Performance Of Integrated Flat-Sheet Membrane Bioreactor For Wastewater Treatment In Malls

In recent years,with the acceleration of urbanization,the number of malls in large and medium-sized cities increased sharply.The treatment and reuse of mall wastewater have become a new issue in the field of environmental engineering sewage treatment.The sewage treatment of mall wastewater is faced with problems such as large changes of water volume,large reuse water and less available land area.The traditional urban domestic sewage treatment process can’t deal with the above problems well.Integrated membrane bioreactor(MBR)can effectively remove pollutants to meet the wastewater reuse standard and reduce the floor space.It is an effective technology for treating mall wastewater,but membrane fouling has always been a key factor perplexing the popularization and application of MBR technology.Firstly,the performance of lab-scale A2O-MBR integrated reactor treating synthetic mall sewage was studied,and the service life of various commercial separation membranes was compared.The results showed that in A2O-MBR,when HRT was 24 h and the concentrations of influent BOD5、NH4+-N were～300 and～100 mg/L,respectively,the average effluent concentrations were 5.07 and 4.26 mg/L with the corresponding average removal rates were 98.27%and 95.56%respectively.By comparing ceramic flat-sheet membrane(FS-TC),polyvinylidene fluoride flat-sheet membrane(FS-PVDF),polysulfone hollow-fiber membrane(HF-PS)and polyvinylidene fluoride hollow-fiber membrane(HF-PVDF),it was found that FS-PVDF has the longest service life under the same operating condition.Through the measurement of membrane resistance,it was found that the inherent resistance and total resistance of FS-PVDF were always the lowest.At the same time,it was found that the cake layer resistance(Rf)was the main resistance type of flat-sheet membrane fouling,and the filtration resistance(Rp)caused by concentration polarization was the main resistance type of hollow-fiber membrane fouling.At the end of the operation,the extracellular polymeric substances(EPS)on the membrane surface were measured.It was found that the concentration of soluble extracellular polymeric substances(S-EPS)on the surface of FS-PVDF was 7.34 mg/gVSS,which was lower than 7.56,422.87,and 416.18 mg/gVSS on the surface of FS-TC,HF-PS,and HF-PVDF.Through the research of living and dead cells on the membrane surface,the proportion of dead cells on the surface of the hollow-fiber membranes(HF)was much higher than that on the surface of the flat-sheet membranes(FS),which might be the main cause of large accumulation of EPS on the surface of HF membranes(p<0.05).Using high-throughput 16S rRNA gene sequencing technology,it was found that Proteobacteria,Bacteroidota and Dependentiae were the bacteria with more accumulation on the membrane surface area.At the genus level,norank_f_Microscillaceae and norank_f_Vermiphilaceae accumulated more on the membrane module surface.The pilot-scale A2O-MBR integrated bioreactor was built with FS-PVDF as membrane modules,and mall wastewater in Shanghai was used for a long-term test.Under the conditions of HRT of 48 h and influent BOD5,NH4+-N concentrations of 200～400 and 60～100 mg/L respectively,the average concentration of effluent was 7.14 and 0.25 mg/L respectively with the average removal rate reaching 97.66%and 99.51%,respectively.The effluent meets the standards for urban greening,toilet flushing and reuse in urban sewage recycling and urban miscellaneous water(GB T18920-2020).During the monitoring time,the trans-membrane pressure remained about 0.001 MPa,the concentration of S-EPS on the membrane surface was 3.94 mg/gVSS,which was still at a low level,and there were few dead cells on the membrane surface.The analysis of membrane surface microbial community found that the bacteria related to membrane fouling were mainly Proteobacteria,Bacteroidota,Actinobacteriota,Chloroflexi,Verrucomicrobiota and Dependentiae.