Synergistic oxidation and coagulation of raw water by novel Fe(II)/sulfite process: A comparative study with...

Latest findings demonstrate that the oxidative Fe(II)/sulfite (Fe(II)/S(IV)) process can rapidly generate iron particles, holding potential for coagulation while simultaneously removing emerging contaminants. Herein, we first report the synergistic oxidation-coagulation treatment of RW by Fe(II)/S(IV) process, and compare with traditional Fe-based coagulation (FeSO₄, Fe₂(SO₄)₃), Fe(II)/PDS and Fe(II)/PMS processes. Results revealed that the Fe(II)/S(IV) process outperformed traditional Fe-based coagulants, Fe(II)/PDS and Fe(II)/PMS in removing turbidity, UV₂₅₄, and DOC. For emerging contaminants removal from RW, Fe(II)/PMS showed the highest efficiency, followed by Fe(II)/PDS, while Fe(II)/S(IV) was slightly less effective, it still demonstrated a significant improvement (40 %∼65 %) over traditional coagulation processes. Moreover, the Fe(II)/S(IV) process is the most effective in reducing DBPs formation (56 %∼86 %). Although Fe(II)/PDS and Fe(II)/PMS also significantly reduce DBPs formation, their high oxidation potential at low pH generated toxic N-DBPs. Mechanistic analysis indicated that the Fe(II)/S(IV) process was most effective in removing humic substances and biopolymers. Its moderate oxidation preserved macromolecular structures, enhancing coagulation. And the hydrolysis of S(IV) generates OH⁻, promoting electrostatic neutralization and floc enlargement. Cost analysis revealed that the Fe(II)/S(IV) process is significantly more economical, with costs only 1/60 of Fe(II)/PMS. These results highlight the Fe(II)/S(IV) process as a promising and cost-effective approach to advanced water treatment.