A novel alkalinity slow-release filler for sulfur autotrophic denitrification: Performance, functional microbial...

Sulfur-based autotrophic denitrification (SAD) is an effective technology for treating nitrate-contaminated wastewater. However, SAD is accompanied by acid production. Denitrifying bacteria are highly susceptible to pH drop, which would suppress microbial activity and ultimately restrict nitrogen removal performance. In this study, a novel alkalinity slow-release filler (CCR-S) was prepared using elemental sulfur, calcium carbide residue (CCR) and activated carbon (AC) as raw materials. It was used for denitrification treatment of low carbon-to-nitrogen ratio wastewater and compared with the ordinary filler (CC-S) made by substituting CCR with calcium carbonate. During the denitrification process, the pH value in the CCR-S system was maintained above 8.00, whereas that in the CC-S system decreased continuously to 6.40. The average and maximum NO₃^- removal efficiencies of CCR-S reached 94.62% and 97.67%, respectively, both higher than those of CC-S (87.69% and 95.40%). The abundance of the unique dominant genera involved in autotrophic denitrification (Annwoodia, Sulfuritalea and Thiobacillus) and their functional genes (e.g., narGHI) was also significantly increased in the CCR-S system. Additionally, we systematically evaluated the performance and operational stability of the CCR-S system and verified its effectiveness based on typical nitrogen and sulfur metabolic pathways. This study developed a novel, high-efficiency alkalinity slow-release filler for SAD, providing theoretical support for its practical application.