Enhancing biodegradability of priority substances (pesticides) by solar photo-Fenton

In this paper, we present the photo-Fenton treatment in a solar pilot-plant scale of several EU priority hazardous substances (Alachlor, Atrazine, Chlorfenvinphos, Diuron and Isoproturon) dissolved in water. The results have been evaluated not only from the point of view of contaminant disappearance and mineralisation, but also of toxicity reduction and enhancement of biodegradability. Degradation was monitored by total organic carbon, pesticide concentration by HPLC–UV, inorganics released by ion chromatography, and biodegradability by the Zahn–Wellens (Z–W) test. The total volume of the solar photoreactor, composed of compound parabolic collectors with a total area of 4.16 m2, was between 70 and 82 L. The treatment was shown to be effective, mineralising all of the pesticides tested, both alone and in mixtures. In order to find out the conditions for biocompatibility using the photo-Fenton reaction as a pre-treatment step, wastewater inoculated with unacclimated municipal sludge containing pesticides after certain degradation time was evaluated by the Z–W test. Biodegradability was enhanced (70% considered biodegradable) by the photo-Fenton treatment after 12–25 min. It may be concluded that the photo-Fenton treatment consistently enhances biodegradability of wastewater containing pesticides.