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Modeling and Simulation of the Activated Sludge Process at a Full-Scale WWTP

Model of a full-scale activated sludge process in a WWTP in Chongqing, China was established by coupling Activated Sludge Model No.2 (ASM2) and secondary settling tank (SST) model. Influent COD of the ASM2 was characterized through combined respirometric and physical-chemical assay and the model parameters were calibrated after evaluating their structural identifiability. The SST model is a flux model based on the consistent modeling methodology, in which a more detailed sludge settling velocity function was proposed to describe the most settling phenomena happened in SST, including discrete settling of floc, zone settling, and compression settling. The coupling model was used to simulate and optimize the operation of the activated sludge process It is concluded that: 1) the effluent COD, SS, TN and TP could be simulated well, 2) the sludge recycle ratio in the SST and the sludge concentration in the bioreactor were optimized to reduce waste sludge, increase the capability to resist load shocks and lower temperature, and improve effluent quality, and 3) an A2/O processes was proposed to upgrade the WWTP for improving the efficiency of N and P removal.