Impacts of carbon source type on metabolic pathways and microbial synergy in the simultaneous anammox and endogenous denitrification process.

Abstract

Simultaneous anammox and endogenous denitrification (SAED) process enables efficient nitrogen removal from low carbon-to-nitrogen wastewater, yet how carbon source type influences microbial synergy and system robustness remains unclear. This study evaluated the sludge characteristics, performance, and ecological traits of three SAED systems fed with acetate (HAc), propionate (HPr), and glucose (Glc) over 476 days. Results showed that the Glc-fed system achieved the highest and most stable nitrogen removal performance (95.0 % ± 2.4 %), significantly outperforming the HAc-fed (93.3 % ± 2.7 %) and HPr-fed (87.6 % ± 2.5 %) systems. Glucose promoted the formation of large (∼870 μm), dense granules with a high organic fraction (0.904), effectively mitigating the sludge washout and inorganic mineral precipitation observed in HAc-fed and HPr-fed systems. Microbial ecological network analysis reveals that different types of carbon sources reconfigured heterotrophic communities by mediating distinct microbial interactions. The Glc-fed system exhibited the highest proportion of positive correlations (90.9 %), particularly between Denitratisoma (13.5 %) and Candidatus Brocadia (22.2 %), bolstering system robustness. Furthermore, metagenomic analysis further confirms that nitrate reductase genes (nar/nap at 674.8 RPKM in total) were significantly more enriched than nitrite reductase genes (nir at 210.6 RPKM in total) in the Glc-fed system, facilitating an efficient nitrate-to-nitrite shunt for anammox bacteria while bypassing the competitive pathways (e.g., full denitrification in HAc-fed; DNRA in HPr-fed). Therefore, leveraging glucose-driven metabolic flux optimizes both sludge characteristics and microbial interactions in SAED process, providing a robust treatment for low-carbon wastewater.