Fe(II)-activated peroxymonosulfate coupled with nanofiltration removes natural organic matter and sulfamethoxazole in natural surface water: Performance and mechanisms

Ferrous-activated peroxymonosulfate (PMS) is regarded as a promising technology to treat organic pollutants. However, the excessive sulfate anions generated in the oxidation process need to be considered with respect to their potential harm to the environment and human health. The removal of organic compounds and sulfate anions by Fe(II)/PMS oxidation coupled with nanofiltration (NF) was studied in this research. The mechanism of Fe(II)/PMS coupled with NF in natural organic matter (NOM) and sulfamethoxazole (SMX) removal were systematically investigated by comparison with single Fe(II)/PMS and NF treatments. The results demonstrated that the hybrid system showed better performance than the single treatments for both pollutants. High-performance size exclusion chromatography (HPSEC) analysis indicated that macromolecular organic matter in Songhua River water was broken down and converted into small fragments with a size of approximately hundreds of Da by Fe(II)/PMS oxidation. Zeta potential analysis showed that the zeta potential of the effluent decreased under the effect of Fe(III) and that some small organic molecules generated in the process of oxidation were negatively charged. The SMX removal experiment showed that Fe(II)/PMS oxidation played a leading role in SMX removal in the hybrid system. Moreover, a radical quenching experiment was conducted to explore the effects of SO₄^·− and HO^· on SMX degradation. Fe(II)/PMS treatment effectively alleviated membrane fouling and improved the flux behaviour, with a stable sulfate anion rejection rate of approximately 90% achieved by NF in the long term. These results suggested that Fe(II)/PMS coupled with NF could control membrane fouling, intercept sulfate anions and improve effluent quality, which provides a new strategy for water treatment.