Detoxification of Aqueous Solutions Containing the Commercial Pesticide Metasystox by TiO2-Mediated Solar Photocatalysis

Abstract

A commercial pesticide, namely metasystox, has been chosen to study its detoxification in aqueous solution by means of solar photocatalysis employing titanium dioxide. Initial toxicity/biodegradability has been checked by means of active sludges respirometry and the Zahn–Wellens test. Laboratory scale experiments indicate that significant detoxification (by approximately one order of magnitude) of a 0.05g∕L solution of the active species can be achieved in only 3h of solar irradiation due to the nearly complete elimination of the active compound, methyloxydemeton. In this case, total organic carbon (TOC) measurements cannot be used to evaluate the process as nonactive organic excipients interfere in the measurement. The experiment has been scaled-up to 25L in a solar pilot plant; also in this case more than 75% elimination of methyloxydemeton is achieved in 5h irradiation (∼1400kJ). Besides detoxification (80% initial inhibition of the active sludges and 20% at the end of the experiments), and moderate TOC reduction (∼20%) are observed together with an increase of the surface tension of the solutions, probably due to elimination of excipients having surfactant properties.

Comparison of different TiO2 samples as photocatalyst for the degradation of a mixture of four commercial pesticides

“…Although the mixture studied in this work is too complex to determine reliable mechanistic data, the individual behaviour of each compound was studied in previous publications . In all cases, pesticide removal was observed to involve a very significant detoxification of the solution, using respirometric measurements and the luminescence of V. fischeri assay.…”

Activated sludge respirometry to assess solar detoxification of a metal finishing effluent

“…Inhibition of the respiration of activated sludge has proven to be a useful tool to estimate their response towards toxicants. In particular, an adaptation of the OECD test 209 has been used to estimate detoxification of aqueous solutions of several commercial pesticides when submitted to TiO 2 -based solar photocatalysis [18][19][20]; this method proved to be suitable to determine the short-term effect of the pollutant on the microorganisms.…”