Research On The Treatment Of Municipal Wastewater By The New Multi-stage AO-MBR Process

With the gradual improvement of the economy and ideology,the public's requirements and expectations for the living environment are increasing,At the same time,the total amount of wastewater discharged has also continued to rise.Wastewater contains a large amount of pollutants,which has a serious impact on the ecological environment.To control water pollution,we must first control the source.At present,the discharge standards of urban sewage plants are quite strict,and the limits of nitrogen and phosphorus emissions in local standards are lower,and traditional biological treatment processes are difficult to fully meet the standards.Membrane bioreactors have received much attention for their unique advantages,and effluent meets stringent standards.Therefore,it is necessary to develop a new multi-stage AO membrane bioreactor process for decentralized sewage or small sewage plants,to explore the process and effect of removing major pollutants,and to provide experimental basis for the selection of process design parameters.In this paper,experimental water is used as raw water for wastewater treatment plant,multi-stage AO-MBR pilot plant experimental equipment is used to study its nitrogen and phosphorus removal technology,and the effects of various main parameters on nitrogen and phosphorus removal effects,and the role and advantages of the sedimentation tank are summarized.The test results prove that:(1)The system performs well on water COD and ammonia nitrogen removal.The average effluent concentration is 18.52 mg/L and 1.85 mg/L,respectively,reaching the Class A standard of DB12/599-201 5 Tianjin N"Emission Standard for Pollutants in Urban Sewage Treatment Plants".The average removal rates of COD and ammonia nitrogen were 96.02%and 94.37%,respectively.The removal of total nitrogen was significant.The removal rate of total nitrogen in the four-stage AO-MBR system under high and low carbon-nitrogen ratios was 91.76%,77.4%,the effluent concentration was 3.21 mg/L and 6.25mg/L,respectively,the system high carbon and nitrogen than the influent is more conducive to the removal of nitrogen and phosphorus.(2)The change of the influent distribution ratio has little effect on the removal of COD and ammonia nitrogen,and the removal rate is stable above 85%,but the removal of total nitrogen and total phosphorus when the three-point influent distribution ratio is 55%:35%:10%.It is better than the three-stage single-point water inflow.The system SRT is most efficient for nitrogen and phosphorus removal when controlled at 42d.(3)The degradation of COD and ammonia nitrogen mainly occurs in the aerobic tank.The effluent of the AO biochemical system is lower than that of the third-class AO.The maximum degradation rate is in the 01 pool,which is 0.013kg/(kgMLSS·h)and 0.0095kg/(kgMLSS·h),the maximum degradation rate of ammonia nitrogen occurs in O1 and 02,respectively 0.001 kg/(kg MLSS h)and 0.0005 kg/(kg MLSS h);and the highest denitrification rate appears in the A1 pool,respectively 0.0023 kg N03-/(kgMLSS·h),0.0009 kg N03-/(kgMLSS·h).The above rates all have a downward trend with the process.The level 4 AO denitrification rate is generally higher than the third-level AO system.(4)The inclined tube sedimentation tank can reduce the dissolved oxygen in the return sludge,so that the concentration in the anaerobic tank is always maintained at about 0.2 mg/L,and the ORP potential is below-200mv in a stable anaerobic environment,which is beneficial to the phosphorus release of the polyphosphate bacteria.And the hydrolytic acidification process of obligate anaerobic fermentation bacteria,eliminating the need for internal reflux energy saving;at the same time,the separation of solid and liquid,reducing the membrane pool MLSS,is conducive to delaying membrane fouling.After the backwashing of sodium hypochlorite solution,the transmembrane pressure difference decreased to 14Kpa,and the membrane flux recovery rate FFR increased to 77.55%.Calculating the energy consumption per ton of water is 1.071KW·h/t,However,MBR working process has a great development in energy saving and consumption reduction.