Modeling of enhanced VFAs production from waste activated sludge by modified ADM1 with improved particle swarm optimization for parameters estimation

Anaerobic fermentation is a promising means of producing volatile fatty acids (VFAs) from waste activated sludge, and thereby recovering resources from solid wastes. This study developed a modified Anaerobic Digestion Model No. 1 (ADM1) to simulate substrate degradation and the influence of pH on VFAs production. Protein and carbohydrate degradations were compared among three substrate degradation models: first-order kinetics, Monod, and Contois. The Monod model best simulated the soluble protein and carbohydrate degradation, whereas the Contois model best simulated the particle protein and carbohydrate degradation. The improved particle swarm optimization (PSO) proved to be the best algorithm for parameter estimation. Next, we proposed linear equations between hydrolysis kinetic constants and different pH values. The relative errors in the simulation results were very low, indicating that the modified ADM1 can accurately simulate the enhanced generation of VFAs under different pH conditions.