Study On Nitrogen And Phosphorus Removal Effects As Well As Its Affecting Factors Of Modified A~2/o Process

The standard of wastewater discharge was controlled more strictly with the severe eutrophication question occurred. Therefore, the wastewater techniques developed gradually from the period of pure COD removal to the period of simultaneous COD, nitrogen and phosphorus removal. Today, the nitrogen and phosphorus removal technology aimed for eutrophication control has been the focused study in the wastewater treatment area.Because of many advantages like simple structure, short total HRT, cost efficient, easy control, and so on, the A2/O process has been wildly used in the municipal wastewater treatment plant for phosphorus and nitrogen removal purpose. But many problems exist in the traditional A2/O process that can remove phosphorus and nitrogen simultaneously by biological method, for instance:firstly, PAO and denitrifying bacteria rival for limited carbon source, which results in that high removal for phosphorus and nitrogen simultaneously is hardly realized in the process; secondly, to obtain a high removal effect for nitrogen, it needs a high internal return sludge ratio, which leads to high operation cost. As for the above mentioned problems, we bring forward to modified A2/O process, which uses the distribulary technology of carbon source from the anaerobic phase and pre-anoxic denitrifying technology of recycled sludge to enhance the nutriment removal and reduce the run expense.The continuous model dynamic experiment operated with artificial municipal wastewater was cayyied out in the experiment. Organic,nitrogen and phosphorus removal efficiency in the system was studied. Furthermore, effect of MLSS, SRT, DO,organic load ratio,nitrate nitrogen on phosphorus and nitrogen removal in the modified A2/O system was discussed. The characteristic of PAO sludge was analyzed, also. The PCR-DGGE technology was applied for the study of populative structure of the microbe in the system.The character and evolution of populative structure was studied by this technology.Study was made on the use of artificial wastewater, the research results showed that the Process has removal rate of 93.7%,84.1% and 93.2% respectively for COD, TN and TP and the effluent concentration of COD, NH4+-N, TN and TP were observed to be 26 mg/L, 0.27mg/L,5.243mg/L and 0.958mg/L in average. The outfall quality of COD, NH4+-N, TN and TP can reach the second class discharge standard in GB18917-2002.The experiment suggested that MLSS above 3000mg/L (and MLSSanaerobic:MLSSanoxic: MLSSaerobic≈1:1:1) were determined as optimal for the phosphorus and nitrogen removal in the modified A2/O system. Changes of MLSS can largely affect the phosphorus and nitrogen removal efficiency, so it'd better be kept in constant. The SRT of the PAO sludge was set in the level of 8d,10d,12d,15d, the phosphorus and nitrogen removal efficiency under each SRT was measured, the results showed that the suitable SRT is 10～12d in the modified A2/O system. Set DO concentration in different range and review the changes of phosphorus and nitrogen removal. The results showed that DO concentration has little affects on COD removal ratio. NH4+-N removal ratio arising and TN removal ratio ascending as DO concentration arising. TP removal ratio can reach or approach optimal when the range of DO concentration was 2.0～3.0mg/L.It was found that the critical organic load ratio of anaerobic phosphorus release is 0.120 (g, COD)/(g, MLSS) in static experiments. Nitrate has deep containment action on anaerobic phosphorus release. Anaerobic phosphorus release occurred after denitrifying reaction finished. Denitrifying rates are faster in higher COD initial concentration and need less time.It was noticed that the SVI of PAO sludge in the system was ranged from 105 mL/g to 194 mL/g. The average specific weight of phosphorus element in the sludge is 3.68%,4.16% and 4.70% in anaerobic reactor,anoxic reactor and aerobic reactor respectively.Populative structure in anaerobic reactor and aerobic reactor when system was start-up and quiet run were analyzed by the methods of PCR-DGGE. The results showed that populative structure changed rapidly during the start-up period and kept stabilize during the quiet run period. Populative structure in anaerobic reactor is quite similar with which in aerobic reactor, but the kinds of predominant populative in anaerobic reactor is more than which in aerobic reactor.