Highly concentrated phenolic wastewater treatment by the Photo-Fenton reaction, mechanism study by FTIR-ATR

Phenol degradation by Photo-Fenton reaction has been studied in highly conc entrated wastewaters and most intermediate species have been identified by Fourier Transform IR-Spectroscopy with ATR device. During the photodegradat ion of highly concentrated phenol solutions, the formation of dissolved and precipitate tannin has been observed. The possibility of a Fe3+-Pyrogallol complex formation, previous to the tannin formation, has been proposed too . The complex formation involving Fe3+ ions could be related to the observe d Photo-Fenton activity decrease. Tannin formation inhibits the complete mi neralization of phenol because . OH radicals attack will produce further co ndensation steps and the polymer size increase. This fact limits the applic ability of the process for highly concentrated phenolic wastes mineralizati on. However, the tannin precipitation allows its separation from the soluti on by conventional filtration, and reduction of the corresponding dissolved organic carbon. These observations have been proved from the identificatio n of primary degradation products, catechol and hydroquinone. Catechol is c onsidered to be the first step for the formation of tannins. Degradation pr ocess for phenol, catechol and hydroquinone have been monitored by total or ganic carbon (TOC) measurements along the reaction time span. From these re sults, a global mechanism for the Photo-Fenton degradation of phenol is pro posed. (C) 2001 Elsevier Science Ltd. All rights reserved.