Modeling and simulation of an extended ASM2d model for the treatment of wastewater under different COD: N ratio

We evaluated the impact of chemical oxygen demand (COD) to nitrogen (N) ratios on the performance of a laboratory-scale anaerobic/anoxic/oxic (A2O) reactor by establishing an extended ASM2d model. This extended model introduced soluble microbial products (SMPs) and extracellular polymeric substances (EPS) to create the ASM2d-E-M. Other variables were introduced in the model to describe processes that already exist in the ASM2d, and those that were previously missing (e.g. EPS/SMP). To improve the accuracy of the simulation, this study included the establishment of the model, the division of model components, a sensitivity analysis, and model calibration and verification. The average errors of COD, ammonia and orthophosphate concentrations between the steady-state simulation data and experimental data, under different COD: N ratios were 7.42 %, 13.2 % and 9.18 %, respectively. Additionally, the average errors from the EPS and SMP simulation results were lower than 1.50 % and 2.59 %, respectively. The dynamic simulation results indicate that effluent COD, ammonia, ortho-phosphate and biopolymer concentrations decrease with an increase in influent COD: N ratio. But orthophos-phate increases when COD: N increases to 16:1. Comparing the steady-state simulation and dynamic simulation of the model with the experimental procedure confirms that the model effectively describes the biological processes in an A(2)O reactor, accurately predicts SMP and EPS production in the activated sludge system under different COD: N ratios and provides a valuable tool for the operation.

Automated summary

The study evaluated the impact of COD to N ratios on A2O reactor performance using an extended ASM2d model, which showed average errors between simulation and experimental data for COD, ammonia, and orthophosphate concentrations. The dynamic simulation results indicated a decrease in effluent COD, ammonia, orthophosphate, and biopolymer concentrations with increasing influent COD: N ratio, except for orthophosphate at 16:1. The comparison of steady-state and dynamic simulation confirmed the model's effectiveness in describing biological processes and predicting SMP and EPS production accurately.