Two wastewater polishing systems were compared in terms of their ability to protect downstream reverse osmosis (RO) processes. A conventional full-scale wastewater treatment system with primary and secondary treatment followed by rotating biological contactors (RBC) and sand filtration were compared in a side-by-side study with a pilot-scale membrane bioreactor (MBR). Effluent from the two pretreatment trains was sent to two identical RO pilot systems. The effluent water quality of the two systems was compared as well as the RO performance. The MBR pretreatment provided effluent with a turbidity (0.11 NTU) that was more than five times lower than that of the conventional system (0.58 NTU). The fouling rate of the RO system with MBR pretreatment was 50–67% of the value found for the RO system with conventional pretreatment and the difference in turbidity values was identified as the major source of this large difference. The RO effluent quality of both systems was excellent, with similar overall removals in both systems. The study emphasizes the importance of removing particulate matter for the prevention of RO fouling within water reclamation.

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