development and application of some renovated technologies for

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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 © Higher Education Press and Springer-Verlag 2007 Abstract China has been experiencing fast economic development in recent decades at the cost of serious environ- mental deterioration. Wastewater discharge, especially municipal wastewater discharge, and non-point pollution sources are becoming the major water pollution source and research focus. Great efforts have been made on water pollu- tion control and a number of renovated technologies and pro- cesses for municipal wastewater treatment and reclamation as 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 treatment systems, anaerobic biological treatment, biofilm reactors and wastewater reclamation technologies, for water pollution control in the country. Keywords China, water pollution, natural treatment technology, anaerobic biological treatment, biofilm reactor, wastewater reclamation 1 Introduction With the rapid development of the industry and urbanization as well as the population growth , China is facing an increas- ingly serious water crisis in terms of water shortage and pollution. The annual average precipitation in the country is 648 mm and the water resource available per capita is 2 220 m 3 /a, which is only 1/4 of that of the world. The low treatment rate of municipal wastewater, illegal discharge of industrial wastewater, and non-point pollution sources have resulted in severe water pollution, expressed by the deteriora- tion of surface water, the eutrophication of lakes, the increase of nitrate in groundwater, etc. Persistence organic pollutants (POPs) have been monitored in some water bodies. To control water pollution in the country, thousands of sci- entists and engineers in this field have made great efforts in developing appropriate technologies of water and wastewater treatment. Preliminary progress has been obtained. This paper reviews the development and application of the appropriate technologies, including natural treatment systems, anaerobic biological treatment and wastewater reclamation technologies, for water pollution control in China. 2 Appropriate process and technology for wastewater treatment in China China is a big developing country with many environmental problems. Developing and applying appropriate wastewater treatment processes and technologies characterized by high efficiency and low cost, is an urgent need for water pollution control in the country. The characteristics of appropriate process or technology for wastewater treatment in China are as follows: High system efficiency and stability in producing high quality effluent to be reused; Lower energy consumption and operational cost; Easy operation and maintenance; Accommodating to local conditions; Lower specific footprint to reduce the occupied land area and the investment cost. In the following paragraphs, some examples of appropri- ate processes and technologies for municipal wastewater treatment and non-point water pollution control developed and renovated by Chinese scientists and engineers are discussed. 3 Natural wastewater purification systems In ancient China, people used excrement and urine to manure the fields, which can be considered as crude natural Received October 10, 2006; accepted December 15, 2006 E-mail: [email protected]

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Front. Environ. Sci. Engin. China 2007, 1(1): 1–12DOI 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

© Higher Education Press and Springer-Verlag 2007

Abstract China has been experiencing fast economic development in recent decades at the cost of serious environ-mental deterioration. Wastewater discharge, especially municipal wastewater discharge, and non-point pollution sources are becoming the major water pollution source and research focus. Great efforts have been made on water pollu-tion control and a number of renovated technologies and pro-cesses for municipal wastewater treatment and reclamation as 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 treatment systems, anaerobic biological treatment, biofilm reactors and wastewater reclamation technologies, for water pollution control in the country.

Keywords China, water pollution, natural treatment technology, anaerobic biological treatment, biofilm reactor, wastewater reclamation

1 Introduction

With the rapid development of the industry and urbanization as well as the population growth , China is facing an increas-ingly serious water crisis in terms of water shortage and pollution. The annual average precipitation in the country is 648 mm and the water resource available per capita is 2 220 m3/a, which is only 1/4 of that of the world. The low treatment rate of municipal wastewater, illegal discharge of industrial wastewater, and non-point pollution sources have resulted in severe water pollution, expressed by the deteriora-tion of surface water, the eutrophication of lakes, the increase of nitrate in groundwater, etc. Persistence organic pollutants (POPs) have been monitored in some water bodies.

To control water pollution in the country, thousands of sci-entists and engineers in this field have made great efforts in developing appropriate technologies of water and wastewater treatment. Preliminary progress has been obtained.

This paper reviews the development and application of the appropriate technologies, including natural treatment systems, anaerobic biological treatment and wastewater reclamation technologies, for water pollution control in China.

2 Appropriate process and technology for wastewater treatment in China

China is a big developing country with many environmental problems. Developing and applying appropriate wastewater treatment processes and technologies characterized by high efficiency and low cost, is an urgent need for water pollution control in the country. The characteristics of appropriate process or technology for wastewater treatment in China are as follows:

High system efficiency and stability in producing high quality effluent to be reused;

Lower energy consumption and operational cost; Easy operation and maintenance; Accommodating to local conditions; Lower specific footprint to reduce the occupied land area

and the investment cost.

In the following paragraphs, some examples of appropri-ate processes and technologies for municipal wastewater treatment and non-point water pollution control developed and renovated by Chinese scientists and engineers are discussed.

3 Natural wastewater purification systems

In ancient China, people used excrement and urine to manure the fields, which can be considered as crude natural

Received October 10, 2006; accepted December 15, 2006

E-mail: [email protected]

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wastewater disposal schemes. Nowadays, there is an expand-ing worldwide interest in the application of natural purifica-tion systems as a low-cost, effective wastewater treatment process to purify wastewater and recycle valuable organics and nutrients.

The natural purification processes, including land treat-ment systems and stabilization ponds, had been intensively studied during the 1980s to the 1990s [1–3] in China. The major research focus was the design, performance, cost anal-ysis and mechanisms of pollutant removal in natural treat-ment systems. More attention to the natural treatment system has been obtained since the late 1990s in the country when non-point source pollution control was introduced. The major processes studied and applied include: rapid infiltration [4–6], slow rate filtration [7–8], overland flow [1,9], subsurface infiltration [10,11], constructed wetland [12–32], anaerobic, facultative, aerobic (aerated), high rate pond, etc. [33–43]. Various unit processes may be arranged in sequence to create an integrated treatment system [44–51].

Since 1990, large scale natural systems have been applied in many areas in China to treat municipal wastewater [8,13,23,28,36,42,47,48] and industrial wastewater [20,30,30]. Some demonstration treatment systems [7,10,14,16,18,29,52] were also established. Table 1 summarizes the effluent quality of different natural treatment systems.

The data in Table 1 show that all the applied natural treat-ment processes produced high quality effluent with low COD, BOD5, SS, TN, and TP. Moreover, the systems were very effective in removing potential and harmful recalcitrant organic compounds [20,40], heavy metals [30], chemicals and biological agents, including viruses [24]. Some kinds of selected plants, like mangrove and reed, were used for enhancing the treatment efficiency of municipal wastewater and for the plant-mediated remediation of persistent organic pollutants and heavy metals [15,27,31,53–55].

Although natural purification systems have high removal efficiency for various pollutants in wastewater, their perfor-mances are highly dependent on climate and temperature. They generally function well in warm seasons or in warm areas in south China. Operation at low temperature in winter or in cold regions in north China can be improved signifi-cantly by employing intensified measures such as adding biofilm carriers in ponds [42], artificial filtration layer [7], plant cover [16] and using integrated treatment systems.

Figure 1 shows a land treatment system applied in Shengyang City, located in the Northeast of China. Consider-ing the low temperature in winter and the seasons for crop irrigation, a system combining a slow rate filtration process and a rapid infiltration process was designed. The slow rate filtration process runs from May 10 to November 25 and the rapid infiltration works in the rest of the year. The treated water is used to irrigate crops when needed or to inject into ground water.

Figure 2 shows a full-scale integrated treatment system including a stabilization pond and two stages of subsurface-flow constructed wetland treating the mixed industrial and domestic wastewater in Shatian, Shenzhen City, Guangdong

Province. The designed treatment capacity is 5000 m3/d and the actual influent flow is in the range of 2000 to 10 000 m3/d. Under normal operational conditions, the final effluent quality meets the National Integrated Wastewater Discharge Standard (GB 8978–1996) very well. Seven species of plants were selected and grow in the wetland. It is noticed that the plants growing in the wetland are vulnerable to lower temperature in winter [23].

In the past few years, the Chinese government has paid great attention to lake eutrophication caused by non-point and point source pollution. Many investigators have been engaged in researching and developing natural systems for rural sewage treatment. There is a considerable body of literature on nitrogen and phosphorus removal efficiencies and mechanisms by natural purification systems [11,21,22,56–64].

Figures 3 and 4 show two sets of natural systems in Dian Lake area, Yunnan Province, which have been successfully used for rural sewage treatment and achieved high nitrogen and phosphorus removal [65,66]. One is a subsurface infiltra-tion system (Fig. 3). The other is a combination treatment system of two kinds of constructed wetlands with a biological pond (Fig. 4). Table 2 shows the performance data of these two full scale systems.

Nowadays, several investigators have began to pay attention to the long-term effects of various types of natural treatment systems on soils and ground water, and the possi-bility of bioaccumulation and migration of toxic materials to the human food chain. Proper system management, includ-ing adequate tracking monitoring, is necessary to assure ecological safety and human health [67].

Practical experiences show that the capital and operational cost of natural treatment systems is very low. Cost-effect analysis on land treatment systems and the comparison with an activated sludge system were made. The results show that the cost-effectiveness of the land treatment system is mainly dependent on the cost of land because the system occupies a large area of land. Results of cost-effect analysis show that there is a critical unit land price for the application of a land treatment system with different capacity. The critical unit land price is defined as the unit land price at which the total capital cost for the land treatment system equals to that of an activated sludge system. It implies that the application of land system is cost-effective or not depending on if the unit land price is lower or higher than the critical unit land price.

Figure 5 shows the critical unit land price for different natural application systems with different capacities based on the price of land in China in 1990.

The operational experiences also showed that land treatment systems required very simple maintenance. When a slow filtration system is used, the economic benefit can be obtained from the crop planted on the land.

Because natural treatment systems have such merits as high quality of effluent, low cost and easy operation and maintenance, they provide environmental, ecological and

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biogas. It can also improve the biodegradability of refractory 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, which has been proven feasible by national and international experiences. Because the treatment efficiency strongly depends on temperature, most full-scale anaerobic treatment plants for municipal wastewater treatment are in the tropical areas.

social benefits for the treatment of sewage in small cities, towns, and villages.

4 Anaerobic biological treatment processes

Compared with aerobic biological treatment, anaerobic bio-logical treatment has significant advantages such as low cost, low sludge yield and energy recovery by utilizing generated

Table 1 Effluent quality of natural application systems

Type of the Loading rate Type of Scale Province BOD5/(mg · L−1) COD/(mg · L−1) Referencesprocess 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] MongoliaSO* 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] MongoliaSP* 0.12 m/d Piggery Full Guangdong 2110 26.8 3700 127 [36]

Type of the Loading rate Type of Scale Province NH4+-N/(mg · L−1) SS/(mg · L−1) 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] MongoliaSO* 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] MongoliaSP* 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) Referencesprocess 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] MongoliaSP* 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

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Fig. 1 A combined wastewater land treatment system

Fig. 2 Integrated treatment system of Shatian

Screen

Primary settling tank

Equalization tank

Subsurface Infiltration

Rainwater overflow

Rural sewage

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

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Since the late 1990s, the price of crude oil has increased dramatically and a serious energy crisis appeared again. The application and investigation on anaerobic treatment of municipal wastewater have become a hot point in China again. The practices focus on:

1) Investigation on operation of high-rate anaerobic reactors treating municipal wastewater

The high-rate anaerobic reactors include:

Upflow anaerobic sludge blanket (UASB) reactor; Anaerobic filter (AF); Anaerobic baffled reactor (ABR); Internal circulation anaerobic (ICA) reactor; Expanded granular sludge blanket (EGSB) reactor etc.

Generally, a UASB reactor with 4–10 h hydraulic reten-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-phase-separators in series. It has a simpler structure and more stable performance. To solve the problem of low SS removal of ICA reactors, researchers from Tsinghua University intro-duced a new ICA reactor by replacing the settling part of the reactor with a filter layer. This improvement was proven with the better SS and colloidal COD removal. An ICA reactor 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 for municipal wastewater treatment in China.

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; 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 hydrolysis+aerobic biofilter process to treat municipal wastewater of about 30 000 m3/d in Shandong Province and the investment was only 50% of that of the activated sludge process. The effluent COD, BOD5 and SS were <60, <30 and <20 mg/L, respectively. Because hydrolysis is less affected by temperature, the process is promising in China.

However, “hydrolysis+aerobic process” cannot generate biogas and the energy consumption in the aerobic unit is still high because hydrolysis can only remove 30%–40% COD. The “Anaerobic+aerobic process” and “multi-stage anaerobic+aerobic process” can compensate for the disad-vantages of the “hydrolysis+aerobic process” and evoke strong interests on a large scale. Table 4 summarizes the prop-erties of the treatment processes with the anaerobic unit as the core technique.

Table 4 Processes with anaerobic unit as core technique

Process ηCOD/% ηBOD/% ηSS/% HRT/h

Hydrolysis+ 75–96 72–98 78–97 2.5–24.4 aerobic processAnaerobic+ 64–98 86–95 74–100 Several hours to aerobic process 15 daysMulti-stage anaerobic+ 70–96 68–90 50–98 10 h to 7 days anaerobic process

3) Integrative installations for treatment of sewage from a building or community

Table 2 Performance of full-scale subsurface infiltration system and constructed wetland system combined with a biological pond

System Subsurface infiltration Constructed wetland combined with biological pond

COD TN TP COD TN TP

Influent/(mg · L−1) 50–450 5–50 0.5–9.5 100–700 5–65 1.4–12Average 28.17 3.53 0.13 47.5 3.2 0.52 effluent/(mg · L−1)Removal rate/% 80–90 80–90 80–98 80–90 75–90 80–95

Fig. 5 Critical unit land price for wastewater land application systems(1 Mu = 666 m2, 1 US $ ≈ 8.3 Yuan)

Table 3 High-rate anaerobic reactors employed in municipal wastewater treatment in China

No. Reactor ηCOD/% ηSS/% Organic loading rate/ HRT/h (kg COD · m−3 · d−1)

1. UASB 44–82 73–87 1.2–2.4 4–102. AF 57–88 57–81 0.5–0.7 4–63. ABR 55–97 59–94 0.6–2.9 3–504. Combined ABR 62–75 43–95 0.8–1.7 3.6–8.45. ICA 73–87 >90 2.0–4.7 46. EGSB 58–76 80 1.2–1.5 2–24

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The practice of anaerobic treatment on domestic wastewa-ter in China not only focuses on process but also on integra-tive installations. Integrative installations for the treatment of sewage from a building or community are rather popular in the country because it is a practical solution for water pollution control without huge construction fees and complex maintenance. Table 5 lists some data from integrative installations for the treatment of sewage from a building or community.

The general features of the integrative installations are low cost and simple maintenance by application of multi anaerobic stages and extended HRT (to several days) in some installations. The COD, BOD5, and SS removals could reach 70%–90%, 70%–90%, and 50%–98%, respectively.

The installations can not only be distributed in buildings and communities in cities but also scattered in corners of rural areas. Biogas is used to replace traditional fuel and the efflu-ent and sludge of the installations are utilized as fertilizers for plants or feed for aquatic animals. In late 2004, 1.54 million families have had their own treatment installations and it is estimated that 0.12 billion families in China will have it in 2020.

5 Bio-film reactor

As the earliest bio-film reactor, tricking filter has been used in wastewater treatment for a long time. Because of its high operation requirement and low organic loading, some renovated bio-filters have been developed and applied for municipal wastewater treatment in recent years, as shown in Table 6. They are also applied in the post-treatment of secondary effluent [78].

A submerged bio-film reactor called bio-contact oxidation tank has been studied and applied for industrial wastewater treatment since the 1970s and is now applied to municipal wastewater treatment in China. It is very similar to the aerated bio-filter developed in Europe except the type and size of the media. Both plastic packing media and slag have been used in bio-contact oxidation tanks. Aeration is provided under the packing media and the flow pattern can be either up flow or down flow.

However, until 2002, the bio-contact oxidation process was not widely used. It was only used in nine wastewater treatment plants in China [85]. The reason is mainly related to the packing media. It plays an important role in promoting the bio-contact reactor performance. Many different types of packing media have been developed sequentially in the country [86], from the rigid packing media firstly used to the flexible, semi-flexible, combined, suspended, to the recently created enzyme catalyzed packing media. The major targets are to provide a larger surface area, larger porosity and better affinity to bio-film. With the development of packing media, it is expected that the submerged bio-film reactor will have even better performance.

The three-phase bio-fluidized bed (TPB) is another advanced bio-film reactor that has many advantages. The reactor was developed in the Netherlands where it is called the air-lift loop reactor. Intensive study has been carried out on TPB in China and it is now applied to both industrial wastewater and municipal wastewater treatment. The reactor is comprised of four zones: riser, downcomer, gas disengagement and solid sedimentation, while the riser and downcomer zones are jointly called as the reaction zone. Due to gas injection into a section of the reactor, the hydrostatic pressure difference is produced to cause the fluid to flow with

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]

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), respectivelyBiological aerated filter with Oyater shell packing NH4

+-N removal efficiency >90% with NH4+-N in influent <120 mg/L [80]

Zeolite biological aerated filter NH4+-N removal rate: 0.7–0.9 kg/(m3 · 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%, respectivelyIntegrated 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 influentTwo-stage biological aerated filter COD in effluent h30 mg/L; [84] NH4

+-N in effluent h3 mg/L

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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-tration can be up to 20–30 g/L in the reactor depending on the influent quality, carrier concentration and operation parame-ters. Such high biomass concentration contributes to a high loading rate varying from 5–20 kg BOD5/(m3 · d) [88]. Table 7 is the comparison between the performances of the conven-tional activated sludge process and the DCITFB process in municipal wastewater treatment [89]. It can be seen that the DCITFB process shows much better performance than the activated sludge process. The COD concentration in DCITFB effluent is below 30 mg/L although the aeration time is only 1/4–1/8 of that of the activated sludge process. The oxygen transfer coefficient is about 2–20 times of that in the activated sludge process. Apart from the organic pollutant removal, NH4

+-N removal loading rate can be up to 1.8 kg/(m3 · d) [90]. These advantages prove that the DCITFB is a cost-effective wastewater treatment process. Figure 6 is a picture of the DEITFB treating wastewater mainly from domestic users in a small-town (Zhoutiezhen) wastewater treatment plant in Yixing, Jiangsu Province. The treatment capacity of one unit reaches 2 500 m3/d. The quality of the treated water meets the national discharge standard.

There are many other types of ITFB developed in China as an improvement over the DCITFB. The high efficient separation composite biological fluidized reactor (HSBCR) is one of them [91]. In the reaction zone, the traditional double cylinder is replaced by the honeycomb-type cross section,

which enables not only the aerobic zone and anoxic zone to concurrently exist but also a decreased height and diameter ratio of the reactor and hence energy consumption decreases accordingly. The high-efficient dissolved air floatation is coupled in the gas disengagement zone of the reactor, which improves the removal efficiency of SS. In addition, a maze-type carrier separator is added in the reactor to avoid losing carrier particles with the effluent.

Two types of pilot scale ITFB are used to treat municipal wastewater for comparison. One is DCITFB and the other is HSBCR. The performance of the reactors is summarized in Table 8 [92]. The results show that HSBCR outperforms DCITFB in many respects. At the HRT of 40 min, both reac-tors achieved good performance in organic pollutant removal. However, the NH4

+-N removal loading rate in HSBCR was about three times higher than that in DCITFB. A lower con-centration of SS (<30 mg/L) was detected in the effluent of HSBCR. Moreover, the energy consumption of HSBCR was only 40% of that of DCITFB.

Based on the above discussion, we can see that the inner-circulation three-phase bio-fluidized bed with its enhanced reactor is a very promising process for treating municipal wastewater. It will have more extensive application in the future in China.

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

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 8.8HSBCR 0.43 30 13 1–27 1.15 11.7

Fig. 6 DEITFB in Zhoutiezhen wastewater treatment plant

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6 Wastewater reclamation

Water shortage is serious in many parts of China. Therefore, there is an increasing interest over the past decade in reclaimed water from municipal sewage as a new reliable water resource in the country [93,94]. The treated wastewater has been used for different purposes such as: (1) industrial application for cooling and washing purposes and process water; (2) municipal application, such as toilet flushing, car washing, landscape irrigation, etc.; (3) agricultural irrigation, and (4) supply to environmental water.

Table 9 lists several practices of wastewater reclamation and reuse in some cities in China that are short of water. It can be seen that reclaimed water in these practices is mainly used for municipal uses and industrial cooling water.

Many different types of treatment processes fit different quality and quantity requirements of wastewaters. The major treatment processes in practice in China are as follows:

contact filtrationmactivated carbon adsorption; sedimentationmfiltrationmozone oxidation; coagulationmsedimentationmmembrane filtration; contact oxidationmsedimentation and filtration; A/O (A2/O) processes, etc.

A disinfection unit is generally the last treatment step to guarantee that the treated effluent is free of pathogens and biologically safe for reuse. Different treatment processes have their advantages and disadvantages. How to choose a proper treatment train to produce qualified effluent with low invest-ment and operational cost is still a very hot research topic nowadays in China. There are also a lot of concerns about the ecological and biological risks in using treated water. In this concern, membrane technology has been noticed as one of the promising solutions for producing microorganism-free effluent.

There are two main types of membrane filtration technol-ogy applied in the field of wastewater reclamation. They are membrane bioreactor (MBR) and direct membrane filtration.

Membrane bioreactor can be defined as the combination of two basic processes: biological degradation and membrane separation. The biomass responsible for biodegradation is separated from the treated water by a membrane filtration unit. Ultra-filtration and micro-filtration are two types of membranes used in the membrane bioreactor system. The membrane filtration unit can be located either outside the bio-reactor or submerged in it. Figure 7 shows the schematic diagrams of these two systems.

The membrane bioreactor system has the advantages of high volumetric loading, small footprint, low sludge

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

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.

The membrane bioreactor has been well-accepted in recent 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-mation. In 1997 and 2005, two large-scale international con-ferences on “membrane technology for water and wastewater treatment” were successfully held by Tsinghua University in Beijing. The biggest wastewater reclamation plant by using MBR in Asia was designed by Tsinghua University, which is the Beijing Miyun Municipal wastewater treatment plant with the designed wastewater treatment capacity of 45 000 m3/d. The plant started operations in April, 2006. Figure 8 shows the aeration tank and membrane tank used in the plant. The operational data of the plant indicate that the effluent can well meet the reused water standard of China. There are growing numbers of MBRs in operation in the country treating domes-tic, municipal and industrial wastewaters for different reuse

purposes. It can be predicted that the application of MBR in China will be booming in the near future.

Direct membrane filtration can act as the main process in the tertiary treatment of secondary effluent and produce high-quality effluent [100]. This kind of process is applied in large-scale water reclamation projects in wastewater treat-ment plants. According to the requirement of the effluent water quality, MF/UF can be chosen as the core treatment technology and NF/RO as the complementary step. The typical processes are “coagulationmmembrane filtration mdisinfection” (as shown in Fig. 9). In China, several large projects have been or are being built, such as the Tianjin Jizhuangzi wastewater reclamation plant, and the Beijing Qinghe wastewater reclamation plant.

Figure 10 shows the membrane combined treatment pro-cess 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 ozona-tion units. The plant also treats 30 000 m3/d water by the con-ventional 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 com-bined 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 pro-cess is also membrane fouling. In some studies, researchers found that membrane fouling is more severe in direct filtra-tion of secondary effluent than in MBR. Different raw water quality may affect membrane fouling. To minimize the foul-ing, one or several different pretreatment methods, such as ozonation, pre-coagulation, backwashing, etc., were studied and (or) applied in practices [104].

Fig. 9 Schematic diagram of a typical advanced wastewater treatment process with membrane filtration

Fig. 8 Pictures of Beijing Miyun Municipal wastewater reclamation MBR Plant

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7 Conclusions

China has been experiencing fast economic development and suffering from environmental pollution. Great efforts have been made for water pollution control in the country and a number of renovated technologies and processes have been developed and applied for municipal wastewater. However, it still has a long way to go to develop more and better appro-priate technologies for water pollution control in China. It is also worth mentioning that source control is more essential for controlling water pollution in the country.

Acknowledgements The authors appreciate the contributions of Dr. Wu Jing, Mr. Zhao Wentao, Miss Zhou Xiaohong, Mr. Zhang Zhichao, and Mr. Li Haitao for assistance of collecting and organizing the information, respectively.

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