In Situ Electrochemical Cleaning Of Carbon Nanotube Conductive Membrane To Alleviate Membrane Fouling

Water resources shortage and serious pollution affect the sustainable development of economy and society.Sewage recycling is the main way to alleviate water resources crisis.Ultrafiltration(UF),a low-pressure membrane filtration technology is often used in fields such as wastewater treatment.With the continuous development of UF technology,membrane fouling has become a major obstacle affecting the efficient operation of UF systems.In previous studies,membrane cleaning is usually used to alleviate membrane fouling and improve the efficiency of using membrane.However,traditional membrane cleaning method using strong acid/alkali is easy to cause damage and secondary fouling to the membrane.In order to reduce the damage caused by membrane cleaning and alleviate the phenomenon of membrane secondary fouling.In recent years,some researchers have combined electrochemistry with membrane technology to prepare conductive filter membrane to improve the efficiency of using membrane.As a common nanometer conductive material Carbon nanotube(CNT)has been widely used in the research of carbon conductive membrane.At present,the researches on electrochemical cleaning of carbon conductive membranes mainly focus on single organic pollutants.There are few researches on biological fouling,organic/biological mixed fouling,and actual water fouling,which restricts the further development of conductive membranes.Therefore,CNT/PTFE conductive membrane was prepared in this study.Sodium alginate(SA),Bovine serum albumin(BSA),Pseudomonas aeruginosa,SA/Pseudomonas aeruginosa and the actual water were selected as the research objects.The characteristics of different pollutants on the membrane surface were investigated.The effect and mechanism of periodic electrochemical cleaning on alleviating membrane fouling were explored.In this study,it was found that periodic electrochemical cleaning could almost completely recover the decline in membrane flux caused by organic matter and the decline in membrane flux caused by some microorganisms.It was found that periodic electrochemical cleaning can effectively solve the problem of membrane fouling,and the application of external voltage can kill most of the bacteria trapped on the surface of the membrane.Specific conclusions of the experimental study are as follows:(1)The composite ultrafiltration membrane coated with conductive carbon material was prepared.Based on introducing CNT into PTFE membrane,SEM characterization shows that the surface of PTFE membrane is interwoven.The thickness of the prepared CNT/PTFE membrane was 68.85μm.Electrical conductivity is 0.9 s/cm;The main elements of the membrane are C=C,C-C,C-O,etc.The contact Angle is 89.9°.(2)With SA as the feed solution,the membrane standardized flux recovered from46%to 99%when 3 V voltage was applied for 3 min electrochemical cleaning.After six fouling/electrochemical cleaning cycles,the membrane standardized flux still recovered to 90%.Using BSA as the source of fouling,the standardized flux of the membrane was restored to 82%after 3 min of electrochemical cleaning with a voltage of 3 V.After 6 fouling/electrochemical cleaning cycles,the standardized flux of the membrane was still restored to 70%.Using Pseudomonas aeruginosa as fouling source,CNT/PTFE membrane was used as anode,and 3 V voltage was applied to the membrane for 3 min electrochemical cleaning.After Pseudomonas aeruginosa fouling,the standardized flux of the membrane could be restored to 75%.At the same time,the bacteria trapped on the membrane surface can be reduced from 6×10~6 CFU/cm~2 to 6CFU/cm~2 by electrochemical cleaning for 3 min,and the bacteria removal rate can reach6 log.(3)When SA/Pseudomonas aeruginosa mixed system was used as feed solution,the membrane standardized flux decreased from 100%to 43%.After 3 min electrochemical cleaning at 3 V voltage,the membrane standardized flux recovered to94%,and after six fouling/electrochemical cleaning cycles,the membrane standardized flux recovered to 74%.(4)The tertiary effluent from the sewage treatment plant is used as the feed solution,the membrane flux increased from 43%to 74%after electrochemical cleaning.The bacterial concentration on the membrane surface was reduced from 8×10~3CFU/cm~2 to 5 CFU/cm~2.The bacterial removal rate reached 3 log.Aquaculture water as the feed solution,the membrane flux increased from 43%to 66%.The bacterial concentration on the membrane surface decreased from 7×10~3 CFU/cm~2 to 5 CFU/cm~2.The bacterial removal rate reached 3 log.When the reservoir water is used as the feed solution,the membrane flux can be increased from 45%to 89%by electrochemical cleaning.The bacterial concentration on the membrane surface decreased from 1×10~4CFU/cm~2to 14 CFU/cm~2.The bacterial removal rate reached 3 log.Using seawater as the feed solution,the membrane flux increased from 46%to 64%after electrochemical cleaning cycle.The bacterial concentration on the membrane surface was reduced from4×10~4 CFU/cm~2 to 3 CFU/cm~2.The bacterial removal rate reached 4 log.(5)When CNT/PTFE membrane was used as anode to relieve membrane pollution,the membrane flux recovered from 45%to 70%with the introduction of free radical quencher tert-butanol.Compared with the reaction without the addition of tert-butanol,the membrane flux decreased by 29%.Therefore,direct oxidation and indirect oxidation acted on the electrochemical cleaning together.By introducing Cl·quencher benzoic acid and·OH quencher nitrobenzene based on electrochemical cleaning,the film flux recovered from 45%to 85%and 88%respectively,and the film flux decreased by 14%and 11%compared with that without adding free radical quencher.Therefore,Cl·and·OH played a role in the indirect oxidation reaction.