An improved ASM-GDA approach to evaluate the production kinetics of loosely bound and tightly bound extracellular polymeric substances in biological phosphorus removal process

This study established an extended activated sludge model no. 2 (ASM2) for providing a new recognition of the contributions of both loosely-bound EPS (LB-EPS) and tightly-bound EPS (TB-EPS) into phosphorus (P) removal by incorporating their formation and degradation processes during the anaerobic–aerobic cycle. For determining the best-fit values for the new model parameters (k(h,TB-EPS), k(h,LB-EPS), f(PP,TB-EPS), and f(PP,LB-EPS)) in this extended ASM2, a novel and convenient gradient descent algorithm (GDA) based ASM (ASM-GDA) method was developed. Sensitivity analysis of f(PP,TB-EPS), f(PP,LB-EPS), k(h,TB-EPS), and k(h,LB-EPS) on the model target outputs of S(PO(4)), X(TB-EPS), X(LB-EPS), and X(PP) proved the accuracy of the chosen parameters. Eight batch experiments conducted under different influential chemical oxygen demand (COD) and P conditions were quantitatively and qualitatively analyzed. Respectively, 9.37–9.64% and 4.17–4.29% of P removal by TB-EPS and LB-EPS were achieved. Self-Organizing Map (SOM) has shown its high performance for visualization and abstraction for exhibiting the high correlations of the influential COD/P concentrations and the P% removal by TB-EPS (and LB-EPS). Comprehensive analyses of the influences of influential COD and P concentration on the biological phosphorus removal process help us in successfully establishing the mechanism kinetics of production and degradation of P in a dynamic P biological-treatment model.