Solar photocatalytic mineralization of 2,4-dichlorophenol and mixtures of pesticides: Kinetic model of mineralization

Phytosanitary run off from agricultural fields represents highly disseminated local sources of pollution and corresponds to relatively small volumes which need to be treated (around 5 m3 for a farm of a few tens of hectares). The simplicity, the robustness and the low energy consumption of the solar heterogeneous photocatalytic process make it well adapted to this application. Mineralization of phytosanitary effluent with this solar eco-technology was tested with a solar laboratory set up for a few tens of litres. Feasibility was explored step by step with preliminary solar experiments performed on 2,4-dichlorophenol (DCP) followed by solar mineralization carried out on two representative commercial pesticides and three real phytosanitary waste products which were directly collected from a vineyard area. The total organic carbon profiles showed advanced mineralization but the presence of a threshold must be underlined at about 70% of mineralization yield in the case of the two pesticides as well as for the phytosanitary wastewater. A complementary eco-toxicity measurement demonstrated that this threshold is not penalizing regarding the detoxification performance. The kinetic law of mineralization, taking into account the discontinuous solar UV irradiation developed and validated for DCP, was applied with success to the commercial solutions and the wastewater from agricultural activities. Scaling up of the process based on the validated kinetics associated with solar data leads to an annual treatment capacity of 3.5 m3 for a reactor surface of 1 m2.

► Solar photocatalytic test-bench designed. ► We model the mineralization of 2,4-dichlorophenol. ► The model is applied with success to commercial pesticide solutions and agricultural effluents. ► Tests on aquatic eco-toxicity reveal a complete elimination of the toxicity.