Enhanced simultaneous removal of cadmium, lead, and acetochlor in hyporheic zones with calcium peroxide coupled with zero-valent iron: Mechanisms and application

[Display omitted] •CaO2/ZVI could remove Cd, Pb, and acetochlor simultaneously and effectively.•Detailed removal mechanisms of Cd and Pb, and degradation pathway of acetochlor were proposed.•Ecotoxicity of acetochlor would be reduced during the degradation by CaO2/ZVI.•CaO2/ZVI can be used in in-situ remediations of hyporheic zone. The hyporheic zone is a key area for water circulation. However, hyporheic zone pollution is widespread all over the world and remediations of hyporheic zones, when polluted by both heavy metals and organics, are challenging. Thus, the mechanisms and application of Calcium peroxide (CaO2) coupled with Zero-valent iron (ZVI) to simultaneously remove cadmium (Cd), lead (Pb), and acetochlor were investigated in this work. The effects of mass ratio of ZVI and CaO2, initial pH, and water matrices were evaluated. At initial pH 3, with the dosage of 1.5 g·L−1 ZVI and 0.5 g·L−1 CaO2, the removal efficiencies of Cd, Pb, and acetochlor were 96.7%, 99.8%, and 100%, respectively. Acetochlor was degraded into four main byproducts, and the toxicity evaluation indicated that the ecotoxicity of acetochlor was reduced during the degradation by CaO2/ZVI. In column transport experiments, with the mass ratios of ZVI and CaO2 to quartz sand of only 0.13% and 0.05%, the mass recovery efficiencies of Cd, Pb, and acetochlor from the effluent were 42.5%, 10.4%, and 0%, respectively. Cd was removed mainly by the adsorption of ZVI and iron(hydr)oxides (represented Fe3O4 and lepidocrocite); removal of Pb chiefly resulted from ZVI reduction, and hydroxyl radicals derived from the Fenton reaction accounted for acetochlor degradation. This work provides new insights and a facile strategy for in-situ remediations of hyporheic zones polluted simultaneously by heavy metals and organics.