Process flow chart of urban sewage treatment

The sewage treatment process is divided into three levels: the first level: physical treatment, mechanical treatment, such as grid, sedimentation or air flotation, to remove stones, sand, fat, grease and so on contained in sewage. Secondary treatment: biochemical treatment. Pollutants in sewage are degraded by microorganisms and converted into sludge.

Tertiary treatment: advanced treatment of sewage, including removal of nutrients and disinfection by chlorination, ultraviolet or ozone technology. According to the different treatment objects and water quality, some sewage treatment processes do not include all the above processes.

1, primary treatment

The mechanical (primary) treatment part includes grids, grit chambers, primary grit chambers and other structures to remove coarse particles and suspended solids. The principle of treatment is to realize solid-liquid separation and separation of pollutants and sewage by physical methods, which is a common method of sewage treatment.

All wastewater treatment processes require mechanical (primary) treatment (although some processes sometimes omit the primary sedimentation tank). The typical removal rates of bod5 and ss in primary treatment of municipal sewage are 25% and 50% respectively.

Aerated grit chamber is generally not recommended for biological phosphorus and nitrogen removal sewage treatment plants to avoid removing rapidly degrading organic matter; Under the condition that the original wastewater quality characteristics are not conducive to phosphorus and nitrogen removal, according to the water quality characteristics of the follow-up process, it is necessary to carefully analyze and consider the setting and setting method of primary sedimentation to ensure and improve the phosphorus and nitrogen removal quality of the follow-up process. .

2. Secondary treatment

Biochemical treatment of sewage belongs to secondary treatment, and its main purpose is to remove non-precipitated suspended solids and soluble biodegradable organic matter. Its technological composition is diverse, which can be divided into activated sludge method, AB method, A/O method, A2/O method, SBR method, oxidation ditch method, stabilization pond method, CASS method, land treatment method and so on. At present, most urban sewage treatment plants adopt activated sludge process.

The principle of biological treatment is to complete the decomposition and synthesis of organic matter through biological action, especially the action of microorganisms, so as to transform organic pollutants into harmless gas products (CO2). Liquid products (water) and solid products (microbial community or biological sludge) rich in organic matter; The remaining biological sludge is separated from the purified biological sludge in the sedimentation tank through solid-liquid separation in the sedimentation tank. Remove from sewage.

3. Three-stage treatment

Tertiary treatment is the advanced treatment of water, and the wastewater treatment process after secondary treatment is the highest treatment measure of wastewater. At present, there are not many sewage treatment plants in China.

Nitrogen and phosphorus are removed from the secondary treated water, residual pollutants in the water are removed by activated carbon adsorption or reverse osmosis, bacteria and viruses are disinfected by ozone or chlorine, and then the treated water is sent to water sources such as flushing toilets, spraying streets, green belts, industrial water and fire fighting.

It can be seen that the function of sewage treatment process is only to purify sewage and enrich pollutants into sludge through biodegradation and solid-liquid separation, including primary sludge and secondary sludge produced in primary treatment stage.

Extended data:

The trend of future development.

1, the overall performance of the industry improved. Performance within the industry has become a top priority, so there is a special project to establish a nationwide industry management performance system in the National Twelfth Five-Year Plan.

2. Service has become the core task and link of our industry. This is consistent with developed countries. In developed countries, service industry accounts for the whole environmental protection industry, with equipment, investment and construction accounting for about 50%, while in China, it is estimated that it accounts for about 10%. Therefore, there is such a large space, and the internal structural adjustment faces the demand from construction to development.

No business entity can occupy an absolute dominant position at the national level, whether it is a state-owned enterprise, a foreign-funded enterprise, a public institution or a joint-stock company, it is diversified.

So it is not easy to integrate opportunities based on assets. This is the difficulty we are facing. On the other hand, it provides a good opportunity. If we look at international asset integration, the early success is Britain. It first solved the problem of integration, and then solved the problem of marketization.

3. From the technical point of view, the problem of water resources itself has begun to show a trend of basin-based, which was previously called "multi-dragon water control", and more and more emphasis is placed on coordination from the basin level. From the basin scale, not only water resources are coordinated, but also reclaimed water is coordinated. Only by considering this problem from the perspective of river basin can we get the greatest benefit.

Baidu encyclopedia-sewage treatment

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