A new perspective of membrane fouling control by ultraviolet synergic ferrous iron catalytic persulfate (UV/Fe(II)/PS) as pretreatment prior to ultrafiltration

Abstract

The main purpose of this study was to control membrane fouling by degrading natural organic matter, mainly based on free radicals, with a dead-end ultrafiltration system integrated with pretreatment. Four advanced oxidation processes, namely, ultraviolet (UV)/Fe(II), UV/persulfate (PS), Fe(II)/PS and UV/Fe(II)/PS, were used to pretreat raw water prior to ultrafiltration. The priority of the pretreatment effect followed the order of UV/Fe(II)/PS > Fe(II)/PS > UV/PS > UV/Fe(II). In the UV/Fe(II)/PS pretreatment (Fe(II) = 100 μM and PS = 400 μM), the removal rates of UV254 with a UV irradiation time of 60 min reached 93.07%. Degradation experiments of free-radical probes (carbamazepine) and free-radical scavenger addition (sodium hyposulfite or tert-butanol) showed that the sulfate radical (SO4−) was dominant in degrading organic compounds. The specific flow rate (J/J0) increased by 139.13% and the irreversible fouling resistance was reduced by 69.94%. The total interfacial energy of the colloid-membrane interaction decreased by 84.42% and the separation distance was shortened to ~2 nm. The release of Fe(III) from water under UV radiation and its possible conversion to Fe(II) were observed on the surface of the fouled membranes. After UV/Fe(II)/PS pretreatment, bulky and rough pollutant particles were transformed into a slew of sheet-contaminated layer with the appearance of numerous permeable holes, and the average surface roughness was reduced to 38.1 nm according to atomic-force-microscopy characterization.