Seeking Sustainability: Multiobjective Evolutionary Optimization for

Dec 30, 2013 - The results present a general picture of wastewater reuse for policy makers in China. ... Seeking urbanization security and sustainabil...
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Seeking Sustainability: Multiobjective Evolutionary Optimization for Urban Wastewater Reuse in China Wenlong Zhang, Chao Wang,* Yi Li,* Peifang Wang, Qing Wang, and Dawei Wang Key Laboratory of Integrated Regulation and Resource Development on Shallow Lakes, Ministry of Education, College of Environment, Hohai University, Nanjing, Jiangsu 210098, P.R. China S Supporting Information *

ABSTRACT: Sustainable design and implementation of wastewater reuse in China have to achieve an optimum compromise among water resources augmenting, pollutants reduction and economic profit. A systematic framework with a multiobjective optimization model is first developed considering the trade-offs among wastewater reuse supplies and demands, costs and profits, as well as pollutants reduction. Pareto fronts of wastewater reuse optimization for 31 provinces of China are obtained through nondominated sorting genetic algorithm trials. The control strategies for each province are selected on the basis of regional water resources and water environment status. On the national level, the control strategies of wastewater reuse scale, BOD5 reduction, and economic profit are 15.39 billion cubic meters, 176.31 kilotons, and 9.68 billion RMB Yuan, respectively. The driving forces of water resources augmenting and water pollution control play more important roles than economic profit during wastewater reuse expanding in China. According to the optimal allocations, reclaimed wastewater should be intensively used in municipal, domestic, and recreative sectors in the regions suffering from quantity-related water scarcity, while it should be focused on industrial users in the regions suffering from quality-related water scarcity. The results present a general picture of wastewater reuse for policy makers in China.

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INTRODUCTION China has been facing increasingly severe water scarcity. Twothirds of China’s 669 cities have water shortages, more than 40% of its rivers are severely polluted, and 80% of its lakes suffer from eutrophication.1 Water shortages and poor water quality are interacting with each other and threatening China’s food security, economic development, and quality of life. Great efforts have been taken in conserving and augmenting the limited water resources to meet the growing demands. Water reclamation, recycling, and reuse should be key components of the national water strategy.2 Wastewater reuse has developed from a basic method of disposing wastewater without any treatment to a highly engineered process of wastewater treatment and water resources augmentation in China. Such a move is driven by two major forces: scarcity of freshwater resources and heightened environmental concerns.3 Meanwhile, economic consideration is also becoming increasingly important amid the introduction of market-based mechanisms in environmental and water resources management.4 In January 2011, the China government’s annual No. 1 Document, which reflects its top priority, clearly pointed out that wastewater reuse should be strengthened. However, the current wastewater reuse is mostly an afterthought of the national water resources development plan. The infrastructure needs, use potentials, and development © 2013 American Chemical Society

costs are not accounted and planned in the initial water development plan.5 Therefore, how to reclaim and reuse the wastewater in an efficient way is still the key consideration for water policy making in China. To make the effective plan, a wide range of studies have been carried out in the past several years, including analysis of wastewater reuse potential,6,7 assessment of wastewater reuse risk,8,9 financing of wastewater reuse projects,10 pricing of reused wastewater,11 and studies of users’ acceptance and willingness to pay for the reused wastewater.12,13 One of the noticeable studies as such is by Chu et al.6 in 2004, in which a linear programming (LP) model was applied to examine tradeoffs between wastewater reuse supplies and demands, as well as the related costs and profits in China. It provides a useful framework for examining the wastewater reuse potential under physical and economic constraints. However, according to the Report on the Work of Government (2005), environmental protection and ecological conservation have been another central task of China. Wastewater reclamation and reuse has been one of the most important measures for point source Received: Revised: Accepted: Published: 1094

September 12, 2013 November 20, 2013 December 30, 2013 December 30, 2013 dx.doi.org/10.1021/es404082f | Environ. Sci. Technol. 2014, 48, 1094−1102

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Figure 1. Methodology Flowchart. S1 is wastewater for reuse from wastewater treatment plants (WWTPs). S2 is wastewater for reuse from in-house gray wastewater and on-site wastewater. Q1, Q2, Q3, and Q6 are the reclaimed wastewater amounts from WWTPs to agricultural irrigation, industry, municipal reuses, and recreation, respectively. Q4 and Q5 are the reclaimed wastewater amounts from in-house gray wastewater and on-site wastewater to municipal and domestic reuses. D1, D2, D5, and D6 are reclaimed water demands for agricultural irrigation, industry, domestic use, and recreation, respectively. D3+4 is reclaimed water demands for municipal and on-site uses.

́ et al.25 showed that multiobjective genetic system. Udias algorithm can be particularly useful in wastewater reclamation and reuse problems as it can provide assistance in the evaluation and selection of water treatment alternatives. Dinesh and Dandy26 developed a computer based decision support system based on GAs to assist planners and decision-makers in the techno-economic assessment of wastewater reclamation technologies. Penn et al.27 presented a multiobjective optimization model for estimating the optimal distribution of different types of greywater reuse homes in an existing municipal sewer system. It is the first model aimed at quantitatively trading off the cost of local/onsite greywater spatially distributed reuse treatments, and the total amount of wastewater flow discharged into the municipal sewer system under unsteady flow conditions. However, so far, modeling wastewater reuse with evolutionary optimization for evaluating the trade-offs among wastewater reuse supplies and demands, costs and profits, as well as pollutants reduction has not been available in the literature. Therefore, the aim of this study is to establish a systematic framework with a multiobjective optimization model, considering the trade-offs among wastewater reuse supplies and demands, costs and profits, as well as pollutants reduction, for studying the potential wastewater reuse scales and allocations at provincial level in China. Based on regional water resources and water environment status, national control strategies of

pollution control, especially in Yangtze and Pearl River basins, where most cities are suffering from quality-related water scarcity.14,15 Therefore, sustainable design and implementation of wastewater reuse in China have to achieve an optimum compromise among water resources augmenting, pollutants reduction and economic profit. The application of evolutionary optimization techniques for multiobjective optimization has been widely reported in water and wastewater engineering.16−18 Genetic algorithm (GA) has proven to be a very powerful technique to find optimal solutions for many real-world optimization problems, especially in the field of water resources planning and management.19 The benefit and potential of application of GAs in urban wastewater systems have been studied recently. Alvarez-Vázquez et al.20,21 presented an application of optimal control theory of partial differential equations combined with multiobjective optimization techniques to solve an economical-ecological problem related to wastewater management. Zeferino et al.22 described a multiobjective model for regional wastewater systems planning. Muschalla23 optimized the performance of an urban wastewater system using a new multiobjective evolution strategy in combination with an integrated pollution-load and waterquality model. Fu et al.24 studied the optimization of multiobjective control of urban wastewater system using GAs. Furthermore, only a few studies focused on multiobjective optimization model on the optimization of wastewater reuse 1095

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wastewater reuse scale and allocation, pollutants reduction, as well as economic profit are delineated. Beijing city and Jiangsu province are selected as examples to expound the optimization process. Moreover, the in-depth analyses of wastewater reuse strategies of Beijing and Jiangsu are important for formulating appropriate wastewater reuse policies in the regions suffering from quantity and quality related water scarcity, respectively. To the best of our knowledge, this is the first study estimating the national wastewater reuse scale and allocation considering trade-offs among water resources augmenting, pollutants reduction, and economic profit. The results could present a general picture of wastewater reuse for policy makers in China.

The function of the second objective, i.e. pollutants reduction during wastewater reclamation and reuse, is shown in formula 10: 6

Maximize F2(Q j) =

j=1

METHODOLOGY AND DATA The Framework of Wastewater Reused System. This work provides a framework for examining the wastewater reuse scales and allocations using the multiobjective algorithm based on nondominated sorting genetic algorithm (NSGA II) under physical constraints.27,28 The flowchart of the solution methodology is presented in Figure 1. The amount of wastewater reuse is subject to both supply of and demand for the reclaimed wastewater. Although other applications are in practice including groundwater recharge, environmental enhancement, and potable reuse, they are not included in the following discussion since their applicability is rather limited in China. Objective Functions. The optimization of wastewater reuse contains three objectives, i.e. minimization of cost, maximization of pollutants reduction, and maximization of wastewater reuse volume. The costs of wastewater reclamation consist of two components: capital cost and operating and management (O&M) cost. The former is a function of depreciation, interest, and replacement cost. The latter is subject to labor, maintenance, and materials. The calculation formulas for these costs are given in formulas 1 and 2:6,7 (1)

⎡ R (1 − R1) RR 1 − Ra ⎤ UCCj = UIj⎢ a + a 2 + ⎥ 365 365L 2 ⎦ ⎣ 365L1

(2)

(10)

The maximization of F2(Qi) can be obtained by optimizing the allocation of Qi. The government of China decree, Urban Wastewater Reuse Category (GB/T 189198-2002), divided wastewater reuse into five use categories, and correspondingly five recommended national standards, namely: Urban Wastewater Reuse Water Quality Standard for Urban Miscellaneous Water (GB/T 18920-2002), Urban Wastewater Reuse Water Quality Standard for Scenic Environment Water (GB/T 189212002), Urban Wastewater Reuse Water Quality Standard for Industrial Water (GB/T 19923-2005), Urban Wastewater Reuse Water Quality Standard for Groundwater Recharge (GB/T 19772-2005), and Urban Wastewater Reuse Water Quality Standard for Farmland Irrigation Water (GB 209222007). Biological oxygen demand (BOD5) is chosen as the representative pollutant index in this study as it is a good indicator for inland waters where shortage of dissolve oxygen is of prime importance.29 Moreover, BOD5 is the sole pollutant index restricted in all of reclaimed wastewater quality standards. Although ammonia nitrogen, total nitrogen, and total phosphorus are also major pollutants in wastewater, they are not considered as the representative pollutant indexes since it is very difficult to collect data of pollutants unrestricted in reclaimed wastewater quality standards. The function of the third objective, i.e. maximization of wastewater reuse volume, is shown in formula 11:

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UTCj = UCCj + UOCj

∑ (Pdj − Psj)*Q j

6

Maximize F3(Q j) =

∑ Qj j=1

(11)

Physical Constraints. The possible maximum demand for wastewater reuse for different uses can be determined by the equations from 12 to 18:

j=1−6

The total costs for different wastewater reuse way j are given in formulas from 3 to 8:

D1 = Va − A v Ev

(12)

D2 = CeEeKe

(13)

D3 + 4 = Ag K g Eg Tg + A r K rEr + Ac KcEc

(14)

D5 = k1Vd

(15)

TC1 = (UTC1 − PA)*Q 1

(3)

D6 = R w

(16)

TC2 = (UTC2 − PI )*Q 2

(4)

S1 = b1Wd + b2Wi

(17)

TC3 = (UTC3 − PM )*Q 3

(5)

S2 = b1Wd

(18)

TC4 = (UTC4 − PM − PW )*Q 4

(6)

TC5 = (UTC5 − PD − PW )*Q 5

(7)

TC6 = (UTC6 − PR − PW )*Q 6

(8)

These equations are formulated based on Urban Wastewater Reuse Water Quality Standards, regional water use status, and previous studies.6,7 Edible vegetable irrigation is not included in the calculation of reclaimed water demand for agricultural irrigation due to its high requirement on water quality. It is uneconomical for agricultural irrigation with high quality water. Circulating cooling water, ash rinsing water and boiler feedwater in thermal power plants are the main utilization patterns for industry in China. Although reclaimed wastewater could be used for production processes, it is not considered since reclaimed wastewater from centralized reclaimed water plants needs to be further treated by users to meet the their

Accordingly, the function of the first objective can be expressed as in formula 9: 6

Minimize F1(Q j) =

∑ TCj j=1

(9) 1096

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statistical reports and previous studies are summarized in Table S1. The parameters related to unit capital cost, O&M cost, and wastewater reuse prices are valued according to our survey in 2010, 2011, and 2012. 54 reclaimed wastewater treatment plants in 33 cities were surveyed. The details of these reclaimed wastewater treatment plants are shown in Table S2. As far as we know, it almost contains all of running centralized reclaimed water plants in China. For the provinces without centralized reclaimed water plants, the capital investment and O&M cost are valued based on the national averages. The reclaimed wastewater prices are valued according to regional wastewater reuse plans and previous studies.7,11,32

production standards. Public green lawn, road cleaning, and car washing are considered as the main demands for municipal and on-site uses. Toilet flushing is the sole use for domestic uses. Based on the framework of wastewater reuse supply demand physical constraint shown in Figure 1, the quantity of wastewater reuse for each category should be less than or equal to the minimum of reclaimed wastewater supply and demand. These restrictions can be determined by the equations from 19 to 28: Q 1 ≤ min(S1 , D1)

(19)

Q 2 ≤ min(S1 , D2)

(20)

Q 3 ≤ min(S1 , D3 + 4 )

(21)

Q 4 ≤ min(S2 , D3 + 4 )

(22)

Q 5 ≤ min(S2 , D5)

(23)

Q 6 ≤ min(S1 , D6)

(24)

Q 1 + Q 2 + Q 3 + Q 6 ≤ S1

(25)

Q 4 + Q 5 ≤ S2

(26)

Q 3 + Q 4 ≤ D3 + 4

(27)

Qj ≥ 0 j = 1 − 6

(28)

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RESULTS AND DISCUSSION Wastewater Reuse in Beijing City. Beijing is a rapidly growing city in both population and economy, while water scarcity is intensifying and water pollution is increasing.33 It is one of the driest cities in the world. The per capita fresh water resources are currently about 137.6 m3 per year, i.e. one-53rd of the world’s average. By the end of 2011, Beijing was the city with the highest wastewater reuse ratio (i.e., 59.12%) in China. In 2011, the volume of reused wastewater was 702.79 million cubic meters (MCM), accounting for 43.38% of urban water supply. Figure 2a and Table S3 present the Pareto solutions for wastewater reuse in Beijing. There exists a clear trade-off between the objectives of minimization of cost (i.e., maximization of economic profit) and maximization of pollutants reduction. The maximizations of water resources augmentation and pollutants reduction are considered as the external sets of criteria since Beijing suffers from both water scarcity and water pollution. Therefore, the solution reddened at the top right corner in Figure 2a is selected as the control strategy as it has the maximization of wastewater reuse volume (984.27 MCM) and BOD5 reduction (9.59 kilotons) in the obtained discrete approximation of the Pareto front. The corresponding economic profit is 610.36 million RMB Yuan (MRY). Furthermore, Pareto optimization of wastewater reuse in Beijing with only two objectives (i.e., maximization of wastewater reuse scale and BOD5 reduction) was carried out (as shown in Figures S1 and S2). According to the external sets of criteria, the solution with wastewater reuse volume of 984.27 million cubic meters and BOD5 reduction of 9723.59 tons is selected as the control strategy. The corresponding economic profit is 585.37 million RMB Yuan. The solution is not included in the Pareto front obtained by NSGA II using threeobjective problems study since it is not in agreement with the idea of this study, i.e. sustainable design and implementation of wastewater reuse in China have to achieve an optimum compromise among water resources augmenting, pollutants reduction, and economic profit. Figure 2b compares the wastewater reuse scales and allocations of Beijing reported in this study, Water Management Report (WMR) of MWR (2011), and a previous research by Yang et, al. who analyzed optimal wastewater reuse scale in Beijing through a LP model under physical and economic constraints.7 It is noticed that approximately 71.4% of optimal wastewater reuse scale had been achieved for Beijing by the end of 2011. It is also found that the current wastewater reuse scale (702.79 MCM) and calculated wastewater reuse volume in this study are larger than that reported in Yang and co-workers’ study (634.50 MCM).7 The result indicates that the driving

Multiobjective Optimization through NSGA II. NSGA II is an effective method for multiobjective optimization developed by Deb et al.28 In NSGA II, the concept of Pareto-dominance is used to rank the individuals (control strategies) of a population. As shown in Figure 1, the implementing process of NSGA II follows the following pseudocodes: Randomly initialize the population P (0) of size N; Fast nondomination sorting on P (0); For every generation t; Select a parent population Pp (t) from P(t) using a binary tournament selection; Create a child population Pc (t) from Pp (t) through crossover and mutation operators; Combine P (t) and Pc (t) into an intermediate population Pi (t); Fast nondomination sorting on Pi (t); Place the best N individuals from Pi (t) to P (t+1); End loop Data. China is a large country with substantial regional variations. It is necessary to calculate the optimal wastewater reuse scales and allocations in regional perspective. 31 provinces of China are included in this study, except Hong Kong and Macao Special Administrative Regions and Taiwan. The main data sources for input parameters are statistical reports from Ministry of Water Resources (MWR), Ministry of Environmental Protection (MEP), Ministry of Housing and Urban-Rural Development (MHUD), State Economic and Trade Commission (SETC), and National Bureau of Statistics (NBS) of China. The parameters coming from statistical reports include Va, Av, Ce, Ag, Ar, Ac, Kg, Kr, Kc, Tg, Vd, Rw, Wd, Wi, b1, and b2. Other parameters related to water use standards and proportions, such as Ev, Ee, Ke, Eg, Er, Ec, and k1, could be found in previous studies.6,7,30,31 The parameters from 1097

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Figure 3. (a) Pareto front obtained by NSGA II using the threeobjective problems study for wastewater reuse in Jiangsu province. The solution reddened represents a control strategy with wastewater reuse scale 1281.77 million m3, BOD5 reduction 12821.89 tons, and economic profit 715.31 million RMB Yuan. (b) Wastewater reuse scales and allocations of Jiangsu province reported in this study and Water Management Report (WMR) of Ministry of Water Resources (MWR). # means the lack of data in WMR of MWR.

Figure 2. (a) Pareto front obtained by NSGA II using the threeobjective problems study for wastewater reuse in Beijing. The solution reddened represents a control strategy with wastewater reuse scale 984.27 million m3, BOD5 reduction 9585.18 tons, and economic profit 610.36 million RMB Yuan. (b) Wastewater reuse scales and allocations of Beijing reported in this study, Water Management Report (WMR) of Ministry of Water Resources (MWR), and a previous study.7 * means that the wastewater reuse volume is 0. # means the lack of data in WMR of MWR.

wherever available for irrigation regardless of whether it is treated or not. It is hard to collect any charge for reclaimed wastewater use for agricultural irrigation. The economically viable scale of wastewater reuse for agricultural irrigation is dependent on the funds from central and local governments. Therefore, agricultural irrigation should not be the main sector for reclaimed wastewater allocation from an economic perspective. Actually, in the past ten years, Beijing’s dependence on the internal water footprint supporting for agricultural products shrank sharply, whereas the external water footprint increased substantially.34,35 Wastewater Reuse in Jiangsu Province. Jiangsu is the second largest provincial economy of China. The province’s GDP exceeded 5405.82 billion Yuan in 2012, registering a growth of over 10% against the previous year. It is a typical coastal region suffering from quality-related water scarcity.36 The per capita fresh water resources are currently about 475.57 m3 per year. In the summer of 2007, an odorous tap water crisis

forces of water resources augmenting and water pollution control play more important roles than economic profit during wastewater reuse expanding in Beijing. It is in agreement with our survey that the Beijing Jingcheng reclaimed water co., Ltd., being responsible for reclaimed wastewater supply in Beijing central region, sold approximate 500 MCM of reclaimed wastewater but lost more than 30 MRY in 2007. For the obtained control strategy of wastewater reuse allocation in different sectors, more than 86.83% of reclaimed wastewater was allocated to municipal, domestic, and recreative use. Only 117.91 MCM of reclaimed wastewater was allocated to agricultural irrigation, which is much lower than the current utilization (284.95 MCM) and Yang and co-workers’ calculated result (445.4 MCM).7 The reasonableness of the result could be explained by the fact that farmers downstream use the water 1098

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Figure 4. (a) Wastewater reuse scales and allocations of China reported in this study and Water Management Report (WMR) of Ministry of Water Resources (MWR). # means the lack of data in WMR of MWR. (b) Regional wastewater reuse ratio reported in this study, Water Management Report (WMR) of Ministry of Water Resources (MWR) and a previous study.6 1: Anhui, 2: Beijing, 3: Chongqing, 4: Fujian, 5: Gansu, 6: Guangdong, 7: Guangxi, 8: Guizhou, 9: Hainan, 10: Hebei, 11: Heilongjiang, 12: Henan, 13: Hubei, 14: Hunan, 15: Jiangsu, 16: Jiangxi, 17: Jilin, 18: Liaoning, 19: Neimenggu, 20: Ningxia, 21: Qinghai, 22: Shandong, 23: Shanghai, 24: Shaanxi, 25: Shanxi, 26: Sichuan, 27: Tianjin, 28: Xinjiang, 29: Tibet, 30: Yunnan, 31: Zhejiang.

which affected two million residents for several days occurred in Wuxi city of Jiangsu province.37,38 The crisis impelled the upgrading and reconstruction of wastewater treatment plants (WWTPs) in Taihu lake basin. Since 2008, advanced wastewater treatment and wastewater reclamation have been expanding in Jiangsu province.39 Currently, the volume of reused wastewater is 176.32 MCM, accounting for 0.32% of regional water supply. The wastewater reuse ratio is 5%, much lower than the goal (15%) of national wastewater reuse plan in the Twelfth Five-Year Plan. Therefore, there is a great market potential for wastewater reclamation and reuse in Jiangsu province. Figure 3a and Table S4 present the Pareto optimal solutions for wastewater reuse in Jiangsu province. The maximization of pollutants reduction is considered as the external set of criteria since Jiangsu is a typical coastal region suffering from qualityrelated water scarcity. Therefore, the solution with maximization of BOD5 reduction (12.82 kilotons) is selected as the control strategy. The corresponding wastewater reuse

Figure 5. Spatial distributions of (a) wastewater reuse scales (million cubic meters, MCM), (b) BOD5 reductions (tons), and (c) economic profits (million RMB Yuan, MRY) in China.

volume supply and economic profit are 1281.77 MCM and 715.31 MRB, respectively. 1099

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of the lack of data in the WMR of MWR (2011). According to our survey, most of the on-site wastewater facilities in residential areas in China are facing closure due to the high processing costs, uncompetitive water price with tap water, and the unguaranteed water quality. Figure 4b compares the wastewater reuse ratio reported in this study, WMR of MWR (2011), and a previous research by Chu et al. who calculated wastewater reuse potential of China through a LP model under physical and economic constraints.6 The wastewater reuse ratio calculated in this study is up to 35.06%, 3.89, and 5.54 times of those in WMR of MWR (2011) and Chu and co-workers’ study.6 Higher wastewater reuse ratio in WMR than that in Chu and co-workers’ study6 indicates that the main driving forces of wastewater reuse expanding in China are not economic profits but water resources augmenting and water pollution control. Among the 31 investigated provinces, Beijing,2 Xinjiang,27 Chongqing,3 and Hebei10 can achieve reuse volumes of more than 50% of regional wastewater produced (i.e., 82.28%, 79.04%, 63.21%, and 56.34%). Beijing has the highest wastewater reuse ratio due to its severe water shortage situation, low reclaimed wastewater prices, and high tap water prices. Although the production cost of reclaimed water is higher than that of tap water in Beijing city, the price at which it retails is much lower (e.g., 1.00 RMB Yuan per cubic meters versus 4.44 RMB Yuan per cubic meters for industrial use). Shandong,22 Guangdong,16 Jiangsu,15 and Hebei 10 have the potential wastewater reuse of more than 1000 MCM, accounting for 53.01% of the national potential reuse volumes. Shandong 22 and Guangdong 16 have the largest quantities of potential wastewater reuse, i.e. 2444.07 and 2174.52 MCM. This is because of the relatively large supplies and demands of reuse potential driving by large population. Figure 5 illustrates the spatial distributions of wastewater reuse scales, BOD5 reductions, and economic profits. Major reuse quantities and BOD5 reductions are found to be concentrated in the east of China. There is a decrease from the east to the west, in accordance with the reducing trend of GDP per capita and the increasing trend of water resource per capita. Guangdong province has the largest economic profit (i.e., 2182.05 MRY) mainly due to its large wastewater reuse volume. However, Shandong province, with the largest wastewater reuse volume, has the smallest economic profit (i.e., −1079.16 MRY) due to its high ratio of capital and O&M costs and reclaimed wastewater price (i.e., 1.37), which is 2.45 times the national average. It is not surprising for its loss since Shandong province pays more attention to establishing wastewater reuse market through reducing reclaimed wastewater prices, increasing reclaimed wastewater quality, and improving pipe networks of reclaimed wastewater. All these measures could increase the capital cost of wastewater reclamation and reuse (as shown in eqs 1 and 2).

Figure 3b compares the wastewater reuse scales and allocations of Jiangsu province calculated in this study and WMR of MWR (2011). It is found that almost 99% of reclaimed wastewater is allocated to industrial reuse (i.e., circulating cooling water and ash rinsing water in thermal power plants) in this study. From the perspective of water quality security, it may be a reasonable allocation. In Jiangsu province, especially in the southern region, a large amount of industrial effluents are discharged into urban WWTPs due to the large-scale township and village enterprises (i.e., Sunan model).40,41 Reusable wastewater should be free of any toxic pollutants which escape from conventional wastewater treatment. Unfortunately, in most countries, including China, the only standard for determining organic pollution in reclaimed wastewater are the chemical oxygen demand (COD) and BOD. Although the treated wastewater could meet the standards of wastewater reuses, it still contains some micropollutants, such as emerging contaminants, which would potentially threaten reclaimed wastewater utility customers, especially for the municipal, domestic, and recreative users.42,43 Such a reclaimed wastewater allocation with high proportion of industrial reuse is in agreement with the principles of sustainable water resources management. Wastewater Reuse in China. According to the water scarcity standard reported by World Development Report, 25 out of 31 investigated provinces have insufficient water supplies (i.e., less than 3000 m3 per capita water resources per year), and 11 are experiencing severe water shortages (i.e., less than 1000 m3 per capita water resources per year).44 For the regions suffering from quantity-related water scarcity, available water resources augmentation (i.e., maximum of wastewater reuse) should be considered preferentially, for the regions suffering from quality-related water scarcity, water pollution control (i.e., maximum of pollutants reduction) should be the primary purpose of wastewater reuse, while for the other regions, the maximization of economic profits from wastewater reclamation and reuse should be focused on. The details of regional water resources status and external sets of criteria for wastewater reuse of the 31 provinces are shown in Table S5. According to the multiobjective evolutionary optimization model, the Pareto solutions of wastewater reuse for 31 provinces of China are obtained (data not shown). According to the external sets of criteria, the control strategies of wastewater reuse scales and allocations are selected and shown in Table S6. On the national scale, the control strategies of wastewater reuse scale, BOD5 reduction, and economic profit are 15.39 billion cubic meters, 176.31 kilotons, and 9.68 billion RMB Yuan, respectively. The corresponding reductions of ammonia nitrogen, total nitrogen, and total phosphorus are 142.92, 9.26, and 6.95 kilotons, respectively. Moreover, it can be found that for the regions suffering from quantity-related water scarcity, reclaimed wastewater should be intensively used in municipal, domestic, and recreative sectors; while for the regions suffering from quality-related water scarcity, reclaimed wastewater should be focused on industrial users. Figure 4a compares the wastewater reuse allocations of China reported in this study and WMR of MWR (2011). It is found that the current volumes of reclaimed wastewater for municipal uses and landscaping have been up to 68.31% and 88.25% of the control strategy, respectively, while for agricultural irrigation and industry, only 23.25% and 14.89%. The analysis for reclaimed wastewater from in-house gray wastewater and onsite wastewater facilities for domestic use is not shown because

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ASSOCIATED CONTENT

S Supporting Information *

Two figures and six tables are provided to present detailed information on Pareto front obtained by NSGA II using the two-objective problems study for wastewater reuse in Beijing, wastewater reuse allocations of Beijing obtained by NSGA II using the three-objective and two-objective problems studies, summary of parameters from statistical reports and previous studies, survey data of 54 reclaimed wastewater plants in 33 cities, Pareto fronts obtained by NSGA II using the threeobjective problems study for wastewater reuse in Beijing city 1100

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and Jiangsu province, spatial distributions of regional water resources and external set of criteria and the control strategies of wastewater reuse scales, allocations, and pollutants reduction for 31 provinces. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Authors

*Phone: 86-25-83786251. Fax: 86-25-83786090. E-mail: [email protected] (C.W.). *Phone: 86-25-83786251. Fax: 86-25-83786090. E-mail: [email protected] (Y.L.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The study was financially supported by the National Natural Science Foundation of China (No. 51322901), the research fund provided by the National Basic Research Program of China (‘973’ program, No. 2010CB429006), Research Fund for innovation team of Ministry of Education (IRT13061), and the Fundamental Research Funds for the Central Universities 536 (2013B5314).

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NOTATIONS

Ac number of car, million Ag area of public green lawn, million m2 Av edible vegetable area, 1000 ha Ar area of road, million m2 b1 percentage of domestic wastewater to wastewater treatment plants, % b2 percentage of industrial wastewater to wastewater treatment plants, % Ce generating capacity of thermal power plants, billion kWh D1 reclaimed water demands for agricultural irrigation, million m3 D2 reclaimed water demands for industry, million m3 D3+4 reclaimed water demands for municipal and on-site uses, million m3 D5 reclaimed water demands for domestic use, million m3 D6 reclaimed water demands for recreation, million m3 Ec water requirement per car per wash, m3 Ee water consumption of unit generating capacity of thermal power plants, m3/kWh Eg lawn water use standard, m3/(d·m2) Er road cleaning water use standard, m3/(d·m2) Ev vegetable unit area irrigation requirement, m3/ha Kc times of car washing pear year Ke ratio of circulating cooling water and ash rinsing water to total water withdrawal of thermal power plants, % Kg ratio of irrigable area to lawn, % Kr times of road cleaning pear year k1 proportion of toilet water use to domestic water use, % L1 life spans of wastewater reclamation facilities, year L2 life spans of wastewater reclamation pipelines, year PA reclaimed wastewater supply prices for agricultural irrigation, RMB Yuan/m3 PD reclaimed wastewater supply prices for domestic uses, RMB Yuan/m3 PI reclaimed wastewater supply prices for industrial uses, RMB Yuan/m3

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PM reclaimed wastewater supply prices for municipal uses, RMB Yuan/m3 PR reclaimed wastewater supply prices for recreation, RMB Yuan/m3 PW wastewater rate, RMB Yuan/m3 Pdj pollutants concentrations in secondary effluent Psj pollutants concentrations in national water quality standards of reclaimed wastewater Q1 centralized reclaimed wastewater for agricultural irrigation, million m3 Q2 centralized reclaimed wastewater for industry, million m3 Q3 centralized reclaimed wastewater for municipal uses, million m3 Q4 decentralized reclaimed wastewater for municipal uses, million m3 Q5 decentralized reclaimed wastewater for domestic uses, million m3 Q6 centralized reclaimed wastewater for recreation, million m3 R1 residue ratios of wastewater reclamation facilities, % R2 replacement ratios of wastewater reclamation facilities, % Ra ratio of unit total cost of wastewater reclamation facilities, % Rw water demand for recreation, million m3 S1 wastewater for reuse from wastewater treatment plants S2 wastewater for reuse from in-house gray wastewater and on-site wastewater TCj total costs of wastewater reclamation treatments for different sectors, million RMB Yuan Tg urban lawn irrigation days per year, day UCCj capital cost of wastewater reclamation treatments for different sectors, RMB Yuan/m3 UIj unit capital investment of wastewater reclamation treatments for different sectors, RMB Yuan·day/m3 UOCj O&M cost of wastewater reclamation treatments for different sectors, RMB Yuan/m3 UTCj unit total cost of wastewater reclamation treatments for different sectors, RMB Yuan/m3 Va agricultural water demand, million m3 Vd domestic water demand, million m3 Wd quantity of domestic wastewater discharge, million m3 Wi quantity of industrial wastewater discharge, million m3

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