Unveiling the Synergic Effect in UV/Acetylacetone for Redox Transformation of Toxic Oxysalts

Redox transformation is a useful strategy to reduce the toxicity of metal oxysalts and to facilitate their removal from water. The synergy of the oxidation and reduction processes in a single system is of great value for the treatment of wastewater containing multiple pollutants. Here, by taking As(III) and Cr(VI) as modeling pollutants, the synergic effect in redox transformation of coexisting oxyanions was evaluated with a typical advanced oxidation process (AOP)-UV/H2O2, a well-established advanced reduction process (ARP)-UV/sulfite, and a newly developed UV/acetylacetone (AcAc) process. At near-neutral pH and low [AcAc]/[oxyanion] stoichiometric ratios (2.5-10:1), UV/AcAc could effectively fulfill As(III) oxidation and Cr(VI) reduction in a single process without any other treatment. More importantly, the electric energy consumption of UV/AcAc per mole of As(III) and Cr(VI) was only 1/7 of the sum of UV/H2O2 and UV/sulfite. We thus propose that UV/AcAc is an advanced oxidation and reduction process (AORP). Owing to the existence of long-lived radicals and multiple pathways, this AORP process showed an obvious synergic effect in redox transformation and was robust in the complex water matrix.