Improved anti-biofouling performance of pressure retarded osmosis (PRO) by dosing with chlorhexidine gluconate

Pressure retarded osmosis (PRO) is an emerging technology capable of extracting energy from salinity gradients of wastewater paired with SWRO brine. However, this process's performance is hindered by irreversible biofouling due to bacteria-containing wastewater and the sponge-like support layer of PRO membranes. In this study, chlorhexidine gluconate (CHG), a non-oxidizing biocide, was continuously added to feed solution to investigate its anti-biofouling performance during PRO. CHG showed higher anti-microbial and anti-biofilm activity than did other non-oxidizing biocides. Even at low dosages of CHG, water flux declines were greatly mitigated and benefited from the internal concentration polarization (ICP)-elevated concentrations within the active-support layer interface. CHG plays a critical role by inhibiting bacterial growth, and a 65–88% reduction of extracellular polymeric substances was achieved on the membrane surface and throughout the feed spacers. Membrane characterization demonstrated that the improved performance could be attributed to a consistent structural parameter and alleviation of ICP self-compensation effects. This study thus shows that a combination of biocide dosing and pressure assisted-osmotic backwashing can be a useful strategy for controlling biofouling during the PRO process.