Modeling and simulation of the biological process for treating wastewater with a low COD:N ratio under different dissolved oxygen conditions using an extended ASM2d model

Abstract

Studies are currently lacking on the reaction mechanism of bacterial biopolymers (extracellular polymeric substances (EPS) and soluble microbial products (SMP)) for biological nutrient removal (BNR) in the activated sludge model No. 2d (ASM2d). Meanwhile, the relationship between biopolymers and BNR under different dissolved oxygen (DO) conditions is not completely clear. Thus, this work presented a modified ASM2d model that combines EPS and SMP (E-S-ASM2d), described in detail the interaction between the different bacteria and biopolymer dynamics in an anaerobic, anoxic, microaerobic and oxic (AAMO) reactor, and simulated the influences of DO on BNR process in low COD:N wastewater and on bacterial biopolymers. In addition, 16S rRNA gene analysis was used to characterize the microbial community dynamics in the AAMO reactor under different DO conditions, thus verifying the necessity of introducing microbial interactions to the E-S-ASM2d model. According to the measurements, the average total nitrogen removal rate of effluent increased 19.4 %, and the average EPS content increased 15.5 % under low DO. According to sensitivity analysis, high sensitivity parameters vary under different DO concentrations (namely 3 mg L−1 and 0.5 mg L−1 DO), which demonstrates the need to determine and separately calibrate these parameters according to DO. Finally, compared with traditional ASM2d model, the correlation likelihood values of E-S-ASM2d model for COD, ammonia nitrogen, total nitrogen and total phosphorus of AAMO effluent increased from 0.622, 0.704, 0.639 and 0.329 to 0.850, 0.894, 0.909 and 0.897, respectively, indicating E-S-ASM2d can significantly improve the simulation of nutrient removal under low influent COD:N.