Application of high-dose UV irradiation as nanofiltration pretreatment for drinking water production: Organic fouling mitigation and micropollutant removal

Nanofiltration (NF) is being increasingly applied to produce high-quality drinking water; however, its costeffective operation remains challenging due to the perennial membrane fouling. On account of the low tolerance of common NF membranes to chemical oxidants, this study proposed high-dose UV irradiation as a pretreatment strategy for organic fouling mitigation. Results showed that the permeate flux decline of the membrane with UV-treated feedwater (with a dose of 750 mJ cm(- 2)) was less drastic than that with raw feedwater, but slightly faster as compared to that with UV/Cl-2 pretreatment. The final normalized fluxes were 0.69, 0.79, and 0.82, respectively, after 10 h of operation with raw, UV- and UV/Cl-2-treated feedwaters. With the characterization of feedwaters and membranes, the fouling was found to be initiated by the adsorption of hydrophilic biopolymers onto the membrane, followed by the deposition of hydrophobic humic substances. Reduction of the "glue" biopolymers was crucial to membrane fouling mitigation. The applicability of UV pretreatment in practice was testified with a pilot-scale UV-NF system where permeate flux of the NF module decreased by 37% after sixweek continuous operation. Moreover, UV pretreatment could remove most of the identified pesticides in the feedwater with a removal efficiency over 80% for metolachlor and imidacloprid, but had no or even a negative effect on perfluorinated compounds. This work discloses the efficacy and mechanism of high-dose UV irradiation for NF membrane fouling control, which facilitates future research and application of NF technology.