The role of iron on the degradation and mineralization of organic compounds using conventional Fenton and photo-Fenton processes

Abstract

a b s t r a c tThe role of iron on the degradation of different organic compounds, differing in their structure (aliphatic versus aromatic) and iron complex formation capacity, by conventional and photo-Fenton processes was investigated. Results show that these chemical characteristics can affect the degree of treatment in terms of COD and TOC removals. While aromatics exhibited a fast and great reduction in the COD by the conventional Fenton process, aliphatic compounds, apart from acetic acid, required the presence of UV light to enhance treatment results. EDTA and oxalic acid responded very positively to UV irradiation in both COD removal and mineralization, reaching the highest values showed by aromatics; and results depended on the intensity of the UV light applied. Phenol and 4-nitrophenol responded favourably to UV irradiation in terms of mineralization and slightly in COD removal. Reductions in the COD were almost total (95.99%), while only an 80% of reduction in the TOC was achieved, for the best photo-Fenton treatment of oxalic acid, phenol and nitrophenol. 60% COD and 40% TOC removals were achieved correspondingly in the case of EDTA. Acetic acid showed almost no mineralization and low COD removal (≈20%) when treated by a conventional Fenton process; and did not enhanced results when assisting the treatment with UV light. Photo-regeneration of ferrous ion and photo-decarboxylation of iron carboxylates are assessed in the framework of these results.

The application of advanced oxidation technologies to the treatment of effluents from the pulp and paper industry: a review

“…Furthermore, acetic acid resulted to be the most difficult final oxidation product to remove, such as it has also been addressed when applying Fenton, photo-Fenton, and electro-Fenton processes to solutions containing different chemical moieties (Hermosilla et al 2009b). …”

“…As a result, the amount of catalytic iron that would be required to produce the same treatment results, and the volume of sludge consequently generated, could be strongly reduced; as well as some additional organic compounds (carboxylates) that are very difficult to treat by AOPs may otherwise be effectively treated by this methodology (Hermosilla et al 2009a;Hermosilla et al 2009b). Consequently, the photo-Fenton alternative has generally been shown to be more efficient in the degradation of effluent components than its dark version (Karimi et al 2010), and improves both the total quantity and the rate of TOC abatement in comparison to the UV/H 2 O 2 system (Catalkaya and Kargi 2007;Hermosilla et al 2009b;Hermosilla et al 2012).…”

“…Consequently, the photo-Fenton alternative has generally been shown to be more efficient in the degradation of effluent components than its dark version (Karimi et al 2010), and improves both the total quantity and the rate of TOC abatement in comparison to the UV/H 2 O 2 system (Catalkaya and Kargi 2007;Hermosilla et al 2009b;Hermosilla et al 2012). …”

“…As a result, photo-Fenton processes may be implemented at a significantly reduced cost when performed using solar irradiation (Pérez et al 2002b). As it has already been pointed out, the optimal treatment would be performed at pH=2.8, which is related to iron speciation in the solution (Hermosilla et al 2009b;Pérez et al 2002a;Torrades et al 2003). Besides, a good TOC removal (> 60%) has also been achieved treating bleaching effluent at an initial pH value of 6, adding the advantage of avoiding the extra operation and cost associated to initial pH adjustment (Xu et al 2007); as well as better treatment results were reported at 50ºC than at a lower treatment temperature in this essay.…”

“…Phenoxyl radicals rapidly react with O 2 •− to produce aromatic ringopening precursors of CO 2 (Antunes et al 2004). On the other hand, aliphatic carboxylic acids are very stable, and their degradation rates by OH· are really low in the absence of UV light (Hermosilla et al 2009b). …”