Degradation kinetics of 2,4-D in water employing hydrogen peroxide and UV radiation

This paper reports the photooxidation of 2,4-dichlorophenoxyacetic acid (2,4-D) in aqueous solution employing hydrogen peroxide and ultraviolet radiation. A kinetic model to represent the degradation of 2,4-D and that of equally toxic intermediate products, such as 2,4-dichlorophenol (DCP) and chlorohydroquinone (CHQ), is presented. The model includes the parallel, direct photolysis of 2,4-D and the most important reaction intermediates. The experimental work was performed in a batch, well-stirred tank reactor irradiated from its bottom using a low power, germicidal, tubular lamp placed at the focal axis of a cylindrical reflector of parabolic cross-section. Herbicide degradation initial rates twenty times faster than those obtained employing UV radiation alone were found. In order to reach more useful conclusions about the ability of the process to reduce the contamination to innocuous final products, simultaneous measurements of the total organic carbon (TOC) were performed. By application of the kinetic model to the whole set of concentration versus time experimental data, the values of the kinetic parameters were obtained. The model permits a good representation of the reaction evolution in a rather wide range of 2,4-D and H(2)O(2) initial concentrations. (C) 2001 Elsevier Science B.V. All rights reserved.