Degradation of Monoazo Pigments Red 53:1 and Red 48:2 by Fenton,Photo‐Fenton and UV/Peroxide Reactions

The degradation reactions of two monoazo pigments, namely, Red 53:1 and Red 48:2, by Fenton, photo‐Fenton and UV/H₂O₂ systems have been studied. The efficiencies of the Fenton reactions increased with temperature, but the formation of solid agglomerates was observed when the reactions were carried out above 50°C indicating a coagulant action of Fe⁺² or Fe⁺³. Photo‐Fenton reactions irradiated by sunlight presented the best rate constants for cleavage of the azo bond and the naphthalene rings. The UV/H₂O₂ system exhibited the highest efficiency with respect to the consumption of H₂O₂. The presence of a carbonyl group in the ortho position of the naphthol ring hampered the oxidation of pigment Red 48:2 by hydroxyl radicals. This finding may be explained in terms of the acceptor character of the COOH group, and suggests the formation of a complex containing two six‐membered rings between Fe⁺³ and the pigment molecule.     

Degradation of Textile Dyeing Wastewater by a Modified Solar Photo‐Fenton Process Using Steel Scrap/H2O2

This experimental research deals with using steel scrap as a heterogeneous catalyst. This catalyzes the oxidation reaction of real textile dye wastewater based on a modified solar photo‐Fenton oxidation process. Morphologic analysis and mapping of the elementary composition of the steel scrap have been carried out by scanning electron microscopy. The effects of concentration of H₂O₂, the pH of the solution and the catalyst loading on the degradation of textile dye wastewater are elucidated. Kinetic studies have been performed for the decolorization of wastewater under optimum conditions. It could be concluded that the steel scrap is a potential substitute for ferrous salts as a catalyst for the solar photo‐Fenton reaction.     

Pilot‐Scale Degradation of Organic Contaminants in a Continuous‐flow Reactor by the Helielectro‐Fenton Method

The feasibility of pilot‐scale mineralization of organic pollutants in wastewaters using the Electro‐Fenton® process is demonstrated. The treatment was applied in a continuous‐flow reactor, to solutions of nitrobenzene, 2,4‐D and benzoic acid and to actual wastewaters from a fine chemicals company along with a pulp and paper company. The results showed mineralization yields from 60 to 84% by simply applying the Electro‐Fenton® process. When a subsequent exposure to sunlight was carried out (Helielectro‐Fenton method), this mineralization almost went to completion, except for the effluent from the fine chemicals industry.