Integrated process for degradation of amitrole in wastewaters: Photocatalysis/biodegradation

Preliminary studies highlight the positive effect of coupling photocatalysis and biological processes for the treatment of biorecalcitrant compounds. Before biological treatment, photocatalysis can be used as a pre-treatment process to increase pesticide biodegradability. Kinetics of amitrole biodegradation during cultures of Pseudomonas fluorescens was examined to ensure that the target compound was biorecalcitrant; its inhibitory effect justified a pre-oxidation. The biodegradation of cyanuric acid, one of the by-products resulting from photocatalyis of amitrole was confirmed. Pseudomonas fluorescens could metabolize this compound as a nitrogen source when a supplementary carbon source was added. The addition of supplementary carbon and nitrogen sources favoured growth and accordingly cyanuric acid degradation. Degradation yields (with TiO2 coated on cellulose fibers, 25 g.m(-2)) in the range 47% to 55% were obtained after 50h of irradiation for solutions of amitrole in the range concentrations between 70 to 6000 ppm. Between 10% and 34% of amitrole was mineralized to carbon dioxide. The production of ammonium and nitrate ions was negligible. An inhibition of TiO2 active sites was assumed to account for the weak mineralization. Identification of some of the intermediate by-products by LC-MS/MS shows negligible quantity of cyanuric acid. This work demonstrates that the hybrid process photocatalysis/bioremediation is a cost-effective promising solution for the treatment of wastewater containing biorecalcitrant compounds.