Bioaugmentation with Bacillus amyloliquefaciens enhances DON removal in activated sludge systems

This study assessed the feasibility of bioaugmentation with Bacillus amyloliquefaciens for degrading dissolved organic nitrogen (DON). The aim was to improve DON conversion and support more efficient nitrogen removal under stringent discharge requirements. Both qualitative and quantitative analyses were conducted to characterize DON transformation in the bioaugmented system and to explore the possible role of B. amyloliquefaciens in this process. Results indicated that inoculation of domesticated B. amyloliquefaciens improved reactor performance. The optimal treatment effect was achieved at a 10% injection rate. Under these conditions, removal rates for DON, ammonium nitrogen (NH₄⁺-N), and total nitrogen (TN) reached 91.68%, 95.79%, and 61.54%, respectively. Additionally, the fluorescence intensity of tryptophan-like protein component decreased by 0.014 relative units (R.U). after inoculation. Proportions of low-molecular-weight DON and hydrophilic DON were reduced by 16% and 2%, respectively. Microbial community analysis suggested that B. amyloliquefaciens contributed to DON removal not only through its ammonification-related activity, but also by influencing the indigenous microbial community and strengthening functions related to nitrogen metabolism. These findings indicate that bioaugmentation with B. amyloliquefaciens is a promising strategy for enhancing DON transformation and nitrogen removal in wastewater treatment systems.