Enhanced Removal Of Pollutants By Carbon-based Conductive Membrane Under Electrochemical Assistance And Its Antifouling Mechanism

Membrane separation technology has been widely used and developed in wastewater treatment because of its advantages of low energy consumption,small floor area,stable effluent quality and easy automatic control.However,membrane fouling caused by membrane filtration,trade-offs between membrane permeability and selectivity,and subsequent processing of concentrates limit the further application of it.Membrane filtration coupled with electrochemistry is an emerging research direction in wastewater treatment.Conductive membranes can simultaneously achieve pore size screening and electrochemical degradation of pollutants.Meanwhile,the potential effectively inhibits deposition and enrichment of pollutants by adjusting interfacial forces between pollutants and membrane,and effectively inhibit membrane fouling.In response to the above problems,this thesis carried out the following work:A carbon fiber-based CC/PVDF conductive composite membrane was prepared on a pretreated carbon fiber substrate by a simple and efficient two-step casting and phase inversion method.The morphology,structure and physic-chemical properties of the membrane materials were characterized and discussed.The results showed that the surface of CC/P VDF membrane was rich in spherulites and sponge structure,and PVDF organic phase casting formed a stable porous membrane structure.With the preparation process,the surface of the membrane was gradually uniform and smooth,the surface contact angle changes from hydrophobic to hydrophilic,CC/P VDF membrane shows potential permeability,stability and antifouling performance.Using methyl orange(MO)as a small-molecule model pollutant,the performance and mechanism of MO removal and antifouling performance of CC/PVDF membrane under electrochemical assistance were explored.The results show that electrochemical assistance can significantly improve removal efficiency of MO and permeability of membrane,and the effect is better at higher voltages.At+3 V and-3 V,the removal efficiency of the CC/PVDF membrane is 5.3 and 5.1 times that of the membrane filtration(0 V)alone,and the permeate flux is 1.2 and 1.3 times that of 0 V.The enhanced performance of MO removal and excellent resistance to membrane fouling benefit from the synergistic effects of electrostatic repulsion,electrochemical degradation,and electrochemistry enhanced wettability.HO· generated by direct electron transfer and Fenton-like reaction are the main reasons for MO oxidation.Mass spectrometry was used to identify intermediate products of MO degradation,and the possible degradation pathway of MO was proposed.It was proved that MO degradation was mainly divided into three stages:bond breaking oxidation,ring opening reaction and complete oxidation.Among them,bond breaking oxidation mainly includes demethylation reaction,desulfurization reaction and hydroxylation reaction.Using humic acid and Escherichia coli as organic and biological pollutants,respectively,antifouling performance and interaction mechanism of CC/PVDF membrane with electrochemical assistance were studied.The results show that electrochemical assistance can significantly improve removal efficiency of pollutant and membrane permeability,and effect of applying negative potential is significantly better than positive one.The removal efficiency and permeate flux of HA filtration at-2 V were 80%and 82%,which were 2.3 and 2.0 times that of 0 V respectively.The permeation flux of Escherichia coli filtration at-2 V was 75%,which was 1.3 times that of 0 V.When the applied potential is greater than or equal to 2 V,severe cell dehydration and E.coli shrinkage on membrane surface was observed,biofilm is completely inactivated,bacteriostatic and anti-adhesion properties of CC/PVDF membrane reach 100%.XDLVO theory was utilized to calculate interfacial forces between humic acid or E.coli and membrane at different potentials.The results show that the Lewis acid-base and electrostatic double layer forces play major roles in the total interfacial force of short-range pollutant-membrane surface,while the Lifshitz-van der Waals force negligible.At-2 V,electrostatic repulsion force is greatly enhanced,which dominates in the enhanced antifouling performance of CC/PVDF membrane.