Basic yellow 28 removal using a hybrid solid waste iron (SWI)/chlorine process: mechanistic insights, process optimization, and the role of reactive species

Abstract

As a promising and efficient alternative for chlorine activation, this study explores the potential of solid waste iron (SWI), in the form of iron rods, as a low-cost and readily available catalyst for generating highly reactive species. The effects of various operational parameters, including solution pH, chlorine, pollutant, and catalyst concentrations, as well as solution temperature, were systematically examined using the removal of Basic Yellow 28 (BY28) as a model pollutant. Furthermore, mathematical models were established to reliably predict the BY28 degradation rate under different operational conditions. Under optimized conditions (150 µM chlorine, solution pH 3, and a BY28 dose of 20 mg L⁻¹), BY28 removal increased with agitation speed, reaching 87.5% at 400 rpm, while solution temperature exerted a negligible influence. Under these conditions, reactive chlorine species and hydroxyl radicals played dominant roles, with a comparatively lower contribution from ferryl species. The chlorine activation mechanism was discussed, with particular emphasis on the influence of water matrices. The performance of the hybrid SWI/chlorine system was adversely affected by the presence of surfactants (Tween 80, Tween 20, Triton X-100, and SDS) and inorganic salts (Na₂SO₄, KBr, NaNO₃, and NaNO₂), with the inhibitory effect being more pronounced for the latter. Nevertheless, a positive impact was observed in the presence of NaCl. A total organic carbon (TOC) reduction of approximately 40% was obtained under optimal conditions. Overall, this study demonstrates the effectiveness of the proposed hybrid advanced oxidation process (AOP) for the removal of recalcitrant contaminants under controlled conditions, while further work is needed to enhance its performance in real water systems and evaluate its potential for scale-up.