222 nm UV Pretreatment to Mitigate Organic Fouling of Reverse Osmosis Membranes in Wastewater Reuse

Reverse osmosis (RO) membranes used for wastewater reuse are vulnerable to organic fouling, necessitating effective pretreatment for a sustainable operation. Here, we evaluate the potential of 222 nm UV irradiation as a chemical-free pretreatment to transform organic matter from secondary wastewater effluent prior to RO. 222 nm UV generally achieved greater fouling control than conventional 254 nm UV with hydrogen peroxide, reducing flux decline from wastewater effluent fouling by 60% (fluence of 400 mJ/cm2) versus 29% for 254 nm + H2O2 (fluence of 1000 mJ/cm2), relative to untreated wastewater. Size-exclusion chromatography revealed that both UV wavelengths decreased high molecular weight (MW) organics, but only 222 nm UV substantially degraded medium-low MW TOC fractions, which correlated with fouling reduction. In contrast, we observed significant protein conformational changes induced by 222 nm UV could increase fouling for certain feed waters and treatment conditions. Characterization of the fouled membrane surface showed that 222 nm UV-treated water formed a more porous fouling layer with more oxidized carbon than did untreated and 254 nm UV-treated waters. Overall, this work found 222 nm UV to be a promising, chemical-free pretreatment to RO and underscores the importance of water-specific process optimization.