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The utilization of slowly-biodegradable organic matter (SBOM) to provide nitrite efficiently for anaerobic ammonia oxidation (anammox) process is an essential topic. High nitrite concentration without inhibition of exogenous organic matter is optimal condition for anammox process. In this study, hydrolytic fermentation (HF) of SBOM was applied to drive an endogenous partial denitrification (EPD) process (nitrate to nitrite) during an anaerobic-anoxic operation in a starch-fed system. With a limited production of exogenous organic matter (22.3 ± 4.9 mg COD/L), 79.0% of SBOM was transformed into poly-hydroxyalkanoates (PHA) through a pathway of simultaneous HF-absorption and endogenous polymer synthesis, corresponding to a hydrolytic fermentation ratio of 86.0%. A high nitrate to nitrite transformation ratio of 85.4% was achieved under an influent carbon to nitrogen ratio of 4.8. Denitrifying glycogen-accumulating organisms (DGAOs) was enriched from 0.6% to 10.9%, with an increase from 0.7 to 1.0 of nitrate reductase genes to nitrite reductase genes ratio. Subsequently, nitrate reduction rate was 5.6-fold higher than the nitrate reduction rate. A prominent migration of exogenous complete denitrification to EPD was accomplished. Furthermore, the starch-fed system exhibited performance with significant adaptability and stability in the presence of different SBOMs (dissolved protein and primary sludge). Therefore, the HF-EPD system achieved efficient nitrite production through EPD with the addition of various SBOMs, providing a potential alternative to anammox systems for the treatment of SBOM-rich wastewater., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022. Published by Elsevier Ltd.)

Integrating endogenous denitrification (ED) into partial nitrification-anammox (PNA) systems by adequately utilizing organics in municipal wastewater is a promising approach to improve nitrogen removal efficiency (NRE). In this study, a novel strategy to inhibit phosphorus-accumulating organisms (PAOs) by inducing phosphorus release and exclusion was adopted intermittently, optimizing organics allocation between PAOs and glycogen-accumulating organisms (GAOs). Enhanced ED-synergized anammox was established to treat real municipal wastewater, achieving an NRE of 97.5±2.2% and effluent total inorganic nitrogen (TIN) of less than 2.0 mg/L. With low poly-phosphorus (poly-P) levels (poly-P/VSS below 0.01 (w/w)), glycogen accumulating metabolism (GAM) acquired organics exceeded that of phosphorus accumulating metabolism (PAM) and dominated endogenous metabolism. Ca. Competibacter (GAO) dominated the community following phosphorus-rich supernatant exclusion, with abundance increasing from 3.4% to 5.7%, accompanied by enhanced ED capacity (0.2 to 1.4 mg N/g VSS /h). The enriched subgroups (GB4, GB5) of Ca. Competibcater established a consistent nitrate cycle with anammox bacteria (AnAOB) through endogenous partial denitrification (EPD) at a ∆NO 2 - -N/∆NH 4 + -N of 0.91±0.11, guaranteeing the maintenance of AnAOB abundance and performance. These results provide new insights into the flexibility of PNA for the energy-efficient treatment of low-strength ammonium wastewater., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier Ltd.)