Metagenomic insights into the effects of volatile fatty acids on microbial community structures and functional genes in organotrophic anammox process

Screening, identification, and application of anaerobic ammonia oxidizing bacteria in activated sludge systems: A comprehensive review

Anaerobic ammonium oxidation (Anammox) has garnered significant attention due to its ability to eliminate the need for aeration and supplementary carbon sources in biological nitrogen removal process, relying on the capacity of anaerobic ammonium oxidizing bacteria (AnAOB) to directly convert ammonium and nitrite nitrogen into nitrogen gas. This review consolidates the latest advancements in AnAOB research, outlining the mechanisms and enzymatic processes of Anammox, and summarizing the molecular biological techniques used for studying AnAOB, such as 16s rRNA sequencing, qPCR, and metagenomic sequencing. Additionally, it also overviews the currently identified AnAOB species and their distinct metabolic traits, while consolidating strategies to improve their performance. It further delineates coupled processes that utilize Anammox technology, offering practical insights for process selection. Eventually, the review concludes by suggesting future research directions and highlighting critical areas for further investigation. This review serves as a theoretical reference for the enrichment and cultivation of AnAOB, environmental impact management, and the selection of effective treatment processes.

Insight into the performance and fouling characteristics of submerged ceramic membrane bioreactor in wastewater treatment

Submerged membrane bioreactor (SMBR) is a promising technology in municipal wastewater treatment, but the membrane fouling has restricted its development. In this study, an integrated submerged ceramic membrane bioreactor (C-SMBR) was constructed to treat domestic wastewater, and the characteristics of membrane fouling and the microbial community structure were investigated. The results showed that the average removal efficiencies of COD, TN, NH4+-N reached 94.97%, 61.69% and 71.61% respectively, under different ammonia nitrogen loading rate (NLR). The increase of soluble microbial products (SMP) and extracellular polymeric substances (EPS) in the suspension jointly accelerated the membrane fouling process, resulting in an increase in the trans-membrane pressure (TMP), which led to membrane fouling. Microbial community structure analysis showed that the dominant phylum bacteria were Patescibacteria, Proteobacteria, Actinobacteria, Bacteroidota and Chloroflexi, and the dominant class bacteria were Saccharimonadia, γ-proteobacteria, Actinobacteria, Bacteroidia, Anaerolineae, α-proteobacteria, etc. In summary, the conditions, microbial information and membrane fouling characteristics of wastewater treated by C-SMBR obtained in this study can provide reference and data support for further promotion and improvement of the application of C-SMBR and membrane fouling control.

Nitrate formation in anammox process: Mechanisms and operating conditions

Anaerobic ammonium oxidation (anammox) is an energy-efficient technology for wastewater nitrogen removal. However, the byproduct nitrate has hindered development and application of anammox process. Meanwhile, the knowledge of nitrate formation during anammox process is insufficient, which prohibits high nitrogen removal. This review firstly summaries and discusses valuable findings on nitrate formation, including molecular mechanism of nitrate production, microbial pathway of nitrate reduction and its net formation. Specially, influences of operating conditions on mechanisms and patterns of nitrate formation are analyzed. Then, based on nitrate formation mechanism, current strategies of nitrate removal from anammox process are reevaluated. Finally, the key knowledge gaps and further process development are presented. Overall, this review sheds light on the understanding of nitrate formation of anammox process, which would further facilitate and optimize the process design and operation for high performance nitrogen removal.

Comparative impact analysis of nitrate reduction by typical components of natural organic compounds in magnetite-bearing riparian zones

As the key interface, the nitrate removal capacity of riparian zones is receiving close attention. Although naturally occurring organic compounds in this environment play a pivotal role in shaping microbial communities and influencing the nitrate removal capacity, the relevant research is inadequate. Given the complexity of riparian environments, in this study, we added representative natural organic matter (fulvic acid, butyric acid, naphthalene, starch, and sodium bicarbonate) as carbon conditions and incorporated magnetite to simulate riparian zone components. The study investigated the nitrate degradation efficiency and microbial responses under different natural carbon conditions in real iron-containing environments. Butyric acid exhibited the most efficient nitrate reduction, followed in descending order by naphthalene, starch, sodium bicarbonate, and humic acid. However, this did not imply that butyric acid efficiently removed nitrogen; instead, the nitrogen would circulate in the environment in the form of ammonium. Denitrification and DNRA were the primary drivers of nitrate reduction in each system, while naphthalene and humic acid systems also exhibited nitrification and mineralization. Nitrogen-fixing bacteria represent a unique microbial community in the butyrate system. Further, the synergistic degradation of naphthalene and nitrate demonstrated significant potential applications. High-throughput sequencing revealed that carbon conditions exerted selective pressure on microorganisms, driving Fe (Ⅱ)/Fe (Ⅲ) transformation by shaping the microbial community structure and influencing the nitrogen cycling process.

Arginine enhances activity of anammox consortia and process stability with increased nitrogen loading

Cross-feeding based on amino acids metabolism is an important strategy by which anammox bacteria and the co-existing heterotrophs facilitate their own growth and survival. Arginine is one of the necessary amino acids required for bacterial protein biosynthesis but whether adding arginine could benefit growth of anammox bacteria remains unknown. In this study, arginine was supplemented at dose of 5 mg·L-1 to promote the nitrogen removal performance of anammox bioreactors under varied loading rates. The results showed that nitrogen removal efficiency increased by 10.2 % under higher loading rates. Arginine addition substantially simulated the secretion of extracellular proteins and polysaccharides within anammox consortia as a strategy against unfavorable conditions. Canditatus Kuenenia dominated the anammox consortia and their 16S rRNA abundance and anammox-related functional genes were significantly increased by up to 0.42 times and 5.81 times, respectively. The findings of this study provided a feasible strategy to improve the performance of anammox reactors with arginine supplementation.

An integrated meta-omics approach reveals the different response mechanisms of two anammox bacteria towards fluoroquinolone antibiotics

The emerging fluoroquinolone antibiotics (FQs) are highly influential in nitrogen removal from livestock wastewater. However, beyond the capability of nitrogen removal, little is known about the molecular mechanisms (e.g., shift of core metabolism and energy allocation) of different anaerobic ammonium-oxidizing bacteria (AnAOB) under continuous FQ stress. This study investigated the effects of ciprofloxacin, ofloxacin and their mixture at concentrations detected in livestock wastewater on two key anammox species in membrane bioreactors. It was found 20 μg/L FQs promoted nitrogen removal efficiency and community stability, and42-51 % of FQs were removed simultaneously. Integrated meta-omics analysis revealed varied gene expression patterns between the two dominant AnAOB, Candidatus Brocadia sapporoensis (B AnAOB) and Candidatus Kuenenia stuttgartiensis (K AnAOB). The nitrogen metabolic processes were bolstered in B AnAOB, while those involved in anammox pathway of K AnAOB were inhibited. This difference was tentatively attributed to the up-regulation of reactive oxygen species scavenger genes (ccp and dxf) and FQ resistance gene (qnrB72) in B AnAOB. Importantly, most enhanced core biosynthesis/metabolism of AnAOB and close cross-feeding with accompanying bacteria were also likely to contribute to their higher levels of biomass yield and metabolism activity under FQ stress. This finding suggests that B AnAOB has the advantage of higher nitrogen metabolism capacity over K AnAOB in livestock wastewater containing FQs, which is helpful for efficient and stable nitrogen removal by the functional anammox species.

Electron transfer mechanism of intracellular carbon-dependent DNRA inside anammox bacteria

Generally, anaerobic ammonium oxidation (anammox) converts nitrite (NO2-) and ammonium (NH4+) to nitrogen gas (N2) but generates some nitrate (NO3-) (equivalent to 11% of inlet total nitrogen (TN)). Although it reported that anammox bacteria could degrade NO3- via dissimilatory nitrate reduction to ammonium (DNRA) pathway using the intracellular carbon as the electron donor, it is still unclear the specific electron transfer mechanism in this intracellular carbon-dependent DNRA inside anammox bacteria, and whether the sole anammox bacteria could achieve higher TN removal efficiency more than the theoretical maximum of 89%. In this study, transcriptome analysis and metabolic inhibitor experiments demonstrated that NADH generated from the decomposition of the intracellular carbon (glycogen) supplied electrons for the NO3-conversion; the electrons were transferred from NADH to nitrate reductase (Nar) and nitrite reductase forming ammonium (NrfA) from ubiquinone (UQ) and complex III, respectively. Combining the intracellular carbon-dependent DNRA with normal anammox process, an average TN removal efficiency of 95% was achieved by the sole anammox bacteria in a sequencing batch reactor. Fluorescent in situ hybridization (FISH) images and real-time fluorescence quantitative PCR (qPCR) results illustrated anammox bacteria could survive and proliferate in the SBR. Our work improved the understanding of the electron transfer mechanism inside anammox bacteria, and further exploit its potential in nitrogen pollutants removal.

Performance and microbial community analysis on nitrate removal in a bioelectrochemical reactor

In this experiment, we took reflux sludge, sludge from an aeration tank, and soil from roots as microbial inoculating sources for an electrochemical device for denitrification with high-throughput sequencing on cathodic biofilms. The efficiency of nitrate nitrogen removal using different microbial inoculates varied among voltages. The optimal voltages for denitrification of reflux sludge, aeration tank sludge, and root soil were 0.7V, 0.5V, and 0.5V, respectively. Further analysis revealed that the respective voltages had a significant effect upon microbial growth from the respective inoculates. Proteobacteria and Firmicutes were the main denitrifying microbes. With the addition of low current (produced by the applied voltage), the Chao1, Shannon and Simpson indexes of the diversity of microorganisms in soil inoculation sources increased, indicating that low current can increase the diversity and richness of the microorganisms, while the reflux sludge and aeration tank sludge showed different changes. Low-current stimulation decreased microbial diversity to a certain extent. Pseudomonas showed a trend of decline with increasing applied voltage, in which the MEC (microbial electrolysis cell) of rhizosphere soil as inoculates decreased most significantly from 77.05% to 12.58%, while the MEC of Fusibacter showed a significant increase, and the sludge of reflux sludge, aeration tank and rhizosphere soil increased by 31.12%, 18.7% and 34.6%, respectively. The applied voltage also significantly increased the abundance of Azoarcus in communities from the respective inoculates.

Alleviating acid inhibition via bentonite supplementation during acidulated swine manure anaerobic digestion: Performance enhancement and microbial mechanism analysis

Swine manure is usually transmitted by the "collection-storage-transport" mode of the biogas project. However, this particular application pattern results in high volatile fatty acids (VFAs) concentration due to the long transition time in the "collection-storage-transport" process. In this work, acidulated swine manure anaerobic digestion (AD) with bentonite supplementation was firstly investigated with an expectation of acid alleviation, performance enhancement and microbial mechanism. Results indicated that the methane production rate in the 20 g/L bentonite-added digester was 2.87 fold higher than that of the control digester. Chemical oxygen demand (COD) removal rate was elevated by 140.1% via bentonite supplementation. Besides, the rapid decrease of VFAs and ammonia indicated that bentonite supplementation could offer buffering capacity and alleviate acid inhibition. Microbial community analysis revealed that acetoclastic methanogenesis (Methanosaeta and Methanosarcina) was the predominant methanogenesis pathway in this AD system. Syntrophic acetate oxidation (SAO) bacteria were discovered in the bentonite-added digester, and they converted acetate into H₂/CO₂ to support hydrogenotrophic methanogenesis. This study could offer guidance for acidulated swine manure AD in the practical biogas project.

A novel multistage anoxic/aerobic process with sludge regeneration zone (R-MAO) for advanced nitrogen removal from domestic sewage

To achieve advanced nitrogen removal from actual municipal sewage, a novel multistage anoxic/aerobic process with sludge regeneration zone (R-MAO) was developed. The reactor was used to treat actual domestic sewage and the nitrogen removal capacity of the sludge regeneration zone (R zone) was investigated during the long-term operation. The best performance was obtained at the R zone's Oxidation-Reduction Potential (ORP) of -50±30 mV and hydraulic residence times (HRT) of 1.2 hr. The average effluent COD, TN, NH₄⁺-N and NO₃^--N of the R-MAO process were 18.0±2.3, 7.5±0.6, 1.0±0.5 and 4.6±0.4 mg/L, respectively, with the corresponding removal efficiency of COD, TN and NH₄⁺-N were 92.9%±1.0%, 84.1%±1.5% and 97.5%±1.1%. Compared to the sole MAO system, the TN removal efficiency of the R-MAO increased by 10.1%. Besides, under the optimal conditions, the contribution of the R zone in the R-MAO that removal COD, TN, NH₄⁺-N and NO₃^--N were 0.36, 0.15, 0.032 and 0.82 g/day. High-throughput sequencing results showed that uncultured_bacterium_f_Burkholderiaceae (5.20%), OLB8 (1.04%) and Ottowia (1.03%) played an important role in denitrification in the R zone. This study provided effective guidance for the design and operation of the R-MAO process in domestic sewage treatment.

Temperature-regulated and starvation-induced refractory para-toluic acid anaerobic biotransformation

Little research was focused on the anerobic degradation of refractory para-toluic acid at present. Thus, temperature-regulated anaerobic system of para-toluic acid fed as sole substrate was built and investigated via microbiota, metabolism intermediates, and function prediction in this study. Results showed that low methane yield was produced in para-toluic acid anaerobic system at alkaline condition. And the causes were owing to anaerobic methane oxidation and potentially H2S production at 37 °C, N2 production by denitrification before starvation and propionic acid occurrence after starvation at 27 °C, and production of N2 and free ammonia, and accumulation of acetic acid at 52 °C. Simultaneously, hydrogenotrophic methanogenesis dependent on syntrophic acetate oxidation (SAO) was predominant, facilitating the removal of para-toluic acid at 52 °C. Moreover, the key intermediate changed from phthalic acid of 37 °C and 27 °C before starvation to terephthalic acid of 52 °C. Starvation promoted removal of para-toluic acid through benzoyl-CoA pathway by Syntrophorhabdus, enrichment of syntrophic propionate degraders of Bacteroidetes and Ignavibacteriaceae, and increase of methylotrophic methanogens.

The organics-mediated microbial dynamics and mixotrophic metabolisms in anammox consortia under micro-aerobic conditions

The engineering applications of mainstream anaerobic ammonium oxidation (anammox) have raised increasing attention due to its energy-efficient, however, the organics-mediated microbial dynamics and mixotrophic metabolisms in anammox consortia under micro-aerobic conditions are still elusive. Here, the response of the anammox process to sodium acetate and glucose at a C/N ratio ranging from 0 to 0.5 was investigated under micro-aerobic conditions, respectively. Results showed that the additional glucose could promote the nitrogen removal efficiency (NRE) and nitrogen removal rate (NRR) of anammox processes at a low C/N ratio (0.3), representing 84.00% and 0.53 N kg·m^-3·d^-1. The introduced organics could regulate the diversity of the microbial community and simplify the microbial relationship in anammox consortia. Anammox could not benefit from the introduced sodium acetate, while glucose could effectively enhance the anammox activity and microbial interactions in anammox consortia. Glucose might also stimulate the mixotrophic mechanism of Ca. Kuenenia, further promotes the proliferation of anammox sludge under micro-aerobic conditions. This study reveals that glucose could positively mediate microbial interactions and mixotrophic metabolism in anammox consortia under micro-aerobic conditions, which raises a new horizon for the proliferation of anammox sludge for mainstream engineering applications.

Six complex microbial inoculants for removing ammonia nitrogen from waters

To determine the effect of microbial inoculants on the removal of ammonia nitrogen (NH₄ ⁺ -N), six different complex microbial inoculants were studied. In this study, their effectiveness on NH₄ ⁺ -N removal was compared, and their microbial community composition was determined. High-throughput sequencing results showed that Proteobacteria and Firmicutes were the dominant phyla in six samples. Before the reaction, Bacillus, Cyanobacteria, and Mitochondria genera were the dominant genera. The dominant genera were significantly different after the reaction with the addition of bacterial agents. The six water samples were Massilia, Escherichia-Shigella, Brevibacillus, Mitsuaria, Bacillus, and Ralstonia. Among the six complex microbial inoculants, "Gandu nitrifying bacteria (NR₄ )" have the best removal effect on NH₄ ⁺ -N. In addition, the removal effect of six different bacterial agents on chemical oxygen demand (COD) was compared. The results showed that "Bilaiqing ammonia nitrogen removal bacteria agent (NR₅ )" has the best removal effect on COD. Single-factor experiments suggested that the optimal conditions for NR₄ bacteria were pH 7, 30°C, 1.0 g/L of bacterial agent dosage and a wide range of NH₄ ⁺ -N from 30 to 300 mg/L. PRACTITIONER POINTS: The nitrogen removal effects of six different microbial agents were compared. High-throughput sequencing provides important insights into the study of ammonia nitrogen removal by microbial communities. Analysis of six different complex bacterial agents by high-throughput sequencing. The relative abundance of microorganisms is not proportional to the ability to remove NH₄ ⁺ -N Good application effect in urban landscape water body.

Effect of sulfamethazine on anaerobic digestion of manure mediated by biochar

Antibiotic contamination from animal production and wastewater treatment process will release antibiotic resistant genes to the environment and potentially threaten human health. Meanwhile, the residual antibiotic in manure could have inactive impacts on anaerobic digestion (AD). This study explores the effect of sulfamethazine on manure AD mediated by biochar. The results show that biochar weakens the adverse effects of sulfamethazine on AD by adsorption sulfamethazine during the initial stage (0-3 days) of AD and promoting the growth of hydrolytic bacteria (especially Firmicutes and Bacteroidetes) and methanogens (especially Methanothrix and Methanosarcina). Besides, the presence of biochar improves the biogas production capacity of AD and promotes microbial diversity and community richness. Thus, the addition of biochar greatly reduces sulfamethazine and is testified to be a desirable strategy to mitigate the inhibition of sulfamethazine on AD.

Unveiling the effect of acetate on the interactions of functional bacteria in an anammox biofilm system

Biodegradable organics make an important impact on anaerobic ammonium oxidation (anammox) system. In this study, acetate was selected as a typical biodegradable organic, and its effect on the anammox biofilm system was comprehensively discussed from the macro and micro perspectives. Under a low influent concentration of acetate (<240 ± 10 mg/L), the best total nitrogen (TN) removal performance was 96%, but it decreased to 83% when the acetate concentration increased to 350 ± 20 mg/L. With the addition of acetate, the relative abundance of the family Brocadiaceae, which contains all known anammox bacteria, gradually increased from 7.97% to 12.79%, indicating that the presence of acetate promoted enrichment of anammox bacteria in the biofilm. Metagenomic analysis further demonstrated that an appropriate concentration of acetate helps to increase the abundances of the key enzymes related to nitrogen removal and enhance the metabolism of anammox and denitrification, thereby promoting the synergy of anammox and denitrifying bacteria. Hydrazine synthase (hzs), which is unique to the anammox process, was detected in association with the genera Candidatus Kuenenia, Candidatus Jettenia and Candidatus Brocadia, with its abundance increasing from 13268 (with no addition of acetate) to 19186 (with acetate addition of 240 ± 10 mg/L). This work provides a deeper understanding of the intrinsic interactions between functional bacteria in an anammox biofilm system.

Analyzing the effect of storage conditions on anammox recovery performance from the perspectives of time, temperature and biomass form

In this study, the effects of different storage conditions, such as temperature, storage time and biomass form, on the properties of anaerobic ammonia oxidation (anammox) were investigated along with the identification of the process mechanism. The results showed that the influence of storage time on anammox properties was stronger than that of storage temperature and biomass form. Also, the anammox recovery activity at 15 °C was better than that at 4 °C, and the anammox recovery activity of immobilized filler was better than that of anammox granular sludge (AnGS). Although cryogenic storage severely damaged anammox activity, lower loss of extracellular polymeric substances maintained the AnGS structure. The maximum recovery of specific anammox activity at 15 °C for the immobilized filler was observed to be 109%. In addition, intermittent substrate supplementation weakened the adverse effect of long-term storage on anammox activity, and was conducive to maintaining stable flora composition and promoting regeneration of anammox bacteria (AnAOB). High-throughput sequencing analysis showed that starvation resulted in increased community diversity, and the functional bacteria Candidatus Brocadia was observed to be more tolerant to starvation than Candidatus Kuenenia. Finally, principal component analysis was used to explain the complex relationship between process performance and preservation conditions. Based on the results of this work, it is recommended to preserve AnAOB in the form of immobilized filler at 15 °C and supplement substrate intermittently during long term storage. This study provides an economical and robust strategy for the short-term and long-term preservation of AnAOB.

Biochar-mediated DNRA pathway of anammox bacteria under varying COD/N ratios

Coupling dissimilatory nitrate reduction to ammonium (DNRA) pathway with anammox process has a prominent advantage in enhancement of nitrogen removal. However, the anammox bacteria driven-DNRA is difficult to proceed at normal autotrophic circumstance. Herein, for the first time, biochar (prepared by bamboo) was used as a mediator to stimulate the DNRA pathway of anammox bacteria under varying chemical oxygen demand (COD) to nitrogen (COD/N) ratios (0.1-0.7), and the underlying stimulation mechanism was elucidated by metagenomics sequencing analysis. Results showed that biochar addition (10 g/L) stimulated DNRA pathway of anammox bacteria at low COD/N ratios (0.1-0.5), thus enhancing the nitrogen removal efficiency (NRE) of the anammox system by 7.2%-16.4% and 0.9%-3.0%, respectively, compared to that of tests without sodium acetate and biochar (p<0.05). This enhancement was attributed to the improved extracellular electron accepting capacity of anammox biomass by biochar. The easily obtained electrons (from sodium acetate) further increased the relative abundances of anammox-related (hzs) and complete DNRA-related (napAB and nrfAH) genes (p<0.05), which catalyze electron-consuming reactions. The stimulated anammox pathway and DNRA pathway further increased the specific anammox activity and the relative abundance of anammox bacteria (especially Ca. Jettenia) by 15.5%-23.0% and 11.3%-82.6% compared with that without biochar, respectively. Metagenomics sequencing also revealed that anammox bacteria, Ca. Jettenia caeni, was the main bacteria for DNRA metabolism in this system. Our findings reveal that biochar could selectively stimulate DNRA pathway of anammox bacteria affiliated by a low amount of carbon, which provides a novel strategy to improve the nitrogen removal of anammox-based processes.

Varied interspecies interactions between anammox and denitrifying bacteria enhanced nitrogen removal in a single-stage simultaneous anammox and denitrification system

The simultaneous anammox and denitrification (SAD) system has received growing interest for the enhanced nitrogen removal, while the ecological traits of microbial community including spatial distribution characteristics, assembly processes and interspecies interactions have not been fully unraveled. The present study applied metagenomics and ecological analysis methods to gain the ecological traits of microbial communities in the SAD system across different organic substrate loadings. Results showed that organic matter significantly affected the bioreactor performance, and the optimal total nitrogen removal efficiency reached 93.4 ± 0.7% under the COD concentrations of 180 ± 18.2 mg/L. Functional organisms including Candidatus Brocadia (3.9%), Denitratisoma (1.6%), Dokdonella (4.4%) and Thauera (4.6%) obviously enriched under the optimal organic loading conditions. Moreover, microbial communities were significantly governed by deterministic process under high organic concentrations, and the denitrifying organisms displayed important ecological roles in the communities. Although anammox bacteria obviously enriched at the middle of bioreactor, it possessed the highest expression activities at both bottom and middle sites. Denitrifying bacteria that enriched at the bottom sites strongly achieved nitrate reduction and provided nitrite for anammox bacteria, while these organisms trended to compete nitrite with anammox bacteria at the middle site. These findings highlight the importance of microbial ecology in the SAD systems, which may expand our understanding of the synergistic patterns between anammox and denitrifying bacteria.

Analysis of the Bacterial Biocenosis of Activated Sludge Treated with Leachate from Municipal Landfills

The influx of toxic pollutants into wastewater treatment plants can negatively affect the quality of the activated sludge (AS). One source is landfill leachate. The identification of microorganisms present in AS is very important, e.g., while improving wastewater treatment technology. Therefore, the aim of the study was to investigate the effect of raw leachate and after purification of Phragmites australis and Ceratophyllum demersum on the composition of the AS bacterial biocenosis. In addition, AS status was assessed by LIVE/DEAD BacLight ™ fluorescent staining. The obtained results showed that the leachate did not significantly affect the cell membranes of AS bacteria, and even a slight improvement was noted. The research carried out using the next-generation sequencing method shows that the origin of the samples (active and closed storage) and the method of processing do not significantly affect the composition of the AS bacterial biocenosis at higher taxonomic levels. However, at the species level, the appearance of bacteria not previously present in AS was observed, namely: Flavobacterium luticocti, Candidimonas nitroreducens and Nitrobacter hamburgensis. The obtained results suggest that the leachate may be a source of microorganisms positively influencing the condition of AS bacteria.

Comparison between two anammox fiber fillers under load impact and the effect of HCO3 - concentration

Based on the establishment of a stable anaerobic ammonia oxidation treatment system in 100 days, the impact resistances of two different anammox fiber fillers (the curtain filler: R1 and the bundle filler: BR) were compared. Furthermore, the effect of HCO₃⁻ concentration on the bundle filler system was also investigated, the results have shown that the activity of the two anammox fiber fillers was not inhibited when the NO₂⁻–N concentration was lower than 750 mg L⁻¹ (FNA = 0.085 mg L⁻¹), while it was significantly suppressed at 900 mg L⁻¹ (FNA = 0.118 mg L⁻¹). However, the two fiber fillers could be recovered and exhibit a good impact resistance reduction of the substrate concentration. On day 95, the structure of the bundle filler was more conducive to the stable attachment, proliferation, and aggregation of anammox bacteria. Dominant anammox bacteria in both the curtain and bundle fillers were Candidatus Kuenenia, which accounted for 25.9% and 35.9% of the total population, respectively. When the influent HCO₃⁻ concentration was 900 mg L⁻¹, the bundled fiber filler had the highest total nitrogen (TN) removal efficiency, which reached 89.0%. Even though it was inhibited under 2000 mg L⁻¹ of HCO₃⁻ concentration, the reactor was able to recover within one week by reducing the substrate concentration. In addition, the HCO₃⁻ inhibition mechanism was independent of pH, which resulted in high FA content.

Based on the establishment of a stable anaerobic ammonia oxidation treatment system in 100 days, the impact resistances of two different anammox fiber fillers (the curtain filler: R1 and the bundle filler: BR) were compared.

Responses of simultaneous anammox and denitrification (SAD) process to nitrogen loading variation: Start-up, performance, sludge morphology and microbial community dynamics

The effects of loading variation on the efficiency, EPS, sludge morphology and microbial population of simultaneous anammox and denitrification (SAD) were thoroughly investigated with the low-abundance SAD sludge. Results indicated that the first stage lasted the longest (33d), and the average removal rate of TN can be maintained above 95%. The specific anammox activity (SAA), specific denitrification activity and PN/PS continued to increase, but the excessive loading caused the effluent to deteriorate rapidly, and SAA and PN/PS also decreased slightly, but it could be recovered quickly. The contribution rate of anammox and denitrification to N removal reached 87.6% and 12.4% eventually, respectively. The abundance of AnAOB was 10.68%-18.01%, 9.01%-15.54%, 5.74%-12.88% in the upper, middle and lower layers, respectively. Candidatus Kuenenia was always the dominant AnAOB, especially after high loading inhibition. The abundance of denitrifying bacteria (mainly Bacillus, Comamonas and Denitratisoma) gradually became the highest.

Effects of chlorine disinfectants on the microbial community structure and the performance of anaerobic digestion of swine manure

The residual chlorine disinfectants (CDs) in swine slurry could negatively impact the anaerobic digestion (AD). The objective of this study was to investigate the effects of CDs on mesophilic and thermophilic AD. The results indicated that CDs exerted inhibition effects on methanogenesis at the initial stage of mesophilic AD, leading to the extension of lag time from 0.62 days for control to 0.85, 1.9, 3.8, and 5.5 days with the increasing CDs concentrations of 50, 100, 200, and 400 mg/L, respectively. Under thermophilic condition, the inhibition effects reduced significantly at the initial stage but a decrease of CMP_u at later stage was observed. The microbial analysis revealed that CDs resulted in the enrichment of chlorine-resistant bacteria (Clostridum_sensu_stricto_1) and archaea (Methanosarcina). Addition of activated carbon (AC), zero-valent iron (ZVI) and biochar (BC) was evaluated for alleviating the inhibitions of CDs and proved to be feasible strategies to alleviate the inhibited AD.

Spatial Variation of Cladophora Epiphytes in the Nan River, Thailand

Cladophora is an algal genus known to be ecologically important. It provides habitats for microorganisms known to provide ecological services such as biosynthesis of cobalamin (vitamin B12) and nutrient cycling. Most knowledge of microbiomes was obtained from studies of lacustrine Cladophora species. However, whether lotic freshwater Cladophora microbiomes are as complex as the lentic ones or provide similar ecological services is not known. To illuminate these issues, we used amplicons of 16S rDNA, 18S rDNA, and ITS to investigate the taxonomy and diversity of the microorganisms associated with replicate Cladophora samples from three sites along the Nan River, Thailand. Results showed that the diversity of prokaryotic and eukaryotic members of Cladophora microbiomes collected from different sampling sites was statistically different. Fifty percent of the identifiable taxa were shared across sampling sites: these included organisms belonging to different trophic levels, decomposers, and heterotrophic bacteria. These heterogeneous assemblages of bacteria, by functional inference, have the potential to perform various ecological functions, i.e., cellulose degradation, cobalamin biosynthesis, fermentative hydrogen production, ammonium oxidation, amino acid fermentation, dissimilatory reduction of nitrate to ammonium, nitrite reduction, nitrate reduction, sulfur reduction, polyphosphate accumulation, denitrifying phosphorus-accumulation, and degradation of aromatic compounds. Results suggested that river populations of Cladophora provide ecologically important habitat for microorganisms that are key to nutrient cycling in lotic ecosystems.

Operational mode affects the role of organic matter in granular anammox process

In the presence of organic matter, the granular anammox system under sequencing batch mode showed more robust anammox performance than that under completely mixed mode, which was attributed to the better biomass retention with high settling ability and stability of granular sludge. Based on the specific anammox activity test, stratified and mixed distribution of heterotrophic bacteria was found under completely mixed and sequencing batch mode, respectively. The stratified microbial distribution resulted in low enzyme activity of anammox bacteria and sludge disintegration by hindering substrate transfer with a large accumulation of EPS on the granular surface. Whereas the heterotrophic bacteria mixed in granules (mixed microbial distribution) act as a "skeleton", which increased the particle size, density, and stability of granular sludge. Compared with biokinetic-based selection, diffusion-based selection with high substrate penetration depth more likely resulted in the mixed granular structure and strong resistance to organic inhibition under sequencing batch mode.

Highly enriched anammox within anoxic biofilms by reducing suspended sludge biomass in a real-sewage A2/O process

This study proposes a novel strategy of stably enriching anammox in mainstream, based on the competitive difference to NO₂^- between anoxic biofilms and suspended sludge. A modified anaerobic-anoxic-oxic (A²/O) process run for 500 days with actual municipal wastewater. Microbial analysis revealed that anoxic-carrier biofilms had a significantly higher abundance of anammox (qPCR: 0.74% - 4.34%) than suspended sludge (P< 0.001). Batch tests showed that anammox within anoxic-carrier biofilms contributed to significant nitrogen removal, coupled with partial-denitrification (NO₃^- → NO₂^-). The anammox genus, Ca. Brocadia, was highly enriched when suspended sludge was accidentally lost. Further batch tests found that reducing suspended biomass helped anammox enrichment in anoxic-carrier biofilms, because the suspended sludge had strong NO₂^- competition (NO₂^- → N₂) with anammox (increased nirK). Metagenomic sequencing revealed that Ca. Brocadia dominates in the anoxic-carrier biofilms, and is the most important narG contributor to NO₃^- → NO₂^-, which could have promoted the competition of NO₂^- with heterotrophic bacteria. For this A²/O process, the low effluent total nitrogen (8.9 mg ± 1.0 mg N/L) was attributed to partial-denitrification coupling with anammox, demonstrating that this process is applicable to the general influent N-concentration range (30 mg - 50 mg NH₄⁺-N/L) of municipal wastewater treatment plants (WWTPs). Based on the special competitive preference of anammox for NO₂^-, this study provides a promising and practical alternative for enriching anammox bacteria in municipal WWTPs.

Deammonification process in municipal wastewater treatment: Challenges and perspectives

The deammonification process has been proved to be an efficient nitrogen removal process in treating high NH₄⁺-N concentration wastewater (sidestream deammonification). It is very hopeful to bring WWTP close to energy autarky. However, the feasibility of applying mainstream deammonification to sewage treatment need to be further explored. Therefore, this review attempts to give an overview of challenges in applying mainstream deammonification and to discuss the impacts of unfavorable conditions on main functional species. In addition, some novel control strategies to maintain the dominant position of desired species were summarized. Efficient solution to the conflict between AnAOB (Anaerobic ammonium-oxidizing bacteria) biomass retention and NOB (Nitrite oxidizing bacteria) wash out was also reviewed. Ultimately, we suggested further studies including effective improved process that achieve combination of autotrophy and organotrophy species based on the metabolic diversity of AnAOB.

Insight into the impacts of organics on anammox and their potential linking to system performance of sewage partial nitrification-anammox (PN/A): A critical review

Partial nitrification-anammox (PN/A) is an energy-efficient process for nitrogen removal from sewage. The influent organics of sewage is usually pre-removed, reducing the risk for enriching anammox bacteria (AnAOB). However, recent studies demonstrate that optimum influent organics could improve nitrogen removal and operational stability of PN/A. Thus, the impact of organics on PN/A-based process should not be overlooked. In this review, the complicated impacts of organics-containing influent on anammox and their linking to apply PN/A are discussed. Firstly, the effect of organics on AnAOB metabolism and the competition relationship between AnAOB and heterotrophic bacteria are summarized. Secondly, the combined effects of influent organics and operational strategies on PN/A-based process were reviewed. Thirdly, how to control influent organics in the real application of PN/A were discussed. Lastly, recent development of the PN/A-based process combined with denitrification were reviewed. Overall, influent organics could be an essential factor for successful application of sewage PN/A.

Evaluation of anammox pathway recovery after high COD loading using water quality, molecular biology and isotope labelling analysis

Anaerobic ammonium oxidation (anammox) pathway is sensitive to organic matter, and its recovery requires reliable evidence regarding the dominance of anammox in N-removal. This study showed that the anammox process deteriorated, with N-removal efficiencies rapidly decreasing from 87.2 to 45.7% when reactors were exposed to COD shocks of 1.12, 2.24 and 3.36 g L^-1 (COD/N ratio 2, 4 and 6). Comprehensive assessments of water quality, microbial characteristics and isotope analysis were adopted to investigate anammox recovery. Operational performance took 8-20 days to recover; anammox relative abundance recovered after 20 days, based on the results of fluorescence in situ hybridisation and quantitative PCR; and the anammox pathway contributed to 80.0-91.5% of N-loss 40 days after COD shock terminated, based on the results of the isotope labelling experiment. Therefore, a complete recovery required 40 days. The isotope labelling method supplied a reliable reference for recovery assessment of anammox system in real-world applications.

Discrepant gene functional potential and cross-feedings of anammox bacteria Ca. Jettenia caeni and Ca. Brocadia sinica in response to acetate

Although the enhancement of anammox performance for wastewater treatment due to the addition of small amount of acetate has been reported, discrepant metabolic responses of different anammox species have not been experimentally evaluated. Based on metagenomics and metatranscriptomic data, we investigated the competitiveness between two typical anammox species, Candidatus Jettenia caeni (J. caeni) and Candidatus Brocadia sinica (B. sinica), in anammox consortia under mixotrophic condition, where complex metabolic interactions among anammox bacteria and heterotrophs also changed with acetate addition. Contrary to J. caeni, the dissimilatory nitrate reduction to ammonium pathway of B. sinica was markedly stimulated for improving nitrogen removal. More acetate metabolic pathways and up-regulated AMP-acs expression for acetyl-CoA synthesis in B. sinica contributed to its superiority in acetate utilization. Interestingly, cross-feedings, including the nitrogen cycle, amino acid cross-feeding and B-vitamin metabolic exchange between B. sinica and other heterotrophs seemed to be enhanced with acetate addition, contributing to a reduction in metabolic energy cost to the whole community. Our work not only clarified the mechanism underlying discrepant responses of different anammox species to acetate, but also suggests a possible strategy for obtaining higher nitrogen removal rates in wastewater treatment under low C/N ratio.

Keystone taxa regulate microbial assemblage patterns and functional traits of different microbial aggregates in simultaneous anammox and denitrification (SAD) systems

Understanding the impacts of the ecological patterns and niche-based selection on microbial community assembly and nitrogen-cycling network is crucial for achieving energy-neutral wastewater treatment. However, little is known about the niche differentiation and microbial nitrogen-cycling traits of keystone taxa in flocs and granules in anammox-based systems. Herein, the aspects of community assemblage patterns, metabolic functions and nitrogen transformation pathways were explored. The findings discovered that the treatment performance and bacterial community assembly were regulated by core taxa and flocs and granules communities harbored core taxa based on their functional traits. Both niche differentiation and environmental filtering have profound influences on functional bacteria. Furthermore, a combined analysis showed that nitrogen removal in flocs and granules was regulated by different nitrogen transformation pathways. These results suggest that core taxa are the key drivers for the microbial nitrogen-cycling network and improve the understanding of cross-feeding and metabolic pathways between anammox and nitrogen-cycling-related microorganisms.

Adding an anaerobic step can rapidly inhibit sludge bulking in SBR reactor

Activated sludge from wastewater treatment plants was seeded into a sequencing batch reactor (SBR) in which synthetic wastewater was used as the influent. The sludge was bulked by decreasing the concentration of dissolved oxygen (DO). By adding a 30 min step of anaerobic stirring after the water inflow, the sludge bulking was rapidly inhibited after 10 running cycles, and the sludge volume index (SVI) decreased from 222 to 74 mL·g^-1. The results of high-throughput sequencing showed that the relative abundance of bacteria Thiothrix, bacteria norank_o_Sphingobacteriales and fungi Trichosporon was increased by 6.3, 4.3 and 81.2%, after initial SBR stages, but these bacteria were inhibited by the addition of an anaerobic step, as their relative abundances decreased by 0.7, 0.8 and 14.7%, respectively. The proliferation of Thiothrix, norank_o_Sphingobacteriales and Trichosporon was the primary reason for the observed sludge bulking in the reactor. After the anaerobic step was added, the sludge extracellular polymeric substances (EPS) concentration was increased from 84.4 to 104.0 mg·(gMLSS)^-1 (grams of mixed liquor suspended solids). Thus, the addition of an anaerobic step can inhibit the growth of filamentous bacteria, increasing the sludge EPS concentration and promoting the precipitation of activated sludge.

Quinoline's influence on nitrogen removal performance and microbial community composition of the anammox process

This study aimed to evaluate the effects of quinoline on nitrogen removal performance and microbial community of an anaerobic biofilm reactor with anammox activity. Results showed that 20 mg L^-1 quinoline addition leading the ammonia and nitrite removal efficiency of the ABR reduced from about 90% to 40%. Illumina MiSeq sequencing study indicated that microbial community structure and composition varied with the additive of quinoline. Planctomycetes and Bacteroidetes, decreased in abundance, suggested that quinoline adversely affects the anammox metabolism within the anammox reactor. The distribution of the anammox bacteria was affected by quinoline addition. Ca. Jettenia prevailed over the other two anammox bacteria (Brodica and Kuenenia) in the recovered phase.

Effects of pipe material on nitrogen transformation, microbial communities and functional genes in raw water transportation

Raw water transportation pipelines are vital in an urban water supply system for transporting raw water to drinking water treatment plants. This study investigated the effects of pipe material on nitrogen transformation, microbial communities and characteristics of related function genes in paint-lined steel pipe (PLSP) and cement-lined steel pipe (CLSP) raw water model systems. We established quantitative relationships between specific functional genes and change rates of nitrogen pollutants, which were verified by field investigation on nitrogen pollutant transformations in real raw water transportation systems. The results showed that the CLSP produced higher ammonia nitrogen (NH₄⁺-N) transformation rates and higher effluent concentrations of nitrate nitrogen (NO₃^--N) and dissolved organic nitrogen (DON) than the PLSP. Both pipes achieved high and stable nitrite nitrogen (NO₂^--N) and low total nitrogen (TN) removal efficiency. Nitrification was found to be the dominant process in both model systems, especially in the CLSP. Characteristics of microbial communities and nitrogen functional genes, which were analysed by high-throughput pyrosequencing and quantitative polymerase chain reaction (qPCR), respectively, varied between the two pipe systems. Nitrogen transformation pathways, identified by path analysis, were also different between the PLSP and CLSP due to different microbial community characteristics and synergistic effects of nitrogen functional genes. In the CLSP, (NH₄⁺-N→NO₂^--N) with part denitrification, was the primary transformation pathway of ammonia nitrogen (NH₄⁺-N), while only ammonia oxidization contributed to NH₄⁺-N transformation in the PLSP. (NO₂^--N→NO₃^--N) was the main pathway involved in NO₂^--N transformation and NO₃^--N accumulation. The TN removal showed complex relationships with nitrification, denitrification and nitrogen fixation processes. These findings provided molecular-level insights into nitrogen pollutant transformations during the transportation of raw water through different types of pipes and technical support for the selection of raw water pipe materials. In our study area, the Taihu basin, China, PLSP was better than CLSP for distributing raw water in a short transportation distance, due to the lower effluent concentrations of DON and NO₃^--N and less abundance of microorganisms.

Abundant and rare microbial sub-communities in anammox granules present contrasting assemblage patterns and metabolic functions in response to inorganic carbon stresses

Nitrogen-transforming microorganisms play pivotal roles for the microbial nitrogen-cycling network in the anammox granular system. However, little is known about the effects of inorganic carbon (IC) stresses on the assemblage patterns and functional profiles of abundant and rare taxa. Herein, the community assemblage and functional traits of abundant and rare sub-communities were investigated. Results revealed that insufficient IC had adverse influences on the process performance, while anammox activity could be recovered by IC addition. Co-occurrence network analysis indicated that abundant and rare sub-communities present divergent co-occurrence patterns. Additionally, environmental filtering had different influences on the ecological adaptability of bacterial sub-communities. Furthermore, qPCR results illustrated that NH₄⁺-N and NO₂^--N consumption were regulated by abundant sub-community, while their accumulation was mediated by rare sub-community. Collectively, these findings suggest that abundant and rare sub-communities present contrasting assemblage patterns and metabolic pathways, and functional profiles dominated selection of bacterial sub-communities under IC stresses.

Sewage Sludge Microbial Structures and Relations to Their Sources, Treatments, and Chemical Attributes

Sewage sludges generation and their disposal have become one of the greatest challenges of the 21st century. They have great microbial diversity that may impact wastewater treatment plant (WWTP) efficiency and soil quality whether used as fertilizers. Therefore, this research aimed to characterize microbial community diversity and structure of 19 sewage sludges from São Paulo, Brazil, as well as to draw their relations to sludge sources [domestic and mixed (domestic+industrial)], biological treatments (redox conditions and liming), and chemical attributes, using molecular biology as a tool. All sludges revealed high bacterial diversity, but their sources and redox operating conditions as well as liming did not consistently affect bacterial community structures. Proteobacteria was the dominant phylum followed by Bacteroidetes and Firmicutes; whereas Clostridium was the dominant genus followed by Treponema, Propionibacterium, Syntrophus, and Desulfobulbus. The sludge samples could be clustered into six groups (C1 to C6) according their microbial structure similarities. Very high pH (≥11.9) was the main sludge attribute segregating C6, that presented very distinct microbial structure from the others. Its most dominant genera were Propionibacterium > > Comamonas > Brevundimonas > Methylobacterium ∼Stenotrophomonas ∼Cloacibacterium. The other clusters' dominant genera were Clostridium > > Treponema > Desulfobulbus ∼Syntrophus. Moreover, high Fe and S were important modulators of microbial structure in certain sludges undertaking anaerobic treatment and having relatively low N-Kj, B, and P contents (C5). However, high N-Kj, B, P, and low Fe and Al contents were typical of domestic, unlimed, and aerobically treated sludges (C1). In general, heavy metals had little impact on microbial community structure of the sludges. However, our sludges shared a common core of 77 bacteria, mostly Clostridium, Treponema, Syntrophus, and Comamonas. They should dictate microbial functioning within WWTPs, except by SS12 and SS13.

Ammonium removal by native microbes and activated sludge within the Jialu River basin and the associated microbial community structures

To explore the availability of native microbes and activated sludge for ammonium removal, the native microbes and activated sludge in Jialu River basin were investigated in terms of ammonium-removing activities and their microbial communities using spectrophotometry and high-throughput sequencing. NH₄⁺-N and total nitrogen (TN) in the targeted river ranged from 2.45 ± 1.76 to 8.56 ± 2.54 mg/L and from 3.42 ± 2.79 to 13.49 ± 5.06 mg/L, respectively. Both the native microbes and activated sludge had strong ammonium-removing activities with the removal efficiencies of more than 94%. High-throughput sequencing results indicated that, after five batches of operation, the class Gammaproteobacteria (28.55%), Alphaproteobacteria (14.55%), Betaproteobacteria (13.89%), Acidobacteria (8.82%) and Bacilli (7.04%) were dominated in native community, and there was a predominance of Gammaproteobacteria (21.57%), Betaproteobacteria (16.33%), Acidobacteria (12.41%), Alphaproteobacteria (10.01%), Sphingobacteriia (6.92%) and Bacilli (6.66%) in activated sludge. These two microbial sources were able to remove ammonium, while activated sludge was more cost-effective.

Evaluating the potential for dissimilatory nitrate reduction by anammox bacteria for municipal wastewater treatment

Anammox bacteria can perform dissimilatory nitrate reduction to ammonium (DNRA) with nitrite as intermediate coupled to the oxidation of volatile fatty acids (VFA). Batch tests with enriched anammox and a co-culture of anammox and heterotrophic bacteria showed the capacity of Candidatus 'Brocadia fulgida' to perform the DNRA coupled to the anammox reaction (DNRA-anammox) at a high rate although the culture was not previously adapted to VFA. From thermodynamic calculations it could be stated that low COD/N influent ratios favour the DNRA-anammox transformation over heterotrophic conversions since more free energy is gained. A process scheme is proposed for an innovative nitrogen removal system in which the nitrate produced by nitrite oxidizing bacteria and/or anammox bacteria is converted during DNRA-anammox pathway, resulting in a sustainable nitrogen removal from municipal wastewater while circumventing the troublesome out-selection of nitrite oxidizing bacteria encountered in mainstream applications.

Distribution and characteristic of nitrite-dependent anaerobic methane oxidation bacteria by comparative analysis of wastewater treatment plants and agriculture fields in northern China

Nitrite-dependent anaerobic methane oxidation (n-damo) is a recently discovered biological process which has been arousing global attention because of its potential in minimizing greenhouse gases emissions. In this study, molecular biological techniques and potential n-damo activity batch experiments were conducted to investigate the presence and diversity of M. oxyfera bacteria in paddy field, corn field, and wastewater treatment plant (WWTP) sites in northern China, as well as lab-scale n-damo enrichment culture. N-damo enrichment culture showed the highest abundance of M. oxyfera bacteria, and positive correlation was observed between potential n-damo rate and abundance of M. oxyfera bacteria. Both paddy field and corn field sites were believed to be better inoculum than WWTP for the enrichment of M. oxyfera bacteria due to their higher abundance and the diversity of M. oxyfera bacteria. Comparative analysis revealed that long biomass retention time, low NH\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}${}_{4}^{+}$\end{document}4+ and high NO\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}${}_{2}^{-}$\end{document}2− content were suitable for the growth of M. oxyfera bacteria.

Symbiotic relationship analysis of predominant bacteria in a lab-scale anammox UASB bioreactor

In order to provide the comprehensive insight into the key microbial groups in anaerobic ammonium oxidation (anammox) process, high-throughput sequencing analysis has been used for the investigation of the bacterial communities of a lab-scale upflow anaerobic sludge bed (UASB) anammox bioreactor. Results revealed that 109 operational taxonomic units (OTUs; out of 14,820 reads) were identified and a domination of anammox bacteria of Candidatus Kuenenia stuttgartiensis (OTU474, 35.42 %), along with heterotrophs of Limnobacter sp. MED105 (OTU951, 14.98 %), Anerolinea thermophila UNI-1 (OTU465 and OTU833, 6.60 and 3.93 %), Azoarcus sp. B72 (OTU26, 9.47 %), and Ignavibacterium sp. JCM 16511 (OTU459, 8.33 %) were detected. Metabolic pathway analysis showed that Candidatus K. stuttgartiensis encountered gene defect in synthesizing a series of metabolic cofactors for growth, implying that K. stuttgartiensis is auxotrophic. Coincidentally, the other dominant species severally showed complete metabolic pathways with full set gene encoding to corresponding cofactors presented in the surrounding environment. Furthermore, it was likely that the survival of heterotrophs in the autotrophic system indicates the existence of a symbiotic and mutual relationship in anammox system.

Enhanced long-term nitrogen removal by organotrophic anammox bacteria under different C/N ratio constraints: quantitative molecular mechanism and microbial community dynamics

The anaerobic ammonium oxidation (anammox) process has mainly been applied to NH₄⁺–N-rich wastewater with very low levels of organic carbon (<0.5 g COD per g N).

Effects of Fe(ii) on microbial communities, nitrogen transformation pathways and iron cycling in the anammox process: kinetics, quantitative molecular mechanism and metagenomic analysis

Appropriate Fe(ii) concentration has been regarded as a significant factor for fast start-up of the anammox (anaerobic ammonium oxidizing) process.