Activation of peroxymonosulfate by WTRs-based iron-carbon composites for atrazine removal: Performance evaluation, mechanism insight and byproduct analysis

Water treatment residuals (WTRs), inevitable waste generated from drinking water production, are potential iron resource and can be used for pollution control. In this study, iron-rich WTRs bonded with powder activated carbon (PAC) were calcinated to synthesize iron-carbon (Fe-C) composites, which were then applied to activate peroxymonosulfate (PMS) for the elimination of herbicide atrazine (ATZ). Characterization results showed that Fe0 and Fe3C coexisted in these Fe-C composites, among which Fe-15%C exhibited the highest degradation efficiency (91.6%) in 120 min under the condition of 0.25 mM PMS, 0.06 g L- 1 Fe-15%C and initial pH 3.58. The effects of Fe-15%C dose, PMS concentration, initial pH and humic acid were systematically investigated. In addition to sulfate radical (SO4 center dot-) and hydroxyl radical (center dot OH), singlet oxygen (1O2) and superoxide radical (O2 center dot- ) were also involved in the Fe-15%C/PMS system. The iron species and carbon structure jointly contributed to PMS activation, and the conversion of Fe(III) to Fe(II) was enhanced by the addition of p-benzoquinone (BQ). LC-MS technique was used to detect the degradation intermediates of ATZ, which were mainly generated through dechlorination-hydroxylation and dealkylation processes. Cl- had a dual effect (inhibitory and accelerating effect) on the degradation of ATZ, and could influence the yield of chlorinated byproducts desethyl-atrazine (DEA) and desisopropyl-atrazine (DIA), i.e., DEA was hardly affected, but DIA was increased to varying degrees. Ultimately, Fe-15%C had potential to be a viable activator for the removal of ATZ as well as protein- and humic-like substances in natural water.

Automated summary

This study successfully synthesized iron-carbon composites using water treatment residuals, which were then applied for the degradation of the herbicide atrazine. Various reactive radicals, including sulfate radical and singlet oxygen, were found to be involved in the degradation process. Additionally, the presence of chlorine ions was found to have a dual effect on the degradation of atrazine and the production of chlorinated byproducts.