The main pollutant of urban sewage is organic matter. The main pollutants in sewage are organic matter, the BOD5: CODCr = 0.48, the ratio is greater than 0.3, more suitable for biochemical methods of choice, so the sewage treatment process to choose a secondary treatment program. At present, the economic methods at home and abroad mainly deal with biological methods. Activated sludge in the biological method accounted for the vast majority. There are many forms of activated sludge, the most widely used are the following three:

Traditional activated sludge method

Traditional activated sludge method and its traditional forms of improved, with A / O and A2 / O method. There are two kinds of A / O methods, one is anaerobic-aerobic process for reducing phosphorus, and the other is an anaerobic-aerobic process for reducing nitrogen. A2 / O law is the nitrogen and phosphorus removal process. Activated sludge process is the most basic flow of air into the sewage aeration, and for some time, the sewage to generate a floc body, the flocs mainly by the mass of microbial population, which is easy to precipitate Separation, and to clarify the sewage, which is "activated sludge." Activated sludge is the principle of activated sludge as the main biological treatment methods, its main structure is the aeration tank and secondary sedimentation tank, as shown below:

Analysis of the most extensive three kinds of activated sludge method

The sewage treatment and the return of the activated sludge into the aeration tank at the same time, as a mixture, with the aeration tank into the air aeration, the sewage and activated sludge fully mixed contact, and the supply of liquid mixture with sufficient dissolved oxygen, Under aerobic conditions, the organic matter in the sewage is decomposed by the microbial population in the activated sludge to be stabilized, and then the mixed liquor enters the secondary sedimentation tank. After the activated sludge is separated from the clarified liquor in the pool, a part is returned to aeration Inoculation of the pool, clear liquid is overflow discharge, throughout the treatment process, activated sludge growing, some of the remaining sludge need to be excluded from the system.

Oxidation ditch method

Oxidation ditch, also known as circulating aeration tank, similar to the delayed aeration activated sludge, oxidation ditch has the characteristics of the traditional activated sludge method, high removal of organic matter, but also has denitrification. Oxidation ditch this efficient, simple features, but the oxidation ditch should not be used underground, covers an area larger. The aeration tank is closed ditch type, the mixture of sewage and activated sludge in which circulating fluid, so the oxidation ditch, also known as "continuous circulating aeration tank." Oxidation ditch structure is simple, easy operation and management and stability. With the continuous improvement of the oxidation ditch wastewater treatment technology, the denitrification function of the oxidation ditch is enhanced. Under certain conditions, better biological phosphorus removal efficiency can also be obtained. There are many types of oxidation ditch, such as Carrousel type oxidation ditch, Three-ditch oxidation ditch and the more advanced Aobel oxidation ditch at home and abroad.

Analysis of the most extensive three kinds of activated sludge method

SBR process

SBR process is intermittent delayed aeration activated sludge method, its basic characteristic is to complete the biochemical reaction of sewage treatment, sedimentation, drainage, sludge discharge in a pond. The SBR process has some features that are superior to the traditional activated sludge process:

(1) The SBR process is simple in operation and basically does not require handling. The five procedures of water ingress, aeration, sedimentation, drainage and idle can be controlled by a small PLC. The running program can be rearranged according to the change of water quality. So that already very cumbersome operation into a fully automatic operation;

(2) low cost, less land occupation, no sedimentation tank, secondary sedimentation tank, no sludge return system, and in most cases, no adjustment tank may be provided so that land occupation can be reduced and the cost can be reduced;

(3) impact resistance load. Sewage gradually into the pool, the pool of water is slowly diluted, the ratio of sewage and the original pool of water is gradually increased, so the impact of changes in water quality;

(4) water quality is good. Sedimentation at the ideal quiescent state where the horizontal flow velocity is zero at the time of sedimentation of the pool water has a good settling effect. Pool dissolved oxygen value changes alternately. Sedimentation drainage, dissolved oxygen close to zero, inhibit the growth of filamentous bacteria, sludge sedimentation performance;

(5) low energy consumption. Due to the alternating change of dissolved oxygen in the pool, the concentration gradient of dissolved oxygen is large, which improves the utilization of oxygen. No sludge return system, saving energy consumption, reducing operating costs;

(6) phosphorus and nitrogen removal. An operation cycle, anaerobic, and oxygen, aerobic alternation, in a pool to achieve the dephosphorization and denitrification. The process is as follows (including sludge treatment).

Analysis of the most extensive three kinds of activated sludge method

With the improvement of SBR process, the current SBR process variants have many forms, the typical cycle of continuous water cycle activated sludge (CASS), intermittent water cycle activated sludge cycle (CAST) , Intermittent circulating aerated activated sludge (ICEAS), activated sludge combined with continuous aeration and intermittent aeration (referred to as DAT-IAT), continuous aeration and rear Alternating aeration combined activated sludge method (referred to as UNITANK method), the above several improved SBR process has its own characteristics.

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