Denitrifying Phosphorus Removal System Research Articles

Metabolomic reveals the responses of sludge properties and microbial communities to high nitrite stress in denitrifying phosphorus removal systems

Nitrite, as an electron acceptor, plays a good role in denitrifying phosphorus removal (DPR); however, high nitrite concentration has adverse affects on sludge performance. We investigated the precise mechanisms of responses of sludge to high nitrite stress, including surface characteristics, intracellular and extracellular components, microbial and metabolic responses. When the nitrite stress reached 90 mg/L, the sludge settling performance was improved, but the activated sludge was aging. FTIR and XPS analysis revealed a significant increase in the hydrophobicity of the sludge, resulting in improve settling performance. However, the intracellular carbon sources synthesis was inhibited. In addition, the components in the tightly bound extracellular polymeric substances (TB-EPS) of sludge were significantly reduced and indicated the disturb of metabolism. Notably, Exiguobacterium emerged as a new genus when face high nitrite stress that could maintaining survival in hostile environments. Moreover, metabolomic analysis demonstrated strong biological response to nitrite stress further supported above results that include the inhibited of carbohydrate and amino acid metabolism. More importantly, some lipids (PS, PA, LysoPA, LysoPC and LysoPE) were significantly upregulated that related enhanced membrane lipid remodeling. The comprehensive analyses provide novel insights into the high nitrite stress responses mechanisms in activated sludge systems.

Insight into the mechanism of nutrients removal and response regulation of denitrifying phosphorus removal system under calcium ion stress

The influent quality is an important factor affecting the nutrients removal and operational stability of denitrifying phosphorus removal (DPR) system. This study investigated the effects of calcium ion (Ca2+) on the nutrients removal, nitrogen oxide (N2O) release, microbial community, and quorum sensing in DPR system. Results showed that high accumulation of Ca2+ had a significant impact on the carbon footprint of DPR system. Specifically, N2O release reached 2.11 mg/L under Ca2+ of 150 mg/L, which represented 214.93% increase compared to 0 mg/L of Ca2+. The DPR system demonstrated its adaptability to elevated Ca2+ concentrations by modifying key enzyme activities involved in nitrogen and phosphorus removal, altering the microbial community structure, and adjusting the type and content of signal molecules. These findings hold significant implications for understanding the stress mechanism of Ca2+ on DPR system, ultimately aiding in the maintenance and enhancement of stable operational performance in biological wastewater treatment process.

Response of a novel denitrifying phosphorus removal (AAO-BCO) system to sinusoidal flow perturbation of municipal sewage: Adaptability, tolerance and improvement

To date, studies on the effect of sewage disturbances on treatment facilities were based on fixed-length flow variations, which are incapable of imitating the actual dynamic flow characteristics of municipal sewage. Here, an innovative dynamic influent disturbance control system is established in this study and applied in a novel denitrifying phosphorus removal (anaerobic anoxic oxic-biological contact oxidation, AAO-BCO) system to simulate seasonal and diurnal sewage fluctuations in laboratory-scale experiments. The results showed that, under sinusoidal influent flow perturbation, the effluent pollutant content followed a relatively gentle sinusoidal trend and did not always result in desired level of pollutant removal. The ability of the system to cope with sinusoidal flow variations was susceptible to the amplitude of diurnal sewage fluctuation, while stronger tolerance capacity was observed to seasonal and momentary increase in wastewater flowrate. There was also a discrepancy in the system buffering capacity towards various pollutants removal (COD > TIN > PO43−), which may be attributed to wide fluctuations in PO43−/NO3− and different decrease in metabolic activity of denitrifying phosphorus removal (DPR) sludge caused by extreme hydraulic retention times. To improve the robustness and stability of the DPR system, a regulating strategy was proposed to alleviate the biomass reduction and uncoordinated PO43−/NO3−.

Simultaneous phosphorus recovery from wastewater and sludge by a novel denitrifying phosphorus removal system

A novel process was proposed for simultaneous denitrification and phosphorus (P) recovery. The increased nitrate concentration facilitated the activity of denitrifying P removal (DPR) in P enrichment, which stimulated P uptake and storage, making P more readily accessible for release into the recirculated stream. The total P content in the biofilm (TPbiofilm) rose to 54.6 ± 3.5 mg/g SS as the nitrate concentration increased from 15.0 to 25.0 mg/L, while the P concentration of the enriched stream reached 172.5 ± 3.5 mg/L. Moreover, the abundance of denitrifying polyphosphate accumulating organisms (DPAOs) increased from 5.6% to 28.0%, and the increased nitrate concentration facilitated the process of carbon, nitrogen, and P metabolism due to the rise in the genes involved in critical functions of metabolism. Acid/alkaline fermentation analysis indicated that the EPS release was the primary P-release pathway. Additionally, pure struvite crystals were obtained from the enriched stream and fermentation supernatant.

Effects of nano metal oxide particles on denitrifying phosphorus removal system: Potential stress mechanism and recovery strategy

The accumulation of nano metal oxide particles (NMOPs) in municipal sewage treatment systems harms the microbial community and its metabolism in activated sludge system, resulting in the degradation of its pollutants removal performance. In this work, the stress effect of NMOPs on the denitrifying phosphorus removal system was systematically investigated in terms of pollutants removal performance, key enzyme activities, microbial community diversity and abundances, and intracellular metabolites. Among the ZnO NPs, TiO2 NPs, CeO2 NPs, and CuO NPs, the ZnO NPs showed the most significant impacts with the chemical oxygen demand, total phosphorus, and nitrate nitrogen removal ratio decreased from above 90 % to 66.50 %, 49.13 %, and 57.11 %, respectively. The addition of surfactants and chelating agents could relieve the toxic effect of NMOPs on the denitrifying phosphorus removal system, and the chelating agents were more effective than surfactants in performance recovery. After adding ethylene diamine tetra acetic acid, the removal ratio of chemical oxygen demand, total phosphorus, and nitrate nitrogen under ZnO NPs stress was restored to 87.31 %, 88.79 %, and 90.35 %, respectively. The study provides valuable knowledge to better understand the impacts and stress mechanism of NMOPs on activated sludge systems and provides a solution to recover the nutrients removal performance of denitrifying phosphorus removal system under NMOPs stress.

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.

Metabolism transformation and free nitrous acid tolerance of denitrifying polyphosphate accumulating organisms under different intracellular polyphosphate levels

Polyphosphate (Poly-P) is a key compound in the known metabolism of denitrifying polyphosphate organisms (DPAOs). This study investigated the efficiency of endogenous denitrification, metabolic changes, and tolerance to free nitrous acid (FNA) of DPAOs at different levels of Poly-P. A high C/P ratio (100:1) made DPAOs transform from polyphosphate accumulating metabolism (PAM) to glycogen accumulating metabolism (GAM), and the nitrate (NO3--N) reduction rate of DPAOs increased significantly in GAM mode. Accumulibacter IA, IIC, and IID were the main dominant DPAOs, and their synergy and the increase of PHA may be responsible for the high NO3--N reduction efficiency. The DPAOs under GAM mode had better tolerance to FNA, and N2O reductase was destroyed due to the FNA influence, leading to a large accumulation of N2O. Flow cytometry results showed that FNA caused DPAOs to over-consume ATP and depolarize, thereby inhibiting their growth. And FNA disrupted the membrane integrity and esterase activity of DPAOs, which may result in early apoptosis. The metabolic transformation and FNA tolerance of DPAOs under GAM mode ensure the stable operation and performance recovery of denitrifying phosphorus removal systems, which demonstrates the DPAOs-dominated biological phosphorus removal has wide application prospects.

Upgrading integrated fixed-biofilm activated sludge (IFAS) system into separated two-sludge denitrifying phosphorus removal system: Nutrient removal and microbial structure

An integrated fixed-biofilm activated sludge (IFAS) system was upgraded into a separated two-sludge denitrifying phosphorus removal system to treat domestic sewage with a low carbon/nitrogen ratio (C/N = 3.6). The system was operated in IFAS mode for 135 days and then converted to the separated two-sludge mode to perform denitrifying phosphorus removal for 110 days. With denitrification and phosphorus removal conducted using “single carbon source”, the experimental results show that the total inorganic nitrogen (TIN) and phosphorus (P) removal efficiencies were improved by 13.4% and 36.5%, respectively. As the activated sludge unit and biofilm unit were separated, Dechloromonas (4.10%) and Candidatus Accumulibacter (1.56%) were enriched in activated sludge system, while the nitrifiers Nitrospira and Nitrosomonas occupied the biofilm with proportions of 19.6% and 5.68%, respectively. The separated two-sludge denitrifying phosphorus removal system was characterized by higher nutrient removal and functional bacteria enrichment.

Performance enhancement and population structure of denitrifying phosphorus removal system over redox mediator at low temperature

The development of denitrifying polyphosphate accumulating organisms (DPAOs) presents a strategy to carbon competition between denitrifying bacteria and phosphorus removing bacteria. However, low temperature inhibits the rate of enzyme-catalyzed and substrate diffusion during denitrifying phosphorus removal (DPR). Therefore, the present study assessed the addition of NQS (100 μmol/L) for enhancing the removal of TP and TN in DPR reactors operated at alternating anaerobic and anoxic phases and different influent phosphate concentrations. The results showed that the removal efficiency of TP and TN in NQS-DPR system at 10 °C were 99.9% and 42.0%, respectively, which were 2.1 and 2.0 times higher than that of DPR system. Adding NQS significantly alleviated the increase of pH under anoxic condition and decreased the ORP value of the reactor, which in turn enhanced the PHAs accumulation process. The determination of functional genes (nirK, narG and phoD) showed that Dechloromonas, Lentimicrobium, and Terrimonas were the dominant functional bacteria in NQS-DPR system at 10 °C with the relative abundance of 3.09%, 2.99% and 2.28%, respectively. This study can provide valuable information for the effects of the addition of the redox mediator on denitrifying phosphorus removal technology.

Understanding the mechanism of denitrifying phosphorus removal from the perspective of intracellular carbon source and extracellular polymeric substances characteristics

Denitrifying phosphorus removal (DPR) is a novel approach for denitrification and phosphorus (P) adsorption simultaneously under an anoxic condition. A well-running DPR system was used in this study to investigate the DPR mechanism based on the changes in intracellular carbon sources and extracellular polymeric substances (EPS) characteristics. In the anaerobic stage, the intracellular carbon source and EPS characteristics test results showed that Poly-β-hydroxyalkanoates (PHA) increased by 1.75 ± 0.58 mmol C/L, which was related to the utilization of proteins slime EPS (S-EPS). Moreover, tyrosine-like substances in S-EPS were mainly used for the PHA synthesis by parallel factor analysis (PARAFAC) and correlation analysis. In addition, concentrations of K+, Mg2+ and Ca2+ in EPS were changed in different stratified EPS. EPS was an extracellular phosphorus reservoir for DPR activated sludge. In the anoxic stage, K+ and Mg2+ in the matrix had a linear relationship with P, but Ca2+ accumulated in TB-EPS. Further, the inorganic phosphorus absorbed by the activated sludge reacts with Ca2+ as P–Ca precipitation. Above the results are helping to preliminarily understand the mechanism of DPR from the perspective of intracellular carbon sources and EPS characteristics.

Combining Different Aerobic/Anoxic Durations with Zoned Sludge Discharge to Optimize Short-cut Nitrification Denitrifying Phosphorus Removal Granules in Domestic Sewage

In this study, domestic sewage was used to inoculate mature short-cut nitrification denitrifying phosphorus removal particles, which were cultivated and matured under artificial water. The operation of the short-cut nitrification denitrifying phosphorus removal system was optimized using different aerobic/anoxic durations combined with zoned sludge discharge. The results showed that regulating the aerobic/anoxic duration, in combination with zoned sludge discharge, can realize the stable operation of the system. In the later stable period, the effluent COD concentration was below 50 mg·L-1, the effluent TN concentration was below 15 mg·L-1, the TN removal rate reached about 83% and remained stable, the effluent P concentration was below 0.5 mg·L-1, and the average P removal rate was 93.72%. At the same time, zoned sludge discharge (70% top sludge and 30% bottom sludge) can be used to screen out microorganisms, maintain good nitrosation and phosphorus removal performance, limit the particle size distribution, and ensure the growth advantages of AOB and DPAOs. Increases in the anoxic duration improved the growth rate of anoxic heterotrophic bacteria, causing them to secrete more EPS and ensuring granular sludge improvements and continued stability.

Effects of Different Nitrite Generation on the Short-cut Nitrification Denitrifying Phosphorus Removal Granules System

To explore the effects of nitrite generation on the system of short-cut nitrification denitrifying phosphorus removal granules, nitrite was produced continuously and intermittently, under continuous and intermittent aeration, in two groups of SBR reactors of the same size. The effects of nitrogen and phosphorus removal, physical characteristics of the sludge, and microbial community structure were investigated. Nitrite was consumed immediately after intermittent production, with better and more stable nitrogen and phosphorus removal performance. In particular, the average rate of TN removal was 92.07% after 72 days. The utilization efficiency of the carbon source (by P/COD) was concentrated at 0.21-0.22 mg ·mg-1, to ensure full utilization of the carbon source and to further promote denitrification and phosphorus removal. Particle sizes were uniform and showed concentrated distribution, with particles exhibiting regular shapes and clear boundaries. Microbial community analysis showed that the abundance and diversity of microbial communities were higher in the intermittent nitrite system and more enriched in DPAOs genera (Dechloromonas and Pseudomonas). The combination of DPAOs genera and Nitrosomonas resulted in a dynamic balance and stable operation of the short-cut nitrification and denitrifying phosphorus removal system.

Nutrients removal by interactions between functional microorganisms in a continuous-flow two-sludge system (AAO-BCO): Effect of influent COD/N ratio

Denitrifying phosphorus removal (DPR) technology is one of the most effective approach to simultaneously realize nitrogen (N) and phosphorus (P) removal from low COD/N ratio wastewater. Identifying the interaction of denitrifying phosphate-accumulating organisms (DPAOs), denitrifying glycogen organisms (DGAOs) and denitrifying ordinary heterotrophic organisms (DOHOs) is critical for optimizing denitrification and anoxic P uptake efficiency in DPR processes. In this study, a novel DPR system of anaerobic anoxic oxic - biological contact oxidation (AAO-BCO) was employed to dispose actual sewage with various influent COD/N ratios (3.5–6.7). High efficiency of TIN (76.5%) and PO43−-P (94.4%) removal was observed when COD/N ratio was between 4.4 and 5.9. At the COD/N ratio of 5.7 ± 0.2, prominent DPR performance was verified by the superior DPR efficiency (88.7%) and anoxic phosphorus uptake capacity (PUADPAOs/ΔTIN = 1.84 mg/mg), which was further proved by the preponderance of DPAOs in C, N and P removal pathways. GAOs have a competitive advantage over PAOs for COD utilization at low COD/N ratio of 3.7 ± 0.2, which further limited the N removal efficiency. High proportion of N removal via DOHOs (21.2%) at the COD/N ratio of 6.5 ± 0.2 restrained the DPR performance, which should be attributed to the outcompete of DOHOs for NO3−. The nutrient removal mechanisms were explicated by stoichiometric calculation methodology to quantify the contribution of diverse functional microorganisms, contributing to improving the robustness of AAO-BCO system when facing the fluctuation of influent carbon source concentration.

Nitrite accumulation and microbial behavior by seeding denitrifying phosphorus removal sludge for partial denitrification (PD): The effect of COD/NO3− ratio

Effect of influent COD/NO3− ratios (2.0–5.0) on partial denitrification (PD, NO3− to NO2−) was investigated by seeding denitrifying phosphorus removal (DPR) sludge at ambient temperature (16 ± 2℃). At COD/NO3− ratio of 2.5, the optimal NO2− effluent and nitrate-to-nitrite transformation ratio (NTR) reached up to 27.18 mg/L and 82.18%, respectively, and nitrate removal efficiency (NRE) (59.34 → 97.98%) showed positive relationship with increasing COD/NO3− ratios. The variations were further illustrated by denitrification kinetics, where faster COD degradation (1.55 g COD/(gVSS·d)), more NO3− consumption (0.55 gN/(gVSS·d)) and higher NO2− production (0.52 gN/(gVSS·d)) were observed although the NO2− peaks happened at anoxic 30 min. Microbial analysis showed lower community diversity and more concentrated composition with dominated genera Thauera (14.10%), Terrimonas (9.40%), Saprospiraceae (13.50%) and Flavobacterium (28.23%) at COD/NO3− ratio of 2.5. Based on the achievement of PD, the application feasibility of integrated PD-DPR-Anammox in a two-sludge DPR system for deep-level nutrient removal was discussed.

Rapid Start-up and Stability of Partial Denitrification Based on Different Waste Sludge Sources

To explore the feasibility of the rapid start-up of partial denitrification and the stable accumulation of NO2--N in different waste sludge sources, three identical SBR reactors (S1, S2, and S3) were inoculated respectively with sludge discharged from a laboratory municipal wastewater denitrifying phosphorus removal system, surplus sludge from a municipal wastewater treatment plant, and river sediment sludge. The characteristics of the partial denitrification start-up and NO2--N accumulation were compared, and the partial denitrification activity of the system or NO3--N→NO2--N transformation performance were investigated by analyzing the characteristics of the functional bacteria genera of the reactor from the perspective of microbiology. The results showed that all three SBR partial denitrification reactors could be launched successfully in a short time with sodium acetate as the sole carbon source, under a high alkalinity, and by using a suitable COD/NO3--N ratio. The average NO3--N→NO2--N transformation ratio of the system was ranked as:S1 > S2 > S3 (75.92% > 73.36% > 69.90%). It was found that S1 and S2 had different degrees of partial denitrification performance deterioration under a continuous low temperature, but that S3 could maintain a good NO2--N accumulation performance. High throughput sequencing showed that Proteobacteria and Bacteroidetes were dominant in the partial denitrification system, and that the abundance of Thauera was significantly different in the three PD reactors:S3 > S1 > S2 (25.09% > 4.71% > 3.60%), thus indicating that S3 had stable and efficient NO2--N accumulation performance and that a high abundance of Thauera might play a significant role in maintaining low temperature partial denitrification activity.

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.

Nutrient metabolism, mass balance, and microbial structure community in a novel denitrifying phosphorus removal system based on the utilizing rules of acetate and propionate

The effect of acetate (HAc) and propionate (HPr) on denitrifying phosphorus removal (DPR) was evaluated in a novel two-sludge A2/O - MBBR (anaerobic/anoxic/oxic - moving bed biofilm reactor) system. Results showed that it was the carbon source transformation and utilization especially the composition of poly-β-hydroxyalkanoates (PHA) (mainly poly-β-hydroxybutyrate (PHB) and poly-bhydroxyvalerate (PHV)) decided DPR performance, where the co-exist of HAc and HPr promoted the optimal nitrogen (85.77%) and phosphorus (91.37%) removals. It facilitated the balance of PHB and PHV and removing 1 mg NO3− (PO43−) consumed 3.04–4.25 (6.84–9.82) mgPHA, where approximately 40–45% carbon source was saved. Mass balance revealed the main metabolic pathways of carbon (MAn,C (consumed amount in anaerobic stage) and MA-O,C (consumed amount in anoxic and oxic stages): 66.38–76.19%), nitrogen (MDPR,N (consumed amount in DPR): 57.01–65.75%), and phosphorus (MWS,P (discharged amount in waste sludge): 81.05–85.82%). Furthermore, the relative abundance and microbial distribution were assessed to elucidate DPR mechanism (e.g. Accumulibacter, Acinetobacter, Dechloromonas, Competibacter, and Defluviicoccus) in the A2/O reactor and nitrification performance (e.g. Nitrosomonas, Nitrosomonadaceae and Nitrospira) in the MBBR. Carbon source was demonstrated as the key point to stimulate the biodiversity and bioactivity related to DPR potential, and the operational strategy of carbon source addition was proposed based on the utilizing rules of HAc and HPr.

Elucidating sludge characteristic, substrate transformation and microbial evolution in a two-sludge denitrifying phosphorus removal system under the impact of HRT

Granule formation has been recognized as a promising biotechnology in denitrifying phosphorus removal (DPR) systems by facilitating phosphorus accumulation organisms (PAOs) especially denitrifying PAOs (DPAOs), and hydraulic selection made this a more difficult task in continuous operation. This study aimed at exploring the microscopic mechanism and putting forward an effective strategy for DPR granulation under the impact of hydraulic retention time (HRT) (12 h, 10 h, 8 h) in a novel Anaerobic Anoxic Oxic - Moving Bed Biofilm Reactor (A2/O - MBBR) system. With the reduction of intracellular carbon storage (CODintra) efficiency (88.58%–78.53%), nitrogen (N) (85.45%–79.11%) and phosphorus (P) (96.55%–92.47%) removals both dropped, but it exhibited a growth of anoxic phosphorus uptake rate (PURA) (3.79–5.68 mg P/(gMLVSS·h)). The batch tests associating with substrate transformation of poly-β-hydroxyalkanoates (PHA), glycogen (Gly) agreed well with the corresponding stoichiometry of phosphorus release rate (PRR) (4.83–7.53 mg P/(gMLVSS·h)), PURA (3.55–5.43 mg P/(gMLVSS·h)), oxic phosphorus uptake rate (PURO) (6.08–6.21 mg P/(gMLVSS·h)), and DPAOs/PAOs ratios (57.17%–89.31%), indicating a shift of microbial community. DPR granules gradually stabilized with low sludge volume index (SVI5/SVI30 ratio = 1.1–1.2), dense and compact structure, higher P content (11.63%), more extracted extracellular polymeric substances (EPS) (111.40–160.31 mg/gMLVSS) as proteins/polysaccharides (PN/PS) ratios (1.70–3.47) increased, leading to better sludge settleability and cell hydrophobicity. Fluorescence in situ hybridization (FISH) results showed that PAOs (mainly Cluster I: 20.20%) were the dominant bacteria in the A2/O reactor although a small amount of Defluviicoccus (3.18–3.48%) was responsible for nitrite accumulation, while ammonium-oxidizing bacteria (AOB) (mainly Nitrosomonas: 10.75%) and nitrite-oxidizing bacteria (NOB) (mainly Nitrospira: 15.06%) were enriched in the MBBR.

Feasibility of applying intermittent aeration and baffles for achieving granular nitritation in a continuous short-cut denitrifying phosphorus removal system.

It was difficult to obtain a stable and efficient short-cut denitrification and phosphorus removal process for domestic sewage treatment, therefore, the possibility of using granulation technology of nitritation sludge and intermittent aeration was evaluated to resolve the difficulty. Results showed that the nitrogen and phosphorus removal efficiencies of the system were 72% and 93%, respectively, under the condition of mode 3 (a period of 10min with aeration 8min and stop 2min) with aeration energy consumption decreasing 20%. Microbial community revealed that Rhodocyclales was the dominant short-cut denitrifying phosphorus removing bacteria in the process, closely related to the performance of short-cut denitrifying phosphorus removal. Furthermore, Thauera and Denitratisoma belonging to the Rhodocyclales play a significant role of short-cut denitrifying phosphorus removal in the process. In addition, Aeromonas improved the performance of short-cut denitrifying phosphorus removal. Finally, nutrient removal efficiency was improved 8% in intermittent aeration mode 3 based on short-cut denitrifying phosphorus removal.

Microbial community at transcription level in the synergy of GAOs and Candidatus Accumulibacter for saving carbon source in wastewater treatment

The microbial community in endogenous denitrification and denitrifying phosphorus removal treatment at transcription level was unknown. This study first confirmed the expression of actually active bacteria in endogenous denitrification and denitrifying phosphorus removal system to treat low C/N municipal wastewater. No external carbon source was added to influent wastewater. The cDNA high throughput sequencing showed that Candidatus Accumulibacter was the most effective polyphosphate accumulating organisms (PAOs) that actually worked rather than Dechloromonas, which was different from the result at gene level. Reverse transcriptional PCR (RT-PCR) and analysis of Variance (ANOVA) suggested that the ratios of dead or dormant bacteria could monitor wastewater treatment process. Identification of active microbial community at transcription level demonstrated that the synergy of endogenous denitrification by glycogen accumulating organisms (GAOs) and denitrifying phosphorus removal by Candidatus Accumulibacter fully utilized the internal carbon source, and effectively solved the problem of carbon source deficiency in municipal wastewater treatment.