Degradation of alachlor with zero-valent iron activating persulfate oxidation

Abstract

Alachlor, a commonly used herbicide in agriculture, has been selected as a target pollutant to evaluate the oxidative performance of zero-valent iron (ZVI) coupling with persulfate (PS) for the first time. Compared with Fe3+ and Fe2+, ZVI achieved the best degradation effect. Bench-scale kinetics tests were conducted to demonstrate the impacts of several key factors controlling the treatment performance, including ZVI dosage, PS dosage, initial pH, temperature, nature organic matter (NOM), citrate and anions. The alachlor degradation followed a pseudo-first-order kinetics pattern and was effective in a broader pH range. The optimum ZVI to PS molar ratio was found to be 2:1. Heat could facilitate production of sulfate radicals and thus enhance the alachlor degradation. Sodium citrate as a chelating agent at an appropriate concentration could improve the alachlor decay in the Fe2++PS and ZVI+PS system. The removal was strongly inhibited in system added NOM, anions of Cl− or HCO3− while it was not obvious impacted by adding NO3− or SO42−. Seven proposed degradation pathways were evaluated, using Liquid Chromatography–Mass Spectroscopy (LC–MS) analysis. In conclusion, ZVI+PS can be as a potential technology for purifying alachlor-polluted water.