Comparison of different pretreatment methods for pressure retarded osmosis (PRO) membrane in bench-scale and pilot-scale systems

Pressure-retarded osmosis (PRO) is a membrane process that uses salinity gradient energy. However, membrane fouling is a critical factor that limits PRO performance. Accordingly, this study strives to improve our understanding of PRO fouling by investigating the effect of feed water properties and pretreatment methods on flux and power density of PRO systems. Experiments were carried out in both bench-scale and pilot-scale systems using commercial-grade thin-film composite PRO membranes. Real wastewater effluents were used as the feed water and synthetic brine was used as the draw solution. In the bench-scale experiment, various pretreatments including cartridge filter (CF), microfiltration (MF), and ultrafiltration (UF), nanofiltration (NF), activated filter media (AFM), and granular activated carbon (GAC) were applied. Only UF was used in the pilot-scale experiments, Results indicated that the flux and power density of the PRO membranes were greatly influenced by the quality of the feed and the types of pretreatment. Based on the results, it seems that not only particles and colloids but also organic matters greatly affect PRO fouling. Hermia's model was used to interpret the mechanisms of flux declines in both systems. The correlations between fouling indexes and fouling ratio/power density in the PRO system were also explored. •The fouling behaviors of PRO membranes were examined in bench-scale and pilot-scale systems•Various pretreatments were compared to mitigate PRO membrane fouling and increase power density.•Hermia's model fits were applied to identify the PRO fouling mechanisms.•Among various fouling indexes, MFI provides relatively reasonable correlations with fouling ratio and power density.