Reclaimed water is also called reclaimed water

Reclaimed water refers to water that has been properly treated to reach certain water quality indicators, meet certain usage requirements, and can be used beneficially. Compared with seawater desalination and cross-basin water transfer, reclaimed water has obvious advantages. From an economic point of view, the cost of reclaimed water is the lowest. From an environmental point of view, sewage recycling can help improve the ecological environment and achieve a virtuous cycle of water ecology.

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Reclaimed water is also water treated by sewage treatment plants that meets the standards. It is generally a secondary treatment and is not affected by climate and is not used in conjunction with recycled water in Beijing

< p> It has the advantages of competing for water in nearby areas, being available locally, being stable and reliable, and having a high guarantee rate. Reclaimed water is the so-called "reclaimed water", which follows the Japanese name. Usually people call tap water "upper water" and sewage "sewage". The quality of recycled water is between upper water and sewage, so it is called "center water". "Water". Although recycled water is not drinkable, it can be used in some situations where water quality is not high, such as flushing toilets, flushing cars, spraying roads, greening, etc. Reclaimed water engineering technology can be considered as a miscellaneous water supply technology between the building's domestic water supply system and the drainage system. The water quality index of recycled water is lower than the drinking water quality index of urban water supply, but higher than the discharge standard of polluted water allowed to be discharged into surface water bodies. Reclaimed water is the city’s second source of water. Urban sewage recycling is one of the effective ways to improve the comprehensive utilization rate of water resources and reduce water pollution. The rational reuse of reclaimed water can not only reduce water environment pollution, but also alleviate the contradiction of water shortage. It is an important measure to implement sustainable development. The recycling and resource utilization of sewage has considerable social, environmental and economic benefits, and has become a must-have for countries around the world in solving water problems.

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Advantages of sewage recycling

Reclaimed water, also called recycled water, has a quality between sewage and tap water It is non-drinking water that can be used within a certain range after urban sewage and wastewater have been purified and treated to meet national standards. It can be used in many aspects of urban landscape and people's lives. In order to solve the problem of water shortage, urban sewage recycling has become increasingly important. Urban sewage recycling has advantages compared with the development of other water sources. First of all, urban sewage is huge, stable, not restricted by climate conditions and other natural conditions, and can be recycled. Wastewater is used as recycled water. The source of recycled water and the generation of sewage can basically occur simultaneously. That is to say, as long as urban sewage is generated, there is a reliable source of recycled water. At the same time, the sewage treatment plant is the source of recycled water, which is relatively close to urban recycled water users and provides convenient water supply. The scale of wastewater recycling is flexible. Large-scale recycled water plants can be built at the edge of the city, or small recycled water plants or integrated treatment equipment can be built in various residential areas and public buildings. The scale can be large or small, depending on local conditions.

Technical feasibility

In terms of technology, there are no technical problems in the use of recycled water in cities. Current water treatment technology can treat sewage to the water quality standards required by people. Urban sewage contains less than 0.1% impurities, and conventional sewage advanced treatment is adopted, such as filter material filtration, microfiltration, nanofiltration, reverse osmosis and other technologies. After pretreatment, the water effluent from the filter material filtration treatment system can meet the water requirements for domestic miscellaneous water, including house flushing, watering green spaces, road washing and general industrial cooling water. The effluent from the microfiltration membrane treatment system can meet the water requirements of landscape water bodies. The effluent quality of the reverse osmosis treatment system is far better than the tap water quality standards. A large number of successful examples of sewage regeneration and reuse projects at home and abroad also illustrate that it is technically feasible for sewage regeneration and reuse to be used in industry, agriculture, municipal miscellaneous uses, river water replenishment, domestic miscellaneous uses, and groundwater recharge. In order to cooperate with China The city carries out urban sewage recycling work. The Ministry of Construction and the National Standardization Administration Committee have compiled the "Code for Quality Acceptance of Urban Sewage Treatment Plant Projects", "Code for Design of Sewage Recycling Project", "Code for Design of Reinforced Water in Construction", and "Code for Urban Sewage Water Quality" A series of standards for sewage recycling and utilization provide technical data for the effective utilization of urban sewage resources and ensuring the quality and safety of sewage treatment.

Economic feasibility

Compared with the development of other water resources, the economic advantages of urban sewage being recycled and treated in separate areas are as follows: (1) Compared with long-distance water diversion Cheap urban sewage recycling is to carry out secondary treatment of sewage, and then use it in an appropriate location as a renewable resource through advanced treatment. Infrastructure investment is far more economical than long-distance water diversion. According to data, if urban sewage is deeply treated to a degree that can be reused as miscellaneous water, infrastructure investment is equivalent to water diversion from 30 kilometers away. To recycle high-demand process water, the investment is equivalent to diverting water from 40 to 60 kilometers away. The middle route of the South-to-North Water Diversion Project transfers more than 10 billion cubic meters of water every year. The investment in the main project exceeds 100 billion yuan, and the investment in the base unit is about 3,500 to 4,000 yuan/t. Therefore, many countries regard urban water utilization as one of the options to solve the water shortage problem and one of the ways to save water, which is very valuable from an economic analysis. In the United States, there are dozens of reclaimed water projects such as 300 Fields, China International Trade Center, and Baoding Lugang Sewage Treatment Plant. Practice has proved that the promotion and application of sewage treatment technology is imperative, and the utilization of reclaimed water as the city's second water source is also an inevitable development trend. (2) It is more economical than seawater desalination. The impurities contained in urban sewage are less than 0.1%, and can be removed by advanced treatment methods. Seawater contains 3.5% dissolved salts and a large amount of organic matter, and its impurity content is 35% of the sewage secondary treatment effluent. More than times, complex pretreatment and expensive treatment technologies such as reverse osmosis or flash evaporation are required. Therefore, regardless of infrastructure costs or unit costs, seawater desalination is higher than recycled water utilization. Internationally, the production cost of seawater desalination is mostly between US$1.1 and US$2.5 per ton, which is equivalent to the price of consumed water. The cost of seawater desalination in China has dropped to about 5 yuan, and it is even more likely to drop to about 3.7 yuan if large-scale facilities are built. Even so, the price is much higher than the reuse price of recycled water, which is less than one yuan. The prospects for achieving technological breakthroughs in the treatment of urban recycled water are still very broad. With the advancement of technology and the continuous innovation of equipment and materials, the safety and reliability of recycled water supply will continue to improve, and the cost of treatment will also decrease. (3) Significant social benefits can be achieved. In today's increasingly scarce water resources, the treated water can be reused for greening, flushing vehicles and flushing toilets, reducing pollutant emissions and thus mitigating the impact on the water environment around the city. , increasing the amount of available recycled water. This change is conducive to protecting the environment, strengthening the self-purification of the water body, and will not have a negative impact on the hydrological environment of the entire region. Its application prospects are broad. Wastewater reuse provides people with a very economical new water source, reducing society's demand for fresh water resources, while also maintaining high-quality drinking water sources. The optimized preparation of this kind of water resources is undoubtedly a project that benefits the country and the people, and achieves Initiatives for sustainable development of water resources. When countries around the world are solving water shortage problems today. Urban sewage has been selected as a reliable and reusable second water source. For many years, urban sewage reuse has been the focus of domestic and foreign research. It has become a strategic countermeasure for many countries around the world to solve water shortages.

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Reclaimed water has a large amount of water, stable water quality, and is not affected by seasons and climate. It is a very precious water resource. There are many ways to use recycled water, which can be divided into direct use and indirect use according to the relationship with users. Direct use can be divided into on-site use and centralized use. Recycled water in most countries is mainly used for farmland irrigation, mainly for indirect use; recycled water in a few countries such as Japan is mainly used for urban non-drinking water, mainly for on-site use; the new trend is to use it for "water landscape" in urban environments. Environmental water. Reclaimed water has many uses and can be used for farmland irrigation, landscaping (parks, campuses, highway green belts, golf courses, cemeteries, green belts and residential areas, etc.), industry (cooling water, boiler water process water), and large building flushing As well as recreation and environment (improving lakes, ponds, marshes, increasing river flow and fish breeding, etc.), as well as municipal miscellaneous uses such as fire protection, air conditioning and water flushing. According to the use of recycled water, recycled water can be reused in five categories: groundwater recharge water, industrial water, agricultural, forestry, and animal husbandry water, urban non-drinking water, and landscape environmental water.

Reclaimed water is reused for groundwater recharge, which can be used to recharge groundwater sources, prevent seawater intrusion, and prevent land subsidence; recycled water is reused in industry and can be used as cooling water, washing water, and boiler water; recycled water is used as recycled water

Water used in agriculture, forestry and animal husbandry can be used as water for irrigation, planting and nursery of food crops and cash crops, irrigation, planting and nursery of trees and ornamental plants, and water for livestock and poultry.

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Current situation

Around the beginning of the 21st century, against the background of China’s increasingly tense water resources, the use of recycled water began to be affected by the Chinese government. of attention. By 2009, China's sewage recycling rate (sewage recycling volume/sewage treatment rate) was about 15%, while the ratio of sewage recycling volume/sewage discharge volume was only about 5%.

Necessity

China is a water-poor country and one of the 13 water-poor countries in the world. Its per capita water resource is 1/4 of the world average. At the same time, China has a vast territory, and the distribution of water resources in time and region is very uneven. There are more in the south and less in the north. In most parts of the north, especially Harbin, the per capita water resources are even lower. The per capita water resources in the Haihe, Huaihe, Liaohe and Yellow River basins are about 1/5 of China's average level. The per capita water resources in the Haihe River basin, including Beijing and Tianjin, are only 1/7 of China's average level. With the acceleration of economic development and urbanization, the problem of urban water shortage is particularly prominent. Currently, a considerable number of cities are experiencing a shortage of recycled water

water resources. The scope of urban water supply continues to expand, and the degree of water shortage is becoming increasingly serious. According to statistics, among 669 cities in China, 400 cities have insufficient water supply all year round. Among them, 110 cities are seriously short of water, with daily water shortages of up to 1,000 yuan and annual water shortages. Due to water shortages, industrial output value is affected by more than 200 billion yuan every year. Tianjin, Large and medium-sized cities such as Changchun, Dalian, Qingdao, Tangshan and Yantai have been seriously threatened by water shortages. According to statistics, the international extreme water shortage level is 500 per capita water resources, while the current per capita water resources in Baoding, Hebei is only 64. Severe water shortage has led to insufficient urban water supply, overexploitation of groundwater, and triggered a series of environmental geological Questions etc. In 2000, a severe drought occurred in the northern region that had not been seen in 100 years, causing many reservoirs and rivers to dry up and dry up like never before. 318 cities at or above the county level in 13 northern provinces were forced to provide water for a limited time, and more than 20 million people were suffering from water shortages. In the 2001 drought, the drought-stricken area in China reached k. While water resources are scarce, China's water resources waste and pollution are very serious. Regarding this situation of coexistence of shortage and waste, traditional thinking believes that water prices should be increased administratively to limit people's water consumption. However, the problem of waste has never been administrative. The price can be solved, because when considering the problem of waste, the utility loss caused by restricting people's behavior itself cannot be ignored. A survey by the Ministry of Construction shows that people will only consider water conservation when water bills account for 2.0% of household income; when it reaches 5%, it will have a greater impact on people's lives; when it reaches 10%, people will Consideration will be given to water reuse. In order to alleviate the contradiction between supply and demand of water resources, sewage reuse within a certain range of use provides us with an economical and reliable new water source, and can save high-quality drinking water sources. With the deepening of reform and opening up, China has entered a new era of economic construction. Although water conservation has been vigorously promoted in recent years, water consumption in various places has increased strongly, exacerbating the seriousness of water resources problems. The impact of water shortages on national economic development has attracted the attention of leaders and experts. It is predicted that the water crisis of this century will rank first among all types of resource crises in the world. Therefore, it is imperative to study the utilization and development of urban water resources, which has far-reaching strategic significance for the healthy circulation of urban water and ensuring sustainable urban development. Therefore, it is very important to realize wastewater resource utilization, alleviate the contradiction between supply and demand of resources, and promote the sustainable development of the national economy.

Usage

Although China began to use sewage irrigation to reuse sewage as early as the 1950s. However, the actual reuse of sewage after deep treatment for urban life and industrial production has only been developed in recent decades. The Ministry of Construction first included the topic of urban sewage reuse in the "Sixth Five-Year Plan" special science and technology plan, respectively in Dalian. and Qingdao for experimental exploration. Research results from these two places show that sewage can be reused through simple and advanced treatment and is a promising water source.

Since 1986, urban sewage reuse has been included in the national key scientific and technological research plans of the “Seventh Five-Year Plan”, “Eighth Five-Year Plan” and “Ninth Five-Year Plan”, and exploration of sewage reuse technology and trials of demonstration projects have begun. The "Seventh Five-Year Plan" research project "Water Pollution Prevention and Urban Sewage Resource Recycling Technology" has conducted systematic research on sewage regeneration processes, reuse technologies for different reuse objects, and technical and economic policies for reuse. The research includes 14 sewage reuse projects to varying degrees or for different objects, including Qingdao Yan'an No. 3 Sewage Plant, which provides a large number of feasible supporting projects for the research on sewage reuse projects during the "Eighth Five-Year Plan" period. The "Eighth Five-Year Plan" research project "Sewage Purification and Resource Technology" has carried out engineering tests based on the large reclaimed water company, Taiyuan, Tianjin, Tai'an and Yanshan Petrochemical. Through a series of productive and practical engineering studies, the "Eighth Five-Year Plan" provides technical specifications and related water quality standards for urban sewage recycling for different purposes such as industrial processes, cooling, chemical industry, petrochemicals, steel industry and municipal landscape. The results provided by the "Eighth Five-Year Plan" have been improved to a practical level compared with the "Seventh Five-Year Plan". The research content has been tested by production and covers most areas of sewage reuse. The "Ninth Five-Year Plan" research project "Integration of Urban Sewage Treatment Technology and Construction of Decision Support System" has two specific parts: one is the research on the integration of reuse technology, and the other is the research on the deep treatment technology of urban sewage underground recirculation. These key research studies have completed a large number of productive tests and obtained rich data. After appraisal and acceptance by national experts, many results have been rated as internationally advanced or internationally leading level. At the "21st Century International Urban Sewage Treatment and Resource Development Strategy Seminar", the Ministry of Construction pointed out at the meeting that "China will comprehensively launch sewage resource projects and extensively strengthen technical cooperation and exchanges with foreign countries in this field. Welcome Financial institutions and enterprises from various countries have invested in China’s urban sewage resource utilization projects,” indicating that China’s urban investment and demand for recycled water utilization will rapidly increase in the next few years.

Planning

In order to alleviate China's water shortage and control water environment pollution, China's recent centralized sewage treatment and reuse plan is shown in Table 1. (1) After sewage treatment, it is reused as industrial water and the secondary treatment effluent of the sewage treatment plant. Depending on the purpose, it can be used directly or after further treatment to achieve higher water quality before being used in industrial processes. Among them, it is the most common and representative The most common use is industrial cooling water. China has conducted a large number of experimental studies on the use of secondary effluent from sewage treatment plants or advanced secondary treatment effluent for industrial cooling, and there are examples of successful operation. The secondary treated effluent from Beijing Gaobeidian Sewage Treatment Plant provides cooling water to Huaneng Thermal Plant, with a supply of 40,000 tons per day. At the same time, the sewage treatment plant also supplies water to industrial enterprises such as Sanhe Thermal Power Plant. Reclaimed water has now become Beijing’s second largest water source. Statistics show that Beijing used 360 million cubic meters of recycled water in 2006, and this year it is expected to reach 480 million cubic meters. Reclaimed water has been widely used in industrial manufacturing, agricultural irrigation, urban greening, river and lake environment and other fields. Of the 480 million cubic meters of recycled water used this year, 60 million cubic meters are used to supplement urban landscape and urban greening water use. Chaoyang Park, Grand View Garden, Taoranting, Wanquan River, South Moat and the Olympic central area are all irrigated with recycled water. At the same time, 20 automatic reclaimed water dispensers have been built in Beijing urban areas, which can provide 20 million cubic meters of renewable water for greening and municipal management every year. (2) Treated sewage is reused as domestic water. Beijing is the most representative example of treating sewage and reusing it as domestic water. In 1984, Beijing carried out the construction of sewage demonstration projects, and in 1987 promulgated the "Implementation Measures for the Management of Reclaimed Water Construction in Beijing". Government research units and newly built living quarters must establish reclaimed water facilities. Based on this, the construction of reclaimed water facilities in Beijing has developed rapidly. So far, more than 160 reclaimed water facilities have been built and put into use in Beijing. Most of these facilities are concentrated in hotels, restaurants and colleges and universities. , they use daily miscellaneous water such as bathing and washing as their water source. After being treated to meet the gray water quality standards, they can be reused for toilet flushing, car washing, greening, etc. At present, the treatment capacity of these reclaimed water facilities has reached 40,000, and the recycled water consumption is about 10,000 tons. Reclaimed water construction has begun to take shape.

In order to realize Beijing's 2008 "Green Olympics" commitment and increase the urban sewage reuse rate to 50%, Beijing will build 9 new reclaimed water plants to increase sewage recycling and promote the use of urban reclaimed water. Beijing has built nine large sewage treatment plants and related supporting pipe networks, and before the 2008 Olympic Games, another five similar sewage treatment plants will be put into operation. At the same time, sewage treatment in the suburbs has also been fully launched. The 14 small and medium-sized sewage treatment plants built in the new city can treat nearly 170 million cubic meters of sewage annually. (3) Wastewater is treated and reused for agricultural irrigation. In northern Chinese cities, urban sewage and industrial wastewater have become one of the main sources of irrigation water for some suburban farmlands (including vegetable fields, rice fields, wheat fields, etc.). It has achieved certain economic benefits. It can improve the soil structure, increase water and fertilizer, and increase crop production. On average, every cubic meter of domestic sewage can increase the production of wheat or rice by about 0.5kg. However, sewage irrigation also reflects some shortcomings. Some farmland is irrigated with toxic and harmful industrial wastewater, resulting in farmland deterioration and agricultural production reduction, and groundwater, soil and agricultural products are polluted. The area of ??recycled water used for crop irrigation is increasing year by year, and 300,000 acres of recycled water irrigation areas have been formed in Daxing, Tongzhou and other regions. This year, the city's agricultural use of recycled water reached 230 million cubic meters. At the end of 2006, as the drainage gate of the Xiaohongmen Sewage Treatment Plant opened, clear recycled water poured into the Liangfeng Irrigation Canal, and 200,000 acres of farmland in eight towns including Qingyundian, Changziying and Caiyu in Daxing District were irrigated with recycled water. Recycling water instead of clean water for farmland irrigation can reduce the extraction of groundwater by 60 million cubic meters every year.

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An effective way to alleviate water shortages

According to relevant statistics, 80% of urban water supply is converted into sewage, which is collected and processed Finally, 70% of the recycled water can be recycled again. This means that through sewage reuse, the city's available water can be increased by at least 50% while the existing water supply remains unchanged. Countries around the world attach great importance to the use of recycled water. As a legal alternative water source, recycled water is being used more and more widely and has become an important part of urban water resources.

An important link in achieving sustainable utilization of water resources

Water is a basic resource and a strategic economic resource for urban development. With the process of urbanization and economic development, water shortages are becoming increasingly serious. Environmental pollution and water resource shortages have become bottlenecks restricting urban development. Promoting advanced sewage treatment and popularizing the use of recycled water are important measures to coordinate the development of humans and nature, create a good water environment, and promote the development of recycling cities. Internationally, the management objectives of water resources have undergone major changes, that is, from controlling water, developing water, and utilizing water to "recycling of water" and "repair and restoration of water ecology" with water quality regeneration as the core. Fundamentally achieve a virtuous cycle of water ecology and ensure the sustainable use of water resources.

Can bring considerable benefits

The rational use of recycled water not only has good economic benefits, but also has huge social and ecological benefits. First of all, as the price of urban tap water increases, the operating cost of recycled water further reduces, and the amount of recycled water increases, the economic benefits will become more and more prominent; secondly, the rational use of recycled water can maintain ecological balance and effectively protect water resources. Changing the traditional "exploitation-utilization-discharge" mining model achieves a virtuous cycle of water resources and plays a positive role in alleviating the city's water shortage situation, which has long-term social benefits; thirdly, the ecological benefits of rational utilization of recycled water The benefits are reflected in that it can not only eliminate the adverse effects of waste sewage on the urban environment, but also further purify and beautify the environment.