Modeling And Simulation Of Integrated Fixed Film Activated Sludge For Urban Wastewater Treatment

Simulation is an effective method for studying,optimizing and controlling the complicated biochemical process of wastewater biological treatment.For the extensive application of integrated fixed-film activated sludge(IFAS)in wastewater treatment plants(WWTPs)in recent years,firstly,a modified ASM1,a biofilm model,and a Integrated fixed film activated sludge model was established respectively based on the ASM1(Activated Sludge Model No.1)released by the International Water Association and BSM1(Benchmark Simulation Model No.1);then,the simulation software was developed with the help of VB6.0,and the sensitivity analysis of the model parameters was conducted;Finally,the pollution index of hybrid process along the Xi’an Fifth Wastewater Treatment Plant was measured,and simulation of the hybrid process in Xi’an Fifth Wastewater Treatment Plant was conducted.The main conclusions are as follows:(1)A modified ASM1 was first established,which can simulate carbon oxidation,nitrogen,and phosphorus removal at the same time,and then a biofilm model,which has the same equation structure with the microbial growth process rate of ASM1 and a definite physical meaning,by combining these two models mentioned above,a new model for IFAS was formed,the model was expressed in the form of matrix,conversion relationship was clear.(2)The simulation software was developed with the help of VB6.0,and the sensitivity analysis of the model parameters was conducted,which provides the basis for the calibration of the model.(3)Taking the hybrid process in Xi’an Fifth Wastewater Treatment Plant as objectfor study,the process of carbon,nitrogen and phosphorus removal was simulated,the results showed that the IFAS model satisfactorily predicted the changes in each effluent pollutant,and it can be used to as reference for the optimization of treatment system.(4)It was found that under the existing conditions,the hybrid process in Xi’an Fifth Wastewater Treatment Plant was not in the best condition,and the contribution of the media-area to nitrification was only 2.1%,through the simulation of influent flow,location of media-area and adding rate of medias.According to the simulation results,it can improve the efficiency of biofilm by advancing the media-area,increasing the influent flow and adding rate of medias.(5)It was found that the compound system can reduce the influence of SRT(Sludge Retention Time)on the concentration of nitrifying bacteria effectively,when media-area was located the head end of aerobic zone,and adding rate of medias was high,through the simulation of the COD,ammonia nitrogen and total nitrogen in the effluent and the concentration of heterotrophic bacteria and autotrophic bacteria in the system,when the SRT was different and with or without medias.According to the simulation results,it can enhance the capacity of phosphorus removal in the system by shortening the SRT appropriately,thereby reducing or avoiding the medicinal use of phosphorus removal,and reducing the cost of treatment,under the premises of reasonable setting up the media-area,and ensure the normal growth of phosphorus bacteria.