Effects of ozone pre-treatment on diclofenac: intermediates, biodegradability and toxicity assessment.

Abstract Diclofenac (DCF), a common analgesic, anti-arthritic and anti-rheumatic drug, is one of the most frequently detected compounds in water. This study deals with the degradation of diclofenac in aqueous solution by ozonation. Biodegradability (BOD 5 /COD ratio and Zahn–Wellens test), acute ecotoxicity and inhibition of activated sludge activity were determined in ozonated and non-ozonated samples. Liquid chromatography coupled with time-of-flight mass spectrometry (LC/TOF-MS) was used to identify the intermediates formed in 1 h of ozonation. Eighteen intermediates were identified by these techniques and a tentative degradation pathway for DCF ozonation is proposed. Experimental results show that ozone is efficient at removing DCF: > 99% removal (starting from an initial concentration of 0.68 mmol L − 1 ) was achieved after 30 min of ozonation (corresponding to an absorbed ozone dose of 0.22 g L − 1 , which is 4.58 mmol L − 1 ). However, only 24% of the substrate was mineralized after 1 h of ozonation. The biodegradability, respiration inhibition in activated sludge and acute toxicity tests demonstrate that ozonation promotes a more biocompatible effluent of waters containing DCF.