Study On Denitrification Performance And Membrane Pollution Of A MBBR-MBR Coupled Reactor

In recent years,with the rapid development of Chinese economy,the problem of eutrophication of water body has become more and more serious due to the excessive discharge of nutrients such as nitrogen and phosphorus.Controlling the release of nitrogen and phosphorus is an important strategy to solve the problem of eutrophication,and denitrification has become one important and indispensable part of water treatment processes.Moving bed biofilm reactor(MBBR)has become an effective method for nitrogen removal because of its flexible operation and long sludge age.MBR can enhance the biological treatment.MBBR-MBR coupled reactor has the unique advantages of removing nitrogen and controlling the membrane fouling.In this study,a coupled reactor of MBBR and MBR was used to explore its denitrification performance and membrane pollution under different biocarrier filling ratios and hydraulic retention times,and the optimum biocarrier filling ratio and hydraulic retention time were determined.The main conclusions are as follows:(1)Under the hydraulic retention time of 12 h,the performance of removing pollutants in the MBBR-MBR reactor was investigated under the biocarrier filling ratios of 10%?15% and 20%.The biocarrier filling ratio had little effect on the removal rates of TOC and NH4 +-N,both of which could reach more than 90%,and filling ratio of15% is relatively prominent with removal rates higher than 98%.The filling ratio had great influence on the removal of SND and TN,and their removal rates for the filling ratio of 15% were also the highest.In the system,nitrification was easier to occur than denitrification,and denitrification was more affected by the filling ratio.The attached biomass and the growth rate of attached biomass on the polyurethane sponge biocarrierwere closely related to the filling ratio,the highest biomass and growth rate of biofilm were achieved at the filling ratio of 15%.(2)The dissolved oxygen and redox potential in the biocarrier were measured by a Unisense microelectrode system.The results showed that the DO concentration and ORP distribution in the biocarrier at 15% filling rate were more reasonable,which was easier to create the environments for facultative anaerobes and aerobic flora.The overall performance of removing pollutants in the MBBR-MBR reactor was satiafactory under the DO concentration of 6 mg/L or so.In addition,high-throughput sequencing showed that the biodiversity in the polyurethane sponge carrier at the 15% filling rate was more complex,and there were more denitrifying bacteria.And the rate of membrane fouling at 15% filling ratio was slower under similar experimental conditions.(3)Under the biocarrier filling ratios of 15%,the performance of removing pollutants in the MBBR-MBR reactor was investigated under the hydraulic retention times of 6h?12h and 24 h.The highest removal rates of TOC and NH4+-N,higher than97%,were achieved at HRT=12h in the MBR-MBR coupled reactor.The average biomass attached to the polyurethane sponge biocarrier monomer was 0.60g/biocarrier,the mean volatile biomass attached to the biocarrier was 0.52g/biocarrier,and the average a VAGBS/a AGBS was 84.5%,indicating relatively high bioactivity and fast growth rate(k=0.01625d-1).(4)Under the hydraulic retention times of 12 h,the volume ratio of sludge with a particle size of 130 um accounts for the largest among the volume distributions,and the average sludge particle size was obviously larger than those at other two hydraulic retention times of 6h and 24 h.The corresponding membrane fouling at HRT=12h was also slower than those at other two HRTs,the filtration resistance of cake layer was improved,and the irreversible pollution of MBR membrane module was alleviated,indicating the increase of service life of MBR filament.At HRT=6h,the EPS concentration,SMP concentration and SMPp/SMPc in the MBR mixture were 16.4mg/L?45.6mg/L?0.4,respectively.At HRT=12h,the EPS concentration,SMP concentration and SMPp/SMPc in the MBR mixture were 11.4mg/L?27.9mg/L?1.31,respectively.At HRT=24h,the EPS concentration,SMP concentration and SMPp/SMPc in the MBRmixture were 12.5mg/L?33.9mg/L?0.9,respectively.When HRTs were 6h?12h?24 h,Rc values were 1.74×1012m-1?1.03×1012m-1?1.44×1012m-1,respectively,indicating that high-concentration EPS and SMP together with low ratio of SMPp/SMPc mainly contributed to the membrane fouling and controlling the content of polysaccharide in SMP in reactor can effectively control membrane fouling.