Impact of biodiversity-regulating factors on inhibition of nitrite-oxidizing bacteria in mainstream partial nitritation/anammox: Microbial dynamic and balance

Abstract

The stability of mainstream partial nitritation/anammox (PN/A) systems is strongly influenced by microbial competition and cooperation. However, conventional operational strategies, such as dissolved oxygen and ammonium limitation, are effective in simplified systems but often fail to account for the complex microbial interactions that are critical for maintaining system stability under mainstream conditions. In this study, biodiversity-regulating strategies were investigated as operational approaches to stabilize mainstream PN/A systems by controlling microbial interactions. Biodiversity regulation was implemented through the combined modulation of electron donor and acceptor availability, as well as stepwise anammox bioaugmentation. A dualcontrol strategy based on ammonium (NH4+-N) and oxygen (O2) limitation was first applied to suppress nitriteoxidizing bacteria (NOB) while maintaining ammonia-oxidizing bacteria (AOB) activity. Subsequently, anammox bioaugmentation was introduced at 5%, 15%, and 30% ratios to further regulate the microbial community structure and evaluate its effect on nitrogen removal performance. Moderate bioaugmentation (15%) maintained balanced interactions among functional microbial groups and supported stable nitrogen removal. By contrast, excessive bioaugmentation (30%) disrupted microbial balance, resulting in reduced AOB activity and increased heterotrophic denitrification. Microbial community analysis revealed that bioaugmentation of Candidatus Brocadia increased microbial diversity, whereas Nitrospira sp. clone b2 became dominant under unstable conditions. These results indicate that the stability of mainstream PN/A systems depends primarily on the regulation of biodiversity-driven microbial interactions, rather than solely on operational parameters.