Osmotic-induced cleaning is effective in long-term fouling mitigation of reverse osmosis elements at pilot plant level

Osmotic backwashing (OBW), a promising environment-friendly membrane cleaning technique, has been mostly studied at the lab scale. In this work, we investigated the efficacy of periodic OBW in fouling mitigation at a pilot-plant level. After initial optimization of the major OBW parameters, it was applied periodically to a singleelement RO module used for seawater desalination. The continuous monitoring of major performance parameters and comparison to a control unit revealed the success of periodic OBW in fouling mitigation: significantly lower feed channel pressure (FCP) drop (50 - 100 kPa vs. 200 kPa), less decline in normalized permeate flow (10 % vs. 30 %), and virtually unaffected salt rejection (99.5% vs. 99.2%). Findings from foulant analyses and membrane autopsy correlated well with the filtration results: fouling layer on the backwashed membrane was less dense and had a lower inorganic content (similar to 57%) compared to the control (similar to 72%), and two important properties, the surface roughness (similar to 160 vs. 270 nm) and zeta potential (18 vs. 10 mV) witnessed a smaller increase. In summary, OBW was quite effective in mitigating fouling and its effects on membrane performance.