Application of a novel advanced oxidation process using sulfite and zero-valent iron in treatment of organic pollutants

Abstract

A novel advanced oxidation process, combined zero-valent iron and sulfite (Fe⁰/sulfite) system containing oxygen, was firstly developed to efficiently degrade organic pollutants at weak acidic and neutral conditions by selecting X-3B as a target compound. The removal of X-3B was attributed to the formed reactive radicals, such as SO₄ ^-, SO₅ ^- and HO^[rad], in the Fe⁰/sulfite system, and SO₄ ^- was evidenced as the principal reactive species. The quite low removal efficiency of X-3B (less than 5%) after reaction for 90 min with purging nitrogen gas suggests oxygen to be an essential factor for producing SO₄ ^- in the system. Optimal dosages of Fe⁰ and sulfite were suggested to be 0.5 mM and 1.0 mM, respectively, in the system as both the two chemicals would scavenge the reactive radicals at overdosing. The presence of 2 mM bicarbonate significantly inhibited the removal of X-3B from 74.1% to 37.5% in the system. Halide ions inhibited the removal of X-3B following a trend that Cl⁻ <Br⁻ <I⁻. HSO₃ ⁻, being effective in complexion of Fe(II) and transferring Fe(III) to Fe(II), is the main species during pHs 4–6, which results in the good reuse of Fe⁰ and the highest removal efficiency of X-3B at weak acidic condition. Fe⁰/sulfite system was also evidenced to be effective in the treatment of actual textile effluents along with improving biodegradability, and the removal of nitrobenzene, methylparaben, bisphenol A, imipramine and amitriptyline. Overall, this study provided a cheap and easy operational advanced oxidation process in treatment of aqueous organic pollutants.