Application And Improvement Of PVDF/Carbon Fiber Cloth Composite Catalytic Cathode Membrane In Integrated MBR/MFC System

When it comes to wastewater treatment,membrane fouling and high energy consumption are common problems faced in Membrane bioreactor(MBR).Microbial fuel cell(MFC)is a newly developed device that extracts energy from wastewater and converted it into electricity;however,low effluent quality is the disadvantage in MFC.Coupling MBR and MFC system exhibits many advantages compared to single MFC or MBR,say using MBR,the effluent quality of MFC are greatly improved,and the micro electric field in MFC helps to reduce membrane fouling in MBR;moreover,energy from wastes can be recovered via MFC.Conductive membrane was always used to integrate MBR/MFC system for its easy fabrication and operation.To date,among studies in cathode membrane coupled MBR/MFC system,there are still some problems,like low power generation,unstable conductive membrane,and low removal efficiency towards antibiotics.Considering the above problems,in this study,polyvinylidene fluoride(PVDF)/carbon fiber cloth composite membrane was firstly prepared.Then in MBR/MFC coupled system,the property of PVDF/carbon fiber cloth composite membrane and the performance of MBR/MFC coupled system were greatly improved via membrane flux improvement,catalytic modification and power generation enhancement.The detailed contents are divided into sections as follows:(1)Carbon fiber cloth was firstly immersed into potassium permanganate and ferric nitrate saturated solution,followed by heating under nitrogen flow.Then as a substrate,it was covered by PVDF binder to prepare PVDF/carbon fiber cloth composite membrane.In the MBR/MFC coupled system,the PVDF/carbon fiber cloth composite membrane operated stably for more than 30 days.In micro electric field,the anti-fouling flux of PVDF/carbon fiber cloth composite membrane was improved by 60%compared to the flux without electric field.The pure water flux of membrane was 164 L m-2 h-1(LMH,10 kPa).In MBR/MFC coupled system,the maximum power density was 1358 mW m-3.(2)To improve the flux of PVDF/carbon fiber cloth composite membrane,the PVDF/carbon fiber cloth composite membrane with high flux was prepared via adding catalyst and carbon nanofiber into PVDF binder.Firstly,the palladium-reduced graphene oxide-CoFe2O4(Pd-rGO-CoFe2O4)catalyst was prepared through microwave heating method.Then,it was added into PVDF and accompanies with carbon nanofiber to prepare PVDF/carbon fiber cloth composite membrane with high flux.The results indicated the pure water flux of the composite membrane was 5563 LMH(10 kPa).The porosity of PVDF/carbon fiber cloth cathode membrane was 94.15%,which was 3 times higher than raw PVDF/carbon fiber cloth cathode membrane without adding catalysts.The results indicated the addition of nanoparticles in PVDF binder helps to improve porosity of membrane.Thinning the scraping thickness from 700 ?m to 300 ?m,the conductivity of PVDF layer increased from 3.1 ×10-6 S cm-1 to 3.3×10-3 S cm-1,improved by 1000 times,and in MBR/MFC coupled system,the maximum power density of MBR/MFC coupled system increased from 506 mW m-3 to 683 mW m-3,improved by 34%.(3)To improve the removal rate of antibiotics,the photocatalytic CoFe2O4-rGO typed PVDF/carbon fiber cloth composite membrane was prepared and used in MBR/MFC coupled system.In the degradation of tetracycline hydrochloride antibiotics,photocatalysis helped to improve the removal rate.In the preparation,four types of bimetallic iron oxides catalyst MFe2O4(M = Co,Zn,Ni,Fe)was prepared,among which CoFe2O4 was picked as the most active catalyst in oxygen reduction reactions.Then the CoFe2O4 was composited with rGO(CoFe2O4-rGO).As additions,CoFe2O4-rGO and carbon nanofiber was added in PVDF binder,followed by membrane scraping.In visible-light irradiation,using CoFe2O4(-rGO)photocatalytic membrane,the power generation of the system was improved by approximately 8%),and the removal rate of hydrochloride tetracycline antibiotics in cathode chamber achieved approximately 95%.The results indicated the photocatalysis in cathode showed improved effect on bioelectrochemical reactions.The photocatalyst was actived in the environment of light irradiation,showing improved catalytic activity in reduction reactions,further improving the performance of MBR/MFC coupled system.(4)To improve power generation,the MBR/MFC coupled system with low-energy consumption was configured.In the system operation,the effluent was got in the action of gravity,and oxygen used in cathode chamber was got from diffusion via outside air.The only energy consumption in the process of operation was from the influent suction.In the system,granular activated carbon(GAC)was added as dynamic additional layer on the surface of cathode membrane.The GAC can not only resist contaminants from flowing to membrane surface,but also performed as expanded cathode in MBR/MFC coupled system.The results indicated the maximum power density of the system achieved 5.1 W m-3,and the coulombic efficiency was 10.89%.After modified GAC with hydroxyl iron oxide(FeOOH)and titanium dioxide(TiO2),hydrogen dioxide(H2O2)was produced in effluent.The existence of H2O2 showed great improvement in the removal process of tetracycline hydrochloride antibiotics,keeping the removal rate at 99%.