MBBR start-up with HN-AD bacteria inoculation: Comparative analysis in simulated and real wastewater for performance, microbial characteristics, and nitrogen removal mechanism

Mobile bed biofilm reactor (MBBR) can effectively remove various pollutants from wastewater. This study was the first to apply a novel pilot-scale of 3 m3 MBBR startup with Heterotrophic Nitrification-Aerobic Denitrification (HN-AD) bacteria inoculation. This study assessed the influence of different wastewater qualities on the operational performance, microbial community dynamics, and changes in the expression of nitrogen removal-related functional genes during the biofilm formation. It was observed that the biofilm formation for real wastewater occurred 30 days faster than for simulated wastewater, achieved within only 45 days. In real wastewater, the average removal efficiencies of NH4+-N and TN surpassed those in simulated wastewater by 16.24 % and 14.90 %, respectively. Furthermore, the relative abundances of Thauera and Zoogloea on the carriers were 9.26 % and 14.09 % higher, respectively. High-throughput sequencing revealed the synergistic action of conventional denitrifying bacteria and HN-AD bacteria, jointly promoting the expression of genes NAP, NAR, and NIR, crucial for the nitrogen removal process. The introduction of HN-AD bacteria into the MBBR (HNAD-MBBR) successfully facilitated pilot-scale biofilm formation in real wastewater. [Display omitted] •HNAD-MBBR system was initially used for treating a 3 m3 pilot-scale real wastewater.•Real wastewater achieved 14.90 % higher TN removal and a 30-day faster startup.•Thauera and Zoogloea drive rapid aerobic denitrification in real wastewater.•The expression of genes narG, napA, norC and nosZ was enhanced by real wastewater.•Denitrifying bacteria and HN-AD bacteria collaborate for nitrogen removal.