| With the improvement of living standards,China produces a large amount of kitchen waste every year,and a large amount of kitchen waste water is generated during the treatment process.Kitchen wastewater has a high concentration of COD and particulate matter,and contains complex organic substances such as oil.Currently,anaerobic biological methods are mainly used to treat kitchen wastewater.However,the concentration of biogas slurry sludge after anaerobic digestion of kitchen wastewater is extremely high,requiring solid liquid separation to enter aerobic treatment.The treatment process is complex,and the separation of biogas slurry from solid liquid will cause problems such as microbial loss in the anaerobic reactor,affecting the efficiency of pollutant degradation.Relevant studies have shown that AnMBR has a good degradation effect on pollutants in kitchen wastewater due to the retention effect of membrane modules on sludge,ensuring the concentration of microorganisms in the anaerobic reactor.However,most of these studies are laboratory scale,and there are relatively serious membrane pollution issues,resulting in poor stability of the AnMBR system in treating kitchen wastewater.The stability of membrane filtration of biogas slurry determines the stability of the continuous operation of the AnMBR system.To understand whether AnMBR can meet the requirements for the treatment of kitchen wastewater on a pilot scale,this article focuses on the membrane filtration characteristics of biogas slurry in AnMBR on a pilot scale,including the removal rate of pollutants before and after membrane filtration of biogas slurry,factors affecting membrane flux,and the impact of different backwashing conditions on membrane flux recovery Study the stability of continuous operation under optimal backwashing conditions and the mechanism of membrane fouling;At the same time,the distribution and succession direction of the microbial community structure of AnMBR before and after operation were explored,and the research results obtained were as follows:(1)Study on the characteristics of biogas slurry membrane filtration.① The COD removal rate is between 77.2 and 86.8%,with an average of 82.3%;VFA removal rates fluctuate between 72 and 92%,with an average removal rate of 86%;The average TN content of influent water is 3177 mg/L,and the average TN content of effluent water is 2427 mg/L;There is no significant difference between pH and NH4+-N in inlet and outlet water,and anaerobic membrane has no significant removal effect on pH and NH4+-N The best backwashing conditions:a single backwashing flow rate of 15m3/h,a single backwashing duration of 5s,and a backwashing frequency of 30min.③ Under the optimal backwashing conditions,continuous operation of biogas slurry membrane filtration has strong stability:After two months of continuous operation,the transmembrane pressure difference increased from the initial 0.013MPa to 0.056MPa before chemical cleaning,the yield water flow decreased from the initial 0.32m3/h to 0.13m3/h,and the membrane flux decreased by about 59.4%.During the two months of continuous operation,the total water production is about 70.3 m3,with an average daily water production of 1.35 m3.The anaerobic membrane produced a total of about 145 m3 of water before the first chemical cleaning.(2)The mathematical model of biogas slurry membrane filtration flux has been established.① The mathematical model expression of biogas slurry membrane filtration flux isJ=△P/10-3(5.8×1012+5.6×1011M),When the pore diameter of the ultrafiltration membrane is 30 nm,the MLSS of the biogas slurry is 5 g/L to 16 g/L,and the △P is 0.023MPa to 0.029MPa,the model is reliable(R2>0.99).Based on this calculation,the biogas slurry membrane flux range is 1.56 ×10 6～3.37×10 6 m3/(m2·s),with an average membrane flux of 2.28×106 m3/(m2·s).②The main mode of membrane pollution of digested biogas slurry from kitchen wastewater is that pollutants form a filter cake layer on the membrane surface,and the total resistance Rt mainly comes from the sum of the membrane resistance Rm and the filter cake layer resistance Rc(where Rm=5.8×1012m-1,Rc=5.6×1011M);The actual viscosity of the biogas slurry will tend to a certain value under high-speed movement conditions within the membrane,which is 1×10 3Pa·s.③ Sensitivity analysis of the model parameters was conducted:When the process parameters varied from 0 to 50%,the sensitivity of each parameter of membrane flux was △ Pμ、Rm and MLSS;When the process parameters vary from-50%to 0%,the sensitivity of each parameter of membrane flux is sequentially as follows μ、△P,Rm,and MLSS.(3)The pollution mechanism of biogas slurry filtration membrane was revealed.During the biogas slurry filtration process,all the proteins in the organic components are returned to the biogas slurry tank,with little residual on the membrane;Not all polysaccharides are returned to the biogas slurry tank,and about 14.5%to 26.9%will remain on the membrane.As the concentration ratio of biogas slurry increases,the residual rate of polysaccharides on the membrane gradually increases.Therefore,the organic component of membrane pollutants is mainly polysaccharide Inorganic components are the main components of membrane pollutants,accounting for about 79.72%,and are mainly magnesium phosphate and calcium carbonate.(4)The distribution and succession direction of microbial community structure were analyzed.①The main phylum level microorganisms of AnMBR before and after operation were consistent,but there were some differences,mainly reflected in the presence of Patescibacteria before operation(accounting for 7.44%),and Caldatribacteriota after operation(accounting for 7.10%).②The main genus level microorganisms before AnMBR operation were Fastidiosipila(accounting for 16.61%)and Rikenellaceae_RC9_gut_Group(accounting for 10.86%);The main genus level microorganisms after operation are Fastidiosipila(accounting for 17.89%)and norank_f_ST-12K33(accounting for 10.11%).③Before and after AnMBR operation,the number of methane producing bacteria at the phylum level significantly increased;The diversity of archaea level microorganisms is more abundant. |
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