Removal of persistent textile dyes from wastewater by Fe(ii)/H2O2/H3NOH+ integrated system: process performance and limitations

Abstract

With the objective of establishing an overview of the limits of hydroxylamine-induced acceleration of the Fenton process, the impact of a wide range of processing conditions and water matrix compositions (water quality) on the degradation of persistent textile dyes is revealed in this study. The co-use of Fenton reagents and hydroxylamine in its protonated form (H₃NOH⁺) enabled the rapid removal of dyes, with a yield improvement of more than 40% compared to the not using H₃NOH⁺. H₃NOH⁺ broadened the Fenton working pH up to pH 5, where higher degradation efficacy is achieved to that at pH 3. The gap between the Fenton-H₃NOH⁺ and Fenton systems in term of dye removal increases with increasing dosages of reactants (i.e., H₃NOH⁺, H₂O₂, Fe(II) and dye) and solution pH (2–5). While sulfate and nitrite ions (up to 10 mM) did not affect the efficiency of the process in the presence or absence of H₃NOH⁺, chloride greatly hindered the Fenton process (60%) while minimally affecting dye removal by the Fenton-H₃NOH⁺ system. The Fenton-H₃NOH⁺ system maintained better degradation performance for the breakdown of Basic Fuchsin (BF) in natural mineral water and treated wastewater. However, the degradation efficiencies in sea and river waters are substantially reduced, with just 61 and 58% elimination being reached, respectively. However, the ternary system outperforms the Fenton process alone in all of the studied water matrices. The findings of this work broaden our understanding of the application of hydroxylamine in the Fenton process and highlight the limitations of its influence in boosting the breakdown efficiency of textile dye contaminants.