Evaluation of different cleaning strategies for different types of forward osmosis membrane fouling and scaling

In this study, various cleaning methods are investigated to effectively control membrane fouling (i.e., organic fouling, colloidal fouling and scaling) in forward osmosis (FO). Simple physical cleanings (i.e., hydraulic flushing and osmotic backwashing) are firstly employed to remove membrane fouling. Both methods achieved higher than 95% efficiency and osmotic backwashing has a better efficiency for organic fouling and scaling in long-term operation, but colloidal fouling was not removed. To enhance the efficiency, intense physical cleanings (i.e., air scouring and the combination of various physical cleaning) and chemical cleanings (i.e., EDTA, low pH and high pH) were conducted but could not remove the fouling layer possibly because of the polymerization of silica colloids. Lastly, four hybrid mitigation methods (i.e., low pH DS, pulsed flow, high crossflow, and periodic sparging of CO2 saturated solution) followed by hydraulic flushing were examined. The combination of CO2 saturated solution and hydraulic flushing completely removed the fouling layer because CO2 bubbles weakened the interaction between the fouling layer and the membrane surface. Periodic air scouring also exhibited similar effect on the fouling layer. Therefore, periodic air scouring can be more feasible option to control the silica colloidal fouling but not organic fouling.