Solar photocatalitycal treatment of carbofuran at lab and pilot scale: Effect of classical parameters, evaluation of the toxicity and analysis of organic by-products

In this work the TiO2 solar-photocatalytical degradation of the pesticide carbofuran (CBF) in water, at lab and pilot scale, was studied. At lab scale the evaluation of CBF concentration (14-282 mu mol L-1) showed that the system followed a Langmuir-Hinshelwood kinetics type. TiO2 concentration (0.05-2 g L-1) and initial pH (3-9) were also evaluated and optimized using the surface response methodology and the Pareto diagram. In the range of variables studied, initial pH 7.60 and 1.43 g L-1 of TiO2 favoured the efficiency of the process. Under optimal conditions the evolution of substrate, chemical oxygen demand, dissolved organic carbon, toxicity and organics by-products were evaluated. In the pilot scale tests, using direct sunlight, 55 mg L-1 of CBF in a commercial formulation was eliminated after 420 min; while after 900 min of treatment 80% of toxicity (1/E-50 on Vibrium Fischeri), 80% of chemical oxygen demand and 60% of dissolved organic carbon were removed. The analysis and evolution of five CBF by-products, as well the evaluation of the treatment in the presence of isopropanol or using acetonitrile as a solvent suggest that the degradation is mainly carried out by (OH)-O-center dot radical attack. Finally, a schema depicting the main degradation pathway is proposed. (C) 2011 Elsevier B.V. All rights reserved.