Unraveling the triple mechanisms of advanced coagulation for removal of emerging and conventional contaminants: Oxidation, hydrolytic coagulation and surface hydroxylation adsorption

Advanced coagulation driven by Ferrate (Fe(VI)) and sulfite (S(IV)) activated Fe(VI) demonstrated the triple role, i.e., oxidation, coagulation, and adsorption. The present study demonstrated the performance of advanced coagulation for the removal of emerging contaminants (ECs) and conventional contaminants (CCs) in simulated surface water and real water, differentiated the contributions of oxidation, hydrolytic coagulation, and surface hydroxylation adsorption, and revealed the triple mechanisms of advanced coagulation. The degradation of ECs was mainly attributed to oxidation, with oxidation, coagulation and adsorption each contributing in the removal of CCs. Hydrolyzed Fe(III), one of the advanced coagulation reduction products, in the form of Fe-a and Fe-b, was effective in the removal of high molecular weight (MW) organics, and the major reduction product, solid Fe(III) particles, exhibited adsorption properties for low MW organics. Solid Fe(III) particles were mainly of nanoscale, bimodal distribution, rounded and granular, a core-shell structure with gamma-Fe2O3 as the core and gamma-FeOOH as the shell, and gamma-FeOOH was the major component. S(IV) activation did not change the core-shell structure, but altered the structural proportions and the particle size. Examined the removal characteristics of advanced coagulation for different MW organics, determined the reaction sequence for contaminants, and discussed the environmental implications. The construction of a multifunctional reactor with advanced coagulation as the core unit is an option, and the results provide theoretical support from the perspective of contaminant removal performance and mechanism, with a view to promoting the innovation of drinking water treatment technology.