Comparative Studies On The Characteristics Of Treating Urban Sewage By A/O Process And A~2/O Process

With the accelerated industrialization and promoted urbanization, the urban sewage and industrial wastewater was emitted increasingly every year, which results in the increasingly serious problem of eutrophication of surface water. To improve the water environment, urban sewage-treatment plants were constructed in many regions. These plants in our country mostly use biological methods, including the A/O process, A2/O process, oxidation ditch process, AB process, SBR process, etc., in which A/O process and the A2/O process are the most widely used. Currently, comparative studies of various processes mainly focus on the A2/O process, the SBR process, and the oxidation ditch process, etc., but the study on the A/O process and the A2/O process is rare reported. This paper takes the example of sewage treatment plant in Jiyang County, discusses the characteristics of the two processes, and provides a certain basis for selecting the treatment process for urban sewage treatment plant.This paper systematically compares the removal effects of COD, NH3-N, TN, TP in the sewage by the A/O process and the A2/O process, analyzes the influence of temperature, inflow C/N ratio, inflow C/P ratio and other factors on denitrification and dephosphorization of the two processes. Studies show that:(1)The removal effects of COD, NH3-N, TN and TP are significantly better in A2/O process than that in A/O process. A2/O process’outflow generally reaches the A Level of "Discharge standard of pollutants for municipal wastewater treatment plant"(2)The increase in temperature can enhance the bacteria activity in both process systems and can enhance the efficiency of denitrification and dephosphorization. However, the dominant bacteria in A/O process system transforms from5℃to15℃, and has a certain influence on the removal of organic matters.(3)Organic load has a certain impact on the A/O process. It influences the removal of organic matters and nitrogen, but has little effect on phosphorus removal. In contrast, the organic load has no significant impact on the organic matter removal of A2/O process. However, with the increase of C/N ratio, the denitrification and dephosphorization performance increases first and then decreases:the TN removal rate increases steadily with the C/N ratio increasing from5to9. It reaches the highest point of83.2%when C/N ratio is8.9. Then the TN removal rate decreases when the C/N ratio increases from9to14. When the C/N ratio increases from5to9, TP removal rate gradually increases. It reaches90%when C/N ratio is between8to9. Then the TP removal rate decreases when C/N ratio increases from9to14, especially when the inflow C/N ratio is greater than11, TP removal rate declines dramatically.(4)The inflow C/P ratio has no remarkable influence on the organic matter removal or the denitrification performance in the two processes.(5)The C/P ratio has an unsteady influence on dephosphorization performance of A/O process. When C/P ratio is higher than80, A2/O process’dephosphorization rate is not influenced by other factors.