Mass transfer affects reactor performance, microbial morphology, and community succession in the methane-dependent denitrification and anaerobic ammonium oxidation co-culture

Deciphering the formation of granules by n-DAMO and Anammox microorganisms

Nitrate/nitrite-dependent anaerobic methane oxidation (n-DAMO) process is a promising wastewater treatment technology, but the slow microbial growth rate greatly hinders its practical application. Although high-level nitrogen removal and excellent biomass accumulation have been achieved in n-DAMO granule process, the formation mechanism of n-DAMO granules remains unresolved. To elucidate the role of functional microbes in granulation, this study attempted to cultivate granules dominated by n-DAMO microorganisms and granules coupling n-DAMO with anaerobic ammonium oxidation (Anammox). After long-term operation, dense granules were developed in the two systems where both n-DAMO archaea and n-DAMO bacteria were enriched, whereas granulation did not occur in the other system dominated by n-DAMO bacteria. Extracellular polymeric substances (EPS) measurement indicated the critical role of EPS production in the granulation of n-DAMO process. Metagenomic and metatranscriptomic analyses revealed that n-DAMO archaea and Anammox bacteria were active in EPS biosynthesis, while n-DAMO bacteria were inactive. Consequently, more EPS were produced in the systems containing n-DAMO archaea and Anammox bacteria, leading to the successful development of n-DAMO granules. Furthermore, EPS biosynthesis in n-DAMO systems is potentially regulated by acyl-homoserine lactones and c-di-GMP. These findings not only provide new insights into the mechanism of granule formation in n-DAMO systems, but also hint at potential strategies for management of the granule-based n-DAMO process.

Future directions in microbial nitrogen cycling in wastewater treatment

Discoveries in the past decade of novel reactions, processes, and micro-organisms have altered our understanding of microbial nitrogen cycling in wastewater treatment systems. These advancements pave the way for a transition toward more sustainable and energy-efficient wastewater treatment systems that also minimize greenhouse gas emissions. This review highlights these innovative directions in microbial nitrogen cycling within the context of wastewater treatment. Processes such as comammox, Feammox, electro-anammox, and nitrous oxide mitigation offer innovative approaches for sustainable, energy-efficient nitrogen removal. However, while these emerging processes show promise, advancing from laboratory research to practical applications, particularly in decentralized systems, remains a critical next step toward a sustainable and efficient wastewater management.

Coupling Partial Nitritation, Anammox and n-DAMO in a membrane aerated biofilm reactor for simultaneous dissolved methane and nitrogen removal

Anaerobic technologies with downstream autotrophic nitrogen removal have been proposed to enhance bioenergy recovery and transform a wastewater treatment plant from an energy consumer to an energy exporter. However, approximately 20-50 % of the produced methane is dissolved in the anaerobically treated effluent and is easily stripped into the atmosphere in the downstream aerobic process, contributing to the release of greenhouse gas emissions. This study aims to develop a solution to beneficially utilize dissolved methane to support high-level nitrogen removal from anaerobically treated mainstream wastewater. A novel technology, integrating Partial Nitritation, Anammox and Methane-dependent nitrite/nitrate reduction (i.e. PNAM) was demonstrated in a membrane-aerated biofilm reactor (MABR). With the feeding of ∼50 mg NH4+-N/L and ∼20 mg/L dissolved methane at a hydraulic retention time of 15 h, around 90 % of nitrogen and ∼100 % of dissolved methane can be removed together in the MABR. Microbial community characterization revealed that ammonia-oxidizing bacteria (AOB), nitrite-oxidizing bacteria (NOB), anammox bacteria, nitrite/nitrate-dependent anaerobic methane oxidation microorganisms (n-DAMO bacteria and archaea) and aerobic methanotrophs co-existed in the established biofilm. Batch tests confirmed the active microbial pathways and showed that AOB, anammox bacteria and n-DAMO microbes were jointly responsible for the nitrogen removal, and dissolved methane was mainly removed by the n-DAMO process, with aerobic methane oxidation making a minor contribution. In addition, the established system was robust against dynamic changes in influent composition. The study provides a promising technology for the simultaneous removal of dissolved methane and nitrogen from domestic wastewater, which can support the transformation of wastewater treatment from an energy- and carbon-intensive process, to one that is energy- and carbon-neutral.

Emerging biotechnological applications of anaerobic ammonium oxidation

Anaerobic ammonium oxidation (anammox) is an energy-efficient method for nitrogen removal that opens the possibility for energy-neutral wastewater treatment. Research on anammox over the past decade has primarily focused on its implementation in domestic wastewater treatment. However, emerging studies are now expanding its use to novel biotechnological applications and wastewater treatment processes. This review highlights recent advances in the anammox field that aim to overcome conventional bottlenecks, and explores novel and niche-specific applications of the anammox process. Despite the promising results and potential of these advances, challenges persist for their real-world implementation. This underscores the need for a transition from laboratory achievements to practical, scalable solutions for wastewater treatment which mark the next crucial phase in the evolution of anammox research.

Granulation of partial denitrification sludge: Advances in mechanism understanding, technologies development and perspectives

The high-rate and stably efficient nitrite generation is vital and still challenges the wide application of partial denitrification (PD) and anammox technology. Increasing attention has been drawn to the granulation of PD biomass. However, the knowledge of PD granular sludge is still limited in terms of granules characterization and mechanisms of biomass aggregation for high nitrite accumulation. This work reviewed the performance and granulation of PD biomass for high nitrite accumulation via nitrate reduction, including the system start-up, influential factors, granular characteristics, hypothetical mechanism, challenges and perspectives in future application. The physiochemical characterization and key influential factors were summarized in view of nitrite production, morphology analysis, extracellular polymer substance structure, as well as microbial mechanisms. The PD granules exhibit potential advantages of a high biomass density, good settleability, high hydraulic loading rates, and strong shock resistance. A novel granular sludge-based PD combined with anammox process was proposed to enhance the capability of nitrogen removal. In the future, PD granules utilizing different electron donors is a promising way to broaden the application of anammox technology in both municipal and industrial wastewater treatment.

Reactivated biofilm coupling n-DAMO with anammox achieved high-rate nitrogen removal in membrane aerated moving bed biofilm reactor

As a promising technology, the combination of nitrate/nitrite-dependent anaerobic methane oxidation (n-DAMO) with Anammox offers a solution to achieve effective and sustainable wastewater treatment. However, this sustainable process faces challenges to accumulate sufficient biomass for reaching practical nitrogen removal performance. This study developed an innovative membrane aerated moving bed biofilm reactor (MAMBBR), which supported sufficient methane supply and excellent biofilm attachment, for cultivating biofilms coupling n-DAMO with Anammox. Biofilms were developed rapidly on the polyurethane foam with the supply of ammonium and nitrate, achieving the bioreactor performance of 275 g N m^-3 d^-1 within 102 days. After the preservation at -20 °C for 8 months, the biofilm was successfully reactivated and achieved 315 g N m^-3 d^-1 after 188 days. After reactivation, MAMBBR was applied to treat synthetic sidestream wastewater. Up to 99.9% of total nitrogen was removed with the bioreactor performance of 4.0 kg N m^-3 d^-1. Microbial community analysis and mass balance calculation demonstrated that n-DAMO microorganisms and Anammox bacteria collectively contributed to nitrogen removal in MAMBBR. The MAMBBR developed in this study provides an ideal system of integrating n-DAMO with Anammox for sustainable wastewater treatment.

Emerging onsite electron donors for advanced nitrogen removal from anammox effluent of leachate treatment: A review and future applications

Partial nitrification-anammox process is promising in leachate treatment, but the 11% residue nitrate limits the total nitrogen removal efficiency. Denitrification or partial denitrification and anammox are both practical polishing processes of anammox effluent, requiring extra electron donors. Fortunately, there are organic matter, sulfide and methane in leachate or produced by leachate treatment, which can serve as onsite electron donors. In this review, the mechanisms and processes using these three kinds of electron donors for residue nitrate reduction in anammox effluent of leachate are systematically summarized and discussed. It can be concluded that, biodegradable organic matter is an effective electron donor, sulfide is a promising electron donor, methane is a potential electron donor. Two possible applications in future based on anammox treatment of fresh and mature leachate using sulfide and methane as onsite electron donors are proposed. Through sulfide reutilization, energy-saving with about 14% of aeration reduction can be achieved.

Denitrifying anaerobic methane oxidation (DAMO) cultures: Factors affecting their enrichment, performance and integration with anammox bacteria

The recently discovered process, denitrifying anaerobic methane oxidation (DAMO), links the carbon and nitrogen biogeochemical cycles via coupling the anaerobic oxidation of methane to denitrification. The DAMO process, in this respect, has the potential to mitigate the greenhouse effect through the assimilation of dissolved methane. Denitrification via methane oxidation rather than organic matter, provides a new perspective to performing this once thought to be well established process. The two main species responsible for this process are "Candidatus Methylomirabilis oxyfera (M. oxyfera), and "Candidatus Methanoperedens nitroreducens" (M. nitroreducens). M. oxyfera is responsible of reducing nitrite while M. nitroreducens reduces nitrate to nitrite. These two microorganisms, despite their different pathways, were found to exist together in nature through a syntrophic relationship. Their co-existence with anaerobic ammonium oxidation (Anammox) bacteria was also revealed in the last decade. Anammox bacteria are chemolithoautotrophs, converting ammonium and nitrite to N₂ and nitrate. They are responsible for the release of more than 50% of oceanic N₂, hence play an important role in the global nitrogen cycle. Factors leading to the enrichment of DAMO cultures and their cultivation with Anammox cultures are of significance for improved nitrogen removal systems with decreased greenhouse effect, and even for further full-scale applications. This study, therefore, aims to present an updated review of the DAMO process, by focusing on the factors that might have a significant role in enrichment of DAMO microorganisms and their co-existence with Anammox bacteria. Factors such as temperature, pH, inoculum and feed type, trace metals and reactor configuration are among the ones discussed in detail. Factors, which have not been investigated, are also elucidated to provide a better understanding of the process and set research goals that will aid in the development of DAMO-centered wastewater treatment alternatives.

Continuous anaerobic oxidation of methane: Impact of semi-continuous liquid operation and nitrate load on N2O production and microbial community

This work proves the feasibility of employing regular secondary activated sludge for the enrichment of a microbial community able to perform the anaerobic oxidation of methane coupled to nitrate reduction (N-AOM). After 96 days of activated sludge enrichment, a clear N-AOM activity was observed in the resulting microbial community. The methane removal potential of the enriched N-AOM culture was then studied in a stirred tank reactor (STR) operated in continuous mode for methane supply and semi-continuous mode for the liquid phase. The effect of applying nitrate loads of ∼22, 44, 66, and 88 g NO₃^- m^-3 h^-1 on (i) STR methane and nitrate removal performance, (ii) N₂O emission, and (iii) microbial composition was investigated. Methane elimination capacities from 21 ± 13.3 to 55 ± 12 g CH₄ m^-3 h^-1 were recorded, coupled to nitrate removal rates ranging from 6 ± 3.2 to 43 ± 14.9 g NO₃^- m^-3 h^-1. N₂O production was not detected under the three nitrate loading rates applied for the assessment of potential N₂O emission in the continuous N-AOM process (i.e. ∼22-66 g NO^-3 m^-3 h^-1). The lack of N₂O emissions during the process was attributed to the N₂O reducing capacity of the bacterial taxa identified and the rigorous control of dissolved O₂ and pH implemented (dissolved O₂ values ≤ 0.07 g m^-3 and pH of 7.6 ± 0.4). Microbial characterization showed that the N-AOM process was performed in absence of putative N-AOM archaea and bacteria (ANME-2d, M. oxyfera). Instead, microbial activity was driven by methane-oxidizing bacteria and denitrifying bacteria (Bacteroidetes, α-, and γ-proteobacteria).

Rapid formation of granules coupling n-DAMO and anammox microorganisms to remove nitrogen

Granular sludge exhibits unique features, including rapid settling velocity, high loading rate and relative insensitivity against inhibitors, thus being a favorable platform for the cultivation of slow-growing and vulnerable microorganisms, such as anaerobic ammonium oxidation (anammox) bacteria and nitrite/nitrate-dependent anaerobic methane oxidation (n-DAMO) microorganisms. While anammox granules have been widely applied, little is known about how to speed up the granulation process of n-DAMO microorganisms, which grow even slower than anammox bacteria. In this study, we used mature anammox granules as biotic carriers to embed n-DAMO microorganisms, which obtained combined anammox + n-DAMO granules within 6 months. The results of whole-granule 16S rRNA gene amplicon sequencing showed the coexistence of anammox bacteria, n-DAMO bacteria and n-DAMO archaea. The microbial stratification along granule radius was further elucidated by cryosection-16S rRNA gene amplicon sequencing, showing the dominance of n-DAMO archaea and anammox bacteria at inner and outer layers, respectively. Moreover, the images of cryosection-fluorescence in situ hybridization (FISH) verified this stratification and also indicated a shift in microbial stratification. Specifically, n-DAMO bacteria and n-DAMO archaea attached to the anammox granule surface initially, which moved to the inner layer after 4-months operation. On the basis of combined anammox + n-DAMO granules, a practically useful nitrogen removal rate (1.0 kg N/m³/d) was obtained from sidestream wastewater, which provides new avenue to remove nitrogen from wastewater using methane as carbon source.

Laboratory scale bioreactor designs in the processes of methane bioconversion: Mini-review

Global methane emissions have been steadily increasing over the past few decades, exerting a negative effect on the environment. Biogas from landfills and sewage treatment plants is the main anthropogenic source of methane. This makes methane bioconversion one of the priority areas of biotechnology. This process involves the production of biochemical compounds from non-food sources through microbiological synthesis. Methanotrophic bacteria are a promising tool for methane bioconversion due to their ability to use this greenhouse gas and to produce protein-rich biomass, as well as a broad range of useful organic compounds. Currently, methane is used not only to produce biomass and chemical compounds, but also to increase the efficiency of water and solid waste treatment. However, the use of gaseous substrates in biotechnological processes is associated with some difficulties. The low solubility of methane in water is one of the major problems. Different approaches have been involved to encounter these challenges, including different bioreactor and gas distribution designs, solid carriers and bulk sorbents, as well as varying air/oxygen supply, the ratio of volumetric flow rate of gas mixture to its consumption rate, etc. The aim of this review was to summarize the current data on different bioreactor designs and the aspects of their applications for methane bioconversion and wastewater treatment. The bioreactors used in these processes must meet a number of requirements such as low methane emission, improved gas exchange surface, and controlled substrate supply to the reaction zone.

The effect of sulfate on nitrite-denitrifying anaerobic methane oxidation (nitrite-DAMO) process

Sulfate is generally found in natural water and wastewater. Nitrite-DAMO bacteria live in natural water or wastewater containing different sulfates. To determine the effect of sulfate on the nitrite-DAMO process, we conducted batch tests and continuous tests to investigate the performance and microbial structure of the nitrite-DAMO system at different sulfate concentrations. The results indicated that the nitrogen removal performance of the nitrite-DAMO system was initially promoted and then inhibited at 0-200 mg SO₄^2-/L, and the denitrification rate was highest at 80 mg SO₄^2-/L which was 1.26 mgN/(L·d). When stimulated by sulfate, protein stabilized nitrite-DAMO bacteria. The denitrification kinetics conformed to the Edward equation, and the initial inhibitory concentration of the nitrite-DAMO system was 189.70 mg SO₄^2-/L. Changes in the proportion of unclassfied_c_ABY1 of the phylum Patescibacteria and norank_f_LD-RB-34 of the phylum Bacteroidetes were the main factors influencing how the nitrogen removal rate of the nitrite-DAMO system responded to sulfate.

Development of granular sludge coupling n-DAMO and Anammox in membrane granular sludge reactor for high rate nitrogen removal

The integration of nitrate/nitrite dependent anaerobic methane oxidation (n-DAMO) and anaerobic ammonium oxidation (Anammox) provides sustainable solution to simultaneously remove nitrate, nitrite and ammonium. This study demonstrated the sludge granulation process coupling n-DAMO and Anammox from mixed inoculum including river sediment, return activated sludge and crushed anaerobic granule sludge in a novel membrane granular sludge reactor (MGSR). Flocculent biomass gradually turned into compact aggregates and retained as granular sludge with an average diameter of 2.2 mm in MGSR after 684 days' operation. When steady state with a hydraulic retention time of 1.19 days was reached, the MGSR achieved a nitrogen removal rate of 1.77 g N L^-1 d^-1. Granules with density of 1.043 g mL^-1, settling velocity of 72 m h^-1 and sludge volume index of 22 mL g^-1 leaded to excellent biomass retention (42 g VSS L^-1). Pyrosequencing analysis revealed that two dominant microbial groups, n-DAMO archaea and Anammox bacteria, in the microbial community of the granule were enriched to 31.09% and 12.45%. Fluorescence in situ hybridization revealed a homogenous distribution of n-DAMO archaea and Anammox bacteria throughout the granule. The granular sludge coupling n-DAMO and Anammox microorganisms provides significant potential for high rate nitrogen removal from wastewater.

Diversity, enrichment, and genomic potential of anaerobic methane- and ammonium-oxidizing microorganisms from a brewery wastewater treatment plant

Anaerobic wastewater treatment offers several advantages; however, the effluent of anaerobic digesters still contains high levels of ammonium and dissolved methane that need to be removed before these effluents can be discharged to surface waters. The simultaneous anaerobic removal of methane and ammonium by denitrifying (N-damo) methanotrophs in combination with anaerobic ammonium-oxidizing (anammox) bacteria could be a potential solution to this challenge. After a molecular survey of a wastewater plant treating brewery effluent, indicating the presence of both N-damo and anammox bacteria, we started an anaerobic bioreactor with a continuous supply of methane, ammonium, and nitrite to enrich these anaerobic microorganisms. After 14 months of operation, a stable enrichment culture containing two types of 'Candidatus Methylomirabilis oxyfera' bacteria and two strains of 'Ca. Brocadia'-like anammox bacteria was achieved. In this community, anammox bacteria converted 80% of the nitrite with ammonium, while 'Ca. Methylomirabilis' contributed to 20% of the nitrite consumption. The analysis of metagenomic 16S rRNA reads and fluorescence in situ hybridization (FISH) correlated well and showed that, after 14 months, 'Ca. Methylomirabilis' and anammox bacteria constituted approximately 30 and 20% of the total microbial community. In addition, a substantial part (10%) of the community consisted of Phycisphaera-related planctomycetes. Assembly and binning of the metagenomic sequences resulted in high-quality draft genome of two 'Ca. Methylomirabilis' species containing the marker genes pmoCAB, xoxF, and nirS and putative NO dismutase genes. The anammox draft genomes most closely related to 'Ca. Brocadia fulgida' included the marker genes hzsABC, hao, and hdh. Whole-reactor and batch anaerobic activity measurements with methane, ammonium, nitrite, and nitrate revealed an average anaerobic methane oxidation rate of 0.12 mmol h^-1 L^-1 and ammonium oxidation rate of 0.5 mmol h^-1 L^-1. Together, this study describes the enrichment and draft genomes of anaerobic methanotrophs from a brewery wastewater treatment plant, where these organisms together with anammox bacteria can contribute significantly to the removal of methane and ammonium in a more sustainable way. KEY POINTS: • An enrichment culture containing both N-damo and anammox bacteria was obtained. • Simultaneous consumption of ammonia, nitrite, and methane under anoxic conditions. • In-depth metagenomic biodiversity analysis of inoculum and enrichment culture.

Denitrifying Anaerobic Methane Oxidation and Anammox Process in a Membrane Aerated Membrane Bioreactor: Kinetic Evaluation and Optimization

Denitrifying anaerobic methane oxidation (DAMO) coupled to anaerobic ammonium oxidation (anammox) is a promising technology for complete nitrogen removal with economic and environmental benefit. In this work, a model framework integrating DAMO and anammox process was constructed based on suspended-growth systems. The proposed model was calibrated and validated using experimental data from a sequencing batch reactor and a membrane aerated membrane bioreactor (MAMBR). The model managed to describe removal rates of ammonium (NH₄⁺), nitrite (NO₂^-), and total nitrogen, as well as biomass changes of DAMO archaea, DAMO bacteria, and anaerobic ammonium oxidizing bacteria (AnAOB) in both reactors. The estimated parameter values revealed that DAMO archaea possessed properties of faster growth and higher biomass yield in suspended-growth systems compared to those in attached-growth systems (e.g., biofilm). Model simulation demonstrated that solid retention time (SRT) was effective in washing out DAMO bacteria, but retaining DAMO archaea and AnAOB in the MAMBR. The optimal SRT and nitritation efficiency (the ratio of the NO₂^- to the sum of NH₄⁺ and NO₂^- in the MAMBR influent) were simulated so that 99% of total nitrogen was removed to meet the discharge standard. MAMBR further suggested to be operated with SRT between 15 and 30 days so that the optimal nitritation efficiency could be minimized to 49% for cost savings.

Granular activated carbon assisted nitrate-dependent anaerobic methane oxidation-membrane bioreactor: Strengthening effect and mechanisms

Eutrophication and global warming are two main urgent environmental problems around the world. Nitrate-dependent Anaerobic Methane Oxidation (NdAMO) is a bioprocess coupling nitrate reduction with anaerobic methane oxidation, which could mitigate of these two environmental issues simultaneously. In this study, a newly granular active carbon-NdAMO-membrane bioreactor (GAC-NdAMO-MBR) system was established to evaluate its nitrogen removal efficiency, membrane fouling property and the probable strengthening mechanism was also uncovered. Results indicated that the nitrate removal rate in GAC-NdAMO-MBR reached 31.85 ± 3.19 mgN·L^-1·d^-1 while it was only 10.35 ± 2.02 mgN·L^-1·d^-1 in NdAMO-MBR system (lack of GAC), which was multiplied three-fold. The membrane flux decay rate of GAC- NdAMO -MBR was 0.15 L/m²·h·d while it was 0.49 L/m²·h·d without GAC, and the addition of GAC could extend membrane fouling time for 2.5 times. Notablely, the relative abundance of NdAMO bacteria sharply increased from 27.15% to 56.91% after GAC addition while the NdAMO archaea showed similar variation trend. The physicochemical property of GAC mainly contributed the strengthening effect. The porous structure of GAC absorbed methane and adhered by microorganism, which enhance microorganism amount and metabolic activity. The mechanical strength of GAC scoured membrane surface to mitigate external fouling and pores absorbed EPS to reduce internal fouling. The combined effects could improve NdAMO microorganism growth and metabolism activity and finally improved nitrogen removal performance and controlled membrane fouling. These findings could deep the knowledge of NdAMO process and help extend its application potential in environment science and engineering.

Granular Sludge Coupling Nitrate/Nitrite Dependent Anaerobic Methane Oxidation with Anammox: from Proof-of-Concept to High Rate Nitrogen Removal

This work developed a novel Membrane Granular Sludge Reactor (MGSR) equipped with a gas permeable membrane module for efficient methane delivery to cultivate nitrate/nitrite dependent anaerobic methane oxidation (n-DAMO) microorganisms in granular sludge. As proof of concept, the MGSR was fed with synthetic wastewater containing nitrate and ammonium to facilitate the growth of n-DAMO microorganisms. The granular sludge of n-DAMO and Anammox was gradually developed and achieved a nitrogen removal rate of 1.08 g NO₃^--N L^-1 d^-1 and 0.81 g NH₄⁺-N L^-1 d^-1. Finally, enriched granular sludge was successfully applied for nitrogen removal from the synthetic partial nitritation effluent. The combined dominance of n-DAMO archaea, Anammox bacteria, and n-DAMO bacteria in the microbial community was confirmed by 16S rRNA amplicon sequencing. Fluorescence in situ hybridization revealed that a layered structure was formed in the granular sludge with Anammox bacteria in the outer layer and n-DAMO microorganisms in the inner layer when granules were fed with nitrite and ammonium. The high performance of nitrogen removal (16.53 kg N m^-3 d^-1) with satisfactory effluent quality (∼8 mg N L^-1) and excellent biomass retention capacity (43 g VSS L^-1) make the MGSR promising for the practical application of n-DAMO and Anammox in wastewater treatment.

Anammox and partial denitrification coupling: a review

As a new wastewater biological nitrogen removal process, anammox and partial denitrification coupling not only plays a significant role in the nitrogen cycle, but also holds high engineering application value. Because anammox and some denitrifying bacteria are coupled under harsh living conditions, certain operating conditions and mechanisms of the coupling process are not clear; thus, it is more difficult to control the process, which is why the process has not been widely applied. This paper analyzes the research focusing on the coupling process in recent years, including anammox and partial denitrification coupling process inhibitors such as nitrogen (NH₄⁺, NO₂⁻), organics (toxic and non-toxic organics), and salts. The mechanism of substrate removal in anammox and partial denitrification coupling nitrogen removal is described in detail. Due to the differences in process methods, experimental conditions, and sludge choices between the rapid start-up and stable operation stages of the reactor, there are significant differences in substrate inhibition. Multiple process parameters (such as pH, temperature, dissolved oxygen, redox potential, carbon-to-nitrogen ratio, and sludge) can be adjusted to improve the coupling of anammox and partial denitrification to modify nitrogen removal performance.

As a new wastewater biological nitrogen removal process, anammox and partial denitrification coupling not only plays a significant role in the nitrogen cycle, but also holds high engineering application value.

Reducing Cost and Environmental Impact of Wastewater Treatment with Denitrifying Methanotrophs, Anammox, and Mainstream Anaerobic Treatment

In water resource recovery facilities, sidestream biological nitrogen removal via anaerobic ammonium oxidation (anammox) is more energy and cost efficient than conventional nitrification-denitrification. However, under mainstream conditions, nitrite oxidizing bacteria (NOB) out-select anammox bacteria for nitrite produced by ammonium oxidizing bacteria (AOB). Therefore, nitrite production is the bottleneck in mainstream anammox nitrogen removal. Nitrate-dependent denitrifying anaerobic methane oxidizing archaea (n-damo) oxidize methane and reduce nitrate to nitrite. The nitrite supply challenge in mainstream anammox implementation could be solved with a microbial community of AOB, NOB, n-damo, and anammox with methane from anaerobic sludge digestion or a mainstream anaerobic membrane bioreactor (AnMBR). The cost and environmental impact of traditional nitrification/dentrification relative to AOB/anammox and AOB/anammox/n-damo systems, with and without an AnMBR, were compared with a stoichiometric model. AnMBR implementation reduced costs and emission rates at moderate to high nutrient loading by lowering aeration and sludge handling demands while increasing methane available for cogeneration. AnMBR/AOB/anammox systems reduced cost and GHG emission by up to $0.303/d/m³ and 1.72 kg equiv. CO₂/d/m³, respectively, while AnMBR/AOB/anammox/n-damo systems saw a similar reduction of at least $0.300/d/m³ and 1.65 kg equiv. CO₂/d/m³ in addition to alleviating the necessity to stop nitrification at nitrate, allowing easier aeration control.

High performance nitrogen removal through integrating denitrifying anaerobic methane oxidation and Anammox: from enrichment to application

Integrating denitrifying anaerobic methane oxidation (DAMO) with Anammox provides alternative solutions to simultaneously remove nitrogen and mitigate methane emission from wastewater treatment. However, the practical application of DAMO has been greatly limited by slow-growing DAMO microorganisms living on low-solubility gaseous methane. In this work, DAMO and Anammox co-cultures were fast enriched using high concentration of mixed sludges from various environments, and achieved nitrogen removal rate of 76.7 mg NH₄⁺-N L^-1 d^-1 and 87.9 mg NO₃^--N L^-1 d^-1 on Day 178. Subsequently, nitrogen removal rate significantly decreased but recovered quickly through increasing methane flushing frequency, indicating methane availability could be the limiting factor of DAMO activity. Thus, this work developed a novel Membrane Aerated Membrane Bioreactor (MAMBR), which equipped with gas permeable membrane for efficient methane delivery and ultrafiltration membrane for complete biomass retention. After inoculated with enriched sludge, nitrogen removal rates of MAMBR were significantly enhanced to 126.9 mg NH₄⁺-N L^-1 d^-1 and 158.8 mg NO₃^--N L^-1 d^-1 by membrane aeration in batch test. Finally, the MAMBR was continuously fed with synthetic wastewater containing ammonium and nitrite to mimic the effluent from partial nitritation. When steady state with nitrogen loading rate of 2500 mg N L^-1 d^-1 was reached, the MAMBR achieved total nitrogen removal of 2496.7 mg N L^-1 d^-1, with negligible nitrate in effluent (~6.5 mg NO₃^--N L^-1). 16S rRNA amplicon sequencing and fluorescence in situ hybridization revealed the microbial community dynamics during enrichment and application. The high performance of nitrogen removal (2.5 kg N m^-3 d^-1) within 200 days operation and excellent biomass retention capacity (8.67 kg VSS m^-3) makes the MAMBR promising for practical application of DAMO and Anammox in wastewater treatment.

Effects of vibration on anammox-enriched biofilm in a high-loaded upflow reactor

An upflow biofilm reactor was operated for 211 days to investigate the effects of vibration on anammox treatment performance. With vibration, the highest nitrogen removal rates (20 kg-N·m^-3·d^-1) were obtained on day 180. Since the vibration could directly applied on the biofilm, it could release the dinitrogen gas accumulated in the biofilm timely and reduce the internal mass transfer resistance sharply. The specific anammox activity increased by more than 3 times with a higher vibration intensity. Meanwhile, the unique random motion caused by mechanical vibration promotes the production of extracellular proteins. Moreover, the VSS reached 20.97 g·L^-1 which was 1.6 times higher than the control reactor. Such enrichment method resulted in a hard and thick anammox biofilm with a special granular morphology, and the nitrite tolerance concentration could reach 500 mg-N·L^-1. Operated with an adequate vibration intensity could maintain the biofilm thickness and conducive to improve the stability of the reactor. In addition, this technique also allowed the microorganisms inside the biofilm and those on the surface to reach the same culture conditions. Base on the batch experiments, intermittent vibration caused a decrease in energy consumption from about 7.757 (kW·h)·(kg-N)^-1 in group 0-Lv7(60-60) to 0.912 (kW·h)·(kg-N)^-1 in group 0-Lv7(5-60). Compared to the internal recycle without vibration, the energy consumption fell by a slice over 65%. Furthermore, the high-throughput sequencing results showed that the relative abundance of Candidatus Kuenenia in reactor 1 increased from 13.2% to 43.9%.