1, Introduction
1. 1 distribution characteristics of water resources in China
China is a country with severe drought and water shortage. The total amount of fresh water resources in China is 2.8 trillion cubic meters, accounting for 6% of the global water resources. However, one of the characteristics of China's water resources is that the total amount is large and the per capita is small. The second feature is that the regional distribution is uneven, decreasing from southeast to northwest, which is inconsistent with the distribution of population and cultivated land.
1.2 the rise and development of sewage reuse
Sewage reuse is one of the effective ways to reduce water pollution, improve the ecological environment and solve the problem of water shortage in cities. The United States began to use reclaimed water on 1920, which formed a virtuous circle of water in the social cycle. By 1980, there were 536 regeneration projects, with an annual water consumption of 937 million m3. Dalian, a coastal water-deficient city in China, took the lead in building a sewage reuse demonstration project in 1992, and achieved practical results.
Modern urban sewage reuse has a history of nearly a hundred years, and the technology is very mature. Compared with foreign developed countries, China's urban sewage reuse started late, but overall, China's urban sewage reuse is not only technically mature, but also feasible in economic and environmental benefits.
2, the main way of sewage reuse
According to the current development of urban sewage reuse technology, the ways of urban sewage reuse mainly include agricultural water, environmental water, industrial water, urban miscellaneous water and groundwater recharge.
2. 1 Agricultural water use
Agricultural water is a big user of urban sewage reuse, mainly including irrigation of field crops, flowers and forest land. When sewage is reused for farmland irrigation, it can not only provide a stable water source for agricultural production, but also provide soil fertility containing nitrogen, phosphorus and potassium, which not only reduces the amount of chemical fertilizer, but also improves crop yield. Moreover, sewage can be further purified through the self-purification ability of soil, especially sewage reuse can control the uncontrolled over-exploitation of groundwater in rural areas.
2.2 Environmental water use
It is mainly used for supplementary water of urban water system, green isolation belt and garden irrigation water. Using reclaimed water instead of other water sources to supplement rivers and lakes not only achieves the purpose of optimizing and saving water, but also beautifies the environment.
2.3 Industrial water use
Industrial water includes cooling water, boiler water, process water and product water. In urban water supply, 50% ~ 80% is industrial water, which accounts for a large proportion of urban water, but compared with domestic drinking water, the required water quality grade is lower. After secondary treatment and proper tertiary treatment, urban sewage can generally meet the water quality requirements of industrial water.
2.4 Municipal miscellaneous water
Mainly used for building construction, spraying pavement, washing cars and flushing toilets. When reclaimed water is reused, special attention should be paid to hygiene, which is free of pathogenic bacteria, clean, odorless and non-toxic, and the content of suspended solids should meet the use requirements.
2.5 Groundwater recharge
The reuse of reclaimed water for groundwater recharge embodies the pollution control principle of "reduction, resource utilization and harmlessness" and the strategic thought of sustainable development. After secondary treatment, urban sewage is reinjected into the ground, and after flowing for a certain distance, it is developed into a new water source together with the original underground water source. This can not only prevent the ground subsidence caused by over-exploitation of groundwater, but also improve the backwater quality by self-purification of soil, and directly supply water to industrial and domestic miscellaneous water.
3. Benefit analysis of sewage reuse
Sewage reuse not only opens up the second largest water source, reduces the consumption of urban fresh water and sewage discharge, alleviates the shortage of urban water supply, effectively saves and utilizes limited and precious fresh water resources, and has obvious social, environmental and economic benefits.
3. 1 social benefit analysis of sewage reuse
Social benefit refers to the social influence, social effect or contribution of human activities. Sewage reuse conforms to the national sustainable development strategy and policy, and is the key area of environmental protection investment in China at this stage. The social benefits brought by sewage reuse are very obvious, which can be divided into direct benefits and indirect benefits.
(1) direct income
The wastewater reuse project takes the secondary effluent of sewage treatment plant as the source water, which can be put into use after reaching the reuse water quality standard after advanced treatment.
(2) Indirect benefits
Sewage reuse project is a public utility project to protect the environment, create a national health city and benefit future generations. After the implementation of the project, it can effectively solve the problem of water shortage in the service area, serve the city and society, improve the appearance of the city, improve the sanitary level, protect people's health, protect natural scenery and promote the development of urban tourism.
3.2 Environmental benefit analysis of sewage reuse
Environmental benefits refer to the effects of human activities on natural and social environmental systems. The environmental benefits brought by sewage reuse are remarkable, which plays a vital role in controlling environmental pollution and ecological destruction.
(1) The sewage reuse project has improved the level of water pollution control in the service area and enhanced the comprehensive strength of regional water pollution prevention and control.
(2) The sewage reuse project alleviates the shortage of water resources, reduces the development and utilization of water resources, and provides the necessary material foundation for the sustainable development of social economy and environment.
(3) Sewage reuse project can indirectly and effectively control environmental problems such as soil erosion and land desertification, and greatly improve environmental quality.
3.3 Economic Benefit Analysis of Sewage Reuse
Sewage reuse projects can produce direct economic benefits and play an important role in the long-term sustainable development of social economy. The direct economic benefits of sewage reuse include the direct economic benefits of sewage plants selling reclaimed water and other products, the direct economic benefits of users replacing high-quality water with reclaimed water, the economic benefits of increasing urban industrial water use and the economic benefits of increasing agricultural water use. However, the effluent from urban sewage treatment plants is sewage after all, and direct discharge will inevitably cause different degrees of pollution. Waste can be treated and reused, and reducing the resulting economic benefits is indirect economic benefits.
(1) wastewater reuse project can effectively save water resources, maximize the use of water resources, and effectively use sewage and wastewater. Macroscopically, it has reduced the development and utilization of water resources and promoted the national economy to a certain extent. Microscopically, it can promote enterprises to effectively use wastewater and improve the economic benefits of enterprises.
(2) The reuse of sewage reduces the pollution of sewage receivers to a certain extent, which can reduce the national investment in sewage treatment.
(3) Sewage reuse project can promote enterprises to adopt new technologies, speed up technological transformation, improve the technical level of enterprises, reduce the environmental expenditure of enterprises, and promote the circulation and reproduction of enterprise funds.
(4) The construction and operation of sewage reuse project can promote the development of a series of emerging industries.
(5) Wastewater reuse can promote the healthy and stable development of regional aquaculture.
4. Conclusion
At the moment when water resources are extremely scarce, sewage reuse can not only reduce pollution and increase water resources, but also reduce the cost of water supply treatment and water supply, improve the ecological environment and socio-economic environment, promote industrial and agricultural development, and promote and protect human health. The economic, social and environmental benefits of sewage reuse are remarkable, which is in line with the national sustainable development and the development strategy of creating a water-saving city. Therefore, it has great development prospects to continue to develop new advanced sewage treatment technologies and actively build sewage reuse facilities.
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