Efficient amino acid capture from sludge fermentation by Tetrasphaera enhances simultaneous nitrification, endogenous...

The simultaneous nitrification endogenous denitrification and phosphorus removal (SNDPR) process shows great potential for carbon, nitrogen, and phosphorus removal. However, its application is challenged by limited carbon availability and the strong reliance of glycogen-accumulating organisms (GAOs) and traditional polyphosphate-accumulating organisms (PAOs) on volatile fatty acids. This study first established a fermentative PAO Tetrasphaera-dominated SNDPR coupled with in-situ sludge fermentation process, achieving stable and efficient nitrogen (95.7 ± 0.6%) and phosphorus (92.6 ± 1.6%) removal using complex organics (e.g., amino acids and proteins) from wastewater and sludge as carbon sources. Extending the anaerobic duration (from 5 h to 17 h) regulated the phosphorus removal and fermentation capacity of Tetrasphaera, promoting its dominance at the genomic (10.89%), transcriptional (6.24%), and translational (24.0%) levels. For phosphorus removal, the denitrifying phosphorus removal (DPR) rate using nitrite increased from 0.98 ± 0.05 mgN/gVSS·h at 5 h to 2.70 ± 0.07 mgN/gVSS·h at 17 h, shifting the system from aerobic phosphorus uptake dominance to a cooperative pattern with DPR, effectively lowering carbon demand. For fermentation, metagenomic analysis revealed that efficient amino acid capture by Tetrasphaera facilitated the retention of substantial sludge hydrolysates for intracellular amino acid storage, improving nutrient removal and mitigating NH₄⁺-N and PO₄^3--P release. Additionally, anammox bacteria (Candidatus Brocadia, 2.67%) self-enriched and synergistically contributed to nitrogen removal. Overall, this study provides new insights into the metabolic shift between fermentation and phosphorus removal in Tetrasphaera, demonstrating the feasibility of stable and efficient carbon, nitrogen and phosphorus removal by the SNDPR process in VFA-limited wastewater.