Degradation of atrazine using metalloporphyrins supported on TiO2 under visible light irradiation

A combined solar photo-Fenton and biological treatment is proposed for the decontamination of a mixture of five commercial pesticides commonly used in intensive agriculture Vydate (10% Oxamyl), Metomur (20% Methomyl), Couraze (20% Imidacloprid), Ditimur-40 (40% Dimethoate) and Scala (40% Pyrimethanil). Photo-Fenton experiments were conducted in a solar pilot reactor consisting of four compound parabolic collectors in which the pesticide mixture was treated at an original dissolved organic carbon (DOC) concentration of 200 mg/L in the presence of Fe²⁺ or Fe³⁺ concentration of 5, 20 and 55 mg/L. Ferrous ions were marginally more active than ferric in terms of active ingredient degradation, which followed zero order kinetics, more so in the early reaction stages. Photo-Fenton was also far more effective (by at least two orders of magnitude) than the respective dark reaction under identical experimental conditions.Irradiation for 50–100 min (normalized at 30 W/m² light intensity) at 20 mg/L Fe²⁺ was able to completely eliminate the active ingredients, and reduce DOC by about 15–50% and COD by 40–70%, respectively. At these conditions, ecotoxicity to the marine bacteria V. fischeri was substantially lessened, while aerobic biodegradability in tests with activated sludge was enhanced.