Current situation and development trend of municipal sewage treatment and reuse in China

In recent years, China has accelerated the process of social urbanization, and the number of people has also shown a trend of rapid growth, the contradiction between sewage treatment and residents' life in urban development has been highlighted, and has received extensive attention from all walks of life. According to relevant data, as of the end of June 2019, the sewage treatment plants of cities in China have reached more than 5,000 (excluding township sewage treatment plants and industries), and the sewage treatment capacity has reached 2.1×108 m3/d. Although the number of urban sewage treatment plants is gradually increasing, it can not meet the current needs of urban development, and the current status of sewage treatment in urban agglomerations in China is still not optimistic. Only by effectively solving the problem of urban sewage treatment can we effectively guarantee the steady improvement of the quality of life of urban residents and ensure the ecological and sustainable development of the city.

First, the current situation of urban sewage treatment and recycling in China

The state increasingly attaches importance to urban sewage treatment and reuse, and sewage treatment plants actively innovate A variety of effective solutions for the treatment and reuse of urban sewage, such as A-A-O process, A-O process, oxidation ditch process and SBR process, and even the deep sewage treatment and reuse technology that has been widely used in urban sewage treatment plants. But at present, the situation of municipal sewage reuse is still not objective. The main reasons for the low efficiency in the reuse of municipal sewage are as follows:

1. Shortage of funds for sewage treatment and reuse

Urban sewage treatment and reuse can be used for flushing toilets, urban road greening, domestic water, landscape water, etc. According to the relevant regulations of reuse water, the requirements of fecal Escherichia coli, residual chlorine, suspended matter and other indicators are stricter than Grade A, and the effluent of most sewage treatment plants has not yet met the requirements. In order to improve the capacity of reuse water for sewage treatment, it is necessary to strengthen the construction of the sewage treatment plant. However, in the process of establishing the plant, a large amount of financial support is urgently needed, such as site construction funds, equipment introduction funds and machinery and equipment maintenance funds. In addition, when purchasing related chemical reagents and updating technical means, it is necessary to improve the quality of the plant. Strong financial backing is needed everywhere. However, at the current stage, the financial support given to urban sewage treatment plants by local government departments in China is not sufficient, which leads to insufficient construction of urban sewage treatment plants and low technical level, and ultimately leads to China's urban sewage treatment plants in the performance of sewage treatment capacity can not get the ideal effect.

2. Technical problems of sewage treatment and reuse

China has a vast area, the urban division is very detailed, at present, the process of urban sewage treatment and reuse is often limited by the level of urban economic development and scientific and technological input, and even affected by the urban geographical environment, resulting in our city in the reuse of sewage is relatively slow. If the technical problems can not be solved in the sewage treatment and reuse of the urban sewage treatment plant, it will lead to the difficulty of the designed sewage treatment and recycling scheme, and it will not be able to successfully achieve the goal of urban sewage treatment and reuse. Most urban sewage factory sewage treatment technology is introduced from abroad, resulting in sewage treatment technology can not match the actual situation of our city, the actual treatment capacity may not be able to reach the design treatment capacity.

Second, China's sewage treatment and reuse process technical support

At present, most domestic and foreign sewage treatment in the use of secondary treatment method, the core is the traditional activated sludge method. The processes used in the treatment of sewage include A-A-O process, A-O process, oxidation ditch process and SBR process. At present, these processes are relatively mature, and the effect of treating sewage is also relatively good.

1, A-A-O sewage treatment process

A-a-o wastewater treatment process is also known as anaerobic - anoxic - aerobic process, this process has A wide range of applications, the southern region of China is more common use of such technology. The principle is to set up anaerobic areas, anoxic areas and aerobic areas in the sewage treatment system to achieve the purpose of biological nitrogen and phosphorus removal.

2. SBR process

SBR process is also known as the continuous batch activated sludge treatment process, this process requires the use of a pool as a tool, the pool as an aeration tank to develop secondary precipitation, this method is different from the traditional way of space or time segmentation, more suitable for sewage treatment in small-scale cities.

3. Oxidation ditch process

This process is called the cyclic aeration tank process, which is a delayed activated sludge treatment method of aeration, through the oxidation channel through the mixed solution between the activated sludge and the wastewater continuous circulation activity. The effluent quality of this method is relatively good, and there are fewer structures, and relatively few procedural steps in the process of operation and management.

4, urban sewage deep treatment and reuse technology

In the advanced treatment process of urban sewage, it is mainly carried out through four steps. First, the mixed water is precipitated, clarified and filtered to remove suspended matter as the main purpose. Second, the use of activated carbon adsorption method, through the huge specific surface area of activated carbon and developed microporous structure, the odor, chroma, heavy metals and organic matter in urban sewage can be removed. The results of relevant experiments show that the use of activated carbon in the treatment of sewage can effectively remove 70% of the relative molecular weight of 500-3000 organic matter. Third, the use of membrane technology to remove bacteria, reduce sewage turbidity and organic composition. The fourth step is to use advanced oxidation method to decompose macromolecular organic matter and improve the biodegradability of urban sewage. At present, the most common methods used in this step are photocatalytic oxidation, catalytic ozone oxidation, and so on. The wastewater reuse process is mainly to apply sewage to people's production and life, and the different reuse ways have different requirements for water quality.

Process water, boiler water quality and circulating cooling water quality requirements are relatively high, in general, it is necessary to combine a variety of processes to carry out in-depth treatment, and the requirements for flushing water, green water and car wash water are relatively reduced. In the process of reuse treatment, one or two combinations of processes can be adopted. The urban sewage treatment process for domestic use is mainly to carry out preliminary treatment of urban sewage through secondary treatment technology, through the comprehensive use of coagulation precipitation, clarification filtration, activated carbon adsorption depth treatment, reuse and greening, car washing and watering flowers and other life fields. The urban sewage treatment process for production purposes also requires secondary treatment technology in advance, and the comprehensive use of filtration technology, catalytic oxidation technology, microfiltration technology and reverse osmosis technology is used in production.

Third, the future development trend of urban sewage treatment and reuse in China

1, constantly update sewage treatment equipment and sewage treatment technology

At present, most of China's urban sewage treatment plants have not achieved deep sewage treatment, so there is a widespread phenomenon of low sewage recovery rate. At present, the scale of urban development is also expanding, urban living and industrial users of water is gradually increasing, the contradiction between supply and demand is becoming increasingly prominent, to solve the problem of urban water shortage, strengthen the sewage reuse capacity, deep treatment of sewage is the most important way, in the future development, should be based on improving the traditional sewage treatment technology and equipment.

2. Expand the scale of urban sewage treatment plants

In the process of urban construction and development, economic development promotes the increase of urban sewage discharge, and the original sewage treatment system is bound to increase the pressure, resulting in low sewage treatment efficiency. The large sewage treatment plant will improve the sewage treatment capacity, stabilize the water quality of the effluent, and facilitate daily management work. Therefore, the scale of sewage treatment plants will be gradually expanded in the future development. In addition, when expanding the scale of urban sewage treatment plants, special attention needs to be paid to the improvement of sewage treatment and reuse standards to provide water sources that meet the standards for urban residents' living and production.

3. Strengthen supervision and management

Sewage treatment equipment improvement and sewage treatment technology progress, but also need to do a good job of adequate management. Government departments should further improve the supervision and management ability of sewage treatment, actively organize the professional skills training of sewage treatment personnel, pay attention to improving the management ability and professional level of staff, improve the inlet and effluent detection system, use modern information technology, and strengthen the real-time supervision ability.

Iv. Concluding remarks

The sustainable development level of a city is directly affected by the level of sewage treatment, and the sewage treatment capacity even has an impact on the life happiness index of urban residents. In the state of increasingly scarce water resources, strengthening the technology of urban wastewater treatment and reuse has become a hot topic. Therefore, it is necessary to strengthen the research of urban wastewater treatment and reuse technology in order to achieve the purpose of in-depth treatment of urban wastewater. Therefore, in the process of urban development, we must pay attention to the improvement of sewage treatment technology and equipment, organically combine the social and economic development environment, and finally enter the sustainable development track.