Kinetics of ultrasound-enhanced electrochemical oxidation of diuron on boron-doped diamond electrodes

Freshwater polluted with herbicides is an environmental problem of concern due to the high toxicity and non-biodegradability of these compounds. This work analyses for the first time the degradation and mineralization of diuron (N-(3,4-dichlorophenyl)-N,N-dimethyl-urea), considered priority substance by the European Commission, by electrochemical oxidation (EO) at a boron-doped diamond anode enhanced by low frequency (20 kHz) ultrasound (US). A synergistic analysis was initially performed to evaluate the relative contribution of individual oxidation technologies to the global abatement and mineralization rates of diuron observed under sonoelectrochemical (US-EO) treatment. Under the operation conditions, j = 60 mA cm(-2), v(US) = 20 kHz, pH = 12, T= 10 degrees C and 8 h of experimental running, results demonstrated improvements on the mineralization kinetics of diuron closely to 43% when ultrasounds are coupled to the electrochemical treatment. The process efficiency was evaluated through the analysis of the mineralization rate as a good indicator of the formation of organic metabolites which may have higher toxic effects than parent diuron. The mineralization kinetics of diuron degradation by US-EO have been experimentally and theoretically analysed working with 20-30 mgL(-1) of diuron, initial pH values between 2 and 12 and temperatures between 10 degrees C and 40 degrees C. The encouraging results showed that alkaline pH favours the mineralization rate obtaining reductions of the total organic carbon higher than the 92% after 6 h of degradation. The temperature in the range between 10 degrees C and 40 degrees C has a weak impact on the kinetics of the sonoelectrochemical mineralization of diuron. (C) 2011 Elsevier B.V. All rights reserved.