Chlorination caused a shift in marine biofilm niches on microfiltration/ultrafiltration and reverse osmosis membranes and UV irradiation effectively inactivated a chlorine-resistant bacterium.

The effect of chlorine disinfection on marine biofilm populations and communities formed on membrane surfaces was investigated under two feedwater conditions: raw seawater and deep bed filtration-treated seawater. As a result of chlorination, the structure of the biofilm community on the microfiltration/ultrafiltration and reverse osmosis membrane coupons shifted significantly at the genus level. However, the total bacterial population was not reduced under the two feedwater conditions. This failure to control the biofilm was attributed to the adaptation and survival of selected bacteria under chlorine stress. Phaeobacter caeruleus, isolated from the biofilm, was examined as a representative chlorine-resistant biofilm-forming bacterium. The number of viable P. caeruleus was significantly reduced (as much as 99.8%) after ultraviolet (UV) disinfection. The results indicated that additional disinfection by UV irradiation can inactivate chlorine-resistant bacteria. Therefore, tandem chlorination-UV disinfection may enhance the efficiency of biofouling control in seawater reverse osmosis processes. The synergistic effects of tandem chlorination-UV irradiation on the marine biofilm community should be investigated in future studies.