The role of Fe(IV) in the zero-valent iron biochar activated persulfate system for treatment of contaminants of emerging concern

Abstract

In this paper, Fe(IV) was analyzed in the zero-valent iron biochar (ZVI-BC) activated persulfate (PS) process with methyl phenyl sulfoxide (PMSO) as the probe compound. Without a reaction terminator, PMSO degradation continued during the sample holding time, resulting in significant errors in the kinetics analysis. When 1 mM NaNO₂, 1 mM NH₂OH, 10 mM Na₂S₂O₃, or 10 mM dimethyl sulfoxide were used as terminators, the concentrations of PMSO and its oxidation product, methyl phenyl sulfone (PMSO₂), were effectively maintained without changes during the sample holding period. Furthermore, the terminators did not interfere with PMSO or PMSO₂ analysis by high performance liquid chromatography. In addition to Fe(IV), free radical (i.e., SO₄^.-, OH, O₂^.-) and nonradical (i.e., ¹O₂) reactive species were also involved in the ZVI-BC/PS system; however, Fe(IV) was the predominant reactive species. Organic contaminants with electron-donating moieties rapidly reacted with Fe(IV), and the relative contribution of Fe(IV) to overall contaminant degradation decreased as the solution pH was increased. Overall, this study provided new insights into the quantitative analysis of Fe(IV) in the ZVI-BC/PS system and its application to treatment of organic contaminants in solutions with variable water quality.