Assessment of solar photocatalysis to purify on-site rinse waters from tractor cisterns used in grapevine pest control: field experimentation

The aim of this study was to assess in a vineyard the effect of purifying by solar photocatalysis the title rinse waters (currently most often rejected) in terms of efficacy and on-site practicality for the wine grower. The on-site, self-functioning, solar purifying unit included a corrugated-steel inclined plate of area S=1m² onto which a TiO₂-coated thin material had been slightly pressed, a tank, and an aquarium-type pump powered by a photovoltaic panel (appropriate for isolated locations). For a vineyard of area A=0.15km², the rinse water (about 90L) corresponding to each of four typical vine treatments in summer was analysed (major pesticides for each treatment, TOC, Microtox test and, in one case, BOD₅) by independent laboratories, before and after purification for 8 days. The S/A ratio tested was found insufficient even if the photocatalytic treatment markedly improved the quality of the rinse waters. From the relatively low final organic content reached in one case, it is calculated that a three-time higher S/A ratio might suffice, but new trials are necessary to determine whether it is valid for other typical cases. Inferred contribution of inorganic ions to the post-photocatalytic treatment toxicity points to the need for an additional detoxification. These field experiments have also demonstrated that the purifying prototype is robust, and easy to install and use on site by the wine grower.