Ultrafiltration with self-generated RO concentrate pulse backwash in a novel integrated seawater desalination UF-RO system

Ultrafiltration as a pretreatment for RO feedwater with enhanced UF backwash, which combines continuous with pulse backwash, was investigated in a novel UF-RO process integration. Direct supply of RO concentrate to the UF module served for UF backwash which was further enhanced with pulse backwash generated using bladder-type hydraulic accumulators. Model analysis of the hydraulic accumulator operation, which was validated via a series of field experiments, demonstrated a capability for accumulator charging directly from the RO concentrate stream within a period of 30–40 s. Moreover, pulse backwash over a short period (~5 s) which was added to the continuous UF backwash (directly from the RO brine stream), enabled peak UF backwash flux up to a factor of 4.2–4.6 higher than the normal filtration flux. The above mode of UF operation with multiple consecutive backwash pulses was more effective than with a single pulse, while inline coagulation further increased the UF performance. Relatively long-term field operation (over eight days where) of the UF-RO system with self-adaptive triggering of UF backwash, whereby the number of consecutive pulses increased when a higher membrane fouling resistance was encountered, was highly effective in enabling stable UF operation over a wider range of water quality conditions and without the need for chemical cleaning. These encouraging results suggest that direct UF-RO integration with enhanced pulse UF backwash is an effective approach for dead-end UF filtration without sacrificing water productivity.