Impact of repeated pressurization on virus removal by reverse osmosis membranes for household water treatment
Reverse osmosis (RO) membranes are commoditized and available for household water treatment (HWT) in areas where access to safe water is limited. The RO membranes for HWT (residential RO) are typically operated intermittently without a cleaning process. This suggests that a unique mechanism of membrane deterioration, membrane oxidation, one of the main causes of RO membrane deterioration in industrial settings (desalination and wastewater reclamation), is not involved. Furthermore, the intermittent operation provides repeated shear stress on the membrane surface. This study aimed to evaluate the impact of repeated pressurization on virus (bacteriophage MS2 and φX-174) removal by residential RO and to determine the location of integrity loss. We repeatedly pressurized and de-pressurized spiral-wound residential RO membranes for up to 10 000 cycles, while periodically evaluating virus removal. E. coli removal was also determined after 10 000 cycles. Moreover, these membranes were examined for virus and E. coli removal in a flat-sheet configuration. For the first 3000–4000 cycles, φX-174 removal was maintained at approximately 4 log10 (99.99%), and then dramatically decreased. After 10 000 cycles, even E. coli leaked from the membrane. The deterioration of virus removal in a flat-sheet configuration indicates integrity loss at the membrane surface. Therefore, repeated pressurization deteriorated the virus removal performance of residential RO. The number of times that the RO membrane can be pressurized should be included as a criterion to determine the frequency of membrane replacement in residential RO.