Enrichment Of Anammox Bacteria Research Articles

Start-up and Recovery Performance of ANAMMOX Reactors Under Long-term Starvation

The application of ANAMMOX technology is constrained by sluggish growth and difficulty in enriching ANAMMOX bacteria. Long-term starvation of functioning bacteria due to limited substrate supply makes the steady operation of ANAMMOX reactors more difficult. Re-examining the start-up and recovery performance of the ANAMMOX reactor and identifying its resistance mechanism are important from the standpoint of long-term starvation. By inoculating nitrifying and denitrifying sludge under various operating circumstances, the ANAMMOX reactors were successfully started. Under various start-up procedures, the tolerance mechanism and recovery performance were examined. The outcomes demonstrated that the denitrifying sludge-inoculated reactor operated steadily with a high substrate concentration and low flow rate. After 85 days of operation, the removal efficiencies of NH4+-N, NO2--N, and total nitrogen reached 98.7%, 99.3%, and 89.3%, respectively. After 144 days of starvation and 30 days of recovery, the better nitrogen removal performance was achieved at a low substrate concentration and high flow rate, and the removal efficiencies were 99.8% （NH4+-N）, 99.8% （NO2--N）, and 93.6% （total nitrogen）. During the starvation, extracellular polymeric substances wrapped the ANAMMOX bacteria and kept them intact to resist long-term starvation stress. The expression of nirS, hzsA, and hdh genes ensured the synthesis of nitrite/nitric oxide oxidoreductase, hydrazine synthase, and hydrazine dehydrogenase to maintain ANAMMOX activity. There was no significant difference in the relative abundance of ANAMMOX bacteria before and after starvation recovery. Candidatus Kuenenia had better anti-hunger ability, and the relative abundance increased by more than 86% after 30 days of recovery, confirming its tolerance to long-term starvation.

Inhibition, Recovery and Stabilization of MBR-Anammox Process: Enhancing Nitrogen Removal by Biochar-supported Nano Zero-valent Iron Adoption

Anaerobic ammonium oxidation (Anammox) is recognized as a promising option to energy-neutral wastewater treatment, yet difficulties encountered in practice due to its poor stability. This work investigated the effects of biochar-supported nano zero-valent iron (nZVI-BC) on nitrogen removal performance of anammox process. Three membrane bioreactors (MBRs) suitable for slowly growing anammox bacteria was operated for 100 days, undergoing startup, dissolved oxygen (DO) inhibition, performance recovery and stabilization periods. The results showed that nZVI-BC adoption could improve the nitrogen removal efficiency (NRE) by 5.5–27.3 % and 3.1–20.7 % and nitrogen removal rate (NRR) by 5.4–28.6 % and 3.2–22.9 %, compared with control group and biochar adoption, respectively. Throughout the experimental periods, nZVI-BC was conducive to enrich anammox bacteria and increased the functional gene copies associated with anammox metabolism. Meanwhile, co-occurrence network analysis promulgated that nZVI-BC boosted the robustness and interaction of microbial community. Furthermore, the electrochemical analysis of the extracellular polymeric substance (EPS) revealed that nZVI-BC adoption augmented the extracellular electron transport (EET) process of anammox biomass. Metagenomic sequencing revealed that nZVI-BC reinforced the complete dissimilatory nitrate reduction to ammonium (DNRA) pathway in Candidatus Brocadia, the dominant anammox bacteria, potentially reducing nitrate production and enhancing nitrogen removal. The study manifested the possibility of nZVI-BC to improve the anammox robustness and nitrogen removal performance, and provided operational guidance for its engineering application.

Strategies for efficient enrichment of anaerobic ammonia oxidizing bacteria in activated sludge

Anaerobic ammonia oxidation (Anammox) is an economical and sustainable wastewater nitrogen removal technology, and its application in the mainstream process is the inevitable trend of the development of Anammox. However, how to effectively enriching Anammox bacteria from the activated sludge remains challenging and restricts its extensive applications. In this study, the rapid and efficient enrichment of Anammox bacteria was achieved by raising the reflux ratio and nitrogen loading rate (NLR) using conventional activated sludge as the inoculant. In the screening phase (days 1–90), the reflux ratio was increased to discharge partial floc sludge, resulting in the relative abundance of Candidatus Brocadiaceae increased from 0.04% to 22.54%, which effectively reduced the matrix and spatial competition between other microorganisms and Anammox bacteria. On day 90, the stoichiometric ratio of the Anammox process closely approached the theoretical value of 1:1.32:0.26, indicating that the Anammox reaction was the primary nitrogen removal process in the system. In the enrichment phase (days 91–238), the NLR increased from 0.43 to 1.20 kgN/(m3·d) and removal efficiency was 71.89%, resulting in the relative abundance of Candidatus Brocadiaceae increased to 61.27% on day 180. The reactor operated steadily from days 444 to 498, maintaining the nitrogen removal rate (NRR) of 3.00 kgN/(m3·d) and achieving successful sludge granulation with the particle size of 392.4 µm. In short, this study provided a simple and efficient approach for enriching Anammox bacteria from the activated sludge, supporting to start an Anammox process efficiently.

Sustainable biochar application in anammox process: Unveiling novel pathways for enhanced nitrogen removal and efficient start-up at low temperature

This study explored the use of biochar to accelerate the establishment of anaerobic ammonium oxidation (anammox) reactors operating at 15 ± 1℃. Incorporating 10 g/L bamboo charcoal in S1 accelerated the start-up of anammox in 87 days, which was significantly shorter than 103 days in S0 (without biochar). After 140 days, S1 exhibited a 10.9 % increase in nitrogen removal efficiency due to a 28.9 % elevation in extracellular polymeric substances, bolstering anammox bacterial resilience. Predominant anammox bacteria (Cadidatus Brocadia and Cadidatus Jettenia) showed relative abundances of 3.19 % and 0.38 % in S1, respectively, which were significantly higher than 0.40 % and 0.05 % in S0. Biochar provides favorable habitats for the enrichment of anammox bacteria and accelerates the establishment of anammox at low temperatures. This finding holds promise for enhancing the efficiency of anammox in cold climates and advancing sustainable wastewater nitrogen removal.

Rapid establishment of municipal sewage partial denitrification-anammox for nitrogen removal through inoculation with side-stream anammox biofilm without domestication

Mainstream partial denitrification anammox was achieved through inoculation of side-stream mature partial nitritation anammox biofilm without domestication. The contribution of anammox to nitrogen removal was 29.4 %. Moreover, prolonging anoxic hydraulic retention time and introducing side-stream nitrite under different carbon/nitrogen ratios enriched anammox bacteria. The abundance of anammox bacteria increased by ∼ 10 times ((2.19 ± 0.17) × 1012 copies gene / g dry sludge) with a total relative abundance of 18.51 %. During 258 days of operation, the contribution of anammox to nitrogen removal gradually increased to 68.8 %. The total nitrogen in the effluent decreased to 8.84 mg/L with a total nitrogen removal efficiency of 76.4 % under a carbon/nitrogen ratio of 3. This paper proposes a novel way to rapidly achieve mainstream partial denitrification anammox via inoculation with side-stream mature partial nitritation anammox biofilm. This method achieves advanced nitrogen removal from municipal wastewater, even under low carbon/nitrogen ratios.

Anammox process in anaerobic baffled biofilm reactors with columnar packings: Characteristics of flow field and microbial community

The enrichment of anammox bacteria is a key issue in the application of anammox processes. A new type of reactor － anaerobic baffle biofilm reactor (ABBR) developed from anaerobic baffle reactor (ABR) was filled with columnar packings and established for effective enrichment of anammox bacteria. The flow field analysis showed that, compared with ABR, ABBR narrowed the dead zone so as to improve the substrate transferring performances. Two ABBRs with different types of columnar packings (Packings 1 and Packings 2) were constructed to culture anammox biofilms. Packings 1 consisted of the single-form honeycomb carriers while Packings 2 was modular composite packings consisting of non-woven fabric and honeycomb carriers. The effects of different types of columnar packings on microbial community and nitrogen removal were studied. The ABBR filled with Packings 2 had a higher retention rate of biomass than the ABBR filled with Packings 1, making the anammox start-up period be shortened by 21.28%. The enrichment of anammox bacteria were achieved and the dominant anammox bacteria were Candidatus Brocadia in both R1 and R2. However, there were four genera of anammox bacteria in R2 and one genus of anammox bacteria in R1, and the cell density of anammox bacteria in R2 was 95% higher than that in R1. R2 has the advantage of maintaining excellent and stable nitrogen removal performance at high nitrogen loading rate. The results revealed that the packings composed of two types of carriers may have a better enrichment effect on anammox bacteria. This study is of great significance for the rapid enrichment of anammox bacteria and the technical promotion of anammox process.

Advanced nitrogen removal from municipal wastewater by autotrophy-heterotrophy coupled anammox system in a novel simultaneous microaerobic/limited-oxygen SBR: Interspecific correlation network

Nowadays, autotrophic nitrogen removal of mainstream municipal wastewater by anammox is highly promising. However, due to the lack of a long-term stable nitrite-oxidizing bacteria (NOB) inhibition strategy, the accumulation of NO3−-N byproducts severely affects the nitrogen removal efficiency (NRE). In this study, a simultaneous autotrophy-heterotrophy coupled anammox system was developed in a microaerobic/oxygen-limited SBR through the co-induction of the regulation of aeration intensity and limited organics to achieve the optimization of the mainstream Partial nitrification-anammox (PN/A) processes. The nitrogen removal system constructed by anammox and denitrification achieved the high NRE of 90.77 ± 1.82 %. Under the autotrophic-heterotrophic multiple induction of nitrite supply (PN, partial denitrification and endogenous partial denitrification), the contribution of the nitrogen removal by anammox increased to 57.93 %. The high-throughput sequencing analysis showed that the relative abundance of AnAOB increased from 0.40 % to 0.67 %. In-situ tests assay further demonstrated that the realization of multi-channel nitrite supply facilitated the enrichment of anammox bacteria (AnAOB). The endogenous denitrifying bacterial genus Candidatus (Ca.) Competibacter was significantly enriched in the system (7.98 %, P ≤ 0.001), which enhanced the deep removal of NOX−-N and organics. Correlation network analysis indicated that closer and more balanced interspecies interactions were the key to the high efficiency and stability of the autotrophy-heterotrophy coupled anammox system. Based on the nitrite recirculation and denitrification performance, the simultaneous autotrophy-heterotrophy coupled anammox system established by the novel SBR provides a potential strategy for mainstream anammox applications.

Metagenomic insights into the mechanism for the rapid enrichment and high stability of Candidatus Brocadia facilitated by Fe(Ⅲ)

The rapid enrichment of anammox bacteria and its fragile resistance to adverse environment are the critical problems facing of anammox processes. As an abundant component in anammox bacteria, iron has been proved to promote the activity and growth of anammox bacteria in the mature anammox systems, but the functional and metabolic profiles in Fe(III) enhanced emerging anammox systems have not been evaluated. Results indicated that the relative abundance of functional genes involved in oxidative phosphorylation, nitrogen metabolism, cofactors synthesis, and extracellular polymers synthesis pathways was significantly promoted in the system added with 5 mg/L Fe(III) (R5). These enhanced pathways were crucial to energy generation, nitrogen removal, cell activity and proliferation, and microbial self-defense, thereby accelerating the enrichment of anammox bacteria Ca. Brocadia and facilitating their resistance to adverse environments. Microbial community analysis showed that the proportion of Ca. Brocadia in R5 also increased to 64.42 %. Hence, R5 could adapt rapidly to the increased nitrogen loading rate and increase the nitrogen removal rate by 108 % compared to the system without Fe(III) addition. However, the addition of 10 and 20 mg/L Fe(III) showed inhibitory effects on the growth and activity of anammox bacteria, which exhibited the lower relative abundance of Ca. Brocadia and unstable or even collapsed nitrogen removal performance. This study not only clarified the concentration range of Fe(III) that promoted and inhibited the enrichment of anammox bacteria, but also deepened our understanding of the functional and metabolic mechanisms underlying enhanced enrichment of anammox bacteria by Fe(III), providing a potential strategy to hasten the start-up of anammox from conventional activated sludge.

Carrier with cyclodextrin and quorum sensing synergy: An efficient method for selective enrichment of anammox bacteria

High-efficiency enrichment of functional bacteria is one of the biggest technical barriers to the application of anaerobic ammonium oxidation (anammox). This study combined biofilm carriers and quorum sensing to achieve rapid biomass accumulation. A biofilm carrier with biomass adsorption and quorum sensing regulation functions was developed for the rapid start-up of the reactor and enrichment of anammox bacteria (AnAOB). The nitrogen removal rates of the three reactors were further tested, and the carrier mechanism was explored. The start-up time of the reactor with the modified carriers was 28 days, which was ∼44 % shorter than that of the reactor without carriers. After 90 days of operation, the absolute abundance of total AnAOB was 3.2 times that in the control group. The modified carrier promoted the rapid adhesion of biomass through the hydrophobic cavity of cyclodextrin and induced rapid proliferation, enhancement of activity, and extracellular protein secretion of AnAOB through quorum sensing signaling molecules. Finally, a special hydrophobic biofilm with granular sludge characteristics was formed on the modified carrier through the self-assembly of hydrophobic biomass particles. Overall, we propose a novel approach to enrich anammox bacteria involving a combination of quorum sensing and biofilm carriers.

Rapid start-up strategy and microbial population evolution of anaerobic ammonia oxidation biofilm process for low-strength wastewater treatment

The implementation of the anaerobic ammonium oxidation (anammox) process in treating low-strength wastewater is limited by the difficulty in enriching anammox bacteria (AnAOB). Here, the first enrichment of AnAOB at a high nitrogen (N) loading rate (NLR) as a strategy was proposed to achieve the rapid start-up of the anammox biofilm process treating low-strength wastewater. The long-term stability of the anammox biofilm process after start-up operating at a low NLR of 0.2–0.4 kg N/(m3⋅d) was evaluated. Results showed that the N removal efficiency was up to 75 % under a low NLR of 0.2 kg N/(m3⋅d) condition. Low-strength organic matter promoted the metabolic coupling between partial denitrifying bacteria (PDB) and AnAOB. The genus Candidatus Brocadia as AnAOB (18 %-27 %) can coexist with Limnobacter (PDB, 9 %-12 %) for efficient N removal. This study offers a rapid start-up strategy of anammox biofilm process in treating low-strength wastewater.

Rapid enrichment of anammox bacteria for low-strength wastewater treatment: Role of influent nitrite and nitrate ratios in sequencing batch reactors (SBRs)

Anaerobic ammonium oxidation (Anammox) bacteria (AnAOB) have a long doubling time, which represents one of the key challenges for starting up anammox-based reactors. This study investigated the effect of varied nitrite/nitrate ratios on the anammox reactor startup process using five lab-scale anammox sequencing batch reactors (SBRs) (R1-R5). Nitrate addition significantly accelerated AnAOB enrichment startup, particularly during nitrite accumulation phase. The total start-up time was shortened by 55–71 days, compared to the reactor without nitrate. In R1 (nitrite/nitrate=10:0), anammox contributed the highest nitrogen removal percentage (91%), while R2 (nitrite/nitrate=7:3), with nitrate added, exhibited the highest anammox activity (53.84 mg NH4+-N/g VSS/day) in the steady-state phase. As nitrate proportions increased (R3-R5), anammox activity gradually declined due to limited available COD required for the conversion of NO3- to NO2-. Furthermore, it was found that nitrate-added improved the sludge settleability, with lower SVI30. 16S rRNA gene revealed that Ca. Brocadia was the predominant AnAOB in R1, R2 and R3, where nitrite was the primary NOx--N species (≥50%) in the influent. While in the reactor with low concentration of nitrite (R4: nitrite/nitrate=3:7), Ca. Kuenenia was the dominant AnAOB. This study successfully established a complex and balanced ecosystem with multi-species coexistence, where AnAOB served as the primary functional group on nitrogen removal, supported by denitrification bacteria and dissimilatory nitrate reduction to ammonium (DNRA) bacteria. This study proposes a rapid start-up strategy for the anammox process, which overcomes the bottleneck of long start-up time and helps to promote the application of anammox in wastewater treatment.

Enhancing anammox bacteria enrichment in integrated fixed-film activated sludge partial nitritation/anammox process via floc retention control

A promising technology for partial nitritation/anammox (PN/A) processes to treat ammonium wastewater is integrated fixed-film activated sludge (IFAS). For practical applications, achieving efficient enrichment of anammox bacteria (AnAOB) remains a challenge. In this study, membranes were temporarily used to separate solid and liquid components to induce changes in the mixed liquor suspended solids of the flocs. With membrane separation, AnAOB proliferated rapidly with a seven-fold increase in the maximum specific growth rate (μ) (from 0.009 to 0.072 d−1) and a three-fold increase in the nitrogen removal rate (from 0.91 to 3.20 kg N/(m3·d)). Moreover, microbial community analysis showed significant changes in bacterial species richness and diversity with and without membrane separation. Overall, the regulation of flocs significantly influenced the microbial community structure of both flocs and biofilms leading to improved nitrogen removal efficiency in the IFAS-PN/A system.

Combination of Sequencing Batch Operation and A/O Process to Achieve Partial Mainstream Anammox: Pilot-Scale Demonstration and Microbial Ecological Mechanism.

In this study, sequencing batch operation was successfully combined with a pilot-scale anaerobic biofilm-modified anaerobic/aerobic membrane bioreactor to achieve anaerobic ammonium oxidation (anammox) without inoculation of anammox aggregates for municipal wastewater treatment. Both total nitrogen and phosphorus removal efficiencies of the reactor reached up to 80% in the 250-day operation, with effluent concentrations of 4.95 mg-N/L and 0.48 mg-P/L. In situ enrichment of anammox bacteria with a maximum relative abundance of 7.86% was observed in the anaerobic biofilm, contributing to 18.81% of nitrogen removal, with denitrification being the primary removal pathway (38.41%). Denitrifying phosphorus removal (DPR) (40.54%) and aerobic phosphorus uptake (48.40%) played comparable roles in phosphorus removal. Metagenomic sequencing results showed that the biofilm contained significantly lower abundances of NO-reducing functional genes than the bulk sludge (p < 0.01), favoring anammox catabolism in the former. Interactions between the anammox bacteria and flanking community were dominated by cooperation behaviors (e.g., nitrite supply, amino acids/vitamins exchange) in the anaerobic biofilm community network. Moreover, the hydrolytic/fermentative bacteria and endogenous heterotrophic bacteria (Dechloromonas, Candidatus competibacter) were substantially enriched under sequencing batch operation, which could alleviate the inhibition of anammox bacteria by complex organics. Overall, this study provides a feasible and promising strategy for substantially enriching anammox bacteria and achieving partial mainstream anammox as well as DPR.

Advances in the Efficient Enrichment of Anammox Bacteria

Anaerobic ammonia oxidation (anammox) process is known as a low-energy and environmentally friendly process for treating nitrogen-rich wastewater. Anammox bacteria are the key microorganisms to achieve this biological process. However, the efficient enrichment of anammox bacteria has been a bottleneck for its practical application because of their slow growth and high sensitivity, and no pure culture has been found. Therefore, the development of efficient anammox bacterial enrichment techniques is of great theoretical and application value. Solving the problem of anammox bacterial activity and improving the process denitrification performance is one of the current research hotspots. In this paper, three aspects of anammox bacteria are described in terms of their physiological properties, environmental influencing factors, and short-term starvation tolerance; a systematic review of the latest research progress in accelerating the activity of anammox bacteria using enrichment strategies for process regulation, the construction of granulation models, suspended sludge biomass management, and strain preservation. Finally, the future frontier development of anammox bacteria was discussed and foreseen.

The Recovery of a Sequencing Biofilm Batch Reactor—Anammox System: Performance, Metabolic Characteristics, and Microbial Community Analysis

The mainstream application of the anammox process is often hindered by its long recovery phase and instability under disturbance. In this study, a lab-scale anammox sequencing biofilm batch reactor (SBBR) was rapidly recovered within 85 days by gradually increasing the influent nitrogen concentration, and the total inorganic nitrogen (TIN) removal efficiency achieved 83.44 ± 0.03%. During the recovery process, the nitrogen removal rate (NRR) increased from 0.05 to 0.34 kg/(m3·d), with the nitrogen loading rate (NLR) changing from 0.08 to 0.40 kg/(m3·d) in the anammox system. The activities of hydrazine oxidase (HZO) in the biofilm also increased from 0.17 to 10.80 μmol Cyt-c/(g VSS·s). Also, the dominant anammox genera in the biofilm were Candidatus Kuenenia and Candidatus Brocadia. The results of this study suggested that an SBBR–anammox system filled with a microbial carrier could facilitate the enrichment of anammox bacteria and contribute to performance recovery.

Enhanced anammox through endogenous partial denitrification/anammox (EPDA) granular sludge: Granule formation, treatment performance, and multi-perspective microbial analysis

The direct application of anammox to wastewater treatment is valuable, but the enrichment of anammox bacteria (AnAOB) is complicated due to the malignant competition of heterotrophic bacteria. Here, we propose the use of endogenous partial denitrification/anammox (EPDA) granular sludge to enhance anammox while achieving simultaneous removals of nitrogen and phosphorus. After operation for 330 days, the EPDA granules were successfully cultured with the mean size of 0.89 mm. Nitrogen and phosphorus were efficiently removed with the effluent total nitrogen (TN) and PO43--P of 6.68±0.41 mg/L and 0.06±0.03 mg/L, respectively. Anammox took a leading role in the removal of TN with a contribution of 75±3%. Moreover, high-throughput sequencing (16S rRNA) results showed that AnAOB could coexist harmoniously with glycogen accumulating organisms (GAOs) and polyphosphate accumulating organisms (PAOs) in the EPDA granules, whereas mature EPDA granules could promote in situ enrichment of AnAOB. Microbial stratification analysis of the EPDA granule found that the inner layer was resided with AnAOB, while the outer layer was employed with GAOs and PAOs. Metagenomic and metatranscriptomic analyses found that the nitrate reductase (1150.56 RPM) was 4.6 times of nitrite reductase (249.98 RPM) at the transcriptome level. Moreover, the key enzymes related to anammox (hydrazine synthase and hydrazine dehydrogenase) were much higher than the other nitrogen conversion functional genes at the transcriptome level, confirming the main role of AnAOB in the removal of nitrogen. This study presents a novel strategy for the application of anammox from EPDA granular sludge.

Improving anammox activity and reactor start-up speed by using CO2/NaHCO3 buffer

Anammox bacteria grow slowly and can be affected by large pH fluctuations. Using suitable buffers could make the start-up of anammox reactors easy and rapid. In this study, the effects of three kinds of buffers on the nitrogen removal and growth characteristics of anammox sludge were investigated. Reactors with CO2/NaHCO3 buffer solution (CCBS) performed the best in nitrogen removal, while 4-(2-hydroxyerhyl)piperazine-1-ethanesulfonic acid (HEPES) and phosphate buffer solution (PBS) inhibited the anammox activity. Reactors with 50 mmol/L CCBS could start up in 20 days, showing the specific anammox activity and anammox activity of 1.01±0.10 gN/(gVSS·day) and 0.83±0.06 kgN/(m3·day), respectively. Candidatus Kuenenia was the dominant anammox bacteria, with a relative abundance of 71.8%. Notably, anammox reactors could also start quickly by using 50 mmol/L CCBS under non-strict anaerobic conditions. These findings are meaningful for the quick start-up of engineered anammox reactors and prompt enrichment of anammox bacteria.

Up-flow dual-loop anammox system treating mature landfill leachate: ultra-efficient nitrogen removal, anammox granules formation, and functional divergence

Achieving the effective retention and rapid enrichment of anammox bacteria (AnAOB) remains a challenge in landfill leachate treatment systems. The application of the anammox process is also restricted by an inadequate supply of nitrite and poor resistance to adverse environments. To overcome these obstacles, an up-flow dual-loop anammox (UDLA) system treating mature landfill leachate was established, based on partial nitrification, anammox, and partial denitrification (PNAPD) technology. The nitrogen removal efficiency and nitrogen loading rate reached 92.9 ± 1.5% and 0.4 kg N/m3/d, and isotope tracing tests demonstrated that 88.2 ± 6.5%-93.9 ± 3.9% of the nitrogen loss contributed by anammox pathway. Under the up-flow dual-loop strategy, anammox granules were successfully cultivated when flux ratios of effluent/influent and produced gas/influent were maintained at 1640.0%, and 250.0%, respectively. The proportion of medium granules (500–1000 μm) with the highest PNAPD activity increased from 0 to 24.9%, whereas the percentage of floc (0–200 μm) reduced from 98.4% to 23.3%. The mechanism of anammox granules formation in the UDLA system was revealed by multidimensional analysis. Candidatus_Brocadia_sapporoensis (13.3%-13.5%), Candidatus_Kuenenia_stuttgartiensis (2.0%-4.8%), and Candidatus_Brocadia_sp. (0.9%-1.1%) were the predominant anammox species, enriched in medium and macro granules. Metagenomic sequencing confirmed the functional divergence of nitrogen and carbon metabolism among the size-fractioned granules, possible functions of specific species, and gene distribution in the nitrogen metabolism pathway. The abundant GlnA, GltB(D), GdhA, GudB (GDH2), and GLUD1_2 genes might promote the synthesis of adhesive proteins and further facilitate microbial aggregation. This study enhanced the comprehension of anammox granules formation and showed important implications for leachate treatment in engineering.

Ecological interactions and the underlying mechanism of anammox and denitrification across the anammox enrichment with eutrophic lake sediments

BackgroundIncreasing attention has recently been devoted to the anaerobic ammonium oxidation (anammox) in eutrophic lakes due to its potential key functions in nitrogen (N) removal for eutrophication control. However, successful enrichment of anammox bacteria from lake sediments is still challenging, partly due to the ecological interactions between anammox and denitrifying bacteria across such enrichment with lake sediments remain unclear.ResultsThis study thus designed to fill such knowledge gaps using bioreactors to enrich anammox bacteria with eutrophic lake sediments for more than 365 days. We continuously monitored the influent and effluent water, measured the anammox and denitrification efficiencies, quantified the anammox and denitrifying bacteria, as well as the related N cycling genes. We found that the maximum removal efficiencies of NH4+ and NO2− reached up to 85.92% and 95.34%, respectively. Accordingly, the diversity of anammox and denitrifying bacteria decreased significantly across the enrichment, and the relative dominant anammox (e.g., Candidatus Jettenia) and denitrifying bacteria (e.g., Thauera, Afipia) shifted considerably. The ecological cooperation between anammox and denitrifying bacteria tended to increase the microbial community stability, indicating a potential coupling between anammox and denitrifying bacteria. Moreover, the nirS-type denitrifiers showed stronger coupling with anammox bacteria than that of nirK-type denitrifiers during the enrichment. Functional potentials as depicted by metagenome sequencing confirmed the ecological interactions between anammox and denitrification. Metagenome-assembled genomes-based ecological model indicated that the most dominant denitrifiers could provide various materials such as amino acid, cofactors, and vitamin for anammox bacteria. Cross-feeding in anammox and denitrifying bacteria highlights the importance of microbial interactions for increasing the anammox N removal in eutrophic lakes.ConclusionsThis study greatly expands our understanding of cooperation mechanisms among anammox and denitrifying bacteria during the anammox enrichment with eutrophic lake sediments, which sheds new insights into N removal for controlling lake eutrophication.CVCoauCFapAiN4c5Sdx-EeVideo

Complete nitrogen removal from low-strength wastewater via double nitrite shunt coupling anammox and endogenous nitrate respiration: Functional metabolism and electron transport

Autotrophic nitrogen removal processes based on anammox are facing huge challenges of high effluent quality in wastewater treatment. In this study, a novel hybrid system of anammox coupled with heterotrophic endogenous metabolisms was developed in a single-stage bioreactor to treat real domestic wastewater. Complete nitrogen removal was achieved at a low carbon to nitrogen (C/N) ratio of 2.8 and more than 95.2% nitrogen removal was maintained under an extremely low C/N ratio of 1.9. The nitrite shunt supplied by dual partial pathways (partial nitritation and endogenous partial denitratation) guaranteed the anammox activity with a high contribution to nitrogen removal above 60%. While endogenous denitrification (ED) and denitrifying phosphorus removal (DPR) both participated in nitrate respiration, contributing more than 28% and 9% to nitrogen removal, respectively. The coexistence and enrichment of anammox bacteria (Ca. Brocadia, 0.9%), glycogen accumulating organisms (Ca. Competibacter, 6.4%) and phosphorus accumulating organisms (Dechloromonas, 3.9% and Ca. Accumulibacter, 0.7%) contributed to the co-metabolism of carbon, nitrogen and phosphorus. The functional genes encoding the above metabolism were highly correlated with the dominant strains, indicating that the multiple pathways of carbon and nitrogen metabolism supported the continuous supply of electrons required for nitrogen removal. This study puts forward a novel complete nitrogen removal process by successfully coupling autotrophic and endogenous heterotrophic metabolism.