Search

Higher nitrite accumulation, which is challenging to achieve reliably, is always sought to obtain better nitrogen removal performance in traditional partial nitritation-anammox (PN/A) process. This study developed a modified PN/A process by introducing nitrite-oxidizing bacteria and endogenous metabolism. Advanced nitrogen removal performance of 95.5 % was achieved at a low C/N ratio of 2.7 under nitrite accumulation ratio (NAR) fluctuations. Higher nitrate accumulation at lower NAR (70 ∼ 40 %) resulted in superior anammox contribution (60 ∼ 75 %) and nitrogen removal performance (93 ∼ 98 %). This was attributed to the higher nitrogen removal efficiency of the post-anoxic endogenous partial denitrification coupling anammox process, although the PN/A process occurring first possessed a faster anammox rate of 2.0 mg NH 4 + -N /(g VSS⋅h). The introduction of nitrate allowed more nitrite flow to anammox, promoting a high enrichment of anammox bacteria (Ca. Brocadia, 0.3 % to 2.8 %). This study provides new insights into the practical application of the PN/A process., 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 © 2024 Elsevier Ltd. All rights reserved.)

A novel two-stage partial nitrification-anammox (PN-A) process was developed, achieving nitrogen removal from low carbon/nitrogen ratio municipal sewage under two typical operational modes and seasonal ambient temperatures. When complete nitritation-anammox was performed at temperatures greater than 19.4 °C, the effluent concentration of total inorganic nitrogen (TIN) was 4.1 mg/L, corresponding to a nitrogen removal efficiency (NRE) of 94.3 %. In contrast, when partial nitritation-anammox was performed at temperatures below 19.4 °C, the effluent TIN was 12.3 mg/L, corresponding to a NRE of 83.6 %. The relative abundance of Nitrosomonas and Nitrosomonadaceae increased from 0.02 % to 0.28 %, while Ca. Brocadia decreased from 1.85 % to 1.30 %, with the contribution of anammox to nitrogen removal being highest under low temperatures (19.4℃ to 13.8℃), at 59.0 %. This novel two-stage PN-A process provides a new approach for the stable operation of wastewater treatment plants (WWTPs) under low ambient temperatures., 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 Elsevier Ltd. All rights reserved.)

[Display omitted] • Advanced nitrogen removal was achieved despite the gradual decrease in C/N. • NRE increased from 43.8% to 91.5% while NAR decreased from 94.1% to 60.7% • Nitrogen removal aerobically by the PNA pathway was enhanced as C/N decreased. • Nitrite supplied by EPD (by GAOs) for anammox compensated the nitrite deficiency. • Enhanced aerobic and anoxic nitrogen removal by enriched AnAOB ensured superior NRE. The chemical oxygen demand (COD) to total inorganic nitrogen ratios (C/N) fluctuations under mainstream conditions has a crucial influence on the performance of partial nitrification-anammox (PNA) systems. In this study, a PNA sequencing batch reactor was applied for real municipal wastewater treatment with a continuous decrease in C/N (4.3 to 1.4). The results showed that with the decrease of C/N, the nitrite accumulation ratio (NAR) decreased from 94.1% to 60.7%, and nitrogen removal by endogenous denitrification was attenuated. However, the nitrogen removal efficiency (NRE) significantly increased from 43.8% to 91.5%, which was attributed to the enhanced performance of PNA under aerobic conditions and additional nitrite provided by endogenous partial denitrification (EPD) for anammox under anoxic conditions. Glycogen accumulating organisms (GAOs) that dominated the EPD process increased remarkably from 0.42% to 2.78% exhibiting a competitive advantage over phosphorus accumulating organisms (PAOs) at low organic loads. Co-existence of highly enriched anammox bacteria (0.91%) and GAOs (2.78%) ensured the enhanced nitrogen removal during the aerobic and anoxic phases. This study provides in-depth perspectives on the PNA combing with EPD under varied C/N and broadening the flexibility of PNA applications. [ABSTRACT FROM AUTHOR]

• Excellent NRE of 97.5% was achieved with TIN below 2.0mg/L by selective enhanced GAOs. • Intermittent phosphorus exclusion with poly-P/VSS below 0.01(w/w) enhanced GAOs. • GAOs gained organics outcompeting PAOs at low poly-P and strengthened ED. • PNA was unaffected by the enhanced ED and coupled to remove nitrogen in the anoxic stage. • EPDA was promoted by the enrichment of GAOs that reduced NO 3 − to NO 2 − exclusively. 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. Competibcate r 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. [Display omitted] [ABSTRACT FROM AUTHOR]