Removal of Pesticides with Endocrine Disruptor Activity in Wastewater Effluent by Solar Heterogeneous Photocatalysis Using ZnO/Na2S2O8

The solar photocatalysis has received increasing attention in the last years due to its great potential as eco-friendly technology to detoxify wastewater polluted with estrogenic and/or androgenic chemicals. In this context, this study aims to demonstrate the photocatalyzed degradation of two fungicides (vinclozoline and fenarimol) and four insecticides (malathion, fenotrothion, quinalphos, and dimethoate) all of them with endocrine-disrupting activity, in a wastewater effluent under natural sunlight and pilot plant scale. For this, we have combined hydroxyl radical (HO•)- and sulfate radical (SO₄●⁻)-based advanced oxidation processes (AOPs) by using of ZnO as photocatalyst and Na₂S₂O₈ as oxidant, respectively. Previously, catalyst loading, effect of electron acceptor, and pH conditions were optimized using a lab photoreactor under artificial light. As a result, 200 mg L⁻¹ of ZnO and 250 mg L⁻¹ of Na₂S₂O₈ were used in the further experiment at pilot plant scale at pH around 7. The results show that the use of the tandem ZnO/Na₂S₂O₈ strongly enhances the reaction rate of the studied pesticides as compared with the photolytic test. All pesticides followed an apparent first-order degradation curve. The necessary time for 90% degradation (DT₉₀) under sunlight irradiation ranged from 26 to 1000 min (2–75 min as normalized illumination time, t₃₀W) for malathion and fenarimol, respectively. At the end of the lighting, the remaining percentage of dissolved organic carbon (DOC) was up to 92% lower than its initial content and toxicity (Vibrio fischeri) decreased from 65% of inhibition to an acceptable value of 12% at the end of the treatment. A weak increase in the electrical conductivity (EC) was observed due to the mineralization process. The findings confirm the efficacy of the treatment to remove pesticides from wastewater using natural sunlight as renewable energy source, mainly in sunny areas as Mediterranean basin.