Study On Nitrogen And Phosphorus Removal Performance Of Aerobic Granular Sludge Treating Municipal Sewage With Low C/N Ratios

Compared to conventional activated sludge flocs,aerobic granular sludge(AGS)has a compact and dense structure and great settling properties which makes easier to separate the sludge and water.The layered structure makes it capable of simultaneous nitrification and denitrification and simultaneous phosphorus removal,which ensure the system can complete denitrification and dephosphorization in one reaction tank,effectively saving energy and occupying area.According to the challenges of the current municipal sewage treatment situation in China including land shortage,low sludge-water separation efficiency and low C/N ratios of raw water,this study was mainly focused on the feasibility and advantages of using aerobic granular sludge technology to treat low C/N ratios municipal sewage.AGS were successfully cultivated with low C/N ratios domestic sewage as raw water.The nitrogen and phosphorus removal process of the aerobic granular sludge reactor and the stability of the effluent during long-term operation were investigated.At the same time,the pollutant removal performance of different C/N ratios and temperatures were investigated and the community succession and microbial diversity of aerobic granular sludge were analyzed,which had practical significance and scientific value.The main research contents of the study are as follows.The aerobic granular sludge was successfully cultivated using the municipal sewage with low C/N ratios in a sequence batch reactor(SBR)in about 50 days by changing the organic load and selection pressure.The SVI value and MLSS of mature aerobic granular sludge was about 50 mL·g-1.and 4.5 g·L-1,with an average particle size of 599.5 ?m.The AGS are brown in color,with clear edges and a spherical or ellipsoidal shape.In the course of 180 days of cultivation and continuous operation,the average COD treatment efficiency is 87.5%,the average TN treatment efficiency is 78.5%,and the TP treatment efficiency can reach more than 70%with the C/N ratio of 2?6 in the influent.Compared with conventional activated sludge systems,the effect of simultaneous nitrification and denitrification was obvious,the accumulation of nitrate nitrogen gradually decreases,and the contradiction between nitrogen and phosphorus removal caused by low C/N ratios water quality gradually disappears.In the process of biochemical reaction in the cycle,pH,DO and ORP can be used as indicators of the degree of progress of the biochemical reaction in the system and whether the system as a whole operates normally,and it has a clear directional effect on the operation and regulation of the system.According to the natural seasonal variation of raw water quality,the influence of different C/N range of raw water on the quality of system effluent was analyzed.C/N ratios do not affect the removal of COD,and the average removal efficiency can reach 86.9%.When C/N>3,it can ensure that the total nitrogen and ammonia effluent meet the standard.When the C/N is reduced to 1?3,the average treatment efficiency drops to 75%.AGS will preferentially denitrify when facing extreme C/N.When C/N>4,the total phosphorus removal efficiency is above 60%.When C/N continues to decrease to 2?4,the average phosphorus removal efficiency of the system decreases to 42.6%,When C/N<2,the total phosphorus removal efficiency will further decrease.By the temperature changes of the raw water due to seasonality,supplemented by a circulating water bath device,the effect of the raw water temperature on the removal of pollutants in the aerobic granular sludge system is analyzed.The results show that the temperature has a small effect on the removal efficiency of COD removal,but worse on nitrogen and phosphorus removal.The first affect is the activity of nitrifying bacteria,which triggered the impact on the removal of ammonia nitrogen and total nitrogen,and ultimately affected the system's phosphorus removal.When the temperature is higher than 18?,the total nitrogen and ammonia treatment efficiency of the system can reach 99%and 80%,respectively,and all can achieve the discharge standard.When the temperature is lowered to 15?18?,the effluent concentration of ammonia nitrogen and total nitrogen in the system will increase obviously in a short period of time,but the removal efficiency of pollutants and the quality of effluent water can be restored to normal levels after the microorganisms are adapted.When the water temperature is reduced to 13?15?,the total nitrogen and ammonia nitrogen in the effluent of the system can not reach the standard,and the removal efficiency is seriously reduced.According to the characteristics of sludge in the reactor and its capacity of nitrogen and phosphorus removal performance,using Miseq high-throughput sequencing to analyze the sludge samples at the 0,100th,200th and 300th days of the reactor operation,and to explore the changes of biodiversity,microbial community succession and population structure in the system during the cultivation and operation.The test results show that the system's biodiversity decreases first and then increases with the time of cultivation and operation.Among them,the system species abundance and biodiversity are the largest at the 300th day.In the phylum horizontal community structure,Proteobacteria,Bacteroidetes and Chloroflexi are the dominant bacterial species.The bacteria related to biological nitrogen removal such as Nitrospira,Thauera,Denitratisoma,and Candidatus Nitrotoga are the dominant bacteria.