Anammox-based Multi-pathway biological nitrogen removal for high ammonia nitrogen wastewater treatment: Rapid startup...

Nitrate produced as a by-product of anammox has emerged as a key factor limiting compliance with effluent standards in high-ammonia nitrogen wastewater treatment. Although acidogenic fermentation can stimulate anammox-associated denitrifiers to remove nitrate, its application is constrained by exogenous addition of fermentation substrates. Herein, a chemical oxygen demand (COD)-restricted starvation strategy induced endogenous fermentation of extracellular polymeric substances (EPS) to sustain denitrification, thereby enabling the construction of a 2000 L system integrating partial nitrification, anammox, denitrification, and in-situ fermentation (SNADF). The system demonstrated excellent performance in treating high-ammonia-nitrogen wastewater (828 mg N/L, C/N = 0.24), achieving 95.9% total nitrogen removal and 91.5% reduction in sludge production. The functional niche differentiation induced by the starvation strategy facilitated efficient nitrogen removal within SNADF system. As the primary driver of nitrogen removal, the relative abundance of anammox bacteria affiliated with the genus Candidatus Kuenenia in granular sludge increased from 37.3% to 43.5%, underpinning the SNADF system's high efficiency. Under starvation, the hydrolytic-acidogenic bacterium OLB8 was significantly enriched in flocculent sludge (increase 6.5-fold), accelerating EPS conversion to bioavailable carbon sources. These carbon sources were subsequently utilized by the biofilm denitrifier SJA-28 (increase 7.1-fold), enabling carbon-self-sufficient nitrate removal. Community assembly analysis further revealed that the observed functional differentiation was governed by stochastic processes. Specifically, dispersal limitation (62.5% contribution) enhanced spatial turnover, promoting OLB8 enrichment in flocs sludge. Meanwhile, ecological drift (100% contribution) removed low-abundance heterotrophs from granular sludge, consolidating Candidatus Kuenenia dominance. In summary, this study offers a feasible pathway for efficient Anammox engineering applications.