In-Situ sulfur implantation efficiently promoting nitrogen removal in low-carbon anoxic-oxic systems.
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75% confidenceAn in-situ sulfur implantation system efficiently promotes nitrogen removal in low-carbon anoxic-oxic systems by redistributing electrons and compensating for carbon deficiency.
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Abstract
Efficient total nitrogen (TN) removal from low-carbon wastewater remains challenging due to electron donor scarcity, often causing incomplete denitrification and nitrite accumulation. To address this, an in-situ sulfur-enhanced anoxic/oxic (HS 0 AD-A/O) system was established, enabling S 0 -driven electron redistribution for enhanced TN removal without additional carbon input or process restructuring. Under decreasing influent C/N ratios (4 to 2), HS 0 AD-A/O outperformed conventional HD-A/O by 32.76-111.16% of TN removal efficiency. Electron balance showed S 0 oxidation contributed 9.21-27.59% of total electron flux, compensating for carbon deficiency. Increasing the S 0 implantation ratio to 28% shifted the dominant pathway toward S 0 -based autotrophic denitrification, where S 0 -derived electrons surpassed those from COD (58.27% vs. 41.73%). Kinetic assays revealed that S 0 -driven denitrification preferentially reduced NO 2 ⁻ over NO 3 ⁻, thereby minimizing NO 2 ⁻ accumulation and yielding a distinct S 0 ‑saving effect (1.14-1.57 g-S 0 /g-N here). Microbial and transcriptional analyses further elucidated a synergistic division of labor: heterotrophic denitrifiers (e.g., Hydrogenophaga, Rhodocyclaceae) in sludge primarily reduced NO 3 ⁻-N but tended to cause partial denitrification, whereas S 0 -attached autotrophs (e.g., Thiobacillus, up to 46.10% in biofilms) specialize in complete denitrification and efficiently converted NO 2 ⁻-N to N 2 , accompanied by marked upregulation of nirKS and nosZ genes. Overall, in-situ S 0 implantation restructured electron transfer networks, enabling stable, efficient, and dual-saving (carbon and S 0 ) TN removal while providing mechanistic insight for scalable applications.