Stabilization of biogenic elemental sulfur in simultaneous nitrogen and sulfur removal via early-stage inhibition

This study aims to enhance biogenic elemental sulfur (S⁰bio) recovery efficiency in Simultaneous Nitrogen and Sulfur Removal (SNSR) processes for dual environmental and economic benefits. The addition of thiosulfate to redirect reaction pathways in a Thiobacillus denitrificans-augmented SNSR system elucidates its regulatory mechanism on S⁰bio yield and stability. Under low sulfide loading (100 mg/L S²⁻), 30 mg/L S₂O₃²⁻ amendment achieved peak S⁰bio yield of 69.85% at 36 h, with sulfur conversion efficiency 3.03-fold higher than the high-loading non-inhibited group (NI). The target pathway (S²⁻→ S⁰bio) intensity increased by 0.53-1.05-fold, while the competing pathway (S²⁻→ S₂O₃²⁻) was inhibited (0.10-0.28-fold reduction). Thiosulfate enabled the S⁰bio generation pathway to dominate over S²⁻→ SO₄²⁻during early-stage low-sulfide SNSR, reaching a maximum contribution of 55.32%. Additionally, the fluorescence intensity contribution of soluble microbial products (SMP) reached a peak of 49.81%, while concurrent measurements showed significant increases in viable cell count and viability (averaging 2.17-fold and 3.18-fold higher than those in the non-thiosulfate-amended groups, respectively). Thiosulfate synergistically drives efficient S⁰bio stabilization through dual mechanisms: (1) enhancing Thiobacillus denitrificans bioactivity to intensify key reaction kinetics; (2) optimizing sulfur speciation transformation to establish target-pathway dominance. This work provides technical insights for resource recovery from sulfur-laden wastewater and stable S⁰bio reclamation.