Electroenhanced Treatment Of Anaerobic MBR With Carbon Nanotube-based Membranes For Low Strength Wastewater

With the accelerating pace of urbanization in China,the demand for freshwater resources and the discharge of urban domestic sewage from human activities are increasing steadily.The anaerobic biological treatment process,represented by the up-flow anaerobic sludge bed reactor?UASB?,is applied to treatment low concentration domestic sewage due to its low excess sludge output,low energy consumption,biogas production,easy operation and controllability.In order to improve effluent quality and achieve effluent discharge with standards,membrane separation technology emerges.Coupled UASB with separation membranes can improve the efficiency of organic pollutants removal and strengthen the quality of effluent water with the result that membranes prolong the contact time between organic pollutants and anaerobic microorganism.However,some traditional problems on membrane fouling and membrane cost limit its wide application.To solve these problems,conductive carbon nanotube-based separation membranes were prepared in this paper that realized the coupling of UASB,membrane separation technology and electrochemical technology by applying electrical bias on the surface of membranes and electrodes.In the experiments,performances of new reactors for low strength wastewater treatment at different hydraulic retention time and different polarization bias of membrane electrode respectively,and influences mechanism of electrochemical assistance on separation processes and membrane foulings were systematically investigated.Besides,a novel concept called anode biofilm reactors with better operating conditions by exploring its treatment performances at different hydraulic residence time was put forward in this paper.The main results were showed as follows.?1?The carbon nanotube-based separation membranes with good conductivity and hydrophilicity were prepared by the acidification–suction-calcination method,and its effective diameter,average pore size and porosity were 40 mm,90 nm and 92.5%respectively.A better performance that SCOD and COD removal rates were more than 90%,and the yield ratio of carbon dioxide was 22%,and the methane conversion rate was 0.039 L/g COD_removedemoved of the new reactor were achieved at the operating condictions of 35°C and 6.5 h.The experiment results showed that the addition of separation membranes in UASB was conducive to maintaining higher concentration of microorganisms and prolonging the contact time between microorganisms and organic pollutants that achieved higher organic pollutants removal efficiency and methane production to get better effluent water quality.?2?Under the operating conditions of 35°C and 6.5 h,the new reactor with+1.0 V electrical bias on the surface of separation membranes showed better performance that SCOD and COD removal rate were more quickly stabilized at over 80%,and the yield ratio of carbon dioxide was 29%,and the methane conversion rate was 0.058 L/g COD_removed.The results indicated that the rapid formation of anode biofilms could achieve a stable removal of organic pollutants more quickly to improve effluent water quality further and alleviate membrane foulings with improving the characteristics of activated sludge mixture.Besides,wherther positive bias or negative bias was applied on the surface of membrane,the addition of electrochemical technology could significantly accelerate the formation of granular sludge and increase the abundance and activity of microorganisms that played an auxiliary role in the removal of organic pollutants and the mitigation of membrane fouling.?3?Comparing the treatment performance of anode biofilm anaerobic sludge bed reactors under different hydraulic residence times,the better operating conditions in which the SCOD and COD removal rate were both over 90%,and the yield ratio of carbon dioxide was 32%,and the methane conversion rate was 0.151 L/g COD_removed was 4.5 h at 35°C.The results showed that the new anode biofilm reactor had good pH buffer capacity and methanogenic capacity owing to the enhanced microbial activity,lower extracellular polymeric substance concentrations and formation of granular sludge with the assistance of electrochemical technology,and the mitigation effects of electrochemical technology on membrane fouling was also of great importance to the long-term and stable operation of anodic biofilm reactors.