Effects of bioaugmentation and K⁺ on manganese removal and microbial community in biofilters

Under high ammonia-nitrogen influent conditions, the start-up of biological manganese removal filters is often prolonged, limiting their engineering application. Meanwhile, K⁺ frequently coexist with ammonia nitrogen, and their combined presence may further delay system start-up. In this study, three biofilter systems were established to investigate the effects of bioaugmentation under elevated K⁺ conditions on the removal of ammonia nitrogen and manganese, as well as the underlying microbial mechanisms. The results demonstrated that bioaugmentation markedly accelerated the development of manganese removal capacity, which was initially established in the lower part of the filter and subsequently expanded upward. In contrast, high K⁺ concentrations inhibit this process by disrupting microbial community assembly and impairing functional taxa colonization. They also reduce the complexity of the co-occurrence network. Microbial analysis revealed that manganese removal relied on the synergistic interactions of multiple low-abundance functional microorganisms. This study provides a theoretical foundation for optimizing the start-up process of biofilter systems under elevated K⁺ conditions. It also offers guidance for improving their start-up efficiency and stability in engineering practice.