Mathematic Simulation Of Multistage AO Process Based On ASM2d And Its Application For System Stability Adjustment

Multistage AO process is an efficient method for wastewater treatment,with the step-feeding and adjustable volume ratio between function areas are adopted,adjusting the volume ratio of anaerobic,anoxic and aerobic zones could maximize the effectiveness of denitrification and phosphorus.This study estabilished a mathematical model for multistage AO process with adjustable volume based on ASM2 d model on the GPS-X software simulation platform,and the influence of the operation condition parameters on the process treatment performance was systemic studied.Accordingly,the calibarated mathematical model was used to regulate the system operation condition to achieve t consistently stable pollutants removal efficiencies to meet the effluent discharge standards.Series of batch tests upon the steady-state of the lab-scale multi-stage AO system were carried out to determine the yield coefficient of the heterotrophic bacteria,the maximum utilization rate of autotrophic bacteria,the maximum growth rate of heterotrophic bacteria.The effects of typical stoichiometric parameters and kinetic parameters on the sensitivity of water quality were firstly studied.The results showed that the yield of polyp,the demand of polyp and the rate conefficients of phosphorus storage significantly affected the pollutants removal efficiencies,i.e.effluent quality parameters.Compared the simulated results with the experimental results,under the condition of static simulation,which corresponded to the maximum likelihood estimate of 95% confidence,the error was within 10%,and under the dynamic simulation condition,the average error was within 10%,indicating that the established model were feasible to predict the system performance.The influence of several of operation parameters on the effluent quality from multi-level AO process was studied.It was found that the effect of DO in the first and second aerobic zone was in significant in the 1 to 6 mg/L range,Hence,considering the rate of phosphorus releasing from 1 to 2 mg/L,it was feasible to reduce the energy consumption by regulate DO concentration.The recirculation rate of sludge affected the effluen effluent,which is the principle of the optimization of energy saving and process effluent,and the R,which should be controlled ranged from 0.5 to 0.6.Keeping the reminder of energy saving and excellent effluent quality,the water inlet ratio was recommended to be in the range of 0.5-0.7,which would be beneficial to both TN and TP.The first mixture reflux ratio displayed limited effect on the process treatment performance,and the first mixture reflux ratio should be controlled within 0.75 to 1.25.The volume ratio between anaerobic region and the first aerobic zone displayed limited effect on the process treatment performance,and when the volume ratio between first anoxia region and the first aerobic zone was controled in the range of 15:54-19:50,the effluent TN and TP were lowest,but effluent TP was unstable.At the same time,effluent TN and TP were stably under the standard when it was controled by 34:35.It was found that the sludge recirculation rate,the water inlet ratio,the volume ratio k2 between first anoxia region and the first aerobic zone,and hydraulic retention time have significante influence on their own effluent qualities.Therefore,these factors were mainly selected to be well regulated during the system adjustment.As for the influent with a rather high sludge load,and the influent with a high operation load rate,the multistage AO process was successfully adjusted,for the first one,it is mainly to improve the water inlet ratio,reduce the aeration volume and mixture reflux ratio,and adjust the volume ratio between first anoxia region and the first aerobic zone to 31:38,for the second one,it is mainly to improve the water inlet ratio,reduce the aeration volume and the second part of the nitrification fluid return flow and decress the water retention time The low C/N operating conditions of the multistage AO process were also adjusted,after optimization,the water discharge is not up to standard,and the additional carbon source can be considered,which the C/N was about 3:1.the water discharge is up to standard.Through the above optimization,each discharge index has the corresponding decrease.Based on this,the stable operation and control strategy for the multi-stage AO system under different loading shocking were presented.