Sodium acetate outperforms glucose in boosting sulfur-driven autotrophic denitrification under high salinity stress

Sulfur autotrophic denitrification (SAD) is widely employed for nitrate (NO₃⁻-N) removal from wastewater due to its advantages. However, high salinity (≥15 g/L) significantly reduces NO₃⁻-N removal efficiency. While adding liquid carbon sources can improve denitrification, their effects and mechanisms under salt stress remain unclear. Here, we compared sodium acetate and glucose in an SAD system at a salinity of 25 g/L. The sodium acetate-enhanced system achieved superior removal rates of 90.55% for NO₃⁻-N and 85.13% for total nitrogen (TN), compared with 82.62% (NO₃⁻-N) and 81.11% (TN) with glucose. Sodium acetate also resulted in significantly lower nitrite (NO₂⁻-N) accumulation. Furthermore, it promoted higher heterotrophic denitrification contribution and chemical oxygen demand (COD) utilization rates than those observed with glucose. Microbial analysis revealed a shift in dominant bacteria: Thiobacillus and Vitellibacter dominated with glucose, while Thiobacillus and Denitromonas prevailed with sodium acetate. Both carbon sources enhanced NO₃⁻-N reduction by upregulating narG and nirS gene expression, though sodium acetate exhibited a stronger effect. These findings provide a theoretical basis for efficient NO₃⁻-N removal from high-salinity wastewater using a sulfur-autotrophic–heterotrophic collaborative system.