Degradation of 4-chloro-2-methylphenol(PCOC), a refractory toxic chemical emitted to the environment from the industrial production of phenoxy herbicides was studied in aqueous solution. Electro-Fenton and photoelectro-Fenton processes were used as the degradation methods. H(2)O(2), produced by the reduction of oxygen at carbon cathode reacted with dissolved metal ions to form hydroxyl radicals, which in turn reacted with PCOC sequentially to degrade the aromatic ring. The effects of using different [Fe(2+)]/[PCOC](0) and the effect of replacing Fe(2+) by Mn(2+) ion have been examined. It was found that degradation rate was increased with increasing [Fe(2+)]/[PCOC](0) ratio from 2 to 4. However, the total charge utilized during the treatment was also increased. The efficiency of PCOC degradation was observed to be higher when Mn(2+) was used as the catalyst. The mineralization of aqueous solutions of PCOC, withdrawn from the reactor at certain time interval. has been followed by total organic carbon (TOC) decay and dechlorination. A fast and complete degradation of the aromatic ring was achieved in photoelectro-Fenton system. 41.7% charge during a 300 min photoelectron-Fenton TOC decay and complete dechlorination were observed by consuming only 141.4 C electrical char treatment. In the case of electro-Fenton system, 280.7 C electrical charge was consumed during 450 min of electrolysis to attain a similar degradation of PCOC. 14.9% TOC removal and 89.3% dechlorination have been obtained in this system under the applied conditions. (c) 2005 Elsevier B.V. All rights reserved.