Microbial community dynamics and mechanistic insights into rapid ammonia nitrogen removal via Acinetobacter harbinensis HITLi7 enhanced activated carbon.

The biological enhanced activated carbon (BEAC) system, utilizing the bioaugmentation with Acinetobacter harbinensis HITLi7, demonstrated remarkable performance in removing ammonia nitrogen (NH-N) from aquatic environments. However, the mechanism through which HITLi7 bioaugmentation influenced microbial communities remains incompletely understood. Therefore, a comparative analysis of startup speed and NH-N removal efficiency was conducted between biological activated carbon (BAC) and BEAC bench-scale systems, with an in-depth examination of microbial dynamics and mechanisms within BEAC. Within 16 days post bioaugmentation, the biomass of BEAC (BEAC_1 and BEAC_2) was 4.75/9.07 times that of BAC, with NH-N removal efficiencies 29.36%/28.68% higher. 16-135 days, there was no significant difference in biomass among the groups. Specifically, from day 17-90, the NH-N removal efficiency of BEAC was still 25.80%/25.37% higher than that of BAC. After 90 days, the effluent NH-N levels from BEAC were more stable. In BEAC, the abundance of HITLi7 decreased while the abundance of Nitrosomonas increased, exhibiting a characteristic of "species compensation". Subsequently, Candidatus_Nitrotoga and Nitrospira became enriched. After 16 days, the total abundance of Nitrosomonas, Candidatus_Nitrotoga, and Nitrospira in BEAC was 3.21%-5.66% and 3.68%-10.07% higher than that in BAC. The microbial community in BEAC was more influenced by diffusion limitation, especially for Nitrosomonas and Nitrospira. Within the microbial co-occurrence network, while Nitrosomonas and Nitrospira lacked a direct correlation with HITLi7, the presence of intermediates might potentially hinder the diffusion of Nitrosomonas and Nitrospira. This study deepened our understanding of how HITLi7 bioaugmentation affects microbial community structure, dynamics, and co-occurrence patterns.