Enhanced in-situ sulfide removal via goethite-fulvic acid bio-reduction and iron-based catalysis in activated sludge recycling odor control system

Abstract

H₂S poses serious challenges in wastewater treatment plants, including unpleasant odors issues, toxicity conditions and infrastructure corrosion. In this study, we propose a novel in-situ H₂S odor control process, which introduced goethite/goethite-fulvic acid (FA) bio-reduction and Fe-based catalysis into activated sludge recycling. This novel process reduced the activated sludge recycling rate from 40 % to 5 %, while increasing the sulfide removal efficiency from 52.97 % to 87.61 %. The sulfide removal capacities were 99.78 mgS/g Fe for goethite and 247.38 mgS/g Fe for goethite-FA. The bio-reduction of recycled sludge further enhanced the sulfide removal capacity to 103.43 mgS/g Fe in goethite and 337.74 mgS/g Fe for goethite-FA. Fulvic acid disrupted crystal structure, reduced electron transfer resistance and increased surface area of goethite, thereby enhancing bio-reduction efficiency and sulfide removal capacity. Moreover, aeration of inlet works further increased the sulfide removal efficiency from 12.67 % to 65.50 % in goethite sludge and from 23.73 % to 87.61 % in goethite-FA sludge. This enhancement was due to the catalytic effect of dissolved and ion-exchangeable Fe, which generated through complexation and electronegativity of recycled Fe-activated sludge. Overall, the novel H₂S control process can achieve high sulfide removal efficiency while maintaining low recycling rate and operation costs.