The activated sludge method is generally used in biochemical treatment, and its main process includes: pretreatment > initial precipitation > mixing > aeration > secondary precipitation. Aeration is an important step in the treatment of wastewater by activated sludge method, and aeration is completed in the aeration tank.Therefore, the design of aeration tank capacity plays a very important role in the whole biochemical treatment process design.One, organic load calculation method to calculate the volume of aeration area, commonly used is the organic load calculation method.There are two ways to express the load, namely sludge load and volume load.Generally, the sludge load is used, and the calculation process is as follows :(1) determine the sludge load the sludge load is generally determined according to the empirical value, which can refer to the value in the relevant mature experience.(2) Determine the amount of microorganisms required The amount of microorganisms (XV) is determined by the total amount of organic matter to be treated and the capacity of a unit microorganism to process the organic matter in a unit time (i.e., sludge load).According to the definition of sludge load: Ns=Q (SO-Se)/(XV), the formula can be obtained as follows: (XV) =Q (So-Se)/NsV — aeration tank volume, m3Q — Inlet design flow rate, m3/dSO — inlet BOD5 concentration, mg/LSe — effluent BOD5 concentration, mg/LX — mixed volatile suspended solids, (MLVSS) concentration mg/LNs — sludge load,KgBOD5 / (kGMLVs.d) (3) Calculation of the effective tank capacity of the aeration tank after determining the total amount of microorganisms, it is necessary to have the value of sludge concentration to calculate the volume of the aeration tank.Sludge concentration is selected according to the empirical value of sludge concentration of the used process, generally between 3000-6000mg /L.X=Rrf106/SVI(1+R) : R — sludge reflux ratio, % R — sludge comprehensive coefficient in secondary sedimentation tank, generally about 1.2 f — MLVSS/MLSS aeration tank volume calculation formula is as follows:In the formula V= (VX) /X=Q (SO-SE)/(XNS) : Q — wastewater volume, M3 /dQ (SO-SE) — daily degradation amount of organic matrix, kg/dV — effective volume of aeration tank, m3 (4) Determine the main size of the aeration tank mainly determine the number, depth, length of the aeration tank and plane form of the aeration tank.According to the daily capacity to determine the number of cell body, at the same time, due to the different process, the style of the aeration tank and the number of each are not identical, so we need to have the scene in the actual design of the actual topographic map and the overall rendering for the basis, this design out of the pool to meet the needs of the process, and in accordance with the surrounding environment.Dynamic methods can also be used to calculate the volume of the aeration tank.The calculation process is as follows :(1) determine the required values of kinetic constants including Y, Kd, Ks and umax, and select appropriate values according to table 2 and table 3 when there is no experimental data.(2) Determine the sludge age according to the formula 1/θmin= (Y× Umax ×SO/ SO+Ks) -kd can determine the θmin value.θmin=1/(Y× Umax-KD) in the formula: Umax — the maximum specific proliferation rate of microorganisms when the saturated concentration of substrate is reached. The value of θC(sludge age. D) used in the actual activated sludge treatment system engineering of D-1 should be greater than the value of θmin. The actual value should be multiplied by the formula 1/θmin= Y× Umax-KD times the safety factor.The safety factor is generally 2-20.It can also be evaluated based on experience, as shown in Table 1.(3) Determine the required microbial biomass according to the formula 1/θC=[Y× Umax ×(SO-Se)/ (SO-Se)+KsIn SO/ Se] -kd to determine the microbial biomass, the calculation formula can be obtained:(XV) =QθCY(SO-Se)/(1+KdθC)V=(VX)/X Check the effluent concentration according to the relevant company;Or check the sludge load according to the definition of sludge load.You can do either of these two things.