Denitrifying Glycogen-accumulating Organisms Research Articles

Nitrate and nitrite utilization during denitrifying phosphorus removal: Electron acceptor preference and feasible process combinations

Denitrifying phosphorus removal (DPR), which is dominated by denitrifying polyphosphate-accumulating organisms (DPAOs), is a promising process for nitrogen and phosphorus removal. Denitrifying glycogen-accumulating organisms (DGAOs) and DPAOs typically coexist in the DPR sludge, complicating the study of DPAOs’ denitrification capacity. In this study, two reactors were fed with nitrate and nitrite during the anoxic phase to cultivate nitrate-DPR and nitrite-DPR sludge. Both reactors yielded high and low DGAO abundance sludges, enabling the evaluation of the denitrification capacity of DPAOs. For the nitrate-DPR sludge, the nitrite reduction rate was 1.63 times higher than the nitrate reduction rate when DPAOs were the primary denitrifiers. For the nitrite-DPR sludge, the reduction rate of nitrite was more than three times that of nitrate, irrespective of DGAO abundance. These findings indicated that DPAOs preferred nitrite to nitrate and were well suited to reduce nitrite rather than reduce nitrate to supply nitrite.

Intermittent hydroxylamine dosing to strengthen stability of partial nitrification and nitrogen removal efficiency through continuous-flow anaerobic–aerobic-anoxic reactor treating municipal wastewater

Intermittent hydroxylamine (NH2OH) dosing strategy was applied to enhance the stability of partial nitrification and total nitrogen (N) removal efficiency (TNRE) in a continuous-flow process. The results showed 2 mg/L of NH2OH dosing (once every 6 h) could maintain stably partial nitrification with nitrite accumulation rate (NAR) of 91.6 % and TNRE of 92.6 %. The typical cycle suggested NH2OH dosing could promote simultaneous nitrification–denitrification (SND) and endogenous denitrification (END) while inhibit exogenous denitrification (EXD). Nitrification characteristics indicated the NH2OH dosing enhanced stability of partial nitrification by suppressing specific nitrite oxidation rate (SNOR), Nitrospira and nitrite oxidoreductase enzyme (Nxr). The microbial community suggested the aerobic denitrfiers, denitrifying glycogen accumulating organisms (DGAOs) and traditional denitrfiers were the potential contributor for advanced N removal. Moreover, NH2OH dosage was positively associated with NAR, SND and END. Overall, this study offers a feasible strategy to maintain sustainably partial nitrification that has great application potential.

Synergistic Integration of Anammox and Endogenous Denitrification Processes for the Simultaneous Carbon, Nitrogen, and Phosphorus Removal.

The feasibility of a synergistic endogenous partial denitrification-phosphorus removal coupled anammox (SEPD-PR/A) system was investigated in a modified anaerobic baffled reactor (mABR) for synchronous carbon, nitrogen, and phosphorus removal. The mABR comprising four identical compartments (i.e., C1-C4) was inoculated with precultured denitrifying glycogen-accumulating organisms (DGAOs), denitrifying polyphosphate-accumulating organisms, and anammox bacteria. After 136 days of operation, the chemical oxygen demand (COD), total nitrogen, and phosphorus removal efficiencies reached 88.6 ± 1.0, 97.2 ± 1.5, and 89.1 ± 4.2%, respectively. Network-based analysis revealed that the biofilmed community demonstrated stable nutrient removal performance under oligotrophic conditions in C4. The metagenome-assembled genomes (MAGs) such as MAG106, MAG127, MAG52, and MAG37 annotated as denitrifying phosphorus-accumulating organisms (DPAOs) and MAG146 as a DGAO were dominated in C1 and C2 and contributed to 89.2% of COD consumption. MAG54 and MAG16 annotated as Candidatus_Brocadia (total relative abundance of 16.5% in C3 and 4.3% in C4) were responsible for 74.4% of the total nitrogen removal through the anammox-mediated pathway. Functional gene analysis based on metagenomic sequencing confirmed that different compartments of the mABR were capable of performing distinct functions with specific advantageous microbial groups, facilitating targeted nutrient removal. Additionally, under oligotrophic conditions, the activity of the anammox bacteria-related genes of hzs was higher compared to that of hdh. Thus, an innovative method for the treatment of low-strength municipal and nitrate-containing wastewaters without aeration was presented, mediated by an anammox process with less land area and excellent quality effluent.

Influence of operation sequences on phosphorus recovery by polyphosphate-accumulating organisms biofilm: Performance, kinetics and metabolic response

Two biofilm sequencing batch reactors (BSBRs) were conducted under alternating aerobic/anaerobic (Ae/An) sequence and alternating anaerobic/aerobic (An/Ae) sequence to investigate the effects of operation sequences on phosphorus removal and recovery performance. The Ae/An BSBR had advantages in phosphate enrichment, phosphorus concentration of enrichment solution can reach 99.08 mg/L. While An/Ae BSBR exhibited a higher kinetic rate for phosphate uptake and release up to 0.48 mmol/gVSS. In An/Ae BSBR, the remarkable increase of phosphate concentration in aerobic stage put a great strain on the phosphate uptake of biofilms that led to an increase of phosphorus accumulation in the biofilm (Pbiofilm). However, the poly-P proportion in TPbiofilm decreased which triggered the metabolisim of polyphosphate accumulating organisms (PAOs) shifting from polyphosphate accumulating metabolism (PAM) to glycogen accumulating metabolism (GAM) and suppressed the phosphorus enrichment performance of the An/Ae BSBR. The phosphate uptake rate (PUR) of biofilms was in alignment with the bulk phosphate concentration. PAOs were dominated by Rhodoplanes and Saprospiraceae in the Ae/An BSBR, whereas Thiothrix was predominant in the An/Ae BSBR. Notably, the Candidatus Competibacter, considered as a denitrifying glycogen accumulating organisms (DGAOs), showed a dominant proportion in the microbial community of both BSBRs. The higher expression of actP in the An/Ae system indicated a greater capacity for the uptake of acetate, while the Ae/An system was is more adept for degrading acetate represented by the higher relative abundance of ackA, pta and acsA genes The high phosphorus loading in the An/Ae system suppressed the ppk expression but enhanced the ppx expression.

Evaluation of various carbon sources on ammonium assimilation and denitrifying phosphorus removal in a modified anaerobic-anoxic-oxic process from low-strength wastewater

A pilot-scale continuous-flow modified anaerobic-anoxic-oxic (MAAO) process examined the impact of external carbon sources (acetate, glucose, acetate/propionate) on ammonium assimilation, denitrifying phosphorus removal (DPR), and microbial community. Acetate exhibited superior efficacy in promoting the combined process of ammonia assimilation and DPR, enhancing both to 50.0 % and 60.0 %, respectively. Proteobacteria and Bacteroidota facilitated ammonium assimilation, while denitrifying phosphorus-accumulating organisms (DPAOs) played a key role in nitrogen (N) and phosphorus (P) removal. Denitrifying glycogen-accumulating organisms (DGAOs) aided N removal in the anoxic zone, ensuring stable N and P removal and recovery. Acetate/propionate significantly enhanced DPR (77.7 %) and endogenous denitrification (37.9 %). Glucose favored heterotrophic denitrification (29.6 %) but had minimal impact on ammonium assimilation. These findings provide valuable insights for wastewater treatment plants (WWTPs) seeking efficient N and P removal and recovery from low-strength wastewater.

Performance and mechanism of glycerol-driven denitrifying phosphorus removal from low organic matter sewage

The performance and mechanism of the glycerol-driven denitrifying phosphorus removal (DPR) process were investigated in low organic matter wastewater treatment using the modified anaerobic-anoxic–oxic (MAAO) system. The results revealed that denitrifying bacteria preferentially utilized glycerol, reducing nitrate interference on anaerobic phosphate release. Fermentation bacteria converted excess glycerol into available carbon sources, which were utilized by denitrifying phosphorus-accumulating organisms (DPAOs). Optimize glycerol dosage (calculated in chemical oxygen demand) could be estimated based on 6 times the effluent NO3−-N of the anoxic zone. As glycerol dosage increased, the relative abundance of fermentation bacteria surged from 8.2% to 17.7%, subsequently boosting the DPR rate from 34.6% to 77.2%. Notably, denitrifying glycogen-accumulating organisms (DGAOs) decreased from 0.5% to 0.2% but remained instrumental in nitrogen removal. The collaborative actions of fermentation bacteria, DPAOs, and DGAOs were vital in upholding the stability of nutrient removal in the glycerol-driven DPR process.

Advanced low-strength wastewater treatment, side-stream phosphorus recovery, and in situ sludge reduction with aerobic granular sludge

Modern paradigm has upgraded wastewater treatment plants (WWTPs) to water resources recovery facilities (WRRFs), where aerobic granular sludge (AGS) is a sewage treatment technology with promising phosphorus recovery (PR) potential. Herein, the AGS-based simultaneous nitrification, denitrification, and phosphorus removal coupling side-stream PR process (AGS-SNDPRr) was developed with municipal wastewater. Results revealed that AGS always maintained good structural stability, and pollutant removal was unaffected and effective after 40 days of anaerobic phosphorus-rich liquid extraction (fixed rate of 30%). The AGS-SNDPRr achieved a stable phosphorus recovery efficiency of 63.40%, and the side-stream PR further exaggerated in situ sludge reduction by 7.7–10%. Apart from responses of extracellular polymeric substances (EPS), the Matthew effect of typical denitrifying glycogen accumulating organisms (DGAOs) Candidatus_Competibacter up to 67.40% mainly contributed to enhanced performance of this new process. This study demonstrated a new approach for simultaneous advanced wastewater treatment, phosphorus recovery, and excess sludge minimization.

Achieving advanced nitrogen removal from low-carbon municipal wastewater using partial-nitrification/anammox and endogenous partial-denitrification/anammox

To achieve advanced nitrogen removal from low-carbon wastewater, a partial-nitrification/anammox and endogenous partial-denitrification/ anammox (PN/A-EPD/A) process was developed in a sequential batch biofilm reactor (SBBR). Advanced nitrogen was achieved with the effluent total nitrogen (TN) of 3.29 mg/L when the influent COD/TN and the TN were 2.86 and 59.59 mg/L, respectively. This was attributed to a stable PN/A-EPD/A, which was achieved through the integration of four strategies, including treating the inoculated sludge with free nitrous acid, inoculating anammox biofilm, discharging excess activated sludge and residual ammonium at the end of oxic stage. The 16S rRNA high-throughput sequencing results demonstrated that anammox bacteria coexisted with ammonia oxidizing bacteria, nitrite oxidizing bacteria, denitrifying glycogen accumulating organisms (DGAOs) and denitrifying phosphorus accumulating organisms (DPAOs) in biofilms. The abundance of anammox bacteria in the inner layer of the biofilm is higher, while that of DGAOs and DPAOs is higher in the outer layer.

Highly efficient transformation of slowly-biodegradable organic matter into endogenous polymers during hydrolytic fermentation for achieving effective nitrite production by endogenous partial denitrification

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.

Advanced nitrogen and phosphorus removal by the symbiosis of PAOs, DPAOs and DGAOs in a pilot-scale A2O/A+MBR process with a low C/N ratio of influent

Cooperating in harmony to avoid competition with dominant functional microbial symbiosis is an efficient way in advanced nitrogen and phosphorus removal in wastewater treatment processes. In this study, a niche-based coordinating strategy was implemented to cooperate in harmony with phosphorus-accumulating organisms (PAOs), denitrifying phosphorus-accumulating organisms (DPAOs) and denitrifying glycogen-accumulating organisms (DGAOs) to advance nitrogen and phosphorus removal based on an anaerobic-anoxic-oxic-anoxic-membrane bioreactor (A2O/A+MBR) under low C/N in municipal wastewater influent. The niche-based strategy was conducted based on the ORP change during the process as an indicator combined with the adjustment of recirculation and anoxic zone shifting. The results indicated that the strategy of the post-anoxic unit could enable significant enhancement of biological nitrogen and phosphorus removal (BNPR) by 9.9% and 16.3%, respectively, with low effluent concentrations of 7.0 ± 2.2 mg N/L and 0.36±0.32 mg P/L. The satisfactory performance was dominated along with the shift in the microbial community: the relative abundance of Tetrasphaera (PAO genus) increased from 0.14±0.08% to 0.32±0.12%, while the relative abundance of Decchloromonas (DGAO genus) and Candidatus Competibacter (DGAO genus) also increased. The advanced combination of anaerobic phosphorus release, anoxic denitrification, denitrifying phosphorus removal and endogenous denitrification was qualified by the modeling simulation of the biochemical kinetics mechanism of activated sludge in the A2O+MBR and A2O/A+MBR processes, which means that cooperation in the harmony of PAOs, DPAOs and DGAOs could be efficiently realized by a promising control strategy to enhance BNPR in an A2O+MBR with a post-anoxic unit. This study provides an efficient and simple novel control strategy to overcome the limitation of traditional nitrogen and phosphorus removal under an insufficient carbon source.

Balancing denitrifying phosphorus-accumulating organisms and denitrifying glycogen-accumulating organisms for advanced nitrogen and phosphorus removal from municipal wastewater

Given the carbon limitation of municipal wastewater, the balance of biological nitrogen and phosphorus removal remains a challenging task. In this study, an anaerobic-anoxic–oxic combining with biological contact oxidation (A2/O-BCO) system treating real municipal wastewater was operated for 205 days, and COD-to-PO43--P ratio was confirmed as the key parameter for balancing denitrifying phosphorus-accumulating organisms (DPAOs) and denitrifying glycogen-accumulating organisms (DGAOs) to enhance N and P removal. When DPAOs dominated in nutrients removal, the increase in COD/P from 17.1 to 38.1 caused the deterioration in nitrogen removal performance decreasing to 71.8 %. As COD/P ratio decreased from 81.3 to 46.8, Ca.Competibacter proliferated from 3.11 % to 6.00 %, contributing to 58.9 % of nitrogen removal. The nitrogen and phosphorus removal efficiency reached up to 79.3 % and 95.2 %. Overall, establishing DGAOs-DPAOs balance by strengthening the effect of DGAOs could enhance the nutrients removal performance and accordingly improve the stability and efficiency of the system.

Mathematical modeling of the dynamic effect of denitrifying glycogen-accumulating organisms on nitrous oxide production during denitrifying phosphorus removal

The large amount of intermediate nitrous oxide (N2O) production from denitrifying phosphorus removal (DPR) increases the carbon footprint of wastewater treatment. However, there is a lack of detailed understanding of the interrelationships between denitrifying polyphosphate-accumulating organisms (DPAOs) and denitrifying glycogen-accumulating organisms (DGAOs) on N2O production during DPR. In this work, a mathematical model was developed for the first time to describe dynamic N2O production in the DPR system coexisting DPAOs and DGAOs. The model took into account a four-step subsequent denitrification of nitrate, nitrite, nitric oxide, and N2O. The validity of model was fully tested by comparing simulation studies with experimental data from three independent reports on DPR, which satisfactorily described the dynamics of N2O production, nitrogen oxide reduction, phosphate release and uptake, and intracellular polymers turnover. The validated model could clarify the source and pathways of N2O production. Subsequently, the combined effects of key operational conditions on the overall N2O production, DPAOs and DGAOs competition, and nutrients removal efficiency were investigated by model simulation. Simulation results showed higher polyhydroxyalkanoate storage rate of DGAOs than that of DPAOs during anaerobic stage and the preference of DGAOs for nitrate electron acceptor during anoxic stage. DGAOs dominated the growth competition over DPAOs at low COD (<150 mg/L) and high nitrate (>35 mg/l) conditions, leading to the anoxic storage of glycogen by DGAOs as the main pathway of N2O production. In addition, both N2O production and generation pathways in the system possessed greater variability compared to single DGAOs or DPAOs system, further indicating the necessity of this model.

Synergistic simultaneous endogenous partial denitrification/anammox (EPDA) and denitrifying dephosphatation for advanced nitrogen and phosphorus removal in a complete biofilm system

To achieve simultaneous biological nitrogen and phosphorus removal from municipal wastewater, the endogenous partial denitrification/anammox (EPDA) was combined with denitrifying dephosphatation in a complete biofilm reactor. Advanced nitrogen and phosphorus removal were achieved with effluent total nitrogen (TN) and PO43−-P concentrations of 7.77 ± 0.33 mg/L and 0.35 ± 0.10 mg/L, respectively. Anammox took a major role in the system, accounting for 76 ± 7% of nitrogen removal. 16S rRNA high-throughput sequencing results showed that the anammox bacteria co-existed with the denitrifying glycogen accumulating organisms (DGAOs) and the denitrifying phosphorus accumulating organisms (DPAOs). Anammox bacteria were mainly distributed in the inner layer, while DGAOs and DPAOs existed in the outer layer of EPDA biofilms. Furthermore, based on the EPDA biofilm system, a promising advanced nitrogen and phosphorus removal process was suggested to achieve lower requirements for energy and reagent consumption.

Enhanced simultaneous partial nitrification and denitrification performance of aerobic granular sludge via tapered aeration in sequencing batch reactor for treating low strength and low COD/TN ratio municipal wastewater

The aerobic granular sludge simultaneous partial nitrification, denitrification and phosphorus removal (AGS-SPNDPR) process was carried out via tapered aeration in sequencing batch reactor (SBR) for treating low strength and low COD/TN ratio municipal wastewater. The results showed that aerobic granular sludge was successfully cultivated with good sedimentation performance when treating the municipal wastewater. Meanwhile, the median granule size increased to 270 (R1) and 257 (R2) μm on day 80. The excellent removal performance of COD (92%) and NH4+-N (95%) were achieved under different aeration modes, while the higher TN removal efficiency (76%) was achieved by tapered aeration. The accumulation of NO2−-N in R2 indicated that the tapered aeration was beneficial to achieve simultaneously partial nitrification and denitrification. Meanwhile, the high-efficiency phosphorus (95%) removal was realized via additional carbon source, and SPNDPR process was formed under tapered aeration. The bacterial community analysis indicated denitrifying glycogen-accumulating organisms (DGAOs) Candidatus_Competibacter and ammonia-oxidizing bacteria (AOB) Nitrosomonas were more effectively enriched via tapered aeration, while phosphorus-accumulating organisms (PAOs) Candidatus_Accumulibacter were effectively enriched under additional organic carbon. AOB, denitrifying bacteria and PAOs were simultaneously enriched by tapered aeration and additional carbon source, which was beneficial to nutrients removal. This study might be conducive to the application of AGS-SPNDPR system for treating low strength and low COD/TN ratio municipal wastewater under tapered aeration.

Simultaneous partial nitrification and denitrifying phosphorus removal (PNDPR) in a sequencing batch reactor process operated at low DO and high SRT for carbon and energy reduction

This study reports on a novel partial nitrification-denitrifying phosphorus sequencing batch reactor (SBR) system enriched with non-conventional denitrifying phosphorus accumulating organisms (DPAOs), treating carbon limited synthetic wastewater over 175 days. The non-conventional operating conditions, such as low DO (0.25 mg/L–0.35 mg/L) and relatively long solids retention time (SRT) of 15 d, favored the enrichment of a wide variety of denitrifying phosphorus accumulating organisms (DPAOs), such as Rhodocyclus, Dechloromonas, and Cytophaga. In contrast to the Accumulibacter, these microorganisms can sustain a very low DO environment and simultaneously perform denitrification and enhanced biological phosphorus removal (EBPR) using oxygen, nitrite, and nitrate as electron acceptors. The low DO also favored the washout of nitrite oxidizing bacteria (NOB), leading to simultaneous partial nitrification-denitrifying phosphorus removal (PNDPR). Partial nitrification at a high nitrite accumulation ratio (NAR ~ 80%) was also unfavourable for the growth of denitrifying glycogen accumulating organisms (DGAOs) in the PNDPR system. Simultaneous nitritation-denitritation (SND), nitrogen, and phosphorus removal efficiencies were maintained above 90%. Online cyclic tests and batch studies showed that nitrite shunt was achieved, and denitrification was predominantly controlled by DPAOs rather than ordinary heterotrophs (OHO). Mass balances showed that the COD/NOX−-N ratio for denitrification was 3.8. Compared to the conventional enhanced biological phosphorus removal (EBPR) process, the low DO-PNDPR process achieves reductions in carbon and aeration energy demands by approximately 47% relative to conventional biological nutrient removal (BNR) plants, and 49%, relative to conventional nitrification/denitrification systems, respectively.

Achieving and control of partial denitrification in anoxic-oxic process of real municipal wastewater treatment plant

Partial denitrification is an alternative process to provide stable nitrite for anammox. In this study, based on full-scale and lab-scale experiments, achieving and control of partial denitrification and the microbial mechanism were studied for 17 months in municipal wastewater treatment plant (MWWTP). Using glucose (GLC) as sole carbon source, partial denitrification was successfully achieved with nitrite accumulation percentage (NAP) higher than 90%; whereas, using sodium acetate (NaAc) as sole carbon source, nitrite accumulation was effectively controlled with economic and efficient carbon usage. Candidatus Competibacter and Thaurea were the dominant communities for partial denitrification. Denitrifying glycogen accumulating organisms (DGAOs), Thauera, denitrifying phosphorus accumulating organisms (DPAOs), GAOs, PAOs and denitrifiers coexisted in MWWTP, resulting in COD specific removal rate (CODSRR) of 883.10 ~ 1188.92mgN/gMLVSS/h during partial denitrification. Through adjustment of Anoxic-Oxic (A/O) operation to anoxic operation, the growth of GAOs and PAOs could be limited.

Advanced nitrogen and phosphorus removal by combining endogenous denitrification and denitrifying dephosphatation in constructed wetlands

To achieve high-efficiency nutrient removal in constructed wetlands (CWs), a novel simultaneous nitrogen and phosphorus removal (SNPR) process was developed by combining nitrification, endogenous denitrification, and denitrifying phosphorus removal. In SNPR process, denitrifying glycogen-accumulating organisms (DGAOs) and denitrifying polyphosphate-accumulating organisms (DPAOs) utilized NOx--N(NO3--N or NO2--N) as electron acceptor and poly-beta-hydroxy-alkanoates (PHAs) as carbon sources for endogenous denitrification and denitrifying phosphorus removal processes. Results from 217 days of operation showed that a high-level of nitrogen removal efficiency of 83.73% was achieved with influent COD/N of 4. The success was attributed to the fact that most of influent carbon sources could be transformed into PHAs before nitrification via enriching DGAOs and DPAOs in CW, which simultaneously improved nitrification and denitrification due to reducing oxygen and carbon sources consumption by aerobic heterotrophs. Phosphorus was mainly removed via denitrifying phosphorus removal, and PO43--P removal efficiency reached up to 87.84% with even common gravel used as substrate. Stoichiometry analysis revealed that DGAOs were the main organisms providing nitrite to DPAOs, suggesting that the effective PO43--P removal under high DGAO abundance condition might be attributed to the coordination of DGAOs and DPAOs in SNRP processes.

Feasibility of achieving advanced nitrogen removal via endogenous denitratation/anammox

For achieving advanced nitrogen removal, a simultaneous endogenous denitratation/anammox (EDA) process was developed that could be undertaken in a sequencing batch reactor. The results indicated that, when the influent COD/TN ratio was 3.16, the advanced nitrogen removal was achieved with the effluent TN of 1.87 mg/L. Nitrogen removal by anammox accounted for 76% of TN removed in the EDA process. Microbial community analysis illuminated that anammox bacteria and denitrifying glycogen accumulating organisms (DGAOs) of 0.91% and 5.05% were detected, respectively. DGAOs could provide nitrite for anammox by using the intracellular carbon source to achieve advanced nitrogen removal. Additionally, based on the EDA process, a promising technique for achieving advanced nitrogen removal was proposed to reduce the consumptions of both the oxygen and the carbon sources.

NADH accumulation during DPAO denitrification in a simultaneous nitrification, denitrification and phosphorus removal system

Denitrifying polyphosphate-accumulating organisms (DPAOs) and denitrifying glycogen-accumulating organisms (DGAOs) are jointly complete the denitrification in a simultaneous nitrification, denitrification and phosphorus removal (SNDPR) system.

Roles of nitrate recycling ratio in the A2/O - MBBR denitrifying phosphorus removal system for high-efficient wastewater treatment: Performance comparison, nutrient mechanism and potential evaluation

The long-term effect of nitrate recycling ratios (R = 100%–500%) on the denitrifying phosphorus removal (DPR) characteristics was studied in a novel two-sludge system, which coupled Anaerobic Anoxic Oxic (A2/O) with Moving Bed Biofilm Reactor (MBBR) for simultaneous nitrogen (N) and phosphorus (P) removals. During the 220 days’ operation, effluent COD (30.87–45.15 mg/L) can meet the discharge standard completely, but N and P removals were significantly affected by the R-value, including CODintra removal efficiency (CODintra-Re: 56.09–85.98%), TN removal (TN-Re: 52.06–80.50%), anaerobic PO43− release (PO43--An: 10.66–29.02 mg/L) and oxic PO43− absorption (PO43--O: 2.22–6.26 mg/L). Meanwhile, N and P displayed close correlation with the ΔPO43−/ΔNO3- ratio of 4.20–4.41 at R = 300%–400%, resulting in the high-efficient anoxic poly-β-hydroxyalkanoates (PHA) utilization (ΔPHAA: 64.88 mgCOD/gVSS). Based on the stoichiometry methodology, at R of 300%–400%, the percentages of phosphorus accumulation organisms (PAOs) and glycogen accumulating organisms (GAOs) contributed to ΔPHAAn (ΔGlyAn) were 71.7%, 28.3% (61.3%, 38.7%) in the anaerobic stage, respectively, while N denitrification rate (NDRA: 3.91–3.93 mg N/(gVSS·h)) and P uptake rate (PURA: 3.76–3.90 mg P/(gVSS·h)) reached the peak, suggesting superior DPR performance with higher contribution of denitrifying PAOs (DPAOs) (70%) than denitrifying GAOs (DGAOs) (30%) in the anoxic stage. Microbial community analysis showed that Accumulibacter (27.66–30.01%) was more enriched than Competibacter (13.41–14.34%) and was responsible for the improved C, N, P removals and DPR characteristics. For optimizing operation, the combined effect of nitrate recycling ratio with other process parameters especially economic evaluation should be considered.