What is the concentration of activated sludge in sewage treatment aeration tank?

2. 1, traditional activated sludge process

The traditional activated sludge process, also known as ordinary activated sludge process, is the earliest activated sludge process used in sewage treatment and has been used ever since. The main processes are aeration tank, secondary sedimentation tank and sludge reflux system. For the traditional activated sludge treatment technology, due to its early theoretical development, mature technology, convenient management, easy operation and stable operation effect, giving priority to effluent quality, the removal rate of BOD5 is over 90%, which has made great contributions to the previous sewage treatment. However, its adaptability to water quality and quantity is poor, the aeration tank is too large, the investment is high, and the nitrogen and phosphorus removal effect is not good. In the process of urbanization, the water quality is poor. Urban environmental protection requires higher effluent quality, so the traditional activated sludge method is difficult to adapt to the future pace, so the traditional activated sludge method is no longer used in today's water plant construction.

2.2, step by step aeration method

Step-by-step aeration is an improvement on the second shortcoming of traditional activated sludge process. The wastewater is not concentrated at the head of the tank, but enters at multiple points along the length of the tank, which makes the distribution of organic load more uniform, thus balancing the oxygen demand; In addition, the concentration of activated sludge in the step-by-step aeration method gradually decreases along the length of the tank, the former is higher than the average concentration, and the latter is lower than the average concentration. The concentration of activated sludge in the effluent of the aeration tank is low, so the operation of the secondary sedimentation tank is also beneficial. Step-by-step aeration method can improve the utilization rate of air and the working capacity of aeration tank, improve the working condition of secondary sedimentation tank and operate flexibly. Compared with the traditional activated sludge process, the volume of aeration tank can be reduced by about 30%, and the BOD removal rate can reach 90%.

2.3, adsorption regeneration activated sludge method

Also known as contact stabilization method, its principle is mainly the first stage of organic matter degradation by activated sludge-adsorption. Compared with the traditional activated sludge process, the adsorption regeneration process has the same type of aeration tank. Both of them are plug flow, but there are two differences: first, the adsorption of wastewater and the oxidative decomposition and metabolism of sludge are carried out in two ponds or 1 pond respectively, and the secondary sedimentation tank is located between them; Second, the sludge return flow is large, generally 50%~ 100%. Therefore, the average concentration of sludge in the aeration tank is large, which can absorb more pollutants.

2.4, complete mixing method

The process flow of complete mixing method is the same as that of traditional activated sludge method, which is an improvement on two shortcomings of traditional activated sludge method. The difference is that the mixing tank is fully mixed and circulated in the aeration tank, and the returned sludge and induced sludge wastewater enter the aeration tank and immediately mix with the original mixed liquid. Its characteristic is that the water quality of each point in the aeration tank is basically the same, that is, the concentration of activated sludge in wastewater is almost the same, so the working conditions of each part in the tank are almost the same. In this way, the oxygen demand of all parts of the aeration tank with complete mixing mode is uniform, and there is no waste of oxygen.

2.5. Extended aeration law

Also known as complete oxidation, it is characterized by long aeration time, so that all sludge is oxidized by microbial endogenous respiration, that is, theoretically, the net increase of sludge is zero. Extended aeration method has long aeration time and high power cost; Aeration tank has large volume, long mud age and high capital construction cost. Extended aeration process is generally not used in large sewage treatment plants, but mainly used in small sewage treatment plants or industrial organic wastewater with high effluent requirements and inconvenient sludge treatment. The oxidation ditch treatment technology currently used is actually an extended aeration method.