Mineralization of 2,4-D by advanced electrochemical oxidation processes

The mineralization process for 2,4-dichiorophenoxyacetic acid (2,4-D) at pH ca. 3 has been studied by advanced electrochemical oxidation processes (AE OPs), such as electro-Fenton and photoelectro-Fenton processes, in which a Pt anode and a carbon-polytetrafluoroethylene O-2-fed cathode, for in situ production of H2O2 are used. A solution of 230 ppm 2,4-D with a low salt co ntent can be completely mineralized by the photoelectro-Fenton process at l ow current, whereas the electro-Fenton process leads to ca. 90% of minerali zation. In both methods. 2,4-D is quickly destroyed at the same rate. The h igh degradation power of these AEOPs is due to the large production of oxid izing hydroxyl radicals by reaction between electrogenerated H2O2 and Fe2added to the solution. The higher mineralization rate found for photoelectr o-Fenton is accounted for by the fast photolytic decomposition of some inte rmediates by UV light. Classical anodic oxidation with a graphite cathode a nd anodic oxidation in the presence of electrogenerated H2O2 are much less efficient methods to degrade 2,4-D and its oxidation products. 2,4-Dichloro phenol. 4,6-dichlororesorcinol, chlorohydroquinone and chlorobenzoquinone h ave been identified as intermediates by GC-MS and their evolution for each process has been followed by reverse-phase chromatography. Chloride ion is released from these chloroderivatives and accumulates in the medium. Short- chain acids, as glycolic, glyoxylic, maleic, fumaric and oxalic, have been detected by ion-exclusion chromatography. A general reaction pathway involv ing all these intermediates is proposed. (C) 2000 Elsevier Science Ltd. All rights reserved.