Solar photocatalytic processes for treatment of soil washing wastewater

In the present work the use of a sequence of two solar photocatalytic processes was investigated for the removal of copper, iron, zinc and ethylenediaminedisuccinic acid (EDDS), used as chelating agent, from real soil washing effluents. Removal efficiencies of 93.5% (copper), 99.6% (iron), 99.4% (zinc), 97.2% (EDDS) and 80.7% (TOC) were achieved through outdoor solar photocatalytic treatments using parabolic trough collectors and carried out in Naples (Italy, N 40°50′, E 14°12′) in the period June–July 2015. These removal efficiencies were achieved for an incident UVA solar energy per unit volume (Qj,n) of 580 kJ·L−1, calculated by taking into account the irradiated surface area of the photoreactor estimated in the present work (9.79 × 10−2 m2) and the solar irradiance measurements collected during the experiments. The results suggest that the two-step solar process adopted can be proposed as a useful solution to the problem of heavy metals and chelating organic agents removals from soil washing. The ecotoxicological assessment, using different living organisms (Daphnia magna, Vibrio fischeri, Pseudokirchneriella subcapitata, Lepidium sativum and Caenorhabditis elegans), showed a noticeable decrease of the ecotoxicity of the soil washing effluents after the two-step photocatalytic process.