Mitigation of biofouling in forward osmosis process by quorum quenching techniques

Abstract

Biofouling, a formation of biofilm on the membrane surface, is an inevitable obstacle in membrane processes including forward osmosis (FO) process. After the initial attachment and early stage of growth of bacteria on the membrane surface, quorum sensing (QS) molecules are secreted and promote group behaviours for the formation of thick and matured biofilm. In this study, we investigated the potential application of QS degrading molecules (quorum quencher, QQ) acylase and lysate from bacteria Rhodococcus sp. BH4 for the mitigation of biofouling on FO membrane surfaces for the first time. In a batch experiment, QQ molecules with the concentration of 10mg/L successfully degraded more than 70% of QS molecules such as N-acyl homoserine lactones. From the continuous lab-scale FO tests, with the presence of acylase and BH4 lysate, FO system was operated 30 and 15 % longer with same number of physical cleaning compared to the absence of QQ molecules. This result was contributed by the difference in the structure and adhesion force of the biofilm with the presence and absence of QQ molecules. The amount of exocellular polymeric substances (EPS) per unit biomass was reduced more than 70% in the existence of 10 mg/L of acylase and BH4 lysate. This further correlated with the CLSM images that formation of looser biofilm in the presence of QQ molecules. In addition, surface force apparatus (SFA) revealed that the adhesion force of EPS with the existence of QQ molecules was 70 % weaker than the non-existence of it. In conclusion, the application of QQ molecules makes the adhesion force of EPS weaker and structure of biofilm looser and finally lead to reversible fouling.