Inorganic Carbon Limitation Shaped the Biofilm Community of Sulfide-Based Denitrification in an AnMBR

The sulfide-based autotrophic denitrification (SAD) process is an organic-free biological nitrogen removal pathway and relies on inorganic carbon (IC) for cell synthesis. However, studies investigating the impact of IC on the SAD process are limited, with most focusing primarily on the reaction kinetics. This study systematically investigated the changes in the denitrification efficiency and microbial community during the gradual reduction of influent IC from sufficient to zero in an anaerobic membrane bioreactor (AnMBR). After 50 days of operation without IC, the nitrogen removal efficiency decreased but remained above 60%. The reduction in the IC concentration significantly increased the evenness and diversity of the biofilm community, strengthened microbial interactions, and enhanced biofilm functions. The core species of the biofilm succeeded from Thiobacillus to a codominance of Thiobacillus, Paracoccus, and Arenimonas. Overall, these findings demonstrate that biofilm communities in the SAD process counteract IC limitations by enhancing bacterial diversity and interactions to maintain the denitrification functionality, providing valuable insights into ecological mechanisms for stabilizing microbial communities in low-nutrient environments.