Effect of peroxymonosulfate pre-oxidation coupled with subsequent Fe-based coagulation on the mitigation of organic matter and the formation of disinfection by-products†

The generative ability of abundant reactive species ensures peroxymonosulfate (PMS) pre-oxidation coupled with subsequent Fe-based coagulation (PPFeC) a promising drinking water treatment process, whereas these abundant reactive species can also oxidize chloride in water matrices to form reactive chlorine species (RCS). These RCS can further oxidize organic compounds, resulting in the unexpected cytotoxic and genotoxic disinfection by-product (DBP) formation. Thus, this study investigated the effect of PMS pre-oxidation coupled with subsequent Fe-based coagulation on the mitigation of organic matter and DBP. Here, results showed that the PPFeC process presented better dissolved organic carbon (DOC) removal performance than PMS pre-oxidation and Fe-based coagulation. Compared to Fe³⁺-based coagulation, Fe²⁺-based coagulation resulted in higher DOC removal performance (increased by 63.5% in natural water), higher DBP concentration and water toxicity (increased by 31.3% for the cytotoxicity index and 18.5% for the genotoxicity index in natural water) during the PPFeC process. DBP concentration and toxicity decreased with the increase of the pre-oxidation time, and increased with the increase of PMS concentration. Furthermore, concentration of DBP and toxicity of water initially increased and then decreased with the increase of sedimentation time and coagulant concentration. In addition, compared to SO₄˙⁻ and PMS, HO· played a more significant role in the DBP formation and toxicity during the PPFeC process. Therefore, Fe³⁺-based coagulants were reliable to ensure drinking water safety as PMS was applied as the pre-oxidant.