Performance Of The Anaerobic Forward Osmosis Membrane Electro-Bioreactor

Wastewater was rich in biomass energy,which could be regarded as misplaced resources.Therefore,it was of great significance to recover the biomass energy effectively for reducing water pollution and alleviating energy crisis.Anaerobic membrane bioreactor(AnMBR)could produce biogas by utilizing organic compounds in the sewage and reduce energy consumption without aeration.Besides,the membrane could retain anaerobic microorganisms which grew slowly to improve the treatment efficiency.At present,AnMBR has drawn widespread attentions in the industry.However,microfiltration and ultrafiltration membranes were unable to retain dissolved pollutants,and membrane fouling was also serious in AnMBR.Forward osmosis(FO)was a membrane separation process driven only by osmotic pressure,and drew the water molecules spontaneously across a semipermeable membrane from feed solution of high water chemical potential to draw solution of low water chemical potential.FO could be used to extract drinking water from wastewater and sewage.In this study,FO membrane was used as the separation membrane in AnMBR to form anaerobic forward osmosis membrane bioreactor(An OMBR),which could not only maintain the advantages in AnMBR for extracting energy from biomass but also improve the performance of AnMBR.In addition,we combined microbial electrolysis cell(MEC)and AnOMBR to form AnOMEBR,which enhanced the degradation of organic compounds at the anode and increased the methane yield at the cathode.Moreover,stainless steel mesh was placed on the membrane surface to control membrane fouling effectively.This paper mainly carried on two aspects of experimental research as follows.(1)Compared with An OMBR,performance of AnOMEBR was evaluated in terms of reverse osmosis,gas composition,methane production,pollutant removal rates and energy recovery,etc.Then the function of electric field in AnOMEBR was analyzed.Magnesium acetate was used as draw solution,and the voltage of 0.5 V was applied.Results showed that the conductivity increasing rate in AnOMEBR and AnOMBR were about 0.08 ms/(cm·d)and 0.11 ms/(cm·d),respectively.Salt accumulation in our study was reduced significantly in contrast with other literatures.In AnOMEBR,the application of anode improved the degradation of organic compounds.As a result,the removal rates of COD,NH4+-N and PO43--P attained 98%,57.77% and 77.29%,respectively,which were better than those in AnOMBR(96%,51.43% and 73.22%).The methane yield of AnOMEBR was about 0.281 L/g COD,and it almost increased by 11.07% compared with AnOMBR(0.254 L/gCOD)Although AnOMEBR increased power consumption compared with AnOMBR,the increasing methane yield could compensate for the extra power consumption in AnOMEBR and about 0.537 KJ per day positive energy gain could be obtained.(2)The changes of membrane flux in AnOMBR and AnOMEBR were investigated.And the mechanism of alleviating membrane fouling was studied carefully for AnOMEBR via the determination of EPS,SMP,protein and polysaccharide.Results demonstrated that the membrane operation cycle in AnOMEBR was about 1.27 times as long as that in AnOMBR.That was to say,membrane fouling rate decreased significantly in AnOMEBR.Due to the electrostatic repulsion,the stainless steel mesh cathode in AnOMEBR could prevent the negatively charged substances from depositing on the membrane surface.Moreover,the contents of LB-EPS and SMP in AnOMEBR were lower than those in AnOMBR,and decreased by 8.93% and 23.92% separately.In addition,the contents of protein and polysaccharide averagely reduced by 12.75% and 17.89% respectively compared to AnOMBR.