Reverse osmosis (RO) has been widely adopted for the treatment of blow-down water to facilitate sustainable water management in thermal power plants. This study investigates membrane fouling in a packaged RO system treating blow-down water to identify the causes of permeate flux decline and develop mitigation strategies. Results from blow-down water analysis, autopsy of the used membrane, and filtration experiments indicate that the RO system was likely under-designed with water recovery exceeding the design limit, creating conditions favourable for flux deterioration. Silica, present in blow-down water at high concentrations (∼50 mg/L), was identified as the dominant and most challenging membrane fouling culprit. Given the sulphate concentrations of 55–88 mg/L, barium sulphate scaling might also occur; however, the evidence was inconclusive. Unlike silica scaling, barium sulphate could be mitigated through appropriate anti-scalant dosing. The filtration experiments indicate that besides fouling, membrane compaction partially contributed to flux decline. Finally, WAVE simulation results suggest key strategies (e.g. lower water recovery, using larger membrane surface area or membrane with improved flux stability, increasing feed water temperature (up to 35 °C), blending with silica-free water sources, and optimising anti-scalant dosing) to enhance RO system water recovery while effectively avert membrane fouling.
