Electrically conductive carbon nanotube/graphene composite membrane for self-cleaning of biofouling via bubble generation

Biofouling is a major operational problem in membrane-based filtration processes, owing to the formation of intractable biofilms. Recently, electrically conductive membranes have attracted significant interest for fouling mitigation by membrane self-cleaning. However, water flux has not been completely recovered by electrochemical self-cleaning using bubble generation on the cathodic membrane surface, with the cause of insufficient water flux recovery not clearly identified. In this study, a carbon nanotube (CNT)/graphene membrane that exhibits high stability even under high voltage (i.e., 15 V) was fabricated. The self-cleaning effect was investigated under different applied voltages and self-cleaning times and evaluated based on water flux recovery and via quantitative biofilm analysis. The developed self-cleaning membrane achieved more than 4 log viable cell removal and 95.2% total extracellular polymeric substance removal on the membrane surface in 10 min. Through filtration and self-cleaning cycles, 100% water flux recovery was achieved, and the stability of the CNT/graphene membrane was verified. It was confirmed that the insufficient recovery of self-cleaning through conventional water electrolysis occurred due to the residual biofilm matrix, and the water flux recovery efficiency was improved using high voltage, suggesting that sufficient recovery can be achieved by a combination of physical and chemical/biological cleaning methods.