Effects of reverse solute diffusion on membrane biofouling in pressure-retarded osmosis processes

Abstract

Biofouling is a critical bottleneck in pressure-retarded osmosis (PRO), as the feed solution inevitably contains microorganisms. Reverse solute diffusion (RSD) from the draw solution may alter biofouling tendency. However, no study has yet explored the relationship between RSD and biofouling in PRO. Here, we investigated the influence of applied hydraulic pressure (ΔP) and draw solution types on RSD properties and solute concentrations in the support layer. RSD of Na+ induced a similar biofouling extent under different ΔP values because the solute concentrations were similar at the support-active layer interface, despite an increased reverse solute flux. Contrarily, RSD of Ca2+ triggered increased water flux decline and severe biofouling in PRO because Ca2+ induced increased bacterial growth and extracellular polymeric substance formation. RSD of Mg2+ exhibited insignificant effects on biofouling in PRO due to the negligible effects of Mg2+ on biofilm formation. We further revealed the roles of influencing factors (ΔP, draw solution type and concentration) on biofouling in PRO. Although ΔP had no significant influence on biofouling, draw solution type and concentration markedly altered biofouling extent in PRO. Collectively, this study provides a comprehensive understanding of the effects of RSD on biofouling and novel insights into biofouling control strategies in PRO.