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

This study aims to enhance biogenic elemental sulfur (S⁰_bio) 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 <i>Thiobacillus denitrificans</i>-augmented SNSR system elucidates its regulatory mechanism on S⁰_bio yield and stability. Under low sulfide loading (100 mg/L S^2-), 30 mg/L S₂O₃^2- amendment achieved peak S⁰_bio 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 (S^2-→ S⁰_bio) intensity increased by 0.53-1.05-fold, while the competing pathway (S^2-→ S₂O₃^2-) was inhibited (0.10-0.28-fold reduction). Thiosulfate enabled the S⁰_bio generation pathway to dominate over S^2-→ SO₄^2-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 S⁰_bio stabilization through dual mechanisms: (1) enhancing <i>Thiobacillus denitrificans</i> 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 S⁰_bio reclamation.<b>Highlights</b>Early-stage inhibition boosts S⁰_bio yield to 69.85% at low sulfide loading with thiosulfate amendment.3.03× higher sulfur conversion efficiency versus high-loading controls via pathway redirection to S⁰_bio generation.Dual regulation: Synergistically enhances <i>Thiobacillus denitrificans</i> activity (↑1.22× viability) and redirects sulfur flux toward S^2-→S⁰_bio (55.32% dominance), suppressing competing pathways.Resource recovery strategy enabling stable S⁰_bio reclamation from sulfur-laden wastewater.