Nitric oxide treatment for the control of reverse osmosis membrane biofouling
Biofouling remains a key challenge for membrane based water treatment systems. This study investigated the dispersal potential of the nitric oxide (NO) donor compound, PROLI NONOate, on single species biofilms formed by bacteria isolated from industrial membrane bioreactor and reverse osmosis (RO) membranes, as well as on mixed species biofilms. The potential of PROLI NONOate to control RO membrane biofouling was also examined. Confocal microscopy revealed that different bacteria responded differently to PROLI NONOate exposure. However, the addition of NO induced dispersal in all but two of the bacteria tested and successfully reduced mixed species biofilms. The addition of 40 µM PROLI NONOate at 24 h intervals to a laboratory-scale RO system led to a 92% reduction in the rate of biofouling (pressure rise over a given period) by a bacterial community cultured from an industrial RO membrane. Confocal microscopy and EPS extraction revealed that PROLI NONOate treatment led to a 48% reduction in polysaccharides, a 66% reduction in proteins and a 29% reduction in microbial cells compared to the untreated control. A reduction in biofilm surface coverage (59% vs. 98%, treated vs. control) and average thickness (20 µm vs. 26 µm, treated vs. control) was also observed. The addition of PROLI NONOate led to a 22% increase in the time required for the RO module to reach its maximum TMP, further indicating that NO treatment delayed fouling. Pyrosequencing analysis revealed that the NO treatment did not significantly alter the microbial community composition of the membrane biofilm. These results present strong evidence for the application of PROLI NONOate for prevention of RO biofouling in an industrial setting.