New insights into atrazine degradation by the novel manganese dioxide/bisulfite system: Product formation and Mn reuse

Abstract

Fenton and Fenton-like systems have been successfully applied in treatment of refractory pollutants in water and wastewater, but the formation and disposal of large amounts of ferric sludge is a matter of concern. This study demonstrated that Mn(IV)/HSO3− system could effectively degrade atrazine (ATZ) through generation of Mn(III) and SO4•− as primary reactive intermediates and meanwhile the sludge could be well controlled. Mn(IV) could be in situ regenerated from oxidation of Mn(II) (i.e., Mn(IV) final transformation product in Mn(IV)/HSO3− system) by oxygen under alkaline condition, and was reused for efficiently catalyzing HSO3− to degrade ATZ. The metal ions (e.g., Ca(II), Mg(II), Zn(II) and Al(III)) commonly used as coagulant had negligible effects on ATZ degradation by Mn(IV)/HSO3− system. The oxidation products of ATZ were identified to further clarify the role of various reactive intermediates in Mn(IV)/HSO3− system. Deethyl-atrazine (DEA) and atrazine amide (CDIT) were two primary products during ATZ transformation by Mn(IV)/HSO3− system. The molar ratio of CDIT to DEA ([CDIT]/[DEA]) was quantified to be 3.0–4.0 during ATZ transformation by Mn(IV)/HSO3− system, which was much higher than those (∼2.3 and ∼0.7) obtained in the cases of authentic SO4•− and •OH oxidation (i.e., UV/PDS and UV/H2O2 system), respectively. This result indicated that Mn(III) was a more selective reactive intermediate than SO4•−, which was also proved by tertiary butanol scavenging experiments. Based on these findings, the Mn(IV)/HSO3− system may be operated in a sequencing batch reactor (SBR) as a durable, efficient, and recyclable technology to treat recalcitrant contaminants in water and meanwhile to achieve ‘zero discharge’ of sludge.