Effect of biofilm inhibitor on biofouling resistance in RO processes

Biofouling is a major operational problem in reverse osmosis (RO) processes. Numerous studies have focused on the control of biofouling using physical and chemical cleaning methods. However, irreversible biofouling, wherein a biofilm adheres firmly to an RO membrane surface, is hard to remove by physical and chemical cleaning methods. Irreversible biofouling originated from the formation of microbial biofilms, which comprised microbial cells and their self-produced extracellular polymeric substances. In this study, we tried to control irreversible biofouling by using a biofilm inhibitor in the RO process. Prior to testing, biofouling was classified into reversible and irreversible biofouling resistance, through laboratory scale RO unit operations under enhanced biofouling conditions. A tightly attached biofilm, which assumed to be caused by irreversible biofouling resistance, emerges after 30 h of laboratory scale RO operation. We have tested the inhibition of irreversible biofouling by using 4-NPO as a quorum sensing inhibitor. The microbial biofilm formation was found to be reduced 46 – 91% by 4-NPO in a concentration-dependent manner without affecting the microbial growth. In addition, irreversible biofouling on the RO membrane was reduced 36 – 67% by 4-NPO in a concentration-dependent manner. Furthermore, 4-NPO was able to decrease the irreversible biofouling resistance, instead of the reversible biofouling resistance, in laboratory scale RO units. The results of this study clearly demonstrated that 4-NPO was an effective biofilm inhibitor that could reduce the biofouling, especially, irreversible biofouling, in RO processes.