Maximizing elemental sulfur production using an enriched sulfur-oxidizing bacterial consortium in a fed-batch bioreactor

Biological desulfurization provides a sustainable and cost-effective alternative to conventional physicochemical methods for removing hydrogen sulfide (H₂S) from industrial gas streams, particularly in medium-scale applications. This study investigates the enrichment and application of an enriched sulfur-oxidizing bacterial (SOB) consortium, isolated from sulfur-rich natural environments in Iran, for the selective biological conversion of sulfide to elemental sulfur in a fed-batch airlift bioreactor. A Central Composite Design-Response Surface Methodology (CCD-RSM) was employed to statistically evaluate and optimize the effect of dissolved oxygen (DO), pH, and sulfide loading rate, aiming to maximize sulfur selectivity while minimizing by-product formation. Optimization results revealed that both DO concentration and sulfide loading rate significantly influenced sulfur selectivity. Notably, low DO levels enhanced the selective production of elemental sulfur, while higher pH and sulfide loading rates promoted thiosulfate formation. The optimal conditions determined were pH 8.5, DO concentration of 0.2 mg L^-1, and a sulfide loading rate of 97.2 mg L^-1 h^-1. Under these optimized fed-batch conditions, 71% of the inlet sulfide was selectively converted to elemental sulfur, with complete (100%) sulfide removal achieved across all experimental runs. These findings demonstrate the potential of using enriched SOB together with well-controlled process conditions can make biodesulfurization more efficient, selective, and environmentally friendly for industrial applications. Compared with conventional physicochemical methods, the optimized biological process operates under mild conditions, is more cost-effective and environmentally sustainable, while maintaining high sulfide removal and sulfur recovery.