems [7,10,14,16,18,29,52] system of two kinds of constructed wetlands with a biological were also established. Table 1 summarizes the effluent pond (Fig. 4). Table 2 shows the performance data of these quality of different natural treatment systems. two full scale systems. The data in Table 1 show that all the applied natural treat- Nowadays, several investigators have began to pay ment processes produced high quality effluent with low COD, attention to the long-term effects of various types of natural

BOD5, SS, TN, and TP. Moreover, the systems were very treatment systems on soils and ground water, and the possi- effective in removing potential and harmful recalcitrant bility of bioaccumulation and migration of toxic materials organic compounds [20,40], heavy metals [30], chemicals to the human food chain. Proper system management, includ- and biological agents, including viruses [24]. Some kinds ing adequate tracking monitoring, is necessary to assure of selected plants, like mangrove and reed, were used for ecological safety and human health [67]. enhancing the treatment efficiency of municipal wastewater Practical experiences show that the capital and operational and for the plant-mediated remediation of persistent organic cost of natural treatment systems is very low. Cost-effect pollutants and heavy metals [15,27,31,53–55]. analysis on land treatment systems and the comparison with Although natural purification systems have high removal an activated sludge system were made. The results show that efficiency for various pollutants in wastewater, their perfor- the cost-effectiveness of the land treatment system is mainly mances are highly dependent on climate and temperature. dependent on the cost of land because the system occupies a They generally function well in warm seasons or in warm large area of land. Results of cost-effect analysis show that areas in south China. Operation at low temperature in winter there is a critical unit land price for the application of a land or in cold regions in north China can be improved signifi- treatment system with different capacity. The critical unit cantly by employing intensified measures such as adding land price is defined as the unit land price at which the total biofilm carriers in ponds [42], artificial filtration layer [7], capital cost for the land treatment system equals to that of an plant cover [16] and using integrated treatment systems. activated sludge system. It implies that the application of land Figure 1 shows a land treatment system applied in system is cost-effective or not depending on if the unit land Shengyang City, located in the Northeast of China. Consider- ing the low temperature in winter and the seasons for crop price is lower or higher than the critical unit land price. irrigation, a system combining a slow rate filtration process Figure 5 shows the critical unit land price for different and a rapid infiltration process was designed. The slow rate natural application systems with different capacities based on filtration process runs from May 10 to November 25 and the the price of land in China in 1990. rapid infiltration works in the rest of the year. The treated The operational experiences also showed that land water is used to irrigate crops when needed or to inject into treatment systems required very simple maintenance. When ground water. a slow filtration system is used, the economic benefit can be Figure 2 shows a full-scale integrated treatment system obtained from the crop planted on the land. including a stabilization pond and two stages of subsurface- Because natural treatment systems have such merits as flow constructed wetland treating the mixed industrial and high quality of effluent, low cost and easy operation and domestic wastewater in Shatian, Shenzhen City, Guangdong maintenance, they provide environmental, ecological and 3 Table 1 Effluent quality of natural application systems

−1 −1 Type of the Loading rate Type of Scale Province BOD5/(mg · L ) COD/(mg · L ) References process wastewater inf eff inf eff

RI* 0.57 m/d Municipal Pilot Beijing 107.7 3.8 405.1 39.8 [4] SR* 0.42−9.63 m/a Municipal Full Inner- 20.3 1 80.9 28 [3] Mongolia SO* 0.0048 m/d Municipal Pilot Beijing 131 19.8 535 107 [1] SI* 0.02 m/d Rural sewage Pilot Yunnan — — 76 11.7 [10] SI* 0.006 cm/d Municipal Full Xinjiang 64 12.5 202 51.5 [3] CW 0.25 m/d Municipal Full Guangdong 27−53 7.3−9.7 61−193 15−37 [53] CW 0.30 m/d Rural sewage Pilot Yunnan — — 61−72 15−23 [19] CW 0.6 m/d Municipal Full Shanghai — — 72−250 20−51 [32] CW* 0.37 m/d Municipal Full Guangdong 92.8 6.9 144.7 38.3 [13] SP 0.12 m/d Municipal Full Inner- 75.2−171 8.5−35.6 176−291 44.1−112.3 [42] Mongolia SP* 0.12 m/d Piggery Full Guangdong 2110 26.8 3700 127 [36]

+ −1 −1 Type of the Loading rate Type of Scale Province NH4 -N/(mg · L ) SS/(mg · L ) References process wastewater inf eff inf eff

RI* 0.57 m/d Municipal Pilot Beijing — — 225.7 11.06 [4] SR* 0.42−9.63 m/a Municipal Full Inner- — — 69 18 [3] Mongolia SO* 0.0048 m/d Municipal Pilot Beijing 5.17 2.43 201 18.4 [1] SI* 0.02 m/d Rural sewage Pilot Yunnan 13.2 4 — — [10] SI* 0.006 cm/d Municipal Full Xinjiang — — 120 33.6 [3] CW 0.25 m/d Municipal Full Guangdong — — 62−70 1−2 [55] CW 0.30 m/d Rural sewage Pilot Yunnan 1.9−2.8 0.3−0.8 — — [19] CW 0.6 m/d Municipal Full Shanghai 6.96−17.2 0.364−6.16 — — [32] CW* 0.37 m/d Municipal Full Guangdong 20.7 18.5 140.9 10.9 [13] SP 0.12 m/d Municipal Full Inner- — — — — [42] Mongolia SP* 0.12 m/d Piggery Full Guangdong 590 11.8 904 53.6 [36] Type of the Loading rate Type of Scale Province TN/(mg · L−1) TP/(mg · L−1) References process wastewater inf eff inf eff

RI* 0.57 m/d Municipal Pilot Beijing 30.54 20.7 2.02 1.41 [4] SR* 0.42−9.63 m/a Municipal Full Inner- Mongolia 4.1 0.6 0.19 0.03 [3] SO* 0.0048 m/d Municipal Pilot Beijing 12.73 4.89 — — [1] SI* 0.02 m/d Rural sewage Pilot Yunnan 21.1 4.7 1.94 0.04 [10] SI* 0.006 cm/d Municipal Full Xinjiang 14.52 2.3 2.15 0.37 [3] CW 0.25 m/d Municipal Full Guangdong 14−37 9.1−9.8 1.5−5.4 0.2−0.5 [55] CW 0.30 m/d Rural sewage Pilot Yunnan 4.9−7.8 1.8−3.2 0.58−0.97 0.19−0.28 [19] CW 0.6 m/d Municipal Full Shanghai 7.63−18 6.44−11.1 1.17−3.06 0.14−1.18 [32] CW* 0.37 m/d Municipal Full Guangdong 23.7 18.2 2.3 1.59 [13] SP 0.12 m/d Municipal Full Inner- 35.1−46.8 12.6−24.1 3.5−3.7 1.1−2.7 [42] Mongolia SP* 0.12 m/d Piggery Full Guangdong 659 32.6 101 2.8 [36] Note: RI = rapid infiltration; SR = slow rate; OF = Overland flow; SI = subsurface infiltration; CW = constructed wetland; SP = stabilization pond; *mean value social benefits for the treatment of sewage in small cities, biogas. It can also improve the biodegradability of refractory towns, and villages. organics in the wastewater by acidification and hydrolysis. The development of the high-rate anaerobic reactor has made it possible to treat municipal wastewater since 1970, 4 Anaerobic biological treatment processes which has been proven feasible by national and international experiences. Because the treatment efficiency strongly Compared with aerobic biological treatment, anaerobic bio- depends on temperature, most full-scale anaerobic treatment logical treatment has significant advantages such as low cost, plants for municipal wastewater treatment are in the tropical low sludge yield and energy recovery by utilizing generated areas. 4

Fig. 1 A combined wastewater land treatment system

Fig. 2 Integrated treatment system of Shatian

Rural sewage

Screen

Primary settling tank

Rainwater overflow

Equalization tank

Subsurface Infiltration

Efflucnt (a) (b)

Fig. 3 A full-scale subsurface infiltration system for rural sewage treatment in Dianchi area, Yunnan Province

Rural sewage

Settling tank

Free water surface constructed wetland

Subsurface constructed wetland

Biological pond

Effluent (a) (b)

Fig. 4 A full-scale constructed wetland treatment system combined with a biological pond for rural sewage treatment established in Dianchi area, Yunnan Province 5 Table 2 Performance of full-scale subsurface infiltration system and Table 3 High-rate anaerobic reactors employed in municipal constructed wetland system combined with a biological pond wastewater treatment in China % % System Subsurface infiltration Constructed wetland No. Reactor ηCOD/ ηSS/ Organic loading rate/ HRT/h combined with (kg COD · m−3 · d−1) biological pond 1. UASB 44–82 73–87 1.2–2.4 4–10 COD TN TP COD TN TP 2. AF 57–88 57–81 0.5–0.7 4–6 3. ABR 55–97 59–94 0.6–2.9 3–50 Influent/(mg · L−1) 50–450 5–50 0.5–9.5 100–700 5–65 1.4–12 4. Combined ABR 62–75 43–95 0.8–1.7 3.6–8.4 Average 28.17 3.53 0.13 47.5 3.2 0.52 5. ICA 73–87 >90 2.0–4.7 4 effluent/(mg · L−1) 6. EGSB 58–76 80 1.2–1.5 2–24 Removal rate/% 80–90 80–90 80–98 80–90 75–90 80–95

Even for the high-rate reactors, aerobic post treatments are generally needed to meet the effluent discharge standard. However, the application could significantly decrease the investment and operation cost of a municipal wastewater treatment plant. 2) Improved processes with hydrolysis/anaerobic reactor as core treatment unit The process consists of a hydrolysis or anaerobic step and an aerobic step has been developed in China for municipal wastewater treatment, which has the following alternatives: Hydrolysis+aerobic process; Anaerobic+aerobic process; Fig. 5 Critical unit land price for wastewater land application systems + (1 Mu = 666 m2, 1 US $ ≈ 8.3 Yuan) Multi-stage anaerobic aerobic process. In full-scale application, the most widely used process is “hydrolysis+aerobic process”. Ma et al. [68] used a hybrid Since the late 1990s, the price of crude oil has increased hydrolysis+aerobic biofilter process to treat municipal dramatically and a serious energy crisis appeared again. wastewater of about 30 000 m3/d in Shandong Province and The application and investigation on anaerobic treatment of the investment was only 50% of that of the activated sludge municipal wastewater have become a hot point in China process. The effluent COD, BOD and SS were <60, <30 again. The practices focus on: 5 and <20 mg/L, respectively. Because hydrolysis is less 1) Investigation on operation of high-rate anaerobic affected by temperature, the process is promising in China. reactors treating municipal wastewater However, “hydrolysis+aerobic process” cannot generate The high-rate anaerobic reactors include: biogas and the energy consumption in the aerobic unit is still Upflow anaerobic sludge blanket (UASB) reactor; high because hydrolysis can only remove 30%–40% COD. Anaerobic filter (AF); The “Anaerobic+aerobic process” and “multi-stage Anaerobic baffled reactor (ABR); anaerobic+aerobic process” can compensate for the disad- Internal circulation anaerobic (ICA) reactor; vantages of the “hydrolysis+aerobic process” and evoke Expanded granular sludge blanket (EGSB) reactor etc. strong interests on a large scale. Table 4 summarizes the prop- erties of the treatment processes with the anaerobic unit as the Generally, a UASB reactor with 4–10 h hydraulic reten- core technique. tion time (HRT) can remove 44%–82% COD and 73%–87% SS from municipal wastewater. AF has similar removal rates. ABR is a reactor with 3–6 UASB reactors without three- Table 4 Processes with anaerobic unit as core technique % % % phase-separators in series. It has a simpler structure and more Process ηCOD/ ηBOD/ ηSS/ HRT/h stable performance. To solve the problem of low SS removal Hydrolysis+ 75–96 72–98 78–97 2.5–24.4 of ICA reactors, researchers from Tsinghua University intro- aerobic process duced a new ICA reactor by replacing the settling part of the Anaerobic+ 64–98 86–95 74–100 Several hours to reactor with a filter layer. This improvement was proven with aerobic process 15 days the better SS and colloidal COD removal. An ICA reactor Multi-stage anaerobic+ 70–96 68–90 50–98 10 h to 7 days anaerobic process with HRT of 4 h and organic loading rate of 2–4.7 kg COD/ (m3 · d) was used to remove 73%–87% COD and >90% SS. Table 3 lists some applications of high-rate anaerobic reactors 3) Integrative installations for treatment of sewage from a for municipal wastewater treatment in China. building or community 6 Table 5 Integrative installations for the treatment of sewage from a building or community % % % No. Process ηCOD/ ηBOD/ ηSS/ HRT References

1 AF+aerobic tank 91 ― ― 6 h [69] 2 Hybrid upflow anaerobic tank+aerobic tank 84 ― ― ― [70] 3 Separation tank+settling tank+anaerobic tank+filter 93–94 86 97 ― [71,72] 4 Two-stage anaerobic tanks+aerobic filter 93 89 ― 5–7 d [73] 5 Two-stage anaerobic reactors+two-stage aerobic tanks 73 81–90 98 ― [74] 6 Grit removal tank+settling tank+two-stage anaerobic tanks+filter 84–85 90 89–91 ― [75] 7 Three-stage anaerobic tanks+facultative filter+oxidation pond+stabilization pond 88 85 90 4 d [76] 8 Grit removal tank+two-stage anaerobic tanks+three-stage filters 87 68 50 4 d [77]

The practice of anaerobic treatment on domestic wastewa- A submerged bio-film reactor called bio-contact oxidation ter in China not only focuses on process but also on integra- tank has been studied and applied for industrial wastewater tive installations. Integrative installations for the treatment treatment since the 1970s and is now applied to municipal of sewage from a building or community are rather popular wastewater treatment in China. It is very similar to the aerated in the country because it is a practical solution for water bio-filter developed in Europe except the type and size of the pollution control without huge construction fees and complex media. Both plastic packing media and slag have been used maintenance. Table 5 lists some data from integrative in bio-contact oxidation tanks. Aeration is provided under the installations for the treatment of sewage from a building or packing media and the flow pattern can be either up flow or community. down flow. The general features of the integrative installations are However, until 2002, the bio-contact oxidation process low cost and simple maintenance by application of multi was not widely used. It was only used in nine wastewater anaerobic stages and extended HRT (to several days) in some treatment plants in China [85]. The reason is mainly related installations. The COD, BOD5, and SS removals could reach to the packing media. It plays an important role in promoting 70%–90%, 70%–90%, and 50%–98%, respectively. the bio-contact reactor performance. Many different types The installations can not only be distributed in buildings of packing media have been developed sequentially in the and communities in cities but also scattered in corners of rural country [86], from the rigid packing media firstly used to the areas. Biogas is used to replace traditional fuel and the efflu- flexible, semi-flexible, combined, suspended, to the recently ent and sludge of the installations are utilized as fertilizers for created enzyme catalyzed packing media. The major targets plants or feed for aquatic animals. In late 2004, 1.54 million are to provide a larger surface area, larger porosity and better families have had their own treatment installations and it is affinity to bio-film. With the development of packing media, estimated that 0.12 billion families in China will have it in it is expected that the submerged bio-film reactor will have 2020. even better performance. The three-phase bio-fluidized bed (TPB) is another advanced bio-film reactor that has many advantages. 5 Bio-film reactor The reactor was developed in the Netherlands where it is called the air-lift loop reactor. Intensive study has been As the earliest bio-film reactor, tricking filter has been carried out on TPB in China and it is now applied to both used in wastewater treatment for a long time. Because of its industrial wastewater and municipal wastewater treatment. high operation requirement and low organic loading, some The reactor is comprised of four zones: riser, downcomer, gas renovated bio-filters have been developed and applied for disengagement and solid sedimentation, while the riser and municipal wastewater treatment in recent years, as shown downcomer zones are jointly called as the reaction zone. Due in Table 6. They are also applied in the post-treatment of to gas injection into a section of the reactor, the hydrostatic secondary effluent [78]. pressure difference is produced to cause the fluid to flow with

Table 6 Newly developed bio-filters for municipal wastewater treatment Reactor Performance References

+ Lateral flow biological aerated filter COD, NH4 -N, and TN removal loading rate: [79] 0.40–2.52, 0.08–0.49, and 0.05–0.59 kg/(m3 · d), respectively + % + Biological aerated filter with Oyater shell packing NH4 -N removal efficiency >90 with NH4 -N in influent <120 mg/L [80] + 3 Zeolite biological aerated filter NH4 -N removal rate: 0.7–0.9 kg/(m · d) [81] Baffled biological aerated filter COD, SS removal efficiency: >90% [82] + % % % NH4 -N, TN, and TP mean removal efficiency: 74.0 , 39.1 , and 46.5 , respectively Integrated biological aerated filter COD removal efficiency >90% with 234 mg COD/L in influent; [83] SS removal efficiency >80% with 112 mg SS/L in influent Two-stage biological aerated filter COD in effluent h30 mg/L; [84] + NH4 -N in effluent h3 mg/L 7 Table 7 Comparison of typical parameters between conventional activated sludge (CAS) process and DCITFB Process Biomass concentration Organic loading HRT SRT Oxygen transfer coefficient Sludge yield Organic removal /(g VSS · L−1) /(kg COD · m−3 · d−1) /(h) /(d) /(h−1) /(kg SS · (kg COD)−1) /(%)

CAS process 1.5–3.0 0.8–1.6 4–8 5–10 4–12 0.4 >90 for BOD5 DCITFB 5.2–6.2 4.2–5.7 1.0 13–18 20–80 0.1–0.12 >86 for COD the bio-carrier circularly. Because the biomass attached on the carrier lives in a suspended state, the technology has the combined advantages of a bio-film reactor and activated sludge process. Two types of three-phase bio-fluidized bed have been distinguished in recent years. One is the inner- circulation three-phase bio-fluidized bed (ITFB) and the other is the external-circulation three-phase bio-fluidized bed (ETFB). Few researches have focused on ETFB [87] because less variety and modifications around the gas disengagement zone can be acquired, which is adverse to the reactor optimi- zation. A kind of double cylinder ITFB (DCITFB) achieves more acceptance in China. In DCITFB, the surface area of the carrier media is in the range of 2 000–3 000 m2/m3, which is about ten times of that in the bio-contact oxidation process. A high biomass concen- Fig. 6 DEITFB in Zhoutiezhen wastewater treatment plant tration can be up to 20–30 g/L in the reactor depending on the influent quality, carrier concentration and operation parameters. Such high biomass concentration contributes to a high which enables not only the aerobic zone and anoxic zone to 3 concurrently exist but also a decreased height and diameter loading rate varying from 5–20 kg BOD5/(m · d) [88]. Table 7 is the comparison between the performances of the conven- ratio of the reactor and hence energy consumption decreases tional activated sludge process and the DCITFB process in accordingly. The high-efficient dissolved air floatation is municipal wastewater treatment [89]. It can be seen that the coupled in the gas disengagement zone of the reactor, which DCITFB process shows much better performance than the improves the removal efficiency of SS. In addition, a maze- activated sludge process. The COD concentration in DCITFB type carrier separator is added in the reactor to avoid losing effluent is below 30 mg/L although the aeration time is only carrier particles with the effluent. 1/4–1/8 of that of the activated sludge process. The oxygen Two types of pilot scale ITFB are used to treat municipal transfer coefficient is about 2–20 times of that in the activated wastewater for comparison. One is DCITFB and the other is sludge process. Apart from the organic pollutant removal, HSBCR. The performance of the reactors is summarized in + 3 NH4 -N removal loading rate can be up to 1.8 kg/(m · d) [90]. Table 8 [92]. The results show that HSBCR outperforms These advantages prove that the DCITFB is a cost-effective DCITFB in many respects. At the HRT of 40 min, both reac- wastewater treatment process. Figure 6 is a picture of the tors achieved good performance in organic pollutant removal. + DEITFB treating wastewater mainly from domestic users in However, the NH4 -N removal loading rate in HSBCR was a small-town (Zhoutiezhen) wastewater treatment plant in about three times higher than that in DCITFB. A lower con- Yixing, Jiangsu Province. The treatment capacity of one unit centration of SS (<30 mg/L) was detected in the effluent of reaches 2 500 m3/d. The quality of the treated water meets the HSBCR. Moreover, the energy consumption of HSBCR was national discharge standard. only 40% of that of DCITFB. There are many other types of ITFB developed in China Based on the above discussion, we can see that the inner- as an improvement over the DCITFB. The high efficient circulation three-phase bio-fluidized bed with its enhanced separation composite biological fluidized reactor (HSBCR) is reactor is a very promising process for treating municipal one of them [91]. In the reaction zone, the traditional double wastewater. It will have more extensive application in the cylinder is replaced by the honeycomb-type cross section, future in China.

Table 8 Comparison of performance between DCITFB and HSBCR

+ Reactor Energy consumption Minimal air demand Oxygen utilization Effluent SS NH4 -N removal loading Organic removal loading /(Yuan · m−3) /(m3 · h−1) ratio/% /(mg · L−1) rate/(kg · m−3 · d−1) rate/(kg · m−3 · d−1)

DCITFB 0.26 3 5 20–120 0.41 8.8 HSBCR 0.43 30 13 1–27 1.15 11.7 8 Table 9 Wastewater reclamation and reuse practice in some water-short cities of China Wastewater treatment plant Capacity/(m3 · d−1) Reclaimed water uses Operation year

Taiyuan Beijiao WWTP 10 000 Cooling water 1992 Taiyuan Chemical plant 24 000 Cooling water 1992 Dalian Chunliuhe WWTP 10 000 Cooling water, supply to boiler water 1992 Dalian Malanhe WWTP 40 000 Municipal uses 2001 Shandong Laizhou WWTP 20 000 Municipal uses and cooling water 1996 Qingdao Haibohe WWTP 40 000 Municipal uses 2003 Beijing Gaobeidian WWTP 300 000 Municipal uses and cooling water 2003 Tianjin Jizhuangzi WWTP 50 000 Municipal uses and cooling water 2003 Tianjin TEDA WWTP 25 000 Municipal uses, cooling and process water, supply to boiler water 2002 Xi’an Beishiqiao WWTP 50 000 Municipal uses and cooling water 2003 Hefei Wangxiao WWTP 100 000 Municipal uses and cooling water 2005

A disinfection unit is generally the last treatment step to 6 Wastewater reclamation guarantee that the treated effluent is free of pathogens and biologically safe for reuse. Different treatment processes have Water shortage is serious in many parts of China. Therefore, their advantages and disadvantages. How to choose a proper there is an increasing interest over the past decade in treatment train to produce qualified effluent with low invest- reclaimed water from municipal sewage as a new reliable ment and operational cost is still a very hot research topic water resource in the country [93,94]. The treated wastewater nowadays in China. There are also a lot of concerns about has been used for different purposes such as: (1) industrial the ecological and biological risks in using treated water. In application for cooling and washing purposes and process this concern, membrane technology has been noticed as one water; (2) municipal application, such as toilet flushing, car of the promising solutions for producing microorganism-free washing, landscape irrigation, etc.; (3) agricultural irrigation, effluent. and (4) supply to environmental water. There are two main types of membrane filtration technol- Table 9 lists several practices of wastewater reclamation ogy applied in the field of wastewater reclamation. They are and reuse in some cities in China that are short of water. It membrane bioreactor (MBR) and direct membrane filtration. can be seen that reclaimed water in these practices is mainly Membrane bioreactor can be defined as the combination used for municipal uses and industrial cooling water. of two basic processes: biological degradation and membrane Many different types of treatment processes fit different separation. The biomass responsible for biodegradation is quality and quantity requirements of wastewaters. The major separated from the treated water by a membrane filtration treatment processes in practice in China are as follows: unit. Ultra-filtration and micro-filtration are two types of membranes used in the membrane bioreactor system. The contact filtrationmactivated carbon adsorption; membrane filtration unit can be located either outside the sedimentationmfiltrationmozone oxidation; bio-reactor or submerged in it. Figure 7 shows the schematic coagulationmsedimentationmmembrane filtration; diagrams of these two systems. contact oxidationmsedimentation and filtration; The membrane bioreactor system has the advantages A/O (A2/O) processes, etc. of high volumetric loading, small footprint, low sludge

Fig. 7 Schematic diagram of two membrane bioreactor systems 9 production, high flexibility, etc. It can produce high quality effluent useable for many purposes safely [95,96]. The major problem in the operation of a membrane bioreactor system is membrane fouling. There are a large number of papers dis- cussing the mechanisms and measures for membrane fouling control [97,98,99]. There are also successful practices of full-scale treatment plant. However, proper design, correct choice of operation parameters, effective membrane fouling control, and clean procedures still have room for study. Fig. 9 Schematic diagram of a typical advanced wastewater The membrane bioreactor has been well-accepted in recent treatment process with membrane filtration years in China as a wastewater reclamation technology. There are a number of membrane technology centers all over the country targeting mainly at wastewater treatment and recla- purposes. It can be predicted that the application of MBR in mation. In 1997 and 2005, two large-scale international con- China will be booming in the near future. ferences on “membrane technology for water and wastewater Direct membrane filtration can act as the main process treatment” were successfully held by Tsinghua University in in the tertiary treatment of secondary effluent and produce Beijing. The biggest wastewater reclamation plant by using high-quality effluent [100]. This kind of process is applied MBR in Asia was designed by Tsinghua University, which is in large-scale water reclamation projects in wastewater treat- the Beijing Miyun Municipal wastewater treatment plant with ment plants. According to the requirement of the effluent 3 the designed wastewater treatment capacity of 45 000 m /d. water quality, MF/UF can be chosen as the core treatment The plant started operations in April, 2006. Figure 8 shows technology and NF/RO as the complementary step. The the aeration tank and membrane tank used in the plant. The typical processes are “coagulationmmembrane filtration operational data of the plant indicate that the effluent can well mdisinfection” (as shown in Fig. 9). In China, several large meet the reused water standard of China. There are growing projects have been or are being built, such as the Tianjin numbers of MBRs in operation in the country treating domestic, municipal and industrial wastewaters for different reuse Jizhuangzi wastewater reclamation plant, and the Beijing Qinghe wastewater reclamation plant. Figure 10 shows the membrane combined treatment process used in the Tianjin Jizhuangzi wastewater reclamation plant [101,102]. The water source for reclamation comes from the secondary effluent of the Jizhuangzi municipal wastewater treatment plant. The reclamation plant treats 40 000 m3/d secondary effluent by the combined system of coagulation, continuous micro-filtration (CMF) and ozonation units. The plant also treats 30 000 m3/d water by the conventional process of coagulation, sedimentation and filtration. The reclaimed water obtained from the combined system has a high quality with turbidity of <5 NTU, SS <5 mg/L, and is reused for toilet flushing, park greening, street spraying and scenic environment water. The quality of the reclaimed water by the conventional process is not as good as that by the combined system. It is mainly reused for the production process in paper mills and cooling water for electric power plants. For some kinds of light polluted wastewater, for example, rainwater and bathing wastewater, direct membrane filtration might be a good choice. Although COD removal rate is only around 32%–54%, the turbidity and bacteria removal rate can reach about 94%–99% and 99.8%–100% respectively when UF is applied [103]. The main problem of the direct membrane filtration process is also membrane fouling. In some studies, researchers found that membrane fouling is more severe in direct filtration of secondary effluent than in MBR. Different raw water quality may affect membrane fouling. To minimize the fouling, one or several different pretreatment methods, such as Fig. 8 Pictures of Beijing Miyun Municipal wastewater ozonation, pre-coagulation, backwashing, etc., were studied reclamation MBR Plant and (or) applied in practices [104]. 10

Fig. 10 Diagram of the combined system of CMF and ozonation in Tianjin Jizhuangzi wastewater reclamation plant

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