Sulfur management is critical for wastewater anaerobic treatment effluent polishing and certain chemical manufacturing processes, and electrochemical sulfide treatment is a promising technology for it. Recovering sulfide as elemental sulfur and sulfate could create valuable products (e.g., sulfuric acid, ammonium sulfate as fertilizer) that enable a circular sulfur economy. In this study, we addressed the methodological and operational barriers of electrochemical sulfur recovery by elucidating the mechanism of electrochemical sulfide oxidation and investigating the effects of operational parameters on process-level performance. We identified thiosulfate oxidation as the rate-limiting step of electrochemical sulfide oxidation and clarified the role of elemental sulfur passivation in preventing reactants from reaching electrode active sites. In addition, we compared sulfide oxidation with and without the oxygen evolution reaction in real anaerobic effluents by evaluating performance metrics (e.g., removal/recovery efficiency, energy) for each pathway. These mechanistic insights regarding kinetics (rate-limiting steps) and mass transport (electrode passivation) were also employed in electrochemical reactor design to facilitate sulfide removal and sulfur product recovery (i.e., separating the products from sulfide removal). To further improve sulfur recovery performance, we adjusted operating parameters (e.g., applied potential) and electrolyte properties (e.g., pH, constituents) to maximize the yield of recoverable sulfur products and correlated energy consumption to recovery efficiency to develop a process-level framework for informing optimal operation. These electrochemical sulfur recovery efforts could mitigate environmental impacts by improving the quality of the discharged effluents, and could thus advance a circular sulfur economy by offsetting chemical inputs with sulfur products recovered from anaerobic effluents.

Advancing a circular sulfur economy: Electrochemical sulfur recovery from anaerobic effluents

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