A Tale of Two Water Supplies in China: Finding Practical Solutions to

Article Cite This: Acc. Chem. Res. XXXX, XXX, XXX−XXX

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A Tale of Two Water Supplies in China: Finding Practical Solutions to Urban and Rural Water Supply Problems Published as part of the Accounts of Chemical Research special issue “Water for Two Worlds: Urban and Rural Communities”. Er Bei,†,# Xiaomei Wu,‡,# Yu Qiu,† Chao Chen,*,†,§ and Xiaojian Zhang†,§

Acc. Chem. Res. Downloaded from pubs.acs.org by EAST CAROLINA UNIV on 03/14/19. For personal use only.

†

State Key Joint Laboratory of Environmental Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing, China 100084 ‡ China Institute of Water Resources and Hydropower Research, Beijing, China 100038 § Research Institute for Environmental Innovation (Suzhou), Tsinghua, Suzhou, China 215163 S Supporting Information *

CONSPECTUS: Access to safe drinking water is among the 17 United Nations sustainable development goals. As the largest developing country, China has confronted large challenges to providing safe and sufficient drinking water to its population of 1.4 billion under the conditions of limited water sources and ubiquitous water contamination. This Account outlines these challenges as well as the practical solutions implemented by Chinese water professionals. We first provide a general introduction of the water supply in China. Next, we describe the main challenges of water source shortages and source water contamination. The practical solutions developed by Chinese water professionals are the core part of this Account, to which we have devoted ourselves to and contributed in some issues and cases. The water supply in China is a binary system that reflects the gap between urban and rural communities. Both urban and rural water supplies have been subject to water source shortages and contamination. Water shortages are mainly solved by longdistance water transportation projects. Urban water utilities generally pay attention to organic matter, ammonia, algae, and chemical spills in source water while also focusing on micro-organisms and disinfection byproducts in tap water. Microorganisms are a widespread concern for rural water supplies, whereas arsenic, fluoride, and ammonia are an endemic concern in some rural communities. Investment in updating of treatment processes significantly benefits urban water supplies, and advanced treatment of ozonation and biologically activated carbon processes are now commonly used to ensure that strict drinking water quality standards are met. However, this is not the case for rural water supplies, where expensive advanced treatment is not affordable. Thus, improving rural water supplies requires approaches such as searching for sources with better water quality, using automated ultrafiltration instruments, or connecting to urban water supply distribution systems. For rural areas with high concentrations of arsenic or fluoride in source water, specific adsorbents are a practical way to help farmers. Similar challenges will be encountered elsewhere in the world; therefore, the practical solutions applied in China will be useful to other countries in different stages of development.

1. BINARY SYSTEM OF WATER SUPPLY IN URBAN AND RURAL CHINA Water supplies for urban and rural communities in China comprise a binary system that reflects the gap between these areas. Urban areas have denser populations and more investment, businesses, industry, and other resources, whereas rural areas mainly rely on agriculture, and the population has been declining continuously. Urban water supplies are overseen by the Ministry of Housing and Urban-Rural Construction (MHURC) and its branches, whereas rural water supplies are supervised by the Ministry of Water Resources (MWR) and its branches. The Ministry of Ecology © XXXX American Chemical Society

and Environment (MEE) and its branches are responsible for water source protection. The National Health Committee (NHC) routinely inspects the water quality of urban and rural water utilities in terms of the Drinking Water Quality Standard of China.1 In 2010, the urban water supply had a capacity of 387 million m3/day, a consumer base of 630 million people, and a total volume of 71.4 billion m3/year2; and these three numbers have been increasing steadily as a result of economic Received: November 28, 2018

A

DOI: 10.1021/acs.accounts.8b00605 Acc. Chem. Res. XXXX, XXX, XXX−XXX

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Accounts of Chemical Research

Figure 1. Word cloud analysis of keywords regarding China’s drinking water quality. The keywords of 2846 related studies were searched using www.webofknowledge.com/, and the results were submitted to https://www.jasondavies.com/wordcloud/ to create the word cloud analysis. The water quality issues are underlined. More details are provided in the Supporting Information.

For example, the second longest river in China, the lower reaches of Yellow River, dried up every year in Shandong Province from 1990 to 2000. To address this shortfall, expensive, long-distance water transport projects had to be conducted. The water shortage situation in rural China is similar to that in urban areas. Farmers in North, Northwest, and some karst areas of Southwest China have experienced severe water shortages because of limited water resources and climate change.3

development and urbanization. There are over 1000 urban water companies in China that focus on local water supply with capacities that vary greatly from several thousand m3/day in small cities to several million m3/day in large metropolitan areas. Recently, there has been a tendency for China’s water companies to merge and provide more reliable water supplies. According to the 2017 China Water Statistical Yearbook,3 there are 1.02 million rural water supply facilities in China, providing 82.16 billion m3 of water to 929 million people. This includes domestic and livestock water consumption in rural areas as well as consumption by some residents in towns. Thus, there is some overlap in the capacities and populations reported for urban and rural water supplies. At the end of 2015, over 82% of rural residents were served by a centralized water supply and 76% had access to tap water in their homes.

2.2. Source Water Quality Deterioration

2.2.1. General Situation. Source water protection is essential to a safe water supply. According to the 2017 Report of the State of the Ecology and Environment in China,4 9.5% of water sources for 338 prefecture-level cities did not meet the water quality standards at least once during monthly inspections. The water sources of approximately 330 nonprefecture-level cities and 2000 counties are monitored locally, and reports are not routinely provided, which is also true for numerous smaller water sources in rural areas. The MEE of China executed a large campaign to improve the safety of 1586 urban water sources in 2018 by eliminating 99.9% of a total of 6251 problems or threats.6 This campaign will be extended to rural water sources in the next few years. The main water quality issues investigated by Chinese scholars are shown in Figure 1 and discussed in the following sections. 2.2.2. Water Quality Deterioration in Urban Areas. 2.2.2.1. Organic Matter and Ammonia Nitrogen. Organic matter and ammonia, which are the most ubiquitous contaminants in source water around China because of domestic, industrial, and agricultural pollution are regulated in the Environmental Quality Standards for Surface Water.7 The Hai, Huai, and Liao Rivers are the most contaminated rivers in China.4 The organic matter present in water sources significantly affects many aspects of the water supply system, including performance of conventional processes in WTPs (i.e., coagulation, sedimentation, filtration, and disinfection)

2. WATER SUPPLY CHALLENGES IN CHINA The water supply challenges in China have two main facets: water quantity shortages and water quality contamination. However, the challenges are different for urban and for rural communities. 2.1. Source Water Shortage

China has limited per capita water resources or availability of 2240 m3, which is only a quarter of the global average.3 Moreover, the population and water resources are unevenly distributed.4 The catchments of the Yellow River, the Hai River, the Liao River, and the Huai River experience the most severe water shortages per capita. Water contamination is endemic throughout China because of weak environmental protection from 1980−2010, exacerbating the water shortage problems.4,5 Urban water shortages are more obvious in North and Northwest China,3 where the water supply used to rely on groundwater. With rapid urbanization and industrialization, increasing numbers of cities have had to find new water sources from rivers and lakes and have had to build reservoirs to store sufficient water. However, even the local surface water sources have been unable to meet the demands of these cities. B

DOI: 10.1021/acs.accounts.8b00605 Acc. Chem. Res. XXXX, XXX, XXX−XXX

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and dental fluorosis because of drinking fluoride-rich water or inhaling fluoride. 2.2.3.2. Iron and Manganese. High concentrations of iron (1−20 mg/L) and manganese (0.5−4 mg/L) are commonly detected in groundwater in Northeast China because of geological conditions.13 These metals bring strong color problems to consumers rather than health risks. These metals are present as reductive cations in groundwater and can be effectively removed by aeration, treatment with strong oxidants, or biological treatment.13 2.2.3.3. Ammonia Nitrogen and Nitrate. High concentrations of ammonia and nitrate are commonly detected in wells in rural areas.13 The sources of inorganic nitrogen include fertilizers and domestic wastewater. Some farmers have constructed pigsties or seepage pits to treat domestic wastewater, too close to their household wells, which greatly increases the concentrations of ammonia, nitrite, and nitrate in their drinking water supplies.

and biostability in networks. Natural organic matter is known to be a strong precursor of carbonaceous disinfection byproducts (DBPs), such as trihalomethanes (THMs) and haloacetic acids (HAAs). The presence of ammonia greatly impairs disinfection of bacteria by free chlorine and favors the formation of nitrosamines and iodinated DBPs. 2.2.2.2. Algae-Related Issues. Eutrophication in lakes and reservoirs has increased because of human impacts and climate change. Algal blooms create problems for WTPs, such as microcystins from cyanobacteria and odor from anabaena. Lakes Taihu, Chaohu, and Dianchi have the highest levels of eutrophication in China.4 The algal bloom problems in Lake Taihu reached a peak in the early summer of 2007, when the massive die-off and decay of an algae mat caused serious deterioration of source water quality and created tap water odor problems for Wuxi City for approximately 1 week.8 The team led by the last author guided the emergency water treatment during this incident. Several volatile sulfide chemicals, including methyl mercaptan, dimethyl sulfide, dimethyl disulfide, and dimethyl trisulfide, were identified as the dominant odorants in the lake and tap water.9 2.2.2.3. Taste and Odor. Taste and odor are among the few items that can be easily detected and are thus subject to complaints by consumers. Musty odorants, such as geosmin and 2-methylisobornoeal, mainly originate from certain algae and actinomyces. Septic odor incidents are caused by volatile sulfide chemicals during the decay of algae and wastewater.8,10 Taste problems are more prevalent in North and Northwest China, where high hardness gives the water a bitter taste. 2.2.2.4. Chemical Spills. Chemical spills occurred frequently during 2000−2015 in China when hundreds of spills occurred annually.4 Some accidents caused the source water quality to deteriorate drastically. The treatment of this water then exceeded the capacity of local WTPs, making water undrinkable for millions of consumers. The factors responsible for the frequent water contamination incidents included the excessive pursuit of economic development at the cost of safe production, unreasonable selection of plant locations, very limited investment in safety and environmental protection, and lenient environmental protection policies and administration.11 These accidents and the Wuxi water crisis caused the government to adjust the economic development mode from industry-oriented to a more sustainable approach. The central government and MEE recently strengthened their measures for protecting water sources and preventing contamination accidents,4 which has led to great improvement and a significant decrease in the frequency of chemical spills. 2.2.3. Water Quality Deterioration in Rural Area. In general, rural water supplies are contaminated more frequently and severely than urban supplies. In addition to the contaminants that impact urban water supplies, the following contaminants are extra concerns for rural water supplies. 2.2.3.1. Arsenic and Fluoride. Ground water rich in arsenic is mainly found in the semiarid areas of North and Northwest China, whereas that rich in fluoride is mainly found in North and Northeast China. Some farmers in Shanxi, Inner Mongolia, Xinjiang, and Ningxia provinces have suffered endemic arseniasis from drinking arsenic-rich water. Scientists from Switzerland and China constructed a geostatistical model and estimated that approximately 19 million people in China are exposed to arsenic levels above 10 μg/L in water.12 Some farmers in Shanxi, Inner Mongolia, Hebei, and Liaoning provinces suffer from an endemic of osteofluorosis

2.3. Tap Water Quality Problems

2.3.1. Tap Water Quality Problems in Urban Water Supplies. 2.3.1.1. Microbial Aspects. Disinfection is essential for drinking water safety but is not easily maintained in the distribution system. Free chlorine and chlorine dioxide are the main disinfectants applied in China. Some metropolitan areas, such as Beijing, Tianjin, Shanghai, and Guangzhou, utilize chloramination to maintain sufficient residual disinfectant levels in their distribution systems. Many WTPs recently changed from using liquid chlorine to stock or to on-siteproduced sodium hypochlorite, for security reasons. Ozone is mainly used as an oxidant to improve organic removal instead of as a disinfectant. The application of ultraviolet light is still quite limited in China, because the occurrence of giardia and cryptosporidium is rare. Moreover, some small utilities have not added sufficient levels of disinfectant in an attempt to improve water odor and to reduce costs. However, this practice decreases biostability and results in bacteria regrowth in networks, which greatly reduces drinking water safety and puts the public at risk.14 These issues appear to make government agencies and water companies in China not confident to encourage people to drink tap water directly. 2.3.1.2. Chemical Aspects. DBPs are among the main chemicals of concern for China’s water industry15 However, there are no open official reports regarding DBP occurrence in China. Generally, THMs, HAAs, and chloral hydrate are the regulated DBPs of most concern to the WTPs applying chlorination, whereas chlorite and chlorate are of greatest concern to WTPs applying chlorine dioxide. Over 10 cities in North China and along the coast have reported having a total THM value that exceeds the standard.15 High concentrations of organic matter and bromide caused by industrial discharge and seawater intrusion are responsible for this situation. The occurrence of HAA is much less common than that of THM. Indeed, Meng et al.16 conducted an HAA survey of 34 cities and found no treated water containing HAAs at levels that exceed the designated limits. Emerging DBPs, including nitrosamines, haloacetonamides, haloacetonitriles, halonitromethanes, and iodinated DBPs in water are currently receiving significant attention in China. Nitrosamines are of high concern in proposed regulations.15 Shanghai issued the first local standards for drinking water quality in June 2018, in which the nitrosodimethylamine (NDMA) limit was set at 100 ng/L based on the World Health C

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Accounts of Chemical Research Organization (WHO) guidelines.17 Before that, a comprehensive NDMA survey in China18 raised concerns for the central government and the public. The survey showed that NDMA was detected 3.6 times more often in China than in the United States. Additionally, the proportions of tap water samples with NDMA concentrations over 10 ng/L (the California notification level), 40 ng/L (the Canadian national guidelines), and 100 ng/L (WHO guidelines) were found to be about 28.4, 9.5, and 2.7% respectively. Toxicity assays are always expected to be capable of evaluating the drinking water safety comprehensively. Several toxicity assays, including the Ames test, SOS/umu test, comet test, and micronuclei test, have been evaluated in China.19,20 However, none have been found to be suitable for inclusion in the drinking water standards of China, the United States, or the WHO. Nevertheless, most of these toxicity assays confirmed that advanced treatment processes can reduce the toxicity of drinking water. 2.3.1.3. Aesthetic Aspects. In addition to the taste and odor issues discussed in Section 2.2.2.3, water discoloration also occurs frequently in China. This is mainly caused by iron released from pipe scale, especially in cities utilizing new water sources acquired via long-distance water transportation. If the new source water contains higher concentrations of sulfate and/or chloride, then these corrosive chemicals will dissolve or break the scale in networks and release iron. Cities such as Beijing21 and Tianjin14 have experienced water discoloration problems because of this phenomenon. 2.3.2. Tap Water Quality Problems in Rural Areas. Except for source water contamination, the main tap water quality issues are the presence of micro-organisms because of a lack of disinfection or incorrect disinfection operations. Over 28% of rural water supply projects have no proper water purification facilities, and over 18% of the small central water supply facilities in rural areas do not have disinfection equipment.1,5 To save costs and because of a lack of skilled operators, many rural water supply facilities do not use disinfectants. Fortunately, in China, people prefer to drink boiled water, which greatly reduces the risk of diarrhea and other gastrointestinal illnesses.

have desalination facilities to supply water to industry. However, the introduction of desalinated seawater to the original distribution system will cause chemical stability problems,22 limiting large-scale application. Many cities have encouraged water reuse to save fresh water, especially for industrial and landscape water consumption. Water reuse has a lower impact on ecology than water transportation but greater water quality concerns. Although direct or indirect potable water reuse has not yet been applied in China, it is under investigation. 3.1.2. Advanced Treatments To Address Source Water Deterioration. 3.1.2.1. Process Choice. Conventional processes in WTPs cannot treat micropolluted water that is rich in organic matter to meet the standard. Enhanced coagulation has been recommended as the best available technology to address natural organic matter in the United States. However, it does not work well in China, because artificial organic matter, which behaves differently from natural organic matter during coagulation, is dominant. In China, advanced treatment with ozonation (O3) and granular or biologically activated carbon (GAC/BAC) filters has been proposed as the best available technology to remove organic matter, because they have lower DBP yields and improved biostability.23 Ultrafiltration is good for removing fine particles and pathogens but not for soluble organic matter and ammonia. Nanofiltration can remove some organic matter and monovalent cations, which makes it a promising treatment process. Pretreatment using powdered activated carbon adsorption and oxidation (including chlorine, permanganate potassium, and ozone) has been applied widely to improve the performance of conventional and advanced treatment processes. Cost is an important influencing factor when selecting the treatment process. The addition of advanced treatment on the basis of conventional processes will increase construction costs by approximately 300 RMB/m3/day and operating costs by 0.2−0.3 RMB/m.3,23 Nevertheless, many cities have updated their WTPs to advanced treatment processes because of increased demand associated with economic development, and the total capacity of advanced treatment in China is currently about 40 million m3/day (Table. 1). 3.1.2.2. Organic Matter Removal and DBP Control. On the basis of the results of our pilot and field studies, we analyzed the performance of each process for removing organic matter (Table 2). The results revealed that a combination of conventional and O3−BAC processes enables integrated removal of several organic materials, including bulk organic matter, DBPs, and biostability issues.23−29 DBP control is achieved by removing their precursors as much as possible before disinfection and/or by optimizing the traditional free chlorination process. GAC was not shown separately in Table 2, because its adsorption capacity is depleted quickly (within several months). WTPs in China prefer to apply BAC processes for several years without frequent regeneration to save costs. Thus, the mechanism for removing DBP precursors by BAC is actually a combination of declining physical adsorption and stable biological treatment.24 Alternative disinfection methods require careful evaluation, because each method has its own disadvantages or side effects, including the creation of other specific DBPs as well as biostability and chemical stability issues. We developed a sequential chlorination process with short-term free chlorina-

3. STRATEGIES TO ADDRESS WATER SHORTAGES AND CONTAMINATION The strategies needed to address urban and rural water challenges must consider source water quality, effluent quality standards, and costs. 3.1. Urban Water Supply

3.1.1. Measures To Solve Water Shortages. 3.1.1.1. Transportation. China has invested heavily in over 100 long-distance projects to transport water to the arid north and northwest areas by canals or pipes.3 The largest project is the South-to-North Water Diversion project. The project’s middle line has the capacity to supply 9.5 billion m3 of water annually from the Dan-jiang-kou Reservoir in Central China to Henan, Hebei, Beijing, and Tianjin in North China over 1400 km away. The project’s east line supplies 1.56 billion m3 of water annually from the main stem of the Yangtze River in Jiangsu Province to the drought-afflicted Shandong and Tianjin approximately 1200 km away. 3.1.1.2. Nontraditional Water Sources. Desalination and water reuse are alternative solutions for supplying water to coastal cities. Cities such as Tianjin, Qingdao, and Tangshan D

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E

23 −37 ± 3% −152 ± 25% 55 ± 21% −65 ± 42%

25 >99.9%

38 ± 20% biostability

micro-organism

TBC < 100 CFU/mL TCC = 0 CFU/100 mL AOC < 100 μg/L

bacteria, virus

10 ± 3%

30 ± 39%

/

0 16% −5% / /

sulfonamide quinolones tetracycline bacteria, virus

11% −6% 5% /

5% 33% 4% /

14% 21% 36% /

49% −2% 31% /

>99.9%

29

24,26−28

>50% decrease vs NH2Cl / less NA yield

antibiotic

Table 2. Performance of Various Treatment Processes

tion and subsequent chloramination.25 Besides effectively inactivating micro-organisms, this method could also reduce THM and HAA yields or nitrosamine yield when compared with free chlorination26 or chloramination.27 3.1.3. Water Quality Stability in Distribution Systems. 3.1.3.1. Biostability. Measures to decrease bacterial regrowth in distribution systems include: (1) maintaining sufficiently high residual disinfectant levels in pipes to inactivate bacteria if DBPs are not a big concern and (2) lowering the available nutrients in WTPs, such as assimilable organic carbon (AOC), as much as possible to starve the bacteria. However, even with advanced treatment, reducing nutrients is difficult because of the high cost of decreasing AOC from approximately 200 μg/L in polluted source water14 to 10−50 μg/L30 in biostable effluent. A more practical way to limit bacteria regrowth is to apply the two measures simultaneously. A previous study revealed that heterotrophic plate count values agreed well with residual chloramine values (r = −0.59, P < 0.001, 0.05−1.0 mg/L) and with AOC (r = 0.39, P = 0.002, 50−200 μg/L) in a large network in North China.31 These relationships suggest that water companies should decrease AOC concentrations to 100 μg/L by simultaneously applying advanced treatment and maintaining residual chloramine concentration at over 0.3 mg/ L in pipes. This is more practical and achievable in China’s water industry. 3.1.3.2. Chemical Stability. In China, chemical stability problems present mainly as yellow water issues caused by release of iron from scale. Beijing suffered a large yellow water incident in 2008 because of the introduction of high-sulfateconcentration source water from some reservoirs in Hebei Province.21 The mechanism was identified as the accelerated breakdown of scale by high concentrations of corrosive anions,

85 ± 5%

39 890

42 ± 8%

173

total

5 ± 18%

0

15 ± 9%

0

12 ± 3%

/

multiple

Northwest

NAFP

300

46 ± 17% 30 ± 12% >50% decrease vs Cl2 >50% decrease vs Cl2

1

27 ± 22% 15 ± 11% higher THM yield higher HAA yield

Yunnan

10% 12% 24% 17%

Southwest China

± ± ± ±

3000

12 20 41 55

7

6 ± 9% 2 ± 4% −29 ± 67% −16 ± 44%

Guangdong

25 ± 10% 13 ± 5% 7 ± 49% 19 ± 25%

South China

7 ± 5% 6 ± 11% −9 ± 37% 21 ± 10%

1000 1400

9% 5% 16% 2%

3 5

± ± ± ±

Henan Hunan

6 2 36 9

Central China

/ / multiple multiple

4600 15 000 5000 80 1600