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[Display omitted] • A two-stage process was developed to treat real low C/N municipal wastewater. • Biological P removal and autotrophic N removal occurred in two separate reactors. • Aerobic granulation in both reactors promoted the process efficiency and stability. • Efficient P (91%) and N removal (81%) were achieved under low C/N ratio of 5.4. • The process can recover 33% of influent organic as biogas and 68% of P as struvite. In this study, a novel two-stage aerobic granular sludge (AGS) system was developed to treat municipal wastewater. High removal efficiencies of phosphorus (91%) and nitrogen (81%) were obtained under a low influent carbon/nitrogen ratio of 5.4. The high nutrient removal was attributed to microbial segregation in the two sequencing batch reactors (SBRs). In the first reactor, the high abundance of polyphosphate-accumulating organisms (Candidatus Accumulibacter 15.3%) promoted a high rate of enhanced biological phosphorus removal (EBPR). In the second reactor, residual ammonium was autotrophically removed via partial nitritation/anammox (PN/A). Moreover, granular sludge was maintained in both SBRs with a sludge volume index of 40–80 mL/g, which reduced the settling time and improved the operational stability. Furthermore, batch tests and mass balance analysis revealed that most influent phosphorus (68%) and some organics (33%) were recovered from the waste sludge as struvite and methane, respectively. Overall, this study illustrates that the novel two-stage AGS system integrating EBPR and PN/A is promising for enhancing nutrient removal, as well as resource and bioenergy recovery from municipal wastewater. [ABSTRACT FROM AUTHOR]

[Display omitted] • Proposed a side-stream sludge treatment method for rapid proliferation of GAOs. • Highly enriched GAOs (3.09–18.25%) facilitated ED while DOHOs decreased by 62.78%. • The abundance of PAOs was reduced but didn't deteriorate the phosphorus removal efficiency. • The TIN and PO 4 3−-P in influent and effluent were 71.26, 8.01 mg/L and 6.40, 0.30 mg/L, respectively at C/N of 3.25. Endogenous denitrification (ED) is an effective approach to achieve advanced nitrogen removal for low COD/N (C/N) municipal wastewater, in which internal carbon sources are used for denitrification. However, phosphorus-accumulating organisms (PAOs) and denitrifying ordinary heterotrophic organisms (DOHOs) outcompeting glycogen-accumulating organisms (GAOs) for carbon sources decreases total inorganic nitrogen (TIN) removal efficiency. This study proposed a novel side-stream sludge treatment strategy, i.e., through phosphorus famine, to selectively strengthen GAOs. Two sequencing batch reactors (SBR) were used, with one served as an anaerobic/aerobic/anoxic SBR (AOA-SBR) and the other as a side SBR. Side-stream phosphorus famine treatment was conducted three times during 140 days' experiment, of which 20–30% of the sludge collected from the AOA-SBR was imposed to phosphorus famine condition in the side SBR for 4 days (24 cycles). Results showed that the average TIN and phosphorus removal efficiencies were 88.76% and 95.31%, and the average TIN and phosphorus in the effluent were 8.01 and 0.30 mg/L, respectively, treating low C/N (~3.25) municipal wastewater in the AOA-SBR. The relative abundance of PAOs decreased from 3.23% to 2.15% and that of DOHOs reduced by 62.78%. In contrast, the abundance of GAOs increased from 3.09% to18.25%, which should be the key reason for the improvement of the ED efficiency. Moreover, the enrichment of GAOs promoted ED simultaneously using glycogen and poly-β-hydroxyalkanoates (PHA) as carbon sources. The strategy of side-stream treatment proved the potential of rapid proliferation of GAOs while achieving improved nitrogen removal. [ABSTRACT FROM AUTHOR]

[Display omitted] • Molecular-level insight of DOM and DON were investigated in PN/A and A2O. • Transformation of DOM and DON were coupled in PN/A, while they were desynchronized in A2O. • PN/A's metabolism for bio-available and aromatic compounds was higher than A2O. • Autotrophs and heterotrophs produced DON with distinct molecular characteristics. There is limited knowledge regarding the differences and relationships in molecular composition between dissolved organic matters (DOM) and dissolved organic nitrogen (DON) in autotrophic and heterotrophic nitrogen removal processes. In this study, the composition of DOM and DON during two full-scale wastewater treatment plants (WWTPs), an autotrophic nitrogen removal with partial nitrification-anammox process (PN/A) and a heterotrophic nitrogen removal with anaerobic/anoxic/oxic process (A2O), were systematically investigated by using ultraviolet–visible spectroscopy, Excitation-Emission Matrix (EEM) and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The results indicated that both PN/A and A2O resulted a decrease in molecular diversity and bio-availability of DOM. However, there were distinct variations in DON between the two processes. In PN/A, transformation of DOM and DON was found to be coupled, while there was a lack of correlation observed between DOM and DON in A2O. Pearson correlation analysis revealed that transformation of DOM and DON in WWTPs was associated with microbial roles. During biotreatment, PN/A exhibited a higher metabolic capacity for degrading high bio-available and high aromatic compounds compared to A2O. The autotrophic nitrogen removal unit in PN/A resulted in an increase in molecular weight (MW) of DON, as well as a decrease in bio-availability and unsaturation degree of DON. Therefore, autotrophic nitrogen removal unit may have a positive influence on control of eutrophication and disinfection by-products (DBPs) formation. This study improved the understanding of molecular composition and relationship between DOM and DON, as well as microbial roles on DON transformation within autotrophic and heterotrophic nitrogen removal processes. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel DPR-PDA process was initiated with fully ordinary suspended sludge. • The deep removal of N and P without aeration was achieved under COD/TN of 1.8. • Candidatus_ Brocadia was enriched from 0.01% to 1.86% by prolonging anoxic stage. • The effluent TN and TP were 0.9 and 0.2 mg/L with influent of 106.0 and 1.4 mg/L. Partial Denitrification coupled with Anammox (PDA) process was used as for nitrogen removal from wastewater. However, the phosphate removal still relies on chemical methods in wastewater treatment plants. Denitrifying Phosphorus Removal (DPR) process allows phosphorus uptake under anoxic conditions using nitrate (NO 3 −) as electron acceptor. In this study, the PDA and DPR processes were successfully coupled into a novel integration (DPR-PDA) for co-treatment of simulated domestic wastewater and NO 3 − wastewater to achieve simultaneous nitrogen and phosphorus removal. The effluent TN and TP were 0.9 and 0.2 mg/L during phase Ⅵ (day450-513) under influent COD/TN of 1.8, respectively. Anammox bacteria was self-enriched in this fully suspended sludge system, with abundances increasing from undetected at day19 to 2.0 × 1010 copies/g dry sludge at day468. Anammox bacteria was effectively retained and was responsible for the main nitrogen removal, accompanied by increasing activity up to 3.1 mg N/g VSS/h. Batch tests demonstrated that denitrifying polyphosphate accumulating organisms exhibited DPR capacity immediately after the introduction of NO 3 −, but not after the introduction of nitrite (NO 2 −) only. Candidatus_Competibacter with endogenous denitrification ability was enriched from 13.30 % to 35.42 %, which coexisted with anammox bacteria stably. The novel DPR-PDA process is a promising technology for simultaneous removal of nitrogen and phosphorus with low carbon demand and without aeration. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A novel process combined SPNA with modified DPR in two SBRs was established for treating ammonia and domestic wastewaters. • Under low DO condition, SPNA contributed to ∼90% NH 4 +-N removal from ammonia sewage (70–200 mg·L−1). • DPR achieved ∼70% PO 4 3−-P removal from domestic wastewater using the generated NO 3 –-N by SPNA. • Post SNEDPR further reduced ∼30% PO 4 3−-P and ∼70% NH 4 +-N contained in domestic wastewater. • The average final effluent TN and PO 4 3−-P concentrations were 5.0 and 0.2 mg·L−1, respectively. Abstract A novel process combined simultaneous partial nitrification-anammox (SPNA) with modified denitrifying phosphorus removal (DPR) in two sequencing batch reactors (terms as SPNA-SBR and mDPR-SBR) was proposed for treating ammonia (NH 4 +-N) and domestic wastewaters. Firstly, NH 4 +-N contained wastewater was fed into SPNA-SBR for autotrophic nitrogen removal. Meanwhile, domestic wastewater was introduced to mDPR-SBR for anaerobic phosphorus release and intracellular carbon storage. Then, nitrate (NO 3 –-N) produced in SPNA-SBR was discharged to mDPR-SBR, where NO 3 –-N was reduced to dinitrogen gas (N2) via anoxic denitrifying phosphorus removal. Finally, the residual NH 4 +-N and PO 4 3−-P in mDPR-SBR were removed via aerobic simultaneous nitrification, endogenous denitrification and phosphorus removal (SNEDPR). The long-term operation (235-day) suggested that a desirable nutrient removal performance was achieved in the SPNA-mDPR process, and the final effluent NH 4 +-N, total nitrogen and PO 4 3−-P concentrations were 1.5, 5.0 and 0.2 mg·L−1, respectively. In the SPNA-SBR, SPNA contributed to ∼90% of NH 4 +-N removal at low aeration intensity (dissolved oxygen (DO): 0.1 mg·L−1); in the mDPR-SBR, ∼70% of PO 4 3−-P and ∼100% of NO 3 –-N were simultaneously removed via anoxic DPR, and post-aerobic SNEDPR further reduced ∼30% of PO 4 3−-P and ∼70% of NH 4 +-N. Stoichiometry-based microbial activity analysis demonstrated that, in the mDPR-SBR, high activity of denitrifying phosphorus accumulating organisms (DPAOs) over denitrifying glycogen accumulating organisms (DGAOs) in anoxic NO 3 –-N removal (71.1% > 28.9%) facilitated DPR, and high percentage of SNEDPR via nitrite (89.6%) over nitrate saved 52% intracellular carbon demand to realize the deep-level nutrient removal without external carbon addition. [ABSTRACT FROM AUTHOR]

[Display omitted] • Anammox coupled with partial denitrification enhanced to nitrogen removal above 55%. • Ultra-high abundance of Ca. Brocadia (5.5, 6.5%, 5.8%) in connected anoxic biofilms. • Ca. Brocadia sapporoensis is acetate-resistant, explaining its high enrichment in biofilms. • Anammox activity increased with decreasing denitrifying activity along anoxic zones. For municipal wastewater treatment via partial-denitrification/anammox (PD/A) in the anoxic zone, the primary challenge is effective enrichment of anaerobic ammonium oxidation (anammox) bacteria with a stable autotrophic nitrogen removal performance. This long-term study investigated a pure-biofilm anoxic/oxic reactor using real municipal wastewater with an ammonia concentration of 49.1 ± 3.6 mg N/L, achieving a total inorganic nitrogen concentration of 11.2 ± 3.5 mg N/L in the effluent, resulting in a removal efficiency of 77.4 ± 7.2%. Driven by partial denitrification, the anammox contribution to total nitrogen removal represented an ultra-high level over 55%, and was considerable in the first anoxic zone. Candidatus Brocadia, the only anammox genus detected by 16S rRNA gene sequencing, reached robust abundances of 5.46, 6.49 and 5.79% in the three sequentially connected anoxic zones. Metagenomic sequencing further identified that the main species was Ca. Brocadia sapporoensis, which is inhibited by nitrite but not by acetate, supporting its high-level enrichment under acetate conditions in the anoxic zone. Batch tests indicate that heterotrophic denitrification activity decreased while anammox activity increased along the anoxic zones, and that excessive heterotrophic denitrifying activity was not conducive to increasing the anammox contribution. This study achieved robust anammox bacterial abundance using a pure-biofilm system, shedding fresh light on the application of mainstream anammox in municipal wastewater treatment. [ABSTRACT FROM AUTHOR]

[Display omitted] • EPD can synergize with PNA or even provide NO 2 − alone during PN deterioration. • The EPD capability of GAOs can further benefit the stabilization of PNA process. • Anammox contributed 80% to the excellent nitrogen removal of 92% with all NO 2 − supplied by EPD. • Outstanding anammox stability was obtained via a flexible NO 2 − supply by EPD. • Coexistence of enriched GAOs (6.0%, EPD) and anammox bacteria (1.5%) favored anammox stability. The application of partial nitritation-anammox (PNA) process suffers severe obstacles due to the instability of partial nitritation (PN) process. This study sought to evaluate the feasibility of endogenous partial denitratation (EPD) as a remediation or alternative to supply nitrite for the unstable PNA process. A novel strategy of optimal organics utilization through pre-anaerobic carbon storage and post-anoxic endogenous denitrification coupled with anammox was developed in a single-stage bioreactor treating actual municipal wastewater with low C/N (∼3.2). Specifically, the undesired NO 2 −/NH 4 + ratio (2.4 to 0.04) and nitrate accumulation were obtained by increasing the aeration rate (0.6 to 1.8 L/min) to simulate the PN instability. Delightedly, advanced nitrogen removal efficiency (92.1%) was maintained despite a dramatic decrease in nitrite accumulation ratio from 97.6% to 2.6%. This was attributed to the significant increase in anammox contribution to total nitrogen removal from 30.2% to 80.5%. The steady nitrite flux supplied from EPD coupled with PN (EPD contribution increased from 0 to 97.0%) was assumed to be the main reason for the continually increasing abundance and bioactivity of anammox bacteria. Both the anammox bacteria (1.5%, Ca. Brocadia) and glycogen accumulating organisms (6.0%, responsible for EPD) were enriched and coexisted stably in the single reactor. Our study confirms that coupling EPD with anammox has great potential as a remediation for the unstable mainstream PNA process. [ABSTRACT FROM AUTHOR]

[Display omitted] • Novel EPDA/PSR process without aeration was established for wastewater treatment. • Effluent TIN and phosphate reached 0.1 mg/L and 0 without external carbon dosage. • Fermentation by Candidatus Phosphoribacter led to sludge reduction in EPDA/PSR. • Amino acids as intracellular carbon storage were associated with P metabolism. • Transcriptional community composition reflected the actual operation state. This study presented a novel process for simultaneous biological nutrient removal and waste activated sludge reduction in one-stage municipal wastewater treating system without aeration on the basis of endogenous partial denitrification, anammox and Candidatus Phosphoribacter dominated biological phosphate removal with sludge reduction (EPDA/PSR). The effluent total inorganic nitrogen and phosphate concentrations were 0.1 mg/L and lower than detection limit (0.1 mg/L), respectively, without dosing external carbon sources. Compared with partial denitrification-anammox process, the daily sludge production in EPDA/PSR process reduced by 50.8 %. The percentage of intact cells measured by flow cytometry reduced from 92.4 % to 77.3 % with the increase of aromatic protein, DNA content of supernatant, soluble microbial byproduct-like substance and decline of particle size. The sludge stabilization structure was destructed, and intracellular organics were released, which resulted in the reduction of sludge production. Microbial community structure at transcriptional level indicated that really working Candidatus Phosphoribacter (phosphorus accumulating organisms with fermentation capacity), Candidatus Competibacter (endogenous partial denitrification bacteria) and Candidatus Brocadia (anammox bacteria) reached 68.4 %, 9.84 % and 8.02 %, respectively, and Candidatus Kuenenia (anammox bacteria) did not play a role in EPDA/PSR system. The novel one-stage EPDA/PSR process realized high efficient biological nutrient removal, achieved waste activated sludge reduction and saved 100 % of aeration energy consumption cost and external carbon source dosage cost, which effectively developed internal carbon source and provided a new idea for wastewater treatment. [ABSTRACT FROM AUTHOR]

[Display omitted] • Stable partial nitrification was achieved in continuous–flow EBPR system. • NAR reached 99.4%, and the removal efficiency of PO 4 3−–P reached 100%. • Effluent concentration of TIN was lower than 2 mg/L without adding external carbon. • Analysis of transcriptional level revealed the mechanisms of partial nitrification. • Fermentation by Tetrasphaera caused cell lysis and reduction of sludge discharge. Simultaneous partial nitrification, biological phosphorous removal and sludge fermentation in continuous–flow system faced many challenges in wastewater treatment plants (WWTPs). In this study, a novel process was developed to achieve partial nitrification, enhanced biological phosphorus removal and in–situ fermentation (PNPRF) in continuous–flow system dominated by Tetrasphaera treating low carbon/nitrogen ratio (COD/N) real domestic wastewater. After 80 days of operation, no external carbon was added into the influent. Nitrite accumulation ratio (NAR) reached 99.4% and removal efficiency of PO 4 3−–P was 100%. The effluent concentration of total inorganic nitrogen (TIN) was lower than 2 mg/L. Compared with traditional biological nitrogen and phosphorus removal processes, the daily sludge discharge in continuous–flow PNPRF decreased by 61.9%. DNA concentration of the sludge supernatant after anaerobic zone was 2.26-fold of that before anaerobic zone, and percentages of intact cells decreased by 6.9% and necrotic cells increased by 8.3%, indicating that cell lysis caused the reduction of sludge discharge. The negative effect of prolonged anaerobic phase on transcriptional response of nxrB gene was more significant than that of amoA and hao gene, which resulted in stable partial nitrification. The activities of ammonium–oxidizing bacteria (AOB) were higher than that of nitrite–oxidizing bacteria (NOB), and reverse transcriptional PCR (RT–PCR) showed that RNA expression of AOB was higher than that of NOB. Achieving partial nitrification, enhanced biological phosphorus removal and in–situ fermentation in continuous-flow system dominated by Tetrasphaera solved the problems of carbon source deficiency and large amount of sludge discharge in treating real domestic wastewater process. [ABSTRACT FROM AUTHOR]