Electromicrobial Hybrid System for High-Purity Sulfur Recovery from High-Salinity Wastewater

Abstract

High-salinity wastewater contains a high concentration of sulfate (SO₄^2–), posing environmental risks while offering potential for resource recovery. This study developed an electromicrobial hybrid system to achieve simultaneous SO₄^2– removal and elemental sulfur (S⁰) recovery by integrating electrolytic hydrogen-mediated microbial sulfate reduction, H₂S stripping, and off-field electrochemical oxidation. Sulfate reduction occurred in the cathode of the electrolytic-hydrogen-fed reactor, where the generated sulfide was stripped as H₂S into an off-field oxidation unit using a FeCN₆^3–/FeCN₆^4– redox mediator. FeCN₆^3– oxidized H₂S to S⁰, while FeCN₆^4– was regenerated to FeCN₆^3– at the anode. The reactor performance was enhanced by introducing PU@RGO@MnO₂ carriers, with the optimal SO₄^2– removal current identified as 300 mA (6.7 A m^–2). SO₄^2– removal and S⁰ recovery performance was tested under this condition. H₂S stripping coupled with sulfate reduction and off-field sulfide oxidation eliminated the inhibition of high concentration sulfide on sulfate-reducing bacteria, achieving 100% H₂S-to-S⁰ conversion. Therefore, the system achieved an efficient SO₄^2– removal rate of 464.3 ± 7.1 mg of SO₄^2–-S L^–1 d^–1 and a S⁰ production rate of 450.6 ± 8.6 mg of S⁰-S L^–1 d^–1 (SO₄^2– removal efficiency = 92.6 ± 1.3%; S⁰ recovery efficiency = 89.8 ± 1.6%), with a remarkable electrical energy efficiency of 62.5 ± 1.9% and an energy consumption of 20 kWh kg S^0–1. The recovered S⁰ exhibited high purity (99.15%) and could be efficiently separated via gravity settling. The recovered S⁰ exhibited an electrochemical performance comparable to that of commercial S⁰ in the lithium–sulfur battery. This study provides a sustainable approach for wastewater treatment and sulfur recovery, bridging environmental remediation with energy storage application.