A novel elemental sulfur reduction and sulfide oxidation integrated process for wastewater treatment and sulfur recycling

Sulfidogenic processes have been successfully used in saline wastewater treatment for sludge minimization, but are inapplicable in treating sulfate-deficit wastewater. This study reported a novel internal sulfur cycling (ISC) process for sulfate-deficit wastewater treatment. The process consisted of a sulfur-reducing reactor (SRR) for organics removal, followed by a sulfide-oxidizing reactor (SOR) and sedimentation tank for sulfur recovery. Under different hydraulic retention times and organic loading rates, the performance of ISC system was evaluated. The lab-scale ISC system removed 94% of chemical oxygen demand (COD), of which 81% were accomplished in the SRR by sulfur reducers without excessive sludge withdrawal throughout the 200 days of operation. The produced sulfide were mainly re-oxidized back to elemental sulfur in the SOR by sulfide-oxidizing bacteria, and sulfur balance demonstrates that 76% of sulfur recycling were achieved. Cost-benefit analysis reveals that the ISC process is a more cost-effective sludge-minimized biotechnology for sulfate-deficit wastewater treatment compared to conventional activated sludge processes.