About reclaimed water

Reclaimed water refers to the water that can be used profitably after the sewage is properly treated, reaches a certain water quality index and meets certain use requirements. Compared with seawater desalination and inter-basin water transfer, reclaimed water has obvious advantages. From the economic point of view, the cost of reclaimed water is the lowest, about 1~3 yuan/ton, while the cost of seawater desalination is about 5~7 yuan/ton and the cost of inter-basin water transfer is about 5~20 yuan/ton. From the point of view of environmental protection, the recycling of sewage is helpful to improve the ecological environment and realize the virtuous circle of water ecology.

Reclaimed water is also the standard water treated by sewage treatment plants, which is generally secondary treatment. It has the advantages of being unaffected by climate, not competing with neighboring areas for water, using local materials, being stable and reliable, and having high guarantee rate. Usually people call tap water "water supply", sewage "water supply", and the quality of reclaimed water is between water supply and water supply, so it is named "reclaimed water". Although it is not drinkable, it can be used in some occasions with low water quality requirements, such as flushing toilets, washing cars, spraying roads and greening. Reclaimed water engineering technology can be considered as a miscellaneous water technology between domestic water supply system and building drainage system. The water quality index of reclaimed water is lower than that of drinking water in urban water supply, but higher than the discharge standard of polluted water allowed to be discharged into surface water.

Reclaimed water is the second water source of the city. Recycling of urban sewage is one of the effective ways to improve the comprehensive utilization rate of water resources and reduce water pollution. Rational reuse of reclaimed water can not only reduce water pollution, but also alleviate the contradiction of water shortage, which is an important measure to implement sustainable development. The recycling of sewage has considerable social, environmental and economic benefits and has become the only way to solve water problems in all countries of the world.

Utilization mode of reclaimed water

Reclaimed water is a very valuable water resource, with large water quantity and stable water quality, which is less affected by seasons and climate. There are many ways to use reclaimed water, which can be divided into direct use and indirect use according to the relationship with users, and direct use can be divided into local use and centralized use. In most countries, reclaimed water is mainly used for farmland irrigation, mainly indirect irrigation; Reclaimed water in a few countries such as Japan is mainly used for urban non-drinking water, mainly for local use; Environmental water use has become a new trend of urban environmental "water landscape".

Reclaimed water has many uses, which can be used for farmland irrigation and landscaping (parks, campuses, highway green belts, golf courses, cemeteries, green spaces, residential areas, etc.). ), industry (cooling water, boiler water process water), large-scale building washing, entertainment and environment (improving lakes, ponds and swamps, increasing river flow and raising fish, etc. ), as well as fire fighting, air conditioning, toilet flushing and other municipal miscellaneous purposes.

According to the use of reclaimed water, reclaimed water can be reused for groundwater recharge, industrial water, water for agriculture, forestry and animal husbandry, urban non-drinking water and landscape environment water. Reclaimed water can be used for groundwater recharge, groundwater recharge, seawater intrusion prevention and land subsidence prevention. Reclaimed water can be used as cooling water, washing water and boiler water in industry. Reclaimed water is used in agriculture, forestry and animal husbandry, and can be used for irrigation, planting and seedling raising of food crops and cash crops, and irrigation, planting and seedling raising of trees, ornamental plants and livestock and poultry.

Hygienic safety evaluation method of reclaimed water

There are two main methods to evaluate the influence of pathogenic microorganisms in water on human health.

1, actual risk assessment method

Also known as low technology/low cost/risk control method, based on epidemiological research, combined with the treatment effect of existing sewage treatment technology on pathogens, the health risk of reclaimed water reuse is analyzed. The water quality standards of reclaimed water reuse in many countries in the world are formulated in this way, such as the reuse guide in the United States. The water quality standard of reclaimed water is based on the experience of reclaimed water reuse and the recognition that the existing sewage treatment technology can effectively remove pathogens.

2. Quantitative risk analysis method.

Also known as high technology/high cost/low risk method. The health risk of human exposure to pathogens in the process of reclaimed water reuse was quantitatively evaluated. The evaluation procedure is the same as the chemical pollutant risk evaluation procedure, including:

(1) Hazard identification: identify pathogens that people may be concerned about in water;

② Exposure assessment: determine the route, duration and exposure of human body to pathogens during the use of reclaimed water;

③ Evaluation of dose-response relationship: According to the dose-response relationship of pathogens, estimate the infection probability under conditions similar to the actual exposure level of the population;

④ Risk characteristic analysis: calculate the theoretical risk according to the assumption of exposure and dose response. [5]

Utilization of reclaimed water in China

condition

After entering the 2 1 century, under the background that water resources in China are increasingly scarce, the utilization of reclaimed water has begun to be paid attention by the China municipal government. By 2009, China's sewage reuse rate (sewage reuse rate/sewage treatment rate) is about 15%, while the ratio of sewage reuse rate/sewage discharge is only about 5%.

Feasibility of reclaimed water utilization

The rational utilization system of reclaimed water is a complex system, which involves many systems such as society, economy, environment and resources. Each subsystem consists of many factors, among which the main factors are: urban basic conditions, tap water price, reclaimed water quality, public acceptance, etc. These factors restrict and influence each other. Taking Beijing as an example, the feasibility of sewage reuse is illustrated from the following aspects.

For example, the construction of sewage treatment plants in Beijing has been accelerated, and it is located near the city, which is convenient for the reuse of nearby reclaimed water. According to Beijing's environmental quality control plan, based on the planning and construction of more than 30 sewage treatment plants, 14 sewage advanced treatment plants have been built, and the corresponding drainage pipe network has been built. The improvement of urban drainage pipe network and the establishment of sewage plant have created conditions for sewage reuse. Reclaimed water reuse is also in line with the commitment in the 2008 Olympic bid report. In 2008, Beijing sewage was reused for greening, river and lake environment, municipal miscellaneous use and agricultural irrigation water, and the reuse rate reached 50%.

The realization of water quality index is the premise of sewage reuse as water resources. With the development of water treatment technology, the treatment technology that can reach a certain water quality has matured. Traditional advanced treatment processes, such as coagulation and sedimentation+filtration and disinfection, ozone and activated carbon adsorption, filtration membrane treatment, combined process of activated carbon and membrane treatment, advanced membrane treatment technology, enhanced secondary treatment technology, etc. Reasonable selection according to the requirements of reuse water quality and existing economic conditions will reach the reuse water quality standard.

For a long time, the price of tap water has been low. With the increasingly severe form of water resources in Beijing, the price of tap water will gradually increase. According to preliminary calculation, the cost of reclaimed water treatment and transportation is about 1. 50 yuan /m3, slightly lower than the price of tap water. After the middle route of South-to-North Water Transfer Project introduces water into Beijing, the price of its source water will be 2. 18-3.9 yuan /m3. If urban tap water is used as the source water, the price of tap water will definitely rise sharply. On the other hand, with the improvement of treatment technology, the treatment cost of reclaimed water will be further reduced. Therefore, the increasing price gap will promote the use of reclaimed water. Considering the economic benefits, some enterprises are willing to accept reclaimed water.

The public's psychological acceptance of sewage reuse is also an important factor in the promotion of sewage reuse projects. According to a public opinion survey in Beijing, 85% people can accept that sewage can be reused for watering green land, watering roads, flushing toilets and washing cars. With the increase of government propaganda and the improvement of public awareness of environmental protection, people will gradually accept the reuse of reclaimed water.

Development goals

In 2006, the Ministry of Construction and the Ministry of Science and Technology of China jointly formulated and promulgated the "Technical Policy for Urban Sewage Recycling", and determined that the national goal of urban sewage recycling is: by 20 10, the direct utilization rate of reclaimed water in water-deficient cities in the north will reach 10%~ 15% of urban sewage discharge, and that in water-deficient cities in the south will reach 5% ~/kloc-. By the year of 20 15, the cities lacking water in the northern region will reach 20%~25%, and the cities lacking water in the southern coastal region will reach 10%~ 15%.

Use strategy

1, direct use and indirect use, according to local conditions.

2. In direct use, the combination of local use and centralized use is suitable for the situation at that time.

Scope of use policy

1. Urban water use is combined with rural water use, with urban priority.

2. In urban water use, industrial water is combined with other water uses, and industry is given priority.

3. From the viewpoint of sustainable development, reclaimed water should be mainly used for groundwater recharge. [6]

[Edit this paragraph] Terminology related to reclaimed water reuse

① Personal cycle

Reuse of sewage reclaimed water from a single building in a building.

② Regional circulation

In relatively concentrated areas, such as residential quarters, urban reconstruction areas and other buildings, sewage reclaimed water is reused.

③ Wide area circulation

The water in the sewage of urban sewers can be reused in buildings and other ways on a large scale.

④ Utilization of toilet flushing water

The recycled water is used to flush the toilet. Toilets with hand washing tanks cannot be used.

⑤ Utilization of sprinkler water

Reclaimed water is used to water lawns and trees in parks and green spaces, and to clean streets.

⑥ Landscape water use

Comfortable use of reclaimed water without contact with people.

⑦ Utilization of hydrophilic water

Comfortable use of reclaimed water under the premise of human contact.

(8) Recovery facilities

Sewage treatment water reuse, set up a set of recycling treatment facilities, water transmission and distribution facilities and equipment utilization facilities.

Pet-name ruby regeneration treatment facilities

The general name of engineering facilities that carry out necessary treatment (sand filtration, chlorination treatment, etc.) for sewage. ). Used for the use of toilet flushing water.

Attending water transmission and distribution facilities

The general name of water distribution facilities for reclaimed water from regeneration treatment facilities to utilization equipment.

Note: The definition of "human contact" in the utilization of landscape water and hydrophilic water refers to the immersion of hands and feet and the contact of body parts in small streams, rather than the whole body contact such as bathing. Examples of contact between water and body parts include catching fish in the current, boating, fishing and other activities. [