Paraquat removal from water by oxidation with Fenton's reagent

Fenton's reaction, an advanced oxidation process (AOP), was studied for paraquat degradation purposes. A parametric study was conducted and the variables considered were the temperature, the pH and the initial iron, hydrogen peroxide and paraquat concentrations, the latter in the range 50–200 mg/L. Under the optimum conditions (T = 30.0 °C, [Fe2+]0 = 5.0 × 10−4 M, [H2O2]0 = 1.6 × 10−2 M, and pH0 = 3.0, for [PQ]0 = 100 mg/L), complete paraquat degradation and about 40% of mineralization were reached after 4 h of reaction (batch reactor). Gramoxone commercial product revealed a slower initial rate of degradation than the paraquat analytical standard, probably due to the parallel consumption of the hydroxyl radicals by other organic compounds. A semi-empirical kinetic model was proposed to simulate the paraquat dichloride concentration histories under a wide range of conditions; the adequacy of the model was statistically checked and also validated by comparison with some additional experiments. The biodegradability and toxicity of the final oxidation products were assessed.

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► The dark Fenton's process was studied for paraquat degradation in a wide range of conditions.
► A semi-empirical kinetic model was successfully employed to simulate paraquat degradation performance.
► Nearly all the pesticide was degraded after only 1 h, with 60% of mineralization after 4 h of reaction.