Degradation of Membrane Concentrates of the Textile Industry by Fenton Like Reactions in Iron-Free Solutions at Biocompatible pH Values (pH ≈ 7–8)

Abstract

Degradative oxidation of membrane concentrates of textile waters were carried out in batch reactors in the dark and under visible light. H2O2 and Nafion-Fe3+/H2O2 as an immobilized Fenton reagent were used as ecological oxidants. The results observed with the Nafion/Fe3+ system lead to a kinetically faster and more complete oxidation than H2O2 alone and comparable to the homogeneous Fenton reaction in solution. This study reports on the Fenton treatment of membrane concentrates resulting from nanofiltration of biologically treated secondary textile effluents produced in a large scale in Northern Italy. The degradation of the membrane concentrates is accelerated under light due to the recycling of the Fe3+-ion in the Nafion avoiding the drawbacks of the homogeneous treatment. A reduction of ∼ 50% is seen in the TOC and of ∼20–50% in optical absorbance after 3 hours pretreatment under light for end of pipe membrane concentrates under light and the process was stable over many cycles. The observed degradation depended on the amount of H2O2, the intensity of the visible light applied. But it varied very little on the pretreatment pH which makes the Fenton immobilized systems suitable to pretreat membrane concentrates up to pH 8. The membrane concentrates showed a decrease in their toxicology when undergoing oxidative pretreatment under visible light mediated by Nafion-Fe3+ (1.78%) adding in solution H2O2 (10 mM). Mathematical modeling of the degradation parameters is presented by constructing a single exponential polynomial function.