Effect of hydraulic retention time on the nitrogen removal performance of pure biofilm rotating biological contactor system inoculated with heterotrophic nitrification-aerobic denitrification bacteria and its corresponding mechanism

The traditional activated sludge biofilm system struggles with poor removal performance and long hydraulic retention time (HRT) in treating high ammonia nitrogen (NH4+-N) wastewater. To solve these problems, this study introduced a pure heterotrophic nitrification-aerobic denitrification (HN-AD) biofilm system which HN-AD bacteria were inoculated in the rotating biological contactor (PH-RBC), with free microorganisms discharged after biofilm formation. Under short HRT (12 h), PH-RBC exhibited 29.23 % and 31.03 % higher NH4+-N and total nitrogen (TN) removal than pure activated sludge biofilm RBC (PS-RBC) (the influent NH4+-N was 505 +/- 45 mg/ L). Flavobacterium and Azoarcus were crucial for nitrogen removal in the PH-RBC. Metabolic analysis revealed that genes CS and IDH3 are crucial for carbon metabolism, with dissimilatory nitrate reduction dominates nitrogen metabolism. Bugbase prediction indicated that decreasing HRT increased the presence of Potentially Pathogenic. This study provides a theoretical basis for using pure biofilm system in high NH4+-N wastewater treatment.