Resources, Conservation and Recycling 51 (2007) 284–293

Sustainable urban sewerage system and its application in China Zhang Jie, Cao Xiang-Sheng ∗ , Meng Xue-Zheng Key Laboratory of Beijing for Water Quality Science and Water Environment Restoration Engineering, School of Civil Engineering, Beijing University of Technology, Beijing 100022, China Received 4 August 2006; received in revised form 30 September 2006; accepted 4 October 2006 Available online 1 March 2007

Abstract China is facing water crisis. More than 400 cities are lacking enough water resources and more than half rivers are polluted. To realize sustainable development in the 21st century, we should first provide enough water resources to every person and keep a friendly, leisurely water environment. Under the idea of sustainability, a concept for a sustainable urban sewerage system (SUSS) is put forward in this article. An urban sewerage system cannot only be a basic facility for draining rainwater and wastewater to protect the urban environment and public water bodies, but must also contribute to the restoration of the water environment in order to maintain a healthy social water cycle. A SUSS should be the basis for urban water reuse and recycling as well as the focus of water resource regeneration in a watershed and the centre of the recycling of nutrients. SUSS practices in the Shenzhen Special Economic Zone and the Beijing region in China are introduced. © 2006 Elsevier B.V. All rights reserved. Keywords: Water; Resources; Wastewater; Reuse; Sustainability; China

1. Introduction Water resources in China are scarce. According to China Bulletin of Water Resources published by China Ministry of Water Resources, in 2004, the total amount of water ∗ Corresponding author at: No. 100, Pingleyuan, Chaoyang District, College of Civil Engineering, Beijing University of Technology, Beijing 100022, China. Tel.: +86 10 67392579; fax: +86 10 67392579. E-mail address: [email protected] (X.-S. Cao).

0921-3449/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.resconrec.2006.10.001

J. Zhang et al. / Resources, Conservation and Recycling 51 (2007) 284–293

285

resources in China is 2.413 × 1013 m3 . It is equal to 1856 m3 per capita per year. Among these, 23%, that is 5.548 × 1012 m3 , was used for agricultural, industry and domestic activities. At the same time, 6930 × 108 m3 wastewater was discharged from Chinese cities. No more than half amounts were subject to the secondary treatment. More than half rivers in China are terribly polluted (Gao et al., 2006). To tackle the water crisis, the government of China had published a lot of regulations; researches had suggested a lot of strategies; engineers had planned and constructed many water supplies and wastewater treatment projects (Bai et al., 2006; He and Xing, 2006; Pan et al., 2006). But with the development of Chinese economics, water resources is becoming increasing deficient and the quality of environment constantly becoming worse in most regions of China. A new water use and treatment strategy must be established to tackle the water problems of China and to realize the sustainable development. The functioning of urban sewerage systems based on traditional concepts is not sustainable; it needs to be changed. An urban sewerage system cannot only be a basic facility for draining rainwater and wastewater to protect the urban environment and public water bodies, but must also contribute to the restoration of the water environment in order to maintain a healthy social water cycle. A social water cycle is defined as a system that includes drawing water from natural bodies, utilizing it and discharging it back to the water bodies (Zhang, 2001). A healthy social water cycle means that we should draw water moderately, use water carefully, purify and reuse wastewater deliberately. We should ensure that the water utilization in the upper reaches of the rivers does not affect the function of water bodies in the lower reaches of the rivers. The ultimate aim is to restore or maintain a healthy water environment for a city or river basin and eventually achieve the sustainable utilization of water resources. A healthy social water cycle is also an essential component of establishing a city that recycles (Guan et al., 2004). The aim of this article is to discuss function and design considerations for a sustainable urban sewerage system using concepts associated with a healthy water cycle. In this paper we will introduce some urban planning suggestions to promote such a healthy water cycle. 2. The development of sustainable urban sewerage systems 2.1. History of urban sewerage system The earliest urban sewerage systems were constructed to only transport excess overland rainwater as quickly as possible from a city to rivers that were downstream from the city (Aminuddin et al., 2000; Angelakis et al., 2005). The flush toilet was invented in the 18th century and became widespread throughout the cities of Europe in the 19th century. The widespread use of flush toilets improved the sanitation conditions of urban residents, but the amount of water supply and sewerage required as a result increased dramatically. At this time, the sewer and run-off sewerage systems were constructed as a combined sewerage system. The function of the urban sewerage system changed to this combined system to protect the inhabitants from bacterial infection as the major component of sanitary engineering. However, rivers and lakes near cities became terribly polluted during this period because of large amount of untreated wastewater containing feces and urine. The pollution of the

286

J. Zhang et al. / Resources, Conservation and Recycling 51 (2007) 284–293

Rhine River in the 20th century is a typical illustration (Carel, 1998). The improvements in living conditions of city inhabitants were obtained at the price of pollution of the water environment. Research and practices of wastewater treatment technology began in the early 20th century with a starting condition in which the rivers and lakes were badly polluted. During the past century, the technologies associated with wastewater treatment advanced dramatically with the removal of pollutants, including suspended solids and organics, subsequently nitrogen and phosphates and finally micropollutants, such as disinfection byproducts and hormone-like substances (Henze, 1997). Currently, the functions of urban sewerage systems are as follows: (1) transport rainwater and wastewater outside a city as soon as possible to protect against floods and prevent the spread of epidemics; (2) treat municipal wastewater to reach or exceed the standards of state or local regulations. 2.2. The pattern of sustainable urban sewerage systems in the 21st century The above-mentioned functions of urban sewerage systems were formed under the hypothesis that water resources were abundant enough to splurge and that the rivers or lakes that wastewater was dumped into had enough capacity for self-purification. This hypothesis was supported when populations were not very large or centralized and industries were underdeveloped. As industries developed, people became increasingly centralized and metropolitan areas emerged. At this time traditional urban sewerage systems could only protect the area within cities. The regions around the cities were badly polluted by wastewater and other wastes produced by the townspeople. From the perspective of the restoration of entire watersheds, urban sewerage systems are part of the overall hydrological cycle. The function of urban sewerage systems should be reevaluated and new missions should be espoused. Urban sewerage systems should play an important role in a healthy water cycle and in sustainable urban construction. If we compare a city to a human body, water can be thought of as blood. The water supply system is analogous to the arteries and the wastewater system is analogous to the veins. A wastewater treatment plant could be considered as analogous to the liver because of the plant’s role in purifying urban wastewater. Urban sewerage systems are of necessity responsible for wastewater collection, transportation, purification and reclamation. An urban sewerage system is the key factor for closing the urban water cycle. The function of an urban sewerage system in the 21st century should shift from traditional waterlogging prevention to the establishment of wastewater recycling, sustainable utilization of water resources and watershed restoration. This new urban sewerage system is called a sustainable urban sewerage system (SUSS) in this article and a sketch of its key features is shown in Fig. 1. A typical SUSS has four modern features described as follows: (1) It is the basis for urban water reuse and recycling. A SUSS has the duty of producing reclaimed wastewater as a steady secondary urban water resource. Reclaimed wastewater can be used as cooling water for industry, irrigation water for landscaping, flowing water for rivulet regeneration and for any other application where non-potable water may be used. A large volume of reclaimed wastewater could reduce fresh water exploitation, and thus promote a healthy water cycle.

J. Zhang et al. / Resources, Conservation and Recycling 51 (2007) 284–293

287

Fig. 1. Sketch of a sustainable urban sewerage system.

(2) Water resource regeneration in a watershed hinges on SUSS. In a watershed, wastewater drained from upriver cities flows into downriver cities. Outflow of upriver SUSS would be a part of the water resource of downriver cities throughout an entire watershed. Each SUSS should have this water resource regeneration capacity. (3) SUSS is central to nutrient recycling. As a product of wastewater treatment, sludge should be treated properly and returned to farmland as fertilizer. Nitrogen and phosphates in wastewater should be recovered as fertilizer during the wastewater collection, transportation and treatment process. SUSS plays an important role in the reparation of natural nutrient cycles. Note: Chinese law states that industrial wastewater must be pretreated for the removal of heavy metals before being released into the municipal wastewater stream. (4) SUSS is the basis for scarce resource recovery and energy recovery. Most metabolic products of city dwellers are discharged into urban sewerage pipeline systems and are transported to the wastewater treatment plant. This kind of wastewater contains much energy. Anaerobic treatment of wastewater or sludge could potentially produce methane, which can be used as fuel (Chan et al., 1999). The energy contained in wastewater could also be extracted by heat pump technology (Baek et al., 2005). Certain valuable metals or other scarce resources are also found in wastewater, particularly in industrial sewerage pipelines. Recycling of valuable substances in industrial wastewater may be an important part of an industrial circular economy. 2.3. Comparison between sustainable and traditional urban sewerage systems 2.3.1. Principles of an urban sewerage system plan In sustainable urban sewerage system planning, convenience both for municipal wastewater reclamation and for rainwater utilization should be emphasized. This is the

288

J. Zhang et al. / Resources, Conservation and Recycling 51 (2007) 284–293

fundamental difference between a conventional urban sewerage system and SUSS (Zhang, 2001). The aim of treatment of wastewater in a SUSS is to produce reclaimed wastewater in what are called reclaimed wastewater production plants (RWPPs). There are distinct differences between RWPPs and wastewater treatment plants (WWTPs) in a traditional urban sewerage system. As key components of SUSS, rainwater sewers and treatment facilities are important to realize the sustainability of the urban sewerage system. Rainwater is the most important source of surface flow and underground flow and should not drain down from the city as quickly as possible, as it does in a traditional urban sewerage system. In a SUSS rainwater should be retained in the city as long as possible and should be treated properly in order to be recycled within the city. 2.3.2. The scale, location and number of reclaimed wastewater production plants According to the regulations of traditional urban sewerage system planning, reclaimed wastewater production plants should be located in the lower reaches of the city. But this arrangement places the sources of reclaimed wastewater far from their consumers. Thus the investment and operational costs of reclaimed wastewater pipeline systems increase. This would not be favourable, as consumers would need to spend more money when they use the reclaimed wastewater. Therefore, the following should be exhaustively investigated in making a decision as to the sewerage zone separation and the number of RWPPs: (1) the functional separation and the terrain of the city, (2) the present wastewater and rainwater pipeline distribution, (3) the environmental capacity of the water bodies that accept the effluent of RWPPs and (4) the location and dimensions of present and future demands of reclaimed wastewater. Based on past practical experience, large-scale WWTPs are highly efficient and the cost of running and construction per cubic meter of wastewater is lower than small WWTPs. So in a traditional urban sewerage system, WWTPs are constructed to be as large as possible and most cities have only one WWTP in the lower reaches of cities. But in a SUSS using an RWPP design, this experience may not be applicable because the length of pipelines for wastewater and reclaimed wastewater are too long so reclaimed wastewater pumping stations must be built if only one RWPP is located in the lower reaches of cities. Therefore decisions about the number of RWPPs cannot be limited by traditional experience. The practical demands of reclaimed wastewater should be carefully considered. RWPPs should not be centralized in the lower reaches of the city, as are the location of WWTPs in traditional urban sewerage system planning. Large, moderate or small RWPPs can be located upstream or downstream or throughout the entire city over the length of the wastewater pipeline so that the reclaimed wastewater pipeline can be shortened and the cost of reclaimed wastewater production reduced. 2.3.3. Wastewater treatment degree and process selection Under the concept of a traditional urban sewerage system, many cities in China pay considerable attention to the secondary treatment of wastewater in order to attain the Integrated Wastewater Discharge Standard (GB8978-1996). But it is not sufficient in most instances to construct a SUSS. It is necessary to increase the discharge criteria for wastewater treatment by using advanced treatments or even super-advanced treatments in order to increase the

J. Zhang et al. / Resources, Conservation and Recycling 51 (2007) 284–293

289

amount of wastewater reuse and to restore the water environment downstream from the cities. When planning an RWPP, the possibility of super-advanced treatment of wastewater should be considered. At a minimum, sufficient space should be set aside and dedicated for the future addition of a super-advanced treatment unit. In China great difficulties exist in planning and constructing advanced or super-advanced wastewater treatment plants due to the opposition of decision-making officials and the huge cost of construction and maintenance. Environmental and civil researchers and engineers play an important advocacy role for the concept and benefits of SUSS. In the traditional urban sewerage systems present in most of China, advanced processes for reclaiming wastewater have been added only after typical secondary treatment WWTPs had already been completely built. The effluent of secondary treatment becomes the influent of RWPPs. This pattern has made the pipelines too long and the process too complex and the costs of reclaimed wastewater production too high when considering the entire process from primary to advanced treatment of wastewater. In SUSS, the principles used in the selection of the processes for traditional wastewater treatment plants are not suited for a RWPPs plan and design. Primary, secondary and tertiary or advanced treatment units should be regarded as parts of the whole system when it comes to the selection of processes for wastewater treatment. Removal of carbon, nitrogen, phosphate and other pollutants should be distributed reasonably throughout the entire treatment sequence. This is the concept behind the Reclaimed Wastewater Production Whole Process (RWPWP), which has been researched for about ten years in China.

3. Practices of sustainable urban sewerage systems in China 3.1. Shenzhen Special Economic Zone Shenzhen is the first and largest special economic zone and it is also one of the seven cities that are most deficient in water resources in China (Xiong et al., 2004). According to an earlier plan, after the Dongshen Water Supply Project and the Eastern Water Resource Project were completed, only 0.768 billion m3 of water per year could be provided to Shenzhen. This translates to 374 m3 of water per capita per year for citizens of the Shenzhen Special Economic Zone (Xiong et al., 2004). This shortage of water resources is a critical factor restricting the development of the Shenzhen region. Meanwhile, the water environment of Shenzhen has become terribly polluted. Although the amount of wastewater treated by secondary treatment was 56% of the total wastewater discharged by the Shenzhen Special Economic Zone, the quality of most of the water in rivers which flow across the zone is Class V according to the Environmental Quality Standard for Surface Water of China (GHZB 1-1999) (Wang and Li, 2002). That is to say, the 5day biochemical oxygen demand (BOD5) concentration exceeds 10 mg/l and the dissolved oxygen concentration is no more than 2 mg/l in the river water. There is no life in Shenzhen rivers, the water bodies are black in colour and there is a bad odour near the rivers. To restore the water environment and realize sustainable utilization of water resources for the Shenzhen Special Economic Zone, a wastewater reuse project was conducted in 2000 (Wang and Li, 2002). In 2001, the specific plan of the wastewater reuse system was

290

J. Zhang et al. / Resources, Conservation and Recycling 51 (2007) 284–293

Fig. 2. Sketch of reclaimed wastewater system in Shenzhen City.

finished by the Chinese Northeast Municipal Engineering Institute. According to this, as yet unrealized, plan, reclaimed wastewater pipe networks were divided into six parts as shown in Fig. 2. The total length of pipeline will be about 130 km and the total volume of reclaimed wastewater is projected to be 500,000 m3 per day. The scale and location of each RWPP has been determined based on the careful consideration of distribution of reclaimed wastewater consumers, the landform of the Shenzhen region, the present wastewater pipeline locations, etc. When all the RWPPs have been completely constructed, the pattern, in which the locations of the RWPPs were all downstream of the city, will be changed and the urban sewerage system in Shenzhen Special Economic Zone will become a centre of water resource recycling. This will then be an application of the concept of SUSS. 3.2. Beijing region The annual precipitation of the Beijing region is 595 mm and the quantity of water resources is no more than 300 m3 per capita per year (Wang, 2003). The quality of surface water in the Beijing region is worse than Class V, according to the Environmental Quality Standard for Surface Water of China (GHZB1-1999). Ground water has been seriously exploited and the level of ground water decreased 1.29 m each year in the initial years of the 21st century (Wang, 2003). In 2001, the Government of Beijing and the Ministry of Water Resources of the People’s Republic of China authorized “the Capital Sustainable Water Resources Utilization at the Beginning of the 21st Century (from 2001 to 2005)”. In June of the same year, the Beijing Group of Wastewater authorized the “Outline Plan of Reclaimed Wastewater in Beijing Region”. In this report the plans for RWPPs and the related reclaimed wastewater pipelines are laid out as shown in Fig. 3. The Beijing Olympics Action Plan promises that Beijing will attain a rate of secondary treatment of wastewater of least 90% and endeavour to reach a recycling rate of wastewater of 50% before 2008. The name of the RWPPs and related pipelines that are scheduled for completion before 2008 are

J. Zhang et al. / Resources, Conservation and Recycling 51 (2007) 284–293

291

Fig. 3. Sketch of reclaimed wastewater system in Beijing city.

shown in Table 1. All these plans mean that SUSS will be mandated for the Beijing region. In 2004, the writers of this paper finished an unpublished report entitled “Water Environment Restoration Strategies for Beijing Region” supported by the Beijing Municipal Table 1 Reclaimed wastewater system those are scheduled for completion before 2008 in Beijing region RWPPs

Scale of RWPPs (tonnes per day)

Length of reclaimed wastewater pipeline (km)

Qinghe Beixiaohe Beiyuan Jiuxianqiao Dongba Wujiacun Lugouqiao Xiaohongmen Wulituo

80,000 60,000 10,000 80,000 10,000 80,000 80,000 70,000 6,000

94 36 14 34 67 48 72 6

292

J. Zhang et al. / Resources, Conservation and Recycling 51 (2007) 284–293

Commission of Education. We suggested strategies for the Beijing region from the perspective of watershed restoration and protection, water and wastewater utilization and water environment restoration. At the same time, a plan for changing the function of the sewerage system in Beijing city was also put forward. According to the research results of this project, the Beijing region has been divided into 12 wastewater reclamation and reuse areas. The amount of reclaimed wastewater is projected to reach 0.87 billion m3 which is one-third of the total amount of currently available fresh water in the Beijing region. In addition the amount of water pollutants is expected to be reduced by 40% before 2010. 4. Conclusions Sustainable Urban Sewerage Systems for the 21st century in China are the lifeline of water environmental restoration. Their function goes beyond the traditional task of discharging rainwater and wastewater and preventing the pollution of public water bodies. Sustainable Urban Sewerage Systems are at the centre of realization of healthy water recycling and are basic to resources and energy recycling. They harmoniously connect the social water cycle of human society with the natural hydrological cycle. The concept of sustainable urban sewerage systems is being planned in China. The Shenzhen Special Economic Zone and the Capital of the People’s Republic of China will probably be the first two regions to realize Sustainable Urban Sewerage Systems. Acknowledgements The authors would like to thank Drs. Edmund F. and Rhoda E. Perozzi, of the Beijing University of Technology for very extensive suggestions, editing and English language assistance. This work is financially supported by Beijing Natural Science Foundation Program and Scientific Research Key Program of Beijing Municipal Commission of Education (KZ200610005001). References Aminuddin AG, Nor AZ, Mahadzir K. Sediment size characteristics of urban drains in Malaysian cities. Urban Water 2000;2:335–41. Angelakis AN, Koutsoyiannis D, Tchobanoglous G. Urban wastewater and stormwater technologies in ancient Greece. Water Res 2005;39:210–20. Baek NC, Shin UC, Yoon JH. A study on the design and analysis of a heat pump heating system using Wastewater as a heat source. Solar Energy 2005;78:427–40. Bai ZG, Wang CW, Li GL. The water pollution status and control in our country. Chem Defence Ships Suppl 2006:15–7 [in Chinese]. Carel D. From open sewer to salmon run: lessons from the Rhine water quality regime. Water Policy 1998;1:471– 85. Chan YSG, Chu LM, Wong MH. Codisposal of municipal refuse, sewage sludge and marine dredgings for methane production. Environ Pollut 1999;106:123–8. Gao TY, Chen HB, Xia SQ. Review on water pollution control in China. Water Wastewater 2006;32(5):9–13 [in Chinese].

J. Zhang et al. / Resources, Conservation and Recycling 51 (2007) 284–293

293

Guan FJ, Wang YSh. Recycling economy, the important approach to cope with resource development and environment protection. Nat Resour Econ China 2004;17:4–6, 22 [in Chinese]. He YW, Xing HG. The urban water pollution status quo and countermeasures in China. Water Conserv Sci Technol Econ 2006;12(1):44–5 [in Chinese]. Henze M. Trends in advanced wastewater treatment. Water Sci Technol 1997;35:1–4. Pan AG, Gui T, Liu BJ. Challenges and countermeasures in west-line project of South-to-North water diversion. China Earth Resour Technol Manage 2006;23(4):1–4 [in Chinese]. Wang JR. Discussion of distribution of Beijing water resources. Water Resour Manage 2003;2:33–4. Wang PF, Li J. Sustainable water resource utilization of Shenzhen Special Economic Zone. Water Wastewater 2002;28(2):25–7 [in Chinese]. Xiong BY, Zhang J, Li J. Research of reclaimed wastewater pipeline plan of Shenzhen Special Economic Zone. Water Wastewater 2004;30(2):16–20 [in Chinese]. Zhang J. Modern concept of city sewerage system. China Eng Sci 2001;3(10):33–5 [in Chinese].