High-valent iron-driven sulfamethoxazole removal during sludge dewatering process

Abstract

Removal of sulfonamides during the dewatering of sludge is critical to lighten the burden on downstream treatment processes such as anaerobic digestion. However, to this end, the preferred peroxide-based advanced oxidation processes are inadequate due to their insufficient oxidation efficiency, resulting in low removal of sulfonamides. The present study introduced a novel sludge dewatering approach, involving scrap iron combined with percarbonate (SPC) to produce high-valent iron for the removal of sulfonamide, with a focus on sulfamethoxazole (SMX) as the representative sulfonamide compound. Under optimized conditions, the treatment involving the combination of scrap iron and SPC resulted in a water content of 54.8% ± 0.3% and removed 46.9% ± 0.5% of SMX at a chemical cost of 19.6 $/t of total solids, demonstrating competitiveness to contemporary peroxides-based advanced oxidation processes. High-valent iron effectively broke down the key binding compounds and sites between extracellular polymeric substances (EPS) and SMX, leading to a shift towards hydrophobic bonding sites, smaller and more dispersed particle configurations, and reduced capacity for retaining water. This facilitated the release of SMX into liquid phases, followed by degradation by reactive oxygen species. These findings collectively demonstrate that the proposed method of using scrap iron in conjunction with SPC can remarkably reduce the volume of sludge and enhance the removal of SMX during the dewatering of sludge.

Graphical abstract

Keywords

Sludge dewatering / Sulfamethoxazole removal / Extracellular polymeric substances / Degradation pathway / High-valent iron

Highlight

	● Fe(IV) oxidation dominated SMX removal during sludge dewatering.
	● Scrap iron + SPC treatment removed 46.9 % SMX from sludge with 54.8 % water content.
	● ROS disrupted key EPS-SMX binding sites for enhancing SMX removal.
	● Twelve SMX intermediates and six degradation pathways were identified.

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