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Although the limitation or deficiency of nutrients, such as nitrogen (N) and phosphorus (P), has been one of the frequently reported factors causing filamentous or non-filamentous bulking of activated sludge, the mechanisms are still unclear. In this work, the long-term effects of N and P limitation or deficiency on sludge settleability and bioflocculation characteristics were investigated in six sequencing batch reactors (SBRs) fed with wastewater with different nutrient availability. The sludge volume index (SVI), microbial community structures, intracellular poly-β-hydroxyalkanoates (PHAs) and extracellular polymeric substances (EPS) were characterised over time. Bulking was not observed in SBRs with N limitation or deficiency, in which SVI remained below 150 mL/g. In contrast, bulking was encountered in those reactors with P deficiency. The occurrence of non-filamentous bulking was associated with a higher carbohydrates fraction and a lower proteins fraction in EPS. In the case of filamentous bulking, SVI correlated negatively with the amount of PHAs. Our experimental data support the hypothesis that the occurrence and/or the type of bulking in activated sludge could be affected by the combination of kinetic selection, microbial storage, as well as the EPS composition. [ABSTRACT FROM AUTHOR]

Abstract: It has been proved that higher total nitrogen removal efficiency could be obtained in step feeding activated sludge process by adjusting the inflow rate distribution and the volume of each stage. But the optimization of the step feeding process would be complicated owing to adjustment of inflow rate and volume. To develop the auto-control and operational decision support system is an urgent and necessary work for well application of step feeding process. Although biological wastewater treatment, especially the biological nitrogen removal process, has the characteristics of complex nonlinear, it provides widespread opportunities for artificial intelligent control. In this paper a fuzzy control model of anoxic/oxic step feeding activated sludge process was developed under the condition of sufficient and insufficient influent carbon source. The detailed information on development of fuzzy model was addressed based on collecting and analyzing previous experimental data. The influent C/N ratio was selected as input variable and inflow rate and volume distribution in each stage were selected as output variables. Moreover, the calibration and application approaches of control model were also studied through pilot-scale experiments (1000 L/d) with domestic sewage. The highlight is that the method and approach of model calibration are well discussed so that it provides good opportunities on practical application. During three months experimental period enhanced total nitrogen removal efficiency of more than 95.1% was reached with the influent C/N ratio of 8.16–12.3, average of 9.78. [Copyright &y& Elsevier]

[Display omitted] • A novel PNA-PDA process was developed for high-level sidestreams treatment. • Desirable polishing treatment of PNA effluent was achieved via PDA approach. • TN removal maintained as high as 98.4% even at low temperature of 13.0 ℃. • Domestic wastewater could be simultaneously treated without aeration. Anaerobic ammonium oxidation (anammox) has been widely accepted as an energy-efficient approach for nitrogen removal from high-strength sidestreams. However, insufficient nitrogen removal due to the excessive NO 3 –-N residue represents the major challenge, especially at low temperature. In this study, highly efficient and synchronous nitrogen removal from ammonia-rich wastewater and real domestic wastewater was achieved via a novel anammox-mediated treatment by coupling with double-nitrite-shunt process in two-stage sequencing batch reactors. Stable partial nitrification/anammox (PNA) was successfully developed, while the total nitrogen (TN) removal efficiency was limited to 86.9 % due to excessive NO 3 –-N accumulation. Significantly, integration with partial denitrification (NO 3 –-N → NO 2 –-N) coupling anammox (PDA) process offered an efficient solution, which transformed the overproduced NO 3 –-N of PNA to NO 2 –-N and subsequently completely removed with NH 4 +-N via anammox pathway by mixing with real domestic wastewater (NH 4 +-N of 69.0 mg/L, COD of 203.6 mg/L). Excellent nitrogen removal performance with average TN removal efficiency of 98.4 % and high-quality effluent with average TN of 4.9 mg/L was maintained despite the temperature dropping to 13.0 ℃. 16S rRNA gene sequencing unveiled the different community of anammox bacteria cooperating stably with AOB and denitrifiers in the two systems. Compared with conventional nitrification/denitrification methods, the novel PNA-PDA process not only enabled 60% saving in aeration energy and 95.5% saving in organic carbon for ammonia-rich wastewater treatment, but also required no aeration energy for domestic wastewater treatment. Overall, this study provides a promising application with simple-control strategy for cost-effective and synchronous nitrogen removal from sidestreams and mainstreams. [ABSTRACT FROM AUTHOR]

[Display omitted] • The stable anammox performance enhanced the stability of nitrogen removal. • Synergize of endogenous denitrification and anammox was critical to 87.1 % NRE. • AnAOB enriched from 4.25 × 106 and remained at 3.1 ± 0.9 × 108 copes/gSS. • Anammox activity was maintained despite temperature decreasing from 28 to 17 ℃. • The anammox contribution to nitrogen removal was above 50 % under varied C/N ratio. The anaerobic ammonium oxidation (anammox) process is a promising method for carbon reduction and energy conservation. However, the advantages of its application in municipal wastewater treatment have not been completely revealed. Stable nitrogen removal was successfully achieved in the anaerobic/aerobic/anoxic (AOA) process by directly integrating stable anammox. Over a 200 + day operating period, the abundance of anammox bacteria (3.1 ± 0.9 × 108 copies/gSS) and anammox activity (0.32 ± 0.07 mgN/(gSS·h)) remained high, despite a temperature decrease (27.8–17.2 °C) and fluctuating carbon-nitrogen (C/N) ratio (1.6–5.0). A stable nitrogen removal efficiency of 87.1 ± 2.5 % was successfully maintained, because the anammox activity compensated for the effect of low temperatures and low C/N ratios on the nitrification and denitrification. Further analysis found that anammox accounted for 52.6 %-57.5 % of N 2 production, and the rest was through nitrification–denitrification. The stable anammox reaction was mainly due to the limitation of oxygen and carbon sources and the stable supply of nitrite by endogenous denitrification. Overall, these findings confirmed that the stability and efficiency of nitrogen removal from municipal wastewater could be increased by integrating anammox under appropriate conditions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Integration of anammox and heterotrophs in biofilms enhances treatment efficiency. • Biofilms protect anammox from heterotrophs in the presence of organics. • The EPS matrix in biofilms facilitates signal exchange among anammox bacteria. • Hybrid anammox biofilm can be achieved by providing sufficient nitrite by denitrification. • Biofilms show promise for coupling partial denitrification with anammox in practice. Biofilms are the most favorable form of microorganism growth in nature. With the urgent demand for energy-efficient wastewater treatment today, biofilms have become a crucial tool for the implementation of new treatment technologies. Anammox-based processes are gaining global attention due to their low cost and high nitrogen removal efficiency. However, the application of anammox in mainstream wastewater treatment is still confined to laboratory settings and faces two major bottlenecks: 1) the relatively slow growth rate of anammox bacteria and 2) unstable nitrite generation. Fortunately, these issues are expected to be relieved through the integration of biofilm technologies that couple autotrophic and heterotrophic pathways. Moreover, both laboratory and full-scale evidence from recent studies highlight the great potential and versatile capability of anammox-based biofilms integrated with heterotrophic microorganisms. A solid understanding of biofilm formation, control, and optimization has thus become increasingly important for further application. This paper provides a comprehensive review of existing methods and microbial mechanisms for enhancing treatment in anammox-based biofilm systems. It critically analyses the potential roles of biofilm formation in anammox process, spatial development of microbial ecology, bioreactor control, associated challenges and perspectives in practical applications. This review is anticipated to contribute significantly to advancing the understanding of biofilm reactor design and operation in the application of new biotechnology. [ABSTRACT FROM AUTHOR]

[Display omitted] • Role of iron in collaboration of anammox and denitrification was revealed. • Iron as electron donor and transporter promoted NH 4 +-N removal. • PD/A with iron exhibited resilience in shocking effect of COD, pH and salinity. • Thauera hold versatile metabolism pathway for NO 2 −-N production utilizing Fe(II). • Candidatus Brocadia participated in iron metabolism with Fe(II) as electron donor. Autotrophic nitrogen removal via anaerobic ammonium oxidation (anammox) technology currently faces significant challenges in treating low-strength wastewater due to inefficient retention of bacteria and unstable activity under fluctuating conditions. This study demonstrates enhanced resilience and stability of anammox coupled with partial denitrification (PD) in granular sludge, assisted by ferric iron (Fe(III)) and nano zero-valent iron (nZVI). The systems treated wastewater with low concentrations of ammonia (NH 4 +-N of 50 ∼ 80 mg/L) and nitrate (NO 3 −-N of 60 ∼ 100 mg/L). Fe(III) and nZVI were intermittently added to two PD coupled with anammox (PD/A) systems, which were subjected to increasing nitrogen loading rates (NLRs) and decreasing temperature. Remarkably, both Fe(III)- and nZVI-assisted systems achieved satisfactory total nitrogen (TN) removal efficiencies of 98.1 % and 96.6 %, respectively, even as the temperature dropped from 28.5℃ to 13.4℃ and the NLR increased from 0.22 to 0.72 kgN/m3/d. Significantly, these two systems exhibited pronounced resilience under the shocking effect of excessive organic load, extremely low pH, and high salinity. The presence of iron, acting as an accelerated electron transporter, enhanced anammox activity and microbial NH 4 +-N oxidation. Additionally, iron reduced the requirement for an organic carbon source, further stimulating the competitiveness of anammox for nitrite (NO 2 −-N) against denitrification. Interestingly, metagenomic analysis revealed that the functional bacteria Thauera, responsible for PD, employed versatile metabolic pathways for NO 3 −-N reduction to NO 2 −-N using Fe(II) as an electron donor. Overall, this study provides new insights into microbial interactions and versatile metabolism in iron-assisted anammox systems, contributing to more energy-efficient wastewater treatment. [ABSTRACT FROM AUTHOR]

[Display omitted] • Biological nitrate removal with municipal wastewater as co-substrate was demonstrated by CANDAN process; • High-efficient nitrogen removal with NRE and NRR of above 84 % and 0.6 Kg N/m3/d achieved; • Efficient denitratation with NTR above 84.6% always obtained despite increased municipal wastewater; • Increased municipal wastewater did not pose an adversely effect on anammox process; • Stable CANDAN process with dominated anammox sustained in treating nitrate sewage with varying concentrations. The innovative Complete Ammonium and Nitrate removal via Denitratation-Anammox over Nitrite (CANDAN) process represents a promising low-carbon technology for wastewater treatment, has been widely studied in sequential batch reactors (SBRs) treating synthetic wastewaters. This work focuses on the development of the CANDAN process within a continuous-flow Upflow Anaerobic Sludge Blanket (UASB) reactor for nitrate sewage treatment (NO 3 –-N: 100–1000 mg N/L), featuring varying proportions of real municipal wastewater as a co-substrate (61.3 mg NH 4 +-N/L, 191.5 mg COD/L). The results demonstrate consistently high N removal performance, with over 84.0 % of total nitrogen (TN) removed from the mixed wastewaters at a rate of approximately 0.6 Kg N/m3/d. As the proportion of municipal wastewater in the feed increased, the activity of denitrifying microorganisms improved. However, their growth was constrained by exacerbated endogenous respiration resulting from prolonged Hydraulic Retention Time (HRT) under a constant loading rate. The ideal nitrite production with the nitrate-to-nitrite transformation ratio (NTR) of above 84.6 % was always obtained. This sustained the dominance of the anammox pathway at around 80 % throughout the operation, underscoring its pivotal role in supporting the exceptional performance of the CANDAN process within the UASB reactor. Microbial analysis revealed an increase in species richness and diversity with higher proportions of municipal wastewater, while anammox functional bacteria exhibited slight enrichment in the later stages, further emphasizing the sustainability of the CANDAN process even with increased proportions of municipal wastewater. The outcomes of this study provide valuable insights into the successful development of a continuous-flow CANDAN process for highly efficient nitrate sewage treatment by incorporating real municipal wastewater as a co-substrate, advancing the goal of achieving carbon–neutral wastewater treatment practices. [ABSTRACT FROM AUTHOR]

[Display omitted] • A two-stage PN/A system for integrated MLL and KWDL treatment had been developed. • The process achieved NRE of 98.1 ± 1.3 % with effluent TIN of 15.2 ± 1.8 mg/L. • Aerobic HRT accounted for just 36.4 % of the whole process with DO < 0.3 mg/L. • The PDA-driving ability of KWDL was comparable to sodium acetate. • Adding KWDL in the later phase of each cycle in A-SBR promoted achieving high NRE. The advanced nitrogen removal of mature landfill leachate (MLL) with low carbon to nitrogen ratio (C/N) is a topic worthy of further research. A two-stage partial nitrification/anammox (PN/A) system for integrated MLL and kitchen waste digestion liquid (KWDL) treatment was established in this study. The nitrogen removal efficiency (NRE) of this process was 98.1 ± 1.3 %, with an effluent TIN concentration of 15.2 ± 1.8 mg/L. In the partial nitrification-sequencing batch reactor (PN-SBR), aerobic hydraulic retention time (HRT) accounted for just 36.4 % of the whole process with dissolved oxygen (DO) < 0.3 mg/L, which significantly reduced energy consumption. Furthermore, the introduction of KWDL heightened anoxic denitrification and aerobic simultaneous nitrification and denitrification (SND) processes, contributing to 74.2 ± 4.3 % and 25.8 ± 4.3 % of the total NRE, respectively. This greatly strengthened the nitrogen removal capacity of PN-SBR. Batch tests indicated that the capacity of KWDL as a carbon source to drive the process of partial denitrification coupled with anammox (PDA) was equal to that of sodium acetate. Adding KWDL in the later phase of each cycle in the anammox-sequencing batch reactor (A-SBR) facilitated achieving stable PDA and advanced nitrogen removal. The nitrate accumulation problem in the traditional two-stage PN/A process has been resolved without the addition of carbon sources. Nitrosomonas (3.7 %→7.9 %), Thauera (0.04 %→40.7 %) and a salt-tolerant AnAOB microbe, unclassified_f_Brocadiaceae (0 %→5.3 %) were dominant in the combined system. This study revealed a pioneering avenue for efficient high-strength wastewater treatment. [ABSTRACT FROM AUTHOR]

[Display omitted] • PD/A granules achieved high-rate and enhanced N removal with continuous feeding. • Dynamic migration of anammox bacteria to outer edge of granules was found in CSTR. • Stratified structure benefited for cross-feeding between anammox and denitrifiers. • Versatile metabolism of anammox bacteria for reducing NO 3 −-N was assumed in PD/A process. • Anammox bacteria could be efficiently enriched at cost of decreased PD bacteria. Anammox coupling with denitrification has attracted increasing attention in low-strength wastewater treatment. However, its wide application in continuous-flow process is seriously restricted by insufficient anammox capacity due to the failed biomass retention. The functional capacities of communities inhabiting the fluctuating habitat has been little understood. This study developed a novel granular sludge-based partial denitrification coupling with anammox (PD/A) process with the feeding strategy shifting from sequencing to continuous flow in a Continuous Stirred Tank Reactor (CSTR), treating low-strength wastewater containing ammonia (NH 4 +-N) of 46.1 mg/L and nitrate (NO 3 −-N) of 60.7 mg/L. Significantly enhanced specific anammox activity was demonstrated, attributed to the robust nitrite (NO 2 −-N) generation with NO 3 −-N to NO 2 −-N transformation ratio (NTR) averaged 84.1 %. Remarkable total nitrogen (TN) removal of 95.4 % was thus achieved with anammox pathway contribution as high as 88.3 %. Interestingly, a dynamic and stratified microbial structure was obtained in CSTR, in which anammox migrated to outer layer together with Thauera capable of partial denitrification (PD) in big granules, resulting in more efficient cross-feeding and strengthening the cooperation between anammox and heterotrophic PD bacteria in CSTR. Metagenomic-based metabolic inferences provide first insight into the versatile microbial metabolic potential of anammox bacteria for reducing NO 3 −-N with acetate as electron donor in PD/A process. They were successfully enriched and retained with the relative abundance of 8.4 %, being attributed to the enhanced mass transfer efficiency. On the contrary, dominant denitrifier Thauera decreased sharply to 4.2 %. This study provides a new alternative of anammox coupling with heterotrophics granular sludge for efficient low-strength wastewater treatment under continuous feeding, and open up new perspectives for selecting distinctive communities that stand out by expansive metabolic versatility and excellent microbial collaboration. [ABSTRACT FROM AUTHOR]

[Display omitted] • Double Anammox was developed on multiple-autotrophic NO 2 − supply. • Instability NO 2 − supply and excessive nitrate residue are comprehensively addressed. • High-efficient nitrogen removal efficiency of 97.8% was obtained with Anammox contributing up to 72.4%. • PN/A-SPDN/A exhibit significant economic and environmental benefits. Anammox holds significant promise as a next-generation technology for achieving energy-positive wastewater treatment. However, its application remains challenging due to unstable nitrite supply and excessive nitrate residue. To address this, a groundbreaking Anammox bioprocess incorporating a double nitrite autotrophic shunt was developed within single system to realize energy-efficient nitrogen removal from wastewater. Partial nitrification/Anammox converted a portion of ammonia in leachate to nitrogen gas in oxic stage. Significantly, sulfur-driven partial denitrification utilizing sulfide as electron donor, efficiently reduced generated nitrate to nitrite in subsequent anoxic stage, facilitating nitrite reutilization via Anammox and removing residual ammonia. Over 200-day monitoring, bioprocess demonstrated desirable effluent quality with 9.0 mg/L NH 4 +-N, 0.6 mg/L NO 2 −-N, and 6.2 mg/L NO 3 −-N. Delightedly, efficient nitrogen removal efficiency of 97.8 % was achieved even under fluctuation conditions. Priority position held by Anammox consortium (Candidatus Kuenenia 11.2 %) mainly derives from similar growth rate of autotrophic bacteria within their shared ecological niche and stable nitrite supply, enabling Anammox to contribute impressive 72.4 % of nitrogen removal. By combing electron flow preference kinetic, stability toward fluctuation, core microbial community, the ecological niche of Candidatus Kuenenia and self consistent logic governing functional microorganisms were revealed. The cost-effective system exhibited significant advantages over conventional bioprocess, reducing organic matter demand by 100 %, aeration energy consumption by 61.7 %, and biomass production by 82.9 %. [ABSTRACT FROM AUTHOR]

A novel post-endogenous denitrification and phosphorus removal (post-EDPR) system was developed by enriching denitrifying glycogen accumulating organisms (DGAOs) and phosphorus accumulating organisms (PAOs) to treat low carbon/nitrogen (C/N) wastewater (C/N = 4.4). The unique feature of the post-EDPR system was the continuous alternating anaerobic/oxic/anoxic zone (3.1 h/3.9 h/7 h) with suspended biofilm carriers in oxic zone. The 132-day test results showed that extended anaerobic and anoxic stage strengthened the intracellular carbon storage and endogenous denitrification. Low dissolved oxygen (DO) concentration (1–2 mg/L) in oxic zone promoted the simultaneous nitrification and denitrification (SND) and saved aeration energy, nitrifiers were enriched with the biofilm carriers and nitrification performance was strengthened, so oxic hydraulic retention time (HRT) could be shortened to avoid excessive polyhydroxyalkanoate (PHA) consumption which would be used for the latter anoxic denitrification. In a steady state, the system achieved advanced nitrogen and phosphorus removal (TIN (total inorganic nitrogen) ≤3 mg/L, PO 4 3−  − P ≤ 0.2 mg/L) with a high removal efficiency of 92.15% and 92.67%, respectively, and PHA played a major role for P-uptake and endogenous denitrification. Microbial community analysis demonstrated that PAOs and GAOs were enriched and performed aerobic P-uptake and anoxic endogenous denitrification, respectively. [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] • Anammox-based process achieved highest NRE of 81.2% at salinity of 2.0%. • With real municipal sewage, influent and effluent TIN are 44.5 and 8.2 mg N/L. • Increased salinity inhibited NOB, nitrite reduction bacteria, and AOB by order. • Enhanced nitrite production and biofilm formation ensure high anammox contribution. • Anammox bacteria occupied 1.07% maximally and has strong adaptability to salinity. Nitrogen removal from saline municipal wastewater has recently attracted attention; thus, developing energy-efficient technology such as anaerobic ammonium oxidation (anammox) for advanced nitrogen removal of hypersaline wastewater is significant. In this study, the long-term salt adaptation and evolution mechanisms of an anammox-based process driven by both nitritation (NH 4 +→NO 2 —, PN) and denitratation (NO 3 —→NO 2 —, PD) were investigated under salinities ranging from 1.0% to 3.0% (10–30 g NaCl/L). At 1.0% salinity, PN evolved into the major nitrite production pathway with thorough suppression of nitrite oxidation. At 1.5% salinity, nitrite reduction was inhibited along with suspended sludge loss due to poor sludge settleability. Under 2.0% salinity with only-biofilm, the highest nitrogen removal efficiency (81.2%) was observed with influent and effluent total inorganic nitrogen concentrations of 44.5 and 8.2 mg N/L, respectively. Notably, results showed that anammox bacteria occupied up to 1.07% of the microbial community (qPCR: 1.14×1011 copies/(g dry sludge)) and has strong adaptability to salinity. With salinity increases, anammox contribution kept over 85% and Ca. Kuenenia (0.57%→0.22%) was more tolerant than Ca. Brocadia (0.46%→0.02%). Metagenomic sequencing revealed that the multiple nitrite substrates production by Nitrosomonas (amoA -enriched), Denitratisoma and Denitromonas (narG -enriched) guaranteed the high anammox contribution. This study provides a multifaceted understanding of the anammox-based process, which can enable improved application in real saline wastewater treatment. [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] • Comammox were enriched in an anammox dominated reactor with low DO. • Advanced nitrogen removal efficiency of 93 % was achieved treating real municipal sewage. • Comammox became dominant over canonical nitrifiers with higher abundance. • Comammox in this reactor belonged to comammox Nitrospira clade A. • Low DO and high SRT might selectively cultivate the comammox. In practical anammox systems, ammonia-oxidizing microbes (AOM) inevitably coexisted with anammox bacteria (AnAOB) due to residue oxygen in influent, but the diversity and impact of AOM in the system remain unclear. In this study, a practical anammox-dominated system with high relative abundance (15.15–19.07 %) of AnAOB (including Ca. Brocadia and Ca. Kuenenia) was studied, which treated low-strength wastewater with dissolved oxygen of 0.24–0.27 mg/L. Results demonstrated that complete ammonia-oxidizing (comammox) bacteria was the most abundant AOM and dominant over other canonical nitrifying bacteria, wherein comammox amoA gene was 8.3-fold more abundant than ammonia-oxidizing bacteria (AOB) amoA gene. Phylogenetic results indicated that the comammox bacteria in this study belonged to comammox Nitrospira clade A. Notably, when treating real nitritation municipal wastewater, cooperative effect of anammox bacteria, comammox bacteria and heterotrophic denitrifiers enhanced nitrogen removal efficiency to 92.9 ± 1.1 %. Hence, these results show that the functional significance of comammox bacteria in engineered ecosystems was previously overlooked. Our findings highlight that comammox bacteria could be an essential functional group in mainstream anammox systems and possess a high potential for energy-efficient nitrogen removal. [ABSTRACT FROM AUTHOR]

[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]

“ Candidatus Accumulibacter” are the dominant polyphosphate-accumulating organism (PAOs) to perform enhanced biological phosphate removal (EBPR) from wastewater. Free nitrous acid (FNA) as inhibitor is an intermediate of nitrification and denitrification commonly present in wastewater treatment plants (WWTPs) and lab-scale reactors. Impact of FNA on EBPR and community structures of Accumulibacter in domestic wastewater treatment was investigated. FNA complete inhibit concentration on aerobic P uptake at pH 6.5 was 6.85 × 10 −3 mg HNO 2 -N/L, higher than that at pH 7.0. Under complete inhibition, poly-β-hydroxyalkanoates degradation was used for nitrite reduction and detoxication rather than P-uptake. The P fraction existed in the forms of complex-P, interstitial-P, chemical participated-P and ortho-P at the end of aerobic phase, and complex-P proportion declined in comparison to non-inhibition. Dominant Accumulibacter clade was IIC, accounting for 70% of total Accumulibacter. Decline of IIF proportion indicated its sensitivity to FNA. Increase of IID percentage implied its strong tolerance to FNA. Under inhibition, Shannon index decreased from 3.45 of seed sludge to 1.92 at pH 7.0, indicating decline of biodiversity. Therefore, FNA inhibition weakened EBPR performance, and remarkably changed clade-level community structures of Accumulibacter. [ABSTRACT FROM AUTHOR]

[Display omitted] • Anammox bacteria was more severely inhibited by FA than HA in both PN/A and PD/A. • PD/A was more robust under HA or FA shocks compared with PN/A. • Combined inhibition of HA and FA was additive on PN/A while antagonistic on PD/A. • HA hindered substrate transport while FA inhibited HZS activity in anammox bacteria. • HA and FA inhibition was alleviated in PD/A by partly participating denitrification. Anammox-based technologies hold great advantages in treating ammonia-rich wastewater where humic substances (HSs), mainly including humic acid (HA) and fulvic acid (FA), are ubiquitous and threaten the anammox activity. Here, the individual and combined effects as well as the mechanism of HA and FA on two typical anammox-based systems, partial nitrification/anammox (PN/A) and partial denitrification/anammox (PD/A), were investigated. Anammox activity was inhibited by 50 % with 1811.0 mg/L HA and 769.1 mg/L FA in PN/A system, but much higher level of 11706.0 mg/L HA and 5016.0 mg/L FA in PD/A system. The combined inhibition of HA and FA on anammox activity was additive in PN/A but antagonistic in PD/A. Transcription responses of functional genes (hzsA , hzsB , hdh , nirK , and nirS) suggested HA mainly inhibited the transmembrane transport of NH 4 + and NO 2 –, while FA mostly inhibited the activity of intracellular hydrazine synthase (HZS). Interestingly, the strengthened denitrification alleviated the HSs stress on anammox in PD/A. Moreover, the protective microstructure with anammox bacteria encapsulated within abundant Thauera in PD/A granules further prevented PD/A from HSs shock. This study enables a better understanding of the HSs impacts on anammox-based systems, which is critical to integrating anammox technology into actual wastewater treatment. [ABSTRACT FROM AUTHOR]

[Display omitted] • Applications of intermittent aeration in N removal are critically reviewed. • Strategies and mechanisms of enhanced N removal efficiency are presented. • Variations in N transformation and microbial interactions are discussed. • Advantages of intermittent aeration in the integrated anammox process are outlined. • Directions for future work in N removal with intermittent aeration are suggested. Intermittent aeration has been shown to be one of the most effective and cost-effective strategies for biological wastewater treatment. This review presents an overview of the application and advantages of intermittent aeration, with the mechanisms of improvement in process stability discussed. Intermittent aeration was applied to maximize the utilization of organic carbon for denitrification rather than oxidized by O 2. Under that condition, advanced nitrogen removal and sludge settleability were achieved and the energy consumption and N 2 O emissions were reduced. With the discovery that nitrite oxidation bacteria are selectively inhibited while ammonium oxidation bacteria are less affected under intermittent aeration conditions, intermittent aeration has been applied to the partial nitrification process. Furthermore, the non-aerated phases of intermittent aeration have been found to facilitate the synergism of anaerobic ammonium oxidizing bacteria (AnAOB) and denitrifying bacteria, providing a suitable environment for AnAOB growth. Therefore, intermittent aeration is considered to be an effective operational strategy for anammox-based processes, such as single-stage partial nitrification-anammox. In addition, simultaneous nutrient removal and sludge reduction could also be achieved. In order to regulate the synergism of microbial species, dissolved oxygen (DO) concentrations and the durations of aerated and non-aerated periods can be adjusted based on the monitored parameters such as nitrogen concentrations, pH and oxidation reduction potential profiles. Finally, the current limitations, gaps in knowledge and the areas requiring further research are proposed. [ABSTRACT FROM AUTHOR]