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Biological nitrogen removal by using a co-culture of Anammox bacteria, ammonia-oxidizing archaea (AOA) and (ammonia-oxidizing bacteria) AOB microorganisms in a sequencing batch reactor (SBR) has previously been demonstrated experimentally. In this work, a mathematical model is developed to describe the microbial interaction among AOA, AOB and Anammox bacteria in the single-stage SBR and provide the first insights on the key role of AOA in such system. In this model, AOA and AOB jointly convert ammonium to nitrite partially, which provides electron acceptors to Anammox bacteria to oxidize the remaining ammonium forming dinitrogen gas. The model is successfully calibrated and validated using the long-term (around 350 days) dynamic experimental data from the SBR system, as well as two independent batch tests at different operational stages of the SBR. The model satisfactorily describes the nitrogen conversion data from the system. Modeling results show that AOA would outcompete AOB under low ammonium concentration and low dissolved oxygen conditions due to the revealed higher NH 4 + affinity ( K N H 4 A O A of 0.06 g N m −3 ) and thus higher ammonia oxidation rate under oxygen-limited conditions, indicating that AOA could be a better partner to Anammox bacteria compared to AOB when treating low strength nitrogen sewage. The developed model could also predict and distinguish the different contributions of AOA and AOB to overall aerobic ammonia oxidizing potential, with more than 50% of ammonia oxidation being mediated by AOB at initial stage (~300 days) and AOA being responsible for up to 90% of the ammonium removal afterwards. The results suggest AOA coupled with Anammox could provide new possibilities for biological nitrogen removal from low strength ammonium wastewater. [ABSTRACT FROM AUTHOR]

ABSTRACT The discovery of denitrifying anaerobic methane oxidation (DAMO) processes enables the complete nitrogen removal from wastewater by utilizing the methane produced on site from anaerobic digesters. This model-based study investigated the mechanisms and operational window for efficient nitrogen removal by coupling nitritation-anaerobic ammonium oxidation (Anammox) and methane-dependent denitrification in membrane biofilm reactors (MBfRs). A mathematical model was applied to describe the microbial interactions among Anammox bacteria, DAMO archaea, and DAMO bacteria. The model sufficiently described the batch experimental data from an MBfR containing an Anammox-DAMO biofilm with different feeding nitrogen compositions, which confirmed the validity of the model. The effects of process parameters on the system performance and microbial community structure could therefore be reliably evaluated. The impacts of nitritation produced NO2−/NH4+ ratio, methane supply, biofilm thickness and total nitrogen (TN) surface loading were comprehensively investigated with the model. Results showed that the optimum NO2−/NH4+ ratio produced from nitritation for the Anammox-DAMO biofilm system was around 1.0 in order to achieve the maximum TN removal (over 99.0%), independent on TN surface loading. The corresponding optimal methane supply increased while the associated methane utilization efficiency decreased with the increase of TN surface loading. The cooperation between DAMO organisms and Anammox bacteria played the key role in the TN removal. Based on these results, the proof-of-concept feasibility of a single-stage MBfR coupling nitritation-Anammox-DAMO for complete nitrogen removal was also tested through integrating the model with ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) processes whilst controlling the dissolved oxygen (DO) concentration in the simulated system. The maximum TN removal was found to be achieved at the bulk DO concentration of around 0.17 g m−3 under the simulation conditions, with the AOB, Anammox bacteria and DAMO organisms coexisting in the biofilm. Biotechnol. Bioeng. 2016;113: 1035-1045. © 2015 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Full-scale application of partial nitritation and anammox in a single floc-based sequencing batch reactor (SBR) has been achieved for high-rate nitrogen (N) removal, but mechanisms resulting in reliable operation are not well understood. In this work, a mathematical model was calibrated and validated to evaluate operating conditions that lead to out-competition of nitrite oxidizers (NOB) from the SBRs and allow to maintain high anammox activity during long-term operation. The validity of the model was tested using experimental data from two independent previously reported floc-based full-scale SBRs for N-removal via partial nitritation and anammox, with different aeration strategies at aeration phase (continuous vs. intermittent aeration). The model described the SBR cycle profiles and long-term dynamic data from the two SBR plants sufficiently and provided insights into the dynamics of microbial population fractions and N-removal performance. Ammonium oxidation and anammox reaction could occur simultaneously at DO range of 0.15–0.3 mg O 2 L −1 at aeration phase under continuous aeration condition, allowing simplified process control compared to intermittent aeration. The oxygen supply beyond prompt depletion by ammonium oxidizers (AOB) would lead to the growth of NOB competing with anammox for nitrite. NOB could also be washed out of the system and high anammox fractions could be maintained by controlling sludge age higher than 40 days and DO at around 0.2 mg O 2 L −1 . Furthermore, the results suggest that N-removal in SBR occurs via both alternating nitritation/anammox and simultaneous nitritation/anammox, supporting an alternative strategy to improve N-removal in this promising treatment process, i.e., different anaerobic phases can be implemented in the SBR-cycle configuration. [ABSTRACT FROM AUTHOR]

Abstract: A multispecies one-dimensional biofilm model considering nitric oxide (NO) and nitrous oxide (N2O) productions for membrane aerated biofilm reactor (MABR) that remove nitrogen autotrophically through aerobic ammonia oxidation followed by Anammox is used to study the role of Anammox activity on the total nitrogen (TN) removal and the productions of NO and N2O. The model is applied to evaluate how periodic aeration as a control parameter reduces NO and N2O production but maintains high TN removal in MABR. The simulation results show over 3.5% of the removed TN could be attributed to NO and N2O production in MABR under the operational conditions optimal for TN removal (72%). An analysis of factors governing the Anammox activity in MABR shows that enhancing Anammox activity not only helps to achieve a high level of nitrogen removal but also reduces NO and N2O productions. Comparison of aeration strategies (periodic aeration vs. continuous aeration) reveals that periodic aeration can reduce NO and N2O production while maintaining a high level of nitrogen removal through promoting Anammox growth. Application of periodic aerations with different cycle frequencies to the MABR indicates that an increase in the cycle frequency of the periodic aeration can further maximize TN removal and minimize the NO and N2O production in membrane aerated biofilm. The information of this paper will be useful for understanding the indirect role of Anammox on NO and N2O productions and for optimizing the design and operation of MABR systems. [Copyright &y& Elsevier]

Abstract: Oxygen limitation has been commonly recognized as an important factor causing nitric oxide (NO) and nitrous oxide (N2O) production. Due to the requirement of low oxygen conditions, membrane aerated autotrophic nitrogen removal biofilm systems that remove nitrogen through aerobic ammonia oxidation followed by Anammox may be prone to NO and N2O production. In this work, a mathematical model was constructed to assess the NO and N2O production potential in membrane aerated autotrophic biofilm under various operational conditions. The AOB-mediated denitrification pathway was used to model NO and N2O production. Simulations showed that a considerable amount of NO (0.2% of TN removed) and N2O (3.0% of TN removed) could be produced in membrane-aerated biofilm under operational conditions optimal for total nitrogen removal with 75% TN removal achieved. Both NO and N2O production is inherently related to TN removal in membrane aerated biofilm reactors (MABRs). NO and N2O production as well as total nitrogen removal depends on both the surface oxygen and ammonium loading rates. Biofilm thickness also has a significant effect on nitrogen removal and on NO and N2O production. An MABR would produce significantly less N2O in comparison to a conventional co-diffusional biofilm system under the same loadings of nitrogen and oxygen, due to the higher nitrite accumulation and outside distribution of AOB in the co-diffusional biofilm. Given the model structure is correct, high TN removal (>70%) with a relative low NO and N2O production (<1.0% of TN removed) in an MABR can be achieved by controlling the oxygen and ammonium surface loading at 2.0gm−2 day−1 and 1.0gm−2 day−1, respectively. These results provide useful support for the design and operation of MABRs. [Copyright &y& Elsevier]

Abstract: Anaerobic ammonium oxidation (Anammox) is a cost-effective new process to treat high-strength nitrogenous wastewater. In this work, the microbial interactions of anaerobic ammonium oxidizers and heterotrophs through the exchange of soluble microbial products (SMP) in Anammox biofilm and the affecting factors were evaluated with both experimental and modeling approaches. Fluorescent in situ hybridization (FISH) analysis illustrated that Anammox bacteria and heterotrophs accounted for 77% and 23% of the total bacteria, respectively, even without addition of an external carbon source. Experimental results showed the heterotrophs could grow both on SMP and decay released substrate from the metabolism of the Anammox bacteria. However, heterotrophic growth in Anammox biofilm (23%) was significantly lower than that of nitrifying biofilm (30–50%). The model predictions matched well with the experimental observations of the bacterial distribution, as well as the nitrogenous transformations in batch and continuous experiments. The modeling results showed that low nitrogen surface loading resulted in a lower availability of SMP leading to low heterotrophic growth in Anammox biofilm, but high nitrogen surface loading would lead to relative stable biomass fractions although the absolute heterotrophic growth increased. Meanwhile, increasing biofilm thickness increased heterotrophic growth but has little influence on the relative biomass fractions. [Copyright &y& Elsevier]

• Autotrophs and heterotrophs in anammox systems are versatile in using organics. • Endogenous organics facilitate biofilm formation and cross-feeding interactions. • 19 core and 7 keystone taxa are identified based on 149 wastewater anammox samples. • Appropriate organics management is key to enhancing nitrogen removal by anammox. Anaerobic ammonium oxidation (anammox) represents a promising technology for wastewater nitrogen removal. Organics management is critical to achieving efficient and stable performance of anammox or integrated processes, e.g., denitratation-anammox. The aim of this systematic review is to synthesize the state-of-the-art knowledge on the multifaceted impacts of organics on wastewater anammox community structure and function. Both exogenous and endogenous organics are discussed with respect to their effects on the biofilm/granule structure and function, as well as the interactions between anammox bacteria (AnAOB) and a broad range of coexisting functional groups. A global core community consisting of 19 taxa is identified and a co-occurrence network is constructed by meta-analysis on the 16S rDNA sequences of 149 wastewater anammox samples. Correlations between core taxa, keystone taxa, and environmental factors, including COD, nitrogen loading rate (NLR) and C/N ratio are obtained. This review provides a holistic understanding of the microbial responses to different origins and types of organics in wastewater anammox reactors, which will facilitate the design and operation of more efficient anammox-based wastewater nitrogen removal process. Image, graphical abstract [ABSTRACT FROM AUTHOR]

• TNRE increased to 87.89 ± 1.82 % after dosing low concentration exogenous glycine. • Candidatus Brocadia and Candidatus Kuenenia emerged as primary enriched genus. • Glycine modulated nitrogen metabolism by altering the content of Hzs & NirS genes. • High dose of exogenous gly in cross-feeding broke the equilibrium of anammox system. • Gly cleavage system could be the initiating point for the cross-feeding imbalance. Strategies to break the cross-feeding equilibrium by dosing essential metabolites and thus enriching and isolating anammox bacteria (AnAOB) have been proposed, but amino acids have not been investigated as important cross-feeding pathways in anammox consortia. In this study, long-term experiments were designed to verify the effect of exgenous glycine on anammox consortia and changes in the bacterial community and metabolic activity after the addition of glycine in a highly active anammox system were investigated. The results showed that the impact of glycine on the activity of anammox highly depended on glycine concentrations, which was manifested as a promotive effect at low concentrations (0–150 mg/L) and an inhibitory effect at high concentrations (300–600 mg/L). The addition of low concentrations of glycine not only enhanced the diversity and richness of bacterial communities but also promoted the enrichment of Candidatus Kuenenia. The qPCR results showed that the content of functional genes Hzs, NirS and anammox 16S rRNA increased while the expression of amoA and NrfA genes was suppressed when glycine acted positively on AnAOB; Hzs and amoA were suppressed when glycine acted negatively on AnAOB, while the expression of NirS and NrfA genes increased dramatically. Specific anammox activity (SAA) experimental results show that 50–150 mg/L glycine was the optimal amount for promoting the activity of AnAOB. Analysis of community metabolic functions indicated that the addition of exogenous glycine resulted in a imbalance of glycine cross-feeding and promoted AnAOB enrichment mainly by affecting pathways such as other glycan degradation and Lysosome. Overall, this study provided new insights into understanding the glycine cross-feeding, which is essential for improving anammox-based technologies. [ABSTRACT FROM AUTHOR]

Anaerobic ammonium oxidation (anammox) is a cost-effective process to treat high-strength nitrogenous wastewater. Even without organic carbon input, the effluent contains bioproducts from autotrophic and heterotrophic bacteria. In this work, excitation–emission matrix (EEM) fluorescence spectroscopy was used to characterize the effluent dissolved organic matter (EfOM) from an anammox reactor treating synthetic wastewater. Two dominant EEM components were identified as humic acid-like (component 1) and protein-like (component 2) substances with excitation/emission peaks at <240, 355, 420/464 nm and <240, 280, 330/346 nm, respectively. The presence of both compounds in the effluent was tracked during an activity recovery period (nitrogen load increased from 0.2 to 1.3 kg N m −3 d −1 ). The effluent concentration of both components increased during this period, indicating correlation between production and bacterial activity. The dynamics of these bioproducts during both substrate consumption and starvation phases was analyzed in batch experiments. Component 1 was only formed during substrate consumption in a rate proportional to ammonium removal and was considered an up-take associated product characteristic of anammox activity. The results show that the composition of the EfOM was qualitatively and quantitatively influenced by process performance. Monitoring the EfOM could, therefore, offer a useful approach to assess anammox process performance and must be further explored. [ABSTRACT FROM AUTHOR]

• An autotrophic system was built by integrating anammox and SCN--denitrification. • The one-stage coupled system could simultaneously remove SCN- and nitrogen. • The concentration of SCN- in the one-stage coupled system could reach 100 mg/L. • Thiobacillus_denitrificans was responsible for SCN- degradation. • The degradation pathway of SCN- was the cyanate pathway. The coupled process of anammox and reduced-sulfur driven autotrophic denitrification can simultaneously remove nitrogen and sulfur from wastewater, while minimizing energy consumption and sludge production. However, the research on the coupled process for removing naturally toxic thiocyanate (SCN-) is limited. This work successfully established and operated a one-stage coupled system by co-cultivating mature anammox and SCN--driven autotrophic denitrification sludge in a single reactor. In this one-stage coupled system, the average total nitrogen removal efficiency was 89.68±3.33 %, surpassing that of solo anammox (81.80±2.10 %) and SCN--driven autotrophic denitrification (85.20±1.54 %). Moreover, the average removal efficiency of SCN- reached 99.50±3.64 %, exceeding that of solo SCN--driven autotrophic denitrification (98.80±0.65 %). The results of the 15N stable isotope tracer labeling experiment revealed the respective reaction rates of anammox and denitrification as 106.38±10.37 μmol/L/h and 69.07±8.07 μmol/L/h. By analyzing metagenomic sequencing data, Thiobacillus_denitrificans was identified as the primary contributor to SCN- degradation in this coupled system. Furthermore, based on the comprehensive analysis of nitrogen and sulfur metabolic pathways, as well as the genes associated with SCN- degradation, it can be inferred that the cyanate (CNO) pathway was responsible for SCN- degradation. This work provided a deeper insight into coupling anammox with SCN--driven autotrophic denitrification in a one-stage coupled system, thereby contributing to the development of an effective approach for wastewater treatment involving both SCN- and nitrogen. [Display omitted] [ABSTRACT FROM AUTHOR]

• A model comprising C/N/S-related bioprocesses was developed and evaluated. • Impact of H 2 S on MBfR/granular bioreactor performing anammox/n-DAMO was assessed. • H 2 S content in inflow gas (v/v: 0∼5%) did not significantly affect MBfR. • Influent H 2 S of granular bioreactor lowered TN removal or increased energy demand. The coupling between anammox and nitrate/nitrite-dependent anaerobic methane oxidation (n-DAMO) has been considered a sustainable technology for nitrogen removal from sidestream wastewater and can be implemented in both membrane biofilm reactor (MBfR) and granular bioreactor. However, the potential influence of the accompanying hydrogen sulfide (H 2 S) in the anaerobic digestion (AD)-related methane-containing mixture on anammox/n-DAMO remains unknown. To fill this gap, this work first constructed a model incorporating the C/N/S-related bioprocesses and evaluated/calibrated/validated the model using experimental data. The model was then used to explore the impact of H 2 S on the MBfR and granular bioreactor designed to perform anammox/n-DAMO at practical levels (i.e., 0∼5% (v/v) and 0∼40 g/S m3, respectively). The simulation results indicated that H 2 S in inflow gas did not significantly affect the total nitrogen (TN) removal of the MBfR under all operational conditions studied in this work, thus lifting the concern about applying AD-produced biogas to power up anammox/n-DAMO in the MBfR. However, the presence of H 2 S in the influent would either compromise the treatment performance of the granular bioreactor at a relatively high influent NH 4 +-N/NO 2 −-N ratio (e.g., >1.0) or lead to increased energy demand associated with TN removal at a relatively low influent NH 4 +-N/NO 2 −-N ratio (e.g., <0.7). Such a negative effect of the influent H 2 S could not be attenuated by regulating the hydraulic residence time and should therefore be avoided when applying the granular bioreactor to perform anammox/n-DAMO in practice. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Multiple mediators function as electron shuttles to promote anammox process; • The EET capability of anammox bacteria can be facilitated by external mediators; • The concurrent presence of mediators triggered the activation of essential enzymes; • The application perspective should focus on the EET-enhanced anammox optimization. The anaerobic ammonium oxidation (anammox) process, transforming ammonia into nitrogen gas in oxygen-free environments using nitrite as an electron acceptor, is increasingly recognized for its potential in treating ammonium-rich wastewater. A major challenge for widespread application of this technology is the limited presence of nitrite in most wastewaters. The intrinsic electroactivity of anammox bacteria implies that the introduction of exogenous additives through the extracellular electron transfer (EET) process could effectively stimulate ammonia oxidation even in the absence of nitrite. This comprehensive review consolidates various approaches to enhance EET-dependent anammox, including the utilization of carbonaceous materials, metal ions, and humic substances. Molecular mechanisms involved in enhancing nitrogen removal performance based on extracellular electron transfer capacity are expounded. The co-occurrence of electron acceptors and exogenous electron shuttles is proposed to increase the activity of c-type cytochromes (c -Cyts) and N-acyl-homoserine lactones (AHLs) in extracellular polymeric substances (EPS), as well as enzymes such as hydrazine synthase (HZS) and hydrazine dehydrogenase (HDH), leading to stable a nitrogen removal performance. This review presents novel insights into the engineering of the EET-enhanced anammox process, providing a theoretical framework for its advancement and optimization. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ideal influent substrates conditions for n-DAMO/anammox-based granular bioreactor. • Smaller granules rich in n-DAMO archaea/AnAOB accelerated bioreactor start-up. • Low diffusivity of solutes promoted bioreactor start-up and CH 4 utilization. In this work, a bioprocess model was applied to first determine the impacts of influent substrates conditions on the granular bioreactor performing nitrate/nitrite-dependent anaerobic methane oxidation (n-DAMO) and anammox integrated processes and then investigate the roles of granular sludge properties in regulating the bioreactor performance and start-up process. The ideal influent substrates conditions were identified at NO 2 −-N/NH 4 +-N of 1:1 and dissolved CH 4 concentration of 85 g COD m−3, which achieved 98.6% total nitrogen removal and 87.7% dissolved CH 4 utilization. Under such ideal influent conditions, the initial properties of granular sludge didn't significantly affect the granular bioreactor performance. However, inoculation of granular sludge with a relatively small granular sludge size and a high abundance of n-DAMO archaea or/and anammox bacteria could effectively shorten the bioreactor start-up. Meanwhile, reducing the diffusivity of solutes within granular sludge was also beneficial for expediting the start-up process and promoting dissolved CH 4 utilization. [ABSTRACT FROM AUTHOR]

Complete nitrogen removal has recently been demonstrated by integrating anaerobic ammonium oxidation (anammox) and denitrifying anaerobic methane oxidation (DAMO) processes. In this work, the effect of methane partial pressure on the performance of a membrane biofilm reactor (MBfR) consisting of DAMO and anammox microorganisms was evaluated. The activities of DAMO archaea and DAMO bacteria in the biofilm increased significantly with increased methane partial pressure, from 367 ± 9 and 58 ± 22 mg-N L −1 d −1 to 580 ± 12 and 222 ± 22 mg-N L −1 d −1 , respectively, while the activity of anammox bacteria only increased slightly, when the methane partial pressure was elevated from 0.24 to 1.39 atm in the short-term batch tests. The results were supported by a long-term (seven weeks) continuous test, when the methane partial pressure was dropped from 1.39 to 0.78 atm. The methane utilization efficiency was always above 96% during both short-term and long-term tests. Taken together, nitrogen removal rate (especially the nitrate reduction rate by DAMO archaea) and methane utilization efficiency could be maintained at high levels in a broad range of methane partial pressure (0.24–1.39 atm in this study). In addition, a previously established DAMO/anammox biofilm model was used to analyze the experimental data. The observed impacts of methane partial pressure on biofilm activity were well explained by the modeling results. These results suggest that methane partial pressure can potentially be used as a manipulated variable to control reaction rates, ultimately to maintain high nitrogen removal efficiency, according to nitrogen loading rate. [ABSTRACT FROM AUTHOR]

The mainstream anaerobic ammonium oxidation (anammox) has attracted extensive attention recently, particularly due to its potential of transforming current wastewater treatment plants from energy consuming to energy neutral or positive. However, the presence of biodegradable chemical oxygen demanding (COD, 20–80 mg COD L −1 ) in the mainstream anammox reactor stimulates the growth of heterotrophic bacteria, which would compete for oxygen with ammonia-oxidizing bacteria (AOB) and for nitrite with anammox bacteria, thus interfering with the autotrophic nitrogen removal process. In the present work, with consideration of granule size distribution, a one-dimensional model describing the mainstream simultaneous partial nitrification, anammox and denitrification (SNAD) in a granule-based reactor was established, calibrated and validated, based on the long-term experimental results. Through applying the verified model, simulation studies were conducted and the results showed that the effluent total nitrogen concentration of <5 mg N L −1 could be achieved at C/N ratio of 0.2–0.6, DO concentration of 0.2–0.4 mg L −1 and granule radius of 300–600 μm. The combined effects indicated that the SNAD process with TN removal efficiency >90% was obtained at C/N ratio and DO concentration of 0.2–1.0 and 0.2–0.4 mg O 2 L −1 respectively. Finally, the various granule size distribution patterns were simulated, which confirmed that the size distribution needed to be incorporated in the model to accurately describe the granular anammox system, considering a model based on a uniform granule size does not reflect the real situations. These results provide guides to optimize the operation of mainstream granular autotrophic nitrogen removal process. [ABSTRACT FROM AUTHOR]

Recent discovery of ammonia-oxidizing archaea (AOA) not only substantially improved our understanding of the global nitrogen cycle, but also provided new possibilities for nitrogen removal from wastewater. In particular, compared to ammonia-oxidizing bacteria (AOB), the high ammonia oxidation under oxygen-limited conditions driven by AOA is potentially more suitable for autotrophic nitrogen removal in a single-stage membrane aerated biofilm reactor (MABR) through coupling with anaerobic ammonia oxidation (Anammox). In this work, mathematical modeling is applied to assess the system performance and associated microbial community structure of an AOA–Anammox MABR under low- (30 mg N L −1 ) and high-strength (500 mg N L −1 ) ammonium conditions, with a side-by-side comparison to an AOB–Anammox MABR system under the same conditions. Results demonstrate that both ammonium surface loading (or hydraulic retention time) and oxygen surface loading significantly affect the system performance. In contrast to AOB–Anammox system, the AOA–Anammox MABR shows higher total nitrogen (TN) removal and lower oxygen supply, with much better repression of NOB and substantially wider operating window for high-level TN removal (>80%) in terms of varied oxygen and ammonium loadings. These results provide first insights and useful information for design and operation of this novel AOA–Anammox MABR system in its potential future applications. [ABSTRACT FROM AUTHOR]

The presence of a high level of dissolved methane (e.g., 20–26 g m −3 ) in the anaerobic sludge digestion liquor represents a major challenge to the treatment of this stream, as its emission to the atmosphere contributes significantly to the carbon footprint of wastewater treatment. Here we propose a new approach to simultaneous ammonium and dissolved methane removal from the anaerobic digestion liquor through integrating partial nitritation-Anammox and denitrifying anaerobic methane oxidation (DAMO) processes in a single-stage membrane biofilm reactor (MBfR). In such an MBfR, the anaerobic digestion liquor is provided in the bulk liquid, while oxygen is supplied through gas-permeable membranes to avoid dissolved methane stripping. A previously developed model with appropriate extensions was applied to assess the system performance under different operational conditions and the corresponding microbial interactions. Both influent surface loading (or hydraulic retention time) and oxygen surface loading are found to significantly influence the total nitrogen (TN) and dissolved methane removal, which jointly determine the overall system performance. The counter diffusion and concentration gradients of substrates cause microbial stratification in the biofilm, where ammonia-oxidizing bacteria (AOB) attach close to the membrane surface (biofilm base) where oxygen and ammonium are available, while Anammox and DAMO microorganisms jointly grow in the biofilm layer close to the bulk liquid where methane, ammonium, and nitrite are available with the latter produced by AOB. These results provide first insights and useful information for the design and operation of this new technology for simultaneous ammonium and dissolved methane removal in its potential future applications. [ABSTRACT FROM AUTHOR]

• Insensitive TN removal to longitudinal heterogeneity at non-excessive CH 4 supply. • Longitudinal gradient in liquid phase affected biomass stratification/CH 4 utilization. • Recommended plug flow operation for MBfR with co-current flow of wastewater and CH 4. Integrating anammox with denitrifying anaerobic methane oxidation (DAMO) in the membrane biofilm reactor (MBfR) is a promising technology capable of achieving complete nitrogen removal from wastewater. However, it remains unknown whether reactor configurations featuring longitudinal gradients parallel to the membrane surface would affect the performance of the CH 4 -driven MBfR. To this end, this work aims to study the impacts of longitudinal heterogeneity potentially present in the gas and liquid phases on a representative CH 4 -driven MBfR performing anammox/DAMO by applying the reported modified compartmental modeling approach. Through comparing the modeling results of different reactor configurations, this work not only offered important guidance for better design, operation and monitoring of the CH 4 -driven MBfR, but also revealed important implications for prospective related modeling research. The total nitrogen removal efficiency of the MBfR at non-excessive CH 4 supply (e.g., surface loading of ≤0.064 g-COD m−2 d−1 in this work) was found to be insensitive to both longitudinal gradients in the liquid and gas phases. Comparatively, the longitudinal gradient in the liquid phase led to distinct longitudinal biomass stratification and therefore played an influential role in the effective CH 4 utilization efficiency, which was also related to the extent of reactor compartmentation considered in modeling. When supplied with non-excessive CH 4 , the MBfR is recommended to be designed/operated with both the biofilm reactor and the membrane lumen as plug flow reactors (PFRs) with co-current flow of wastewater and CH 4 , which could mitigate dissolved CH 4 discharge in the effluent. For the reactor configurations with the biofilm reactor designed/operated as a PFR, multi-spot sampling in the longitudinal direction is needed to obtain a correct representation of the microbial composition of the MBfR. Graphical abstract [Display omitted]. [ABSTRACT FROM AUTHOR]

[Display omitted] • Impacts of granule properties on reactors performing partial nitritation/anammox. • Big anammox-enriched granules inoculated for high TN removal & low N 2 O production. • Optimum boundary layer thickness increased with decreasing diffusivity in granules. This work studied the impacts of key granule properties on the granular reactor performing partial nitritation/anammox from the modeling perspective. The results could guide not only future reliable modeling but also practical startup/operation of the reactor. To achieve high total nitrogen (TN) removal whilst avoiding significant N 2 O production, inoculated granules should be big and anammox-enriched. The optimum boundary layer thickness for maximum TN removal increased with the decreasing diffusivity of soluble components in the granule structure. Even though a thick boundary layer could protect anammox bacteria from elevated dissolved oxygen (DO) (e.g., 0.5 g-O 2 /m3) and obtain high TN removal (>90.0%) and low N 2 O production (<1.8%), even complete removal of the boundary layer would fail to provide sufficient substrate for anammox and therefore couldn't increase TN removal to 90.0% and decrease N 2 O production to <2.4% at insufficient DO (e.g., 0.3 g-O 2 /m3 in the presence of lifted influent NH 4 + concentration). [ABSTRACT FROM AUTHOR]

[Display omitted] • A SPANADA process was first established in a continuous flow air-lift bioreactor. • Effluent TIN of 8.6 mg/L was achieved in low C/N real wastewater with NH 4 +-N of 100 mg/L. • Anammox was the dominant nitrogen removal pathway in SPANADA system. • Meta-omics revealed the undergoing microbial interaction for nitrogen transformation. • Nitrogen conversion flux was evaluated based on kinetic and stoichiometric parameters. This study describes the development of an air-lift internal circulation reactor that integrates partial nitrification, anammox and denitratation (SPANADA) into a single stage bioprocess for the treatment of low C/N coal gasification wastewater. During 245 days of operation, the compartmental fluidized bed reactor achieved a total inorganic nitrogen (TIN) removal efficiency of 91.4%. Reads-based metatranscriptomic analysis found the expression of the amoA and hao genes essential for nitritation and the hzsA and hdh genes essential for anammox increased dramatically as reactor performance improved and stabilized. Another notable trend was that the total expression of the napA and narG genes, essential for denitratation, was 3-fold higher than the combined reads for nirK and nirS whose products, nitrite reductases, would lower nitrite levels reducing available substrate for anammox. Analysis of metagenome-assembled genomes revealed members of Nitrosomonas and Candidatus Brocadia, were the dominant genera of ammonium-oxidizing bacteria and anammox bacteria, respectively, and accounted for 5.5% and 10.0% of the total reads in the transcriptome. For denitratation, Thiolinea , whose only relevant gene involved in N-metabolism is narG , accounted for 8.5% of the total reads in the transcriptome and, remarkably, 84.1% of narG expression. Mass balance confirmed anammox was the dominant nitrogen removal pathway, accounting for 67.0% of the TIN removed. Nitritation and denitratation accounted for 82.7% and 17.3% of the nitrite production, respectively. The analysis reported demonstrates the development of a novel and effective one-stage nitrogen removal alternative for low C/N wastewater treatment and also helps gain insight into the underlying microbial interactions. [ABSTRACT FROM AUTHOR]

• A granule model embedding metabolisms of DAMO microbes and AnAOB was proposed. • The model predictions matched experimental data from two granular sludge reactors. • The estimated parameter values indicated a stimulated growth of DAMO archaea. • The model managed to simulate the microbial abundance and stratified distribution. • Short HRT and small granule size increased DAMO archaea but reduced DAMO bacteria. The granular bioreactor, characterized by excellent settling velocity, high rate and low cost is an ideal choice for achieving coupled nitrate/nitrite dependent denitrifying anaerobic methane oxidation (n-DAMO) and anaerobic ammonium oxidation (Anammox) process. To fundamentally understand its underlining mechanisms and provide suggestions for process optimization, a granule-based model framework was developed to describe simultaneous anaerobic methane and ammonium oxidation by functional microbes. The proposed model was evaluated based on long-term experimental data from two membrane granular sludge reactors (MGSRs) with different operational conditions. The model possessed of good predictive ability to reproduce removal rates and effluent concentrations of nitrogen species. The predicted biomass abundance in two MGSRs and stratified microbial distribution along granule depth were consistent with experimental observations. The estimated parameter values, with good identifiability and reliability indicated a stimulated growth of DAMO archaea in MGSRs. Both hydraulic retention times (HRTs) and granule sizes have influences on microbial abundance in the MGSR and community distribution inside granules. Within the investigated HRTs from 1.4 h to 20 h and granule sizes from 500 μm to 2900 μm, it was revealed that a proper control of relatively short HRTs and small granule sizes resulted in an increased fraction of DAMO archaea and a reduced DAMO bacteria abundance with AnAOB less impacted, which would lower the required nitrite nitrogen to ammonium nitrogen ratio in the nitritation reactor (prior unit) and thus minimize operational cost in sidestream treatment lines. [ABSTRACT FROM AUTHOR]