Advanced oxidation of the pharmaceutical drug diclofenac with UV/H2O2 and ozone

Abstract Diclofenac, a widely used anti-inflammatory drug, has been found in many Sewage Treatment Plant effluents, rivers and lake waters, and has been reported to exhibit adverse effects on fish. Advanced oxidation processes, ozonation and H 2 O 2 /UV were investigated for its degradation in water. The kinetic of the degradation reaction and the nature of the intermediate products were still poorly defined. Under the conditions adopted in the present study, both ozonation and H 2 O 2 /UV systems proved to be effective in inducing diclofenac degradation, ensuring a complete conversion of the chlorine into chloride ions and degrees of mineralization of 32% for ozonation and 39% for H 2 O 2 /UV after a 90 min treatment. The reactions were found to follow similar, but not identical, reaction pathways leading to hydroxylated intermediates (e.g. 2-[(2,6-dichlorophenyl)amino]-5-hydroxyphenylacetic acid) and C–N cleavage products (notably 2,5-dihydroxyphenylacetic acid) through competitive routes. Subsequent oxidative ring cleavage leads to carboxylic acid fragments via classic degradation pathways. In the pH range 5.0–6.0 kinetic constants (1.76×10 4 –1.84×10 4  M −1  s −1 ) were estimated for diclofenac ozonation.