Enhanced Simultaneous Nitrification and Denitrification from Wastewater with Low C/N Ratio in a Bioaugmented Sequencing Batch Biofilm Reactor

Biological nitrogen removal from wastewater with limited organic carbon is challenging, and carbon supplementation increases treatment inputs. We assessed whether an aerobically pre-acclimated microbial consortium could improve nitrogen removal in sequencing batch biofilm reactors treating real domestic wastewater with a low carbon-to-nitrogen ratio. Two reactors with matched carriers, seed sludge, and operating conditions ran for 80 days at ambient temperature without external carbon addition; the bioaugmented reactor received consortium additions during the first 40 days. Influent chemical oxygen demand/total nitrogen averaged 2.14 ± 1.09. During stable operation, total nitrogen removal reached 83.3–88.6% in the bioaugmented reactor versus 69.1–75.9% in the control. The bioaugmented reactor also showed greater ammonium removal and lower effluent nitrate concentrations, whereas chemical oxygen demand removal was similar. Cycle-resolved nitrogen profiles and apparent simultaneous nitrification and denitrification efficiency were consistent with closer coupling of nitrogen transformations. Microbial community profiles, nitrogen-cycling gene abundances, and dissolved organic matter fluorescence indicated accompanying changes in microbial composition, functional potential, and organic-matter characteristics. These findings support consortium addition as a promising approach for improving nitrogen removal from real low-carbon wastewater without external carbon supplementation. Its performance in replicated and larger-scale systems warrants further evaluation.