Advanced total nitrogen removal in low C/N wastewater through simultaneous nitrification-heterotrophic denitrification coupled with sulfur-driven autotrophic denitrification: Performance and microbial succession

Traditional heterotrophic denitrification encounters challenges in the treatment of wastewater with a low carbon to nitrogen ratio (C/N). This study successfully achieved complete nitrogen removal with energy efficiency through the anaerobic-anoxic-anoxic sulfur autotrophic (A 3 ) process in the treatment of low C/N wastewater. Notably, this process enabled simultaneous nitrification-heterotrophic denitrification (SND) coupled with sulfur-driven autotrophic denitrification (SAD) with a nitrogen removal rate of 0.15 kg N/m 3 /d (100 % of NH 4 + -N and 92 % of total nitrogen (TN) removal). More than 85 % of TN removal and 50 % of SND contribution were obtained under low-temperature conditions (about 10–14 °C). After cultivation in the A 3 system, the dominant bacterial genus changed from norank_f__Saprospiraceae (11.22 %–5.21 %) to Ferruginibacter (0.89 %–19.31 %). Additionally, Nitrospira (1.34 %) and Thiobacillus (2.14 %) exhibited a synergistic effect in the anoxic tank, collectively promoting the simultaneous nitrification and denitrification process. This study proposes a novel and energy-efficient approach for the treatment of low C/N wastewater.