Study On Denitrifying Phosphorus Removal Process In A Post-Anoxic SBR System For Domestic Wastewater

Water gives birth to the life, and it is fundamental to the survival of humans. China is a country lack of water resources. With the development of industry and the propulsion of urbanization, a large amount of nitrogen and phosphorus is discharged into the water, the problem of water pollution becomes worse and worse. Nitrogen and phosphorus in sewage is the main culprit of eutrophication. Although the nitrogen and phosphorus removal in traditional biological technology can reach a certain level, there are some issues, such as the contradiction of the sludge age between nitrogen removal and phosphorus removal, high energy consumption, the need of adding additional carbon source, high sludge production, etc. Denitrifying phosphorus removal technology can remove nitrogen and phosphorus simultaneously, which solves the contradiction of the removal between denitrification and phosphorus fundamentally. Compared with the traditional process, denitrifying phosphorus removal technology can reduce 30% aeration rate, 50% carbon source consumption and 50% sludge production, and it is suitable for low influent carbon-nitrogen ratio?C/N? sewage treatment. However, for the current denitrifying phosphorus removal technology, the removal of phosphorus is very low when the influent phosphorus concentration is high. Then the help of chemical phosphorus removal is often needed. This subject adopted a post-anoxic SBR reactor. With the control of aeration intensity and time, we achieved denitrifying phosphorus removal in anoxic period by realizing nitration and removing some phosphorus in aerobic period, which maintained the advantages of the denitrifying phosphorus removal technology, and ensured the efficient removal of phosphorus.The sludge was taken from the second pond in sewage plant. The denitrifying phosphorus removal process was launched in 39 days by firstly shortening the SRT to enrich poly-phosphate accumulating organisms?PAOs?, and then extending the SRT and introducing the anoxic phase. COD, TP, NH₄⁺-N and TN removal efficiency were 92.9%, 98.4%, 100% and 87.6%, respectively. The results showed that the influent C/N affect nitrogen and phosphorus removal efficiency to some content. There was no obvious change on nitrogen and phosphorus removal efficiency when the decrease of C/N was below 17.65% in a short term. When it exceeded 33.3%, the system had a bad performance on both nitrogen and phosphorus removal, but in the long run, the effluent COD concentration fell, and the proportion of denitrifying phosphorus accumulating organisms?DPAOs? in PAOs increased, which supplemented the removal efficiency of decline to some extent. The cycle test indicated that p H and DO can be the real-time control parameters which decided whether the anaerobic phosphorus release and the cycle ended or not. The reaction time and energy consumption of aeration could be reduced significantly. Batch experiment indicated that the proportion of DPAOs with nitrate as electron acceptor in PAOs was 67.3% and 85.9% when C/N was 6 and 4, respectively.In order to further improve the ability of nitrogen and phosphorus removal efficiency, the realization of nitritation and denitrifying phosphorus removal by nitrite pathway was investigated. The results indicated that nitritation and denitrifying phosphorus removal in low concentration of ammonia water at normal temperature was established with the strategy which discharges sludge in the condition of limited oxygen. This system showed a good denitrifing phosphorus removal efficiency, the effluent meeted and partly exceeded the first class level A of Discharge standard of pollutants for municipal wastewater treatment plant?GB18918-2002?. According to the batch experiments, the ratio of DPAOs which took nitrite as electron acceptor in total PAOs could reach 70%. Studies indicated that overlong anoxic reaction time had negative effects on phosphorus removal, and it should be stopped when the nitrite was completely consumed. Aeration mode only affected the removal of nitrogen. With the adoption of the aeration strategy of higher at the beginning and then lower, and control of appropriate aeration intensity with total oxygen changeless, nitrogen removal efficiency could be improved.Finally, we investigated the efficiency of nitritation- denitrifying phosphorus removal system treating actual sewage. The results showed that the system showed a good performance of removing COD, TP and NH₄⁺-N and TN, whose removal rate could reach 83.8%, 94.6%, 100% and 79.1%, respectively. Although the available organic carbon source decreased, DPAOs still could guarantee the pollutant removal in the system, which was more suitable for low C/N sewage treatment. It was found that although the actual sewage water was complex, sludge discharge in condition of limited oxygen could still maintain the stability of nitritation.