Oxidative degradation of propachlor by ferrous and copper ion activated persulfate

The process of in situ chemical oxidation (ISCO) by persulfate (S₂O₈^2-) can be accelerated by metal ion activation, which more effectively degrades subsurface pollutants by enhancing sulfate radical (SO₄^-) generation. This study compared the results of propachlor degradation by Cu²⁺ and Fe²⁺ activated persulfate and revealed differing degradation kinetics and mechanisms between the two types of activation system. The activation of persulfate by Fe²⁺ ions generally resulted in rapid degradation in the early stage, but was accompanied by a dramatic decrease in efficiency due to the rapid depletion of Fe²⁺ by the sulfate radicals generated. In contrast, the Cu²⁺ activated persulfate had a longer lasting degradation effect and a proportionally greater degradation enhancement at elevated Cu²⁺ concentrations. An optimal Fe²⁺ concentration should be sought to activate the persulfate, as a high Fe²⁺ concentration of 2.5mM or above, as was used in this study, may inhibit propachlor degradation due to the competitive consumption of sulfate radicals by the excess Fe²⁺ ions. Higher temperatures (55°C compared with 30°C) resulted in enhanced metal activation, particularly with the Cu²⁺ activated system. Furthermore, acidic conditions were found to be more favorable for propachlor degradation by metal activated persulfate. The ecotoxicity of degraded propachlor samples, which was indicated by average well color development (AWCD) for its microbial community activity, was confirmed to be decreased during the degradation processes with these two ions activated persulfate.