1994-2004: 10 years of research on the anaerobic oxidation of ammonium

Impacts of crude glycerol on anaerobic ammonium oxidation (Anammox) process in wastewater treatment

This work investigated the impact of a waste-derived carbon source, crude glycerol (CG), on Anammox. Batch bioassays were conducted to identify inhibitory component(s) in CG, and the relationship between Anammox activity and the concentration of CG, pure glycerol, and methanol were assessed. The results showed that the half-maximal inhibitory concentration of CG and methanol are 434.5 ± 51.8 and 143.0 ± 19.6 mg chemical oxygen demand (COD) L-1, respectively, while pure glycerol at 0-2283 mg COD L-1 had no significant adverse effect on Anammox. The results suggested methanol is the major inhibitor in CG via a non-competitive inhibition mechanism. COD/total inorganic nitrogen ratio of > 1.3 was observed to cause a significant Anammox inhibition (>20 %), especially at low substrate level. These results are valuable for evaluating the feasibility of using CG for nitrogen removal in water resource recovery facilities, promoting sustainable development.

Application of positively charged red mud-based carriers for anaerobic ammonium oxidizing bacteria biofilm formation

Enrichment of anaerobic ammonium oxidizing bacteria (AnAOB) in the anaerobic ammonium oxidation (anammox) process remains a challenge in engineering applications. In this study, for faster enrichment of AnAOB, red mud-based carriers were positively charged with FeCl3 and microbial promoters. The experimental results showed that the average nitrogen removal rates of the red mud-based carriers (RMGA), FeCl3-modified red mud-based carriers (RMGA-Fe), and microbial promoter-modified red mud-based carriers (RMGA-MA) increased by 24.4%-175% compared with the commercially available K3 carriers. Combining the results of SEM and laser confocal microscope, electrostatic attraction played a leading role on loading AnAOB. The increase in the surface roughness and specific area of the carriers after the attachment and the presence of Fe2+, Ca2+, and Mg2+ plasma were necessary for the subsequent growth of AnAOB, while the leaching of Cr(VI) promoted the nitrogen removal effect of AnAOB.

Nitrification and beyond: metabolic versatility of ammonia oxidising archaea

Ammonia oxidising archaea are among the most abundant living organisms on Earth and key microbial players in the global nitrogen cycle. They carry out oxidation of ammonia to nitrite, and their activity is relevant for both food security and climate change. Since their discovery nearly 20 years ago, major insights have been gained into their nitrogen and carbon metabolism, growth preferences and their mechanisms of adaptation to the environment, as well as their diversity, abundance and activity in the environment. Despite significant strides forward through the cultivation of novel organisms and omics-based approaches, there are still many knowledge gaps on their metabolism and the mechanisms which enable them to adapt to the environment. Ammonia oxidising microorganisms are typically considered metabolically streamlined and highly specialised. Here we review the physiology of ammonia oxidising archaea, with focus on aspects of metabolic versatility and regulation, and discuss these traits in the context of nitrifier ecology.

The microbial landscape in bioturbated mangrove sediment: A resource for promoting nature-based solutions for mangroves

Globally, soils and sediments are affected by the bioturbation activities of benthic species. The consequences of these activities are particularly impactful in intertidal sediment, which is generally anoxic and nutrient-poor. Mangrove intertidal sediments are of particular interest because, as the most productive forests and one of the most important stores of blue carbon, they provide global-scale ecosystem services. The mangrove sediment microbiome is fundamental for ecosystem functioning, influencing the efficiency of nutrient cycling and the abundance and distribution of key biological elements. Redox reactions in bioturbated sediment can be extremely complex, with one reaction creating a cascade effect on the succession of respiration pathways. This facilitates the overlap of different respiratory metabolisms important in the element cycles of the mangrove sediment, including carbon, nitrogen, sulphur and iron cycles, among others. Considering that all ecological functions and services provided by mangrove environments involve microorganisms, this work reviews the microbial roles in nutrient cycling in relation to bioturbation by animals and plants, the main mangrove ecosystem engineers. We highlight the diversity of bioturbating organisms and explore the diversity, dynamics and functions of the sediment microbiome, considering both the impacts of bioturbation. Finally, we review the growing evidence that bioturbation, through altering the sediment microbiome and environment, determining a 'halo effect', can ameliorate conditions for plant growth, highlighting the potential of the mangrove microbiome as a nature-based solution to sustain mangrove development and support the role of this ecosystem to deliver essential ecological services.

A review on characterizing the metabolite property of anammox sludge by spectroscopy

As one of the most promising autotrophic biological nitrogen removal technology, anaerobic ammonia oxidation (anammox) has gained intense attention for the past decades and several full-scale facilities have been implemented worldwide. However, anammox bacteria are easily affected by disturbed external environmental factors, which commonly leads to the fluctuations in reactor performance. The response of anammox sludge to external stress results in changes in components and structural characteristics of intracellular and extracellular polymer substances. Real-time and convenient spectral analysis of anammox sludge metabolites can give early warning of performance deterioration under external stresses, which is of great significance to the stable operation of bioreactor. This review summarized the research progress on characterizing the intracellular and extracellular metabolites of anammox sludge through spectroscopic techniques. The correlation between anammox sludge activity and its key metabolites was analyzed. Also, the limitations and future prospects of applying spectral analytical techniques for anammox bioreactor monitoring were discussed and outlooked. This review may provide valuable information for both scientific study and engineering application of anammox based nitrogen removal technology.

Anammox Bacteria Are Potentially Involved in Anaerobic Ammonium Oxidation Coupled to Iron(III) Reduction in the Wastewater Treatment System

Anaerobic ammonium oxidation coupled to nitrite reduction (termed as Anammox) was demonstrated as an efficient pathway to remove nitrogen from a wastewater treatment system. Recently, anaerobic ammonium oxidation was also identified to be linked to iron(III) reduction (termed Feammox) with dinitrogen, nitrite, or nitrate as end-product, reporting to enhance nitrogen removal from the wastewater treatment system. However, little is known about the role of Anammox bacteria in the Feammox process. Here, slurry from wastewater reactor amended with ferrihydrite was employed to investigate activity of Anammox bacteria in the Feammox process using the ¹⁵N isotopic tracing technique combined with 16S rRNA gene amplicon sequencing. A significantly positive relationship between rates of ¹⁵N₂ production and iron(III) reduction indicated the occurrence of Feammox during incubation. Relative abundances of Anammox bacteria including Brocadia, Kuenenia, Jettenia, and unclassified Brocadiaceae were detected with low relative abundances, whereas Geobacteraceae dominated in the treatment throughout the incubation. ¹⁵N₂ production rates significantly positively correlated with relative abundances of Geobacter, unclassified Geobacteraceae, and Anammox bacteria, revealing their contribution to nitrogen generation via Feammox. Overall, these findings suggested Anammox bacteria or cooperation between Anammox bacteria and iron(III) reducers serves a potential role in Feammox process.

Recent technologies for nutrient removal and recovery from wastewaters: A review

Water scarcity and its pollution has become a concern in recent times. The disposal of nutrient-rich (nitrogen and phosphorous) wastewater is also one of the main cause of water pollution through eutrophication, reduced dissolved oxygen that poses threat to aquatic ecosystems. As a result, nutrient removal has become a mandate apart from the removal of organics. However, the removal of nutrients from sewage is a challenging task. Conversely, conventional biological treatment processes provide little relief in nutrient removal. The treated effluents from conventional biological processes do not achieve the stringent nutrient removal disposal standard limits and become primary cause of pollution in the receiving water bodies. This has stressed upon the need for eco-friendly, low-energy and cost-efficient nutrient removal treatment technologies. Various biological treatment combinations or variants are in use for the efficient removal of nutrients. The biological processes in itself or in combination with chemical processes are preferred over technologies based solely on physico-chemical processes for its treatment performance at lower cost. This review summarizes the existing treatment processes and their possible up-gradation with the aim to accomplish the marked effluent standards for the nutrients. The concept of conventional systems and advanced systems for nutrients (nitrogen and phosphorous) removal which are already developed or under development are deeply discussed. Further, the challenges of each treatment systems are abridged. Finally, the possible suggestions for the modification/retrofitting of existing treatment systems for achieving stringent disposal standards are pointed out.

Novel microbial nitrogen transformation processes in constructed wetlands treating municipal sewage: a mini-review

Traditionally nitrogen transformation in constructed wetlands (CWs) has been attributed to the activities of aerobic autotrophic nitrifiers followed by anoxic heterotrophic denitrifiers. However, the nitrogen balances in such systems are far from being explained as a large fraction of the losses remain unaccounted for. The classical nitrification-denitrification theory has been successfully employed in certain unit processes by culturing fast-growing bacteria, but the CWs offer an ideal environment for slow-growing bacteria that may be beneficially exploited to achieve enhanced nitrogen removal by manipulating the environmental conditions in their favor. In the last three decades, many novel microorganisms have been isolated from CWs that have led to the discovery of some other routes that have made researchers believe could play a significant role in nitrogen transformation processes. The increased understanding of novel discerned pathways like anaerobic ammonium oxidation (ANAMMOX), heterotrophic nitrification and aerobic denitrification, which are mediated by specialized bacteria has indicated that these microorganisms could be enriched by applying selection pressures within CWs for achieving high rates of nitrogen removal. Understanding these novel nitrogen transformation processes along with the associated microbial population can provide new dimensions to the design of CWs for enhanced nitrogen removal.

Effect of biomass immobilization and reduced graphene oxide on the microbial community changes and nitrogen removal at low temperatures

The slow growth rate and high optimal temperatures for the anaerobic ammonium oxidation (anammox) bacteria are significant limitations of the anammox processes application in the treatment of mainstream of wastewater entering wastewater treatment plant (WWTP). In this study, we investigate the nitrogen removal and microbial community changes in sodium alginate (SA) and sodium alginate–reduced graphene oxide (SA-RGO) carriers, depending on the process temperature, with a particular emphasis on the temperature close to the mainstream of wastewater entering the WWTP. The RGO addition to the SA matrix causes suppression of the beads swelling, which intern modifies the mechanical properties of the gel beads. The effect of the temperature drop on the nitrogen removal rate was reduced for biomass entrapped in SA and SA-RGO gel beads in comparison to non-immobilized biomass, this suggests a ‘‘protective” effect caused by immobilization. However, analyses performed using next-generation sequencing (NGS) and qPCR revealed that the microbial community composition and relative gene abundance changed significantly, after the implementation of the new process conditions. The microbial community inside the gel beads was completely remodelled, in comparison with inoculum, and denitrification contributed to the nitrogen transformation inside the beads.

Temperature modulates stress response in mainstream anammox reactors

Autotrophic nitrogen removal by anaerobic ammonium oxidizing (anammox) bacteria is an energy-efficient nitrogen removal process in wastewater treatment. However, full-scale deployment under mainstream conditions remains challenging for practitioners due to the high stress susceptibility of anammox bacteria towards fluctuations in dissolved oxygen (DO) and temperature. Here, we investigated the response of microbial biofilms with verified anammox activity to DO shocks under 20 °C and 14 °C. While pulse disturbances of 0.3 mg L-1 DO prompted only moderate declines in the NH4+ removal rates, 1.0 mg L-1 DO led to complete but reversible inhibition of the NH4+ removal activity in all reactors. Genome-centric metagenomics and metatranscriptomics were used to investigate the stress response on various biological levels. We show that temperature regime and strength of DO perturbations induced divergent responses from the process level down to the transcriptional profile of individual taxa. Community-wide gene expression differed significantly depending on the temperature regime in all reactors, and we found a noticeable impact of DO disturbances on genes involved in transcription, translation, replication and posttranslational modification at 20 °C but not 14 °C. Genome-centric analysis revealed that different anammox species and other key biofilm taxa differed in their transcriptional responses to distinct temperature regimes and DO disturbances.

Whether glycine betaine improves the thermotolerance of mesophilic anammox consortia

While the application of mesophilic anammox process is currently the state of the art, the feasibility of a thermophilic anammox bioprocess is still unclear. In this study, we investigate whether glycine betaine (GB) addition can enhance the thermotolerance of mesophilic anammox biomass in the upflow anaerobic sludge blanket (UASB) reactors fed with synthetic wastewater at a nitrogen loading of approximately 4 kg N m^-3 d^-1. The results showed that during a long-term operation at 45°C with GB (0, 0.1, 1, 2 mM) addition, anammox performance became worse with the final effluent concentrations of NO₂ ^-N of 145 ± 11.6 mg L^-1 and nitrogen removal efficiency decreased from 92.3-6.9%. Specific anammox activity decreased from 392.1 ± 12.1-6.0 ± 0.8 mg N g^-1 VSS d^-1, which were not significantly higher than those in the control reactor. The content of heme c showed a stronger downward trend in T₁ (with GB addition) than in the control reactor T₀. The qPCR results showed that the relative abundance of Candidatus Kuenenia decreased in both the experimental (from 53.5-28.8%) and control reactors (from 54.1-35.1%). Overall, continuous addition of exogenous GB did not improve the thermotolerance of mesophilic anammox consortia at 45°C.

Bias of marker genes in PCR of anammox bacteria in natural habitats

The identification of anammox bacteria is mostly relied on PCR with various marker genes. However, the community composition revealed by different marker genes and whether the marker genes influence the resulted community composition remain unclear. We compared the community structure of anammox bacteria in enriched and natural environments revealed by 16S rRNA and functional genes (hzo, hzsA and hzsB) from public database and published papers. The genus of Ca. Scalindua showed the lowest similarities with other genera, especially for the hzsA gene (66.9%-68.6%). The 16S rRNA gene is the most commonly used marker gene in natural habitats with 151 out 221 papers in total. The anammox bacterial community composition is distributed according to the source of habitat regardless the use of various marker genes. The role of marker gene is limited with explanatory of 5.4% for variance of community composition, versus 20.5% of habitat. The effect of marker gene is mainly acted on freshwater habitat, which shows significant different community composition revealed by 16S rRNA and hzo, with Ca. Brocadia and Ca. Jettenia as dominant genus, respectively.

Soil anammox and denitrification processes connected with N cycling genes co-supporting or contrasting under different water conditions

The anaerobic ammonium oxidizing bacteria (anammox) are the hidden culprit behind the excessive nitrogen loss under a favorable environment, since their detection and abundance get disturbed by several unknown factors. This study intends to find the gap between actual anammox working capacity under different water conditions and fertilizers in the laboratory. The ¹⁵N-isotopic tracer technique was used to measure anammox and denitrification rate, and anammox community structure was analyzed through high-throughput sequencing with cytochrome cd-1 nitrite reductase functional gene (an_nirS gene, initially found in Candidatus Scalindua). The experiment consisted of four treatments, i.e., (I) CK_ Control, (II) UR_Urea, (III) PM_Pig Manure, and (IV) SRF_ Slow release fertilizer, under two water conditions, i.e., (a) Continuous flooding_ CF, (b) Alternate wetting and drying_ AWD. Results showed that anammox under CF decreased over time by -40.24%, and denitrification increased up to 39.25%. However, anammox activity under AWD increased up to 10.62% with the availability of NO₂^-, and surprisingly accompanied by the reduction in denitrification loss (-31.97%), being the most critical factor. We found that soil nifH and AOB genes were strongly favorable for anammox activity, while we observed the presence of anammox and AOB genes co-existing at the same time in paddy soil. The high-throughput sequencing with an_nirS functional gene showed a much higher diversity of anammox genera ever reported, mostly uncultured and unidentified. We concluded that water management is more prominent than fertilizer for anammox, and the most critical factor is the duration of AWD cycle, because of short term air supply could boost anammox activity and gene abundance, and could reduce denitrifier activity as well as nirK gene abundance.

Biogeographic pattern of the nirS gene-targeted anammox bacterial community and composition in the northern South China Sea and a coastal Mai Po mangrove wetland

Functional genes, namely hzo/hao, nirS, hzs, and ccs gene, are efficient with high specificity for detecting anammox bacteria. Sc-nirS and An-nirS primer sets were proposed for targeting Scalindua/non-Scalindua anammox bacterial groups; previously, they have not been assessed for biogeographic study on marine-terrestrial transitional systems, specifically marine and terrestrial ecosystems. Here, we report phylogenetic distribution pattern of anammox bacteria in both northern South China Sea (nSCS) and Mai Po wetland (a coastal mangrove) using nirS gene-based primers. A well-delineated biogeographic distribution pattern from ocean to continental shelf was evident by combining both gene-based analyses as previously depicted using 16S rRNA as the biomarker. Furthermore, factors affecting the abundance and composition of An-nirS genes in Mai Po wetland were identified as substrate (NO₃^-/NO₂^- concentration) and anoxic/oxic condition in association to depth. An-nirS gene abundance was from 2.6 × 10³ to 1.2-1.4 × 10⁴ copies/g dry sediment in nSCS; and it was around 5 × 10³ and 1-2 × 10⁴ copies/g dry sediment in surface and subsurface sediments of Mai Po wetland, respectively. In addition, nirS gene abundance and distribution pattern of denitrifiers and anammox bacteria in the wetland indicates a competition relationship between them. Mangrove vegetation affected the community composition of An-nirS gene considerably, and a more homogeneous distribution pattern was observed in the mangrove forest than intertidal mudflats. Sc/An-nirS gene-based biogeographic insights on anammox bacteria have shed lights on the compositional and potential functional dynamics and emphasized the importance of molecular tools on refining the current microbial ecological patterns.

Application of the Anammox in China-A Review

Anaerobic ammonia oxidation (anammox) has been one of the most innovative discoveries for the treatment of wastewater with high ammonia nitrogen concentrations. The process has significant advantages for energy saving and sludge reduction, also capital costs and greenhouse gases emissions are reduced. Recently, the use of anammox has rapidly become mainstream in China. This study reviews the engineering applications of the anammox process in China, including various anammox-based technologies, selection of anammox reactors and attempts to apply them to different wastewater treatment plants. This review discusses the control and implementation of stable reactor operation and analyzes challenges facing mainstream anammox applications. Finally, a unique and novel perspective on the development and application of anammox in China is presented.

Comparative genomics reveals a novel genetic organization of the sad cluster in the sulfonamide-degrader 'Candidatus Leucobacter sulfamidivorax' strain GP

Background

Microbial communities recurrently establish metabolic associations resulting in increased fitness and ability to perform complex tasks, such as xenobiotic degradation. In a previous study, we have described a sulfonamide-degrading consortium consisting of a novel low-abundant actinobacterium, named strain GP, and Achromobacter denitrificans PR1. However, we found that strain GP was unable to grow independently and could not be further purified.

Results

Previous studies suggested that strain GP might represent a new putative species within the Leucobacter genus (16S rRNA gene similarity < 97%). In this study, we found that average nucleotide identity (ANI) with other Leucobacter spp. ranged between 76.8 and 82.1%, further corroborating the affiliation of strain GP to a new provisional species. The average amino acid identity (AAI) and percentage of conserved genes (POCP) values were near the lower edge of the genus delimitation thresholds (65 and 55%, respectively). Phylogenetic analysis of core genes between strain GP and Leucobacter spp. corroborated these findings. Comparative genomic analysis indicates that strain GP may have lost genes related to tetrapyrrole biosynthesis and thiol transporters, both crucial for the correct assembly of cytochromes and aerobic growth. However, supplying exogenous heme and catalase was insufficient to abolish the dependent phenotype. The actinobacterium harbors at least two copies of a novel genetic element containing a sulfonamide monooxygenase (sadA) flanked by a single IS1380 family transposase. Additionally, two homologs of sadB (4-aminophenol monooxygenase) were identified in the metagenome-assembled draft genome of strain GP, but these were not located in the vicinity of sadA nor of mobile or integrative elements.

Conclusions

Comparative genomics of the genus Leucobacter suggested the absence of some genes encoding for important metabolic traits in strain GP. Nevertheless, although media and culture conditions were tailored to supply its potential metabolic needs, these conditions were insufficient to isolate the PR1-dependent actinobacterium further. This study gives important insights regarding strain GP metabolism; however, gene expression and functional studies are necessary to characterize and further isolate strain GP. Based on our data, we propose to classify strain GP in a provisional new species within the genus Leucobacter, ‘Candidatus Leucobacter sulfamidivorax‘.

Global Distribution of Anaerobic Ammonia Oxidation (Anammox) Bacteria - Field Surveys in Wetland, Dryland, Groundwater Aquifer and Snow

The discovery of anaerobic ammonia oxidation (anammox) expanded our knowledge on the microbial nitrogen cycle. Previous studies report that anammox bacteria are distributed in a wide range of habitats and plays significant roles in the global nitrogen cycle. However, most studies focus only on individual ecosystems or datasets from public databases. To date, our understanding of how anammox bacteria respond to environmental properties and are distributed in different habitats on a global scale, remain unclear. To explore the global distribution of anammox bacteria, samples were collected from different habitats at different locations globally, including wetlands, drylands, groundwater aquifers and snow from 10 countries across six continents. We then used high-throughput amplicon sequencing targeting the functional gene hydrazine synthase (HZS) and generated community profiles. Results showed that Candidatus Brocadia is detected as the dominant genus on a global scale, accounting for 80.0% to 99.9% of the retrieved sequences in different habitats. The Jettenia-like sequences were the second most abundant group, accounting for no more than 19.9% of the retrieved sequences in all sites. The samples in drylands, wetlands and groundwater aquifers showed similar community composition and diversity, with the snow samples being the most different. Deterministic processes seem stronger in regulating the community composition of anammox bacteria, which is supported by the higher proportion explained by local-scale factors. Groundwater aquifers showed high gene abundance and the most complex co-occurrence network among the four habitat types, suggesting that it might be the preferred habitat of anammox bacteria. There is little competition between anammox bacterial species based on co-occurrence analysis. Hence, we could infer that environmental factors such as anaerobic and stable conditions, instead of substrate limitations, may be vital factors determining the anammox bacteria community. These results provide a better understanding of the global distribution of anammox bacteria and the ecological factors that affect their community structuring in diverse habitats.

A novel anammox granules-circulating expanded granular sludge bed reactor for the efficient circulation and retention of floating anammox granules

In application of anammox process, the operation of the conventional expanded granular sludge bed reactor (EGSB_conv.) is severely limited by the blocking and decay of floating anammox granules.To address this emerging issue, a novel three-phase separator configuration was designed and an anammox granules circulating EGSB (EGSB_GC) was proposed in this study. In the EGSB_GC, an influent scour on floating granules, whose effect was confirmed by simulation with a three-dimensional flow model, was obtained by integrating the external three-phase separator with the influent and the external cycle. After 166-d operation, the nitrogen removal efficiency of the EGSB_GC reached 75.6%, being 1.28-times that of the EGSB_conv. (58.9%). The sludge concentration in the main body of the EGSB_GC reached 3112 ± 65 mg/L, compared with 2613 ± 42 mg/L in the EGSB_conv. (p < 0.05). Moreover, the severe granules blockage and decay problem that is frequently encountered in the EGSB_conv. no longer occurred in the EGSB_GC. The relative abundance of anammox bacteria in granules from the three-phase separator of the EGSB_GC was 29.7%, significantly higher than that from the EGSB_conv. (16.1%, p < 0.05). The blockage and decay of granules in the three-phase separator of the EGSB_conv. led to an obvious proliferation of heterotrophic bacteria, with their relative abundance increased by 9.4% compared with the seed sludge (38.6% vs. 29.2%). This study proposed a practical three-phase separator configuration to sustain efficient and stable operation of anammox processes toward the promotion of granules circulation, retention and reaction.

Effects of Ca2+ Concentration on Anaerobic Ammonium Oxidation Reactor Microbial Community Structure

The anaerobic ammonium oxidation (anammox) reaction removes nitrogen from wastewater, the performance of which is influenced by Ca2+; however, the effect of Ca2+ on microbial community structure is unclear. Therefore, the effects of Ca2+ concentration on the treatment performance of an anammox reactor and microbial community structure of anammox sludge were investigated. Ca2+ concentration minimally influenced the removal efficiency of NO2−–N and NH4+–N, but substantially influenced total N removal. Changing the Ca2+ concentration (between 25 and 125 mg/L) caused the average removal rate of total nitrogen to fluctuate by 3.3 percentage points. There were five major bacterial phyla in the anammox sludge: Proteobacteria, Chloroflexi, Acidobacteria, Planctomycete, and Chlorobi. Microbiological analysis revealed that the genera Acidobacterium, Anaerolinea, and Denitratisoma were positively correlated with Ca2+ concentration, and improved treatment performance of the anammox reactor. Moreover, uncultured Chlorobi bacterium clone RUGL1-218 (GQ421108.1) and uncultured sludge bacterium A21b (KT182572.1) may be key microorganisms for the immobilization of anammox bacteria. These findings offer a theoretical basis for improved wastewater treatment using the anammox process.

A secret of high-rate mass transfer in anammox granular sludge: "Lung-like breathing"

The granulation of anaerobic ammonium oxidation (Anammox) biomass can play a key role in developing stable and high-rate working of anammox process. It is important to know the working mechanism of anammox granular sludge (AnGS) for the optimization of reactor performance. In this study, a "lung-like breathing" determinator was invented to investigate the working behavior of AnGS in the bioreactor. The results showed that the AnGS had a regular expansion and contraction phenomenon, which was called "lung-like breathing". With the biological loading rate (BLR) at 0.114 kg-N/(kg-VSS·d), the expansion and contraction amplitude (ExCA) was 1.29 ± 0.05%, and the expansion and contraction frequency (ExCF) was 39.3 ± 1.6 times/h. The AnGS cultivated in a bioreactor with higher nitrogen removal rate (NRR) was found to have the higher ExCA and ExCF when determinated at the same BLR, and the "lung-like breathing" behavior of one type of AnGS was revealed to bear a significantly (p < 0.05) positive correlation with the specific anammox activity (SAA). The mass transfer flux from "lung-like breathing" was far greater than that from molecular diffusion, which was regarded as a vital mechanism for the AnGS to demonstrate its high activity. These findings provided theoretical basis and technical parameters for the optimization of anammox nitrogen removal process.

Changes of nitrogen-removal performance and that of the bacterial community in a mixed culture comprising freshwater and marine anammox bacteria under averaged environmental condition

Nitrogen-removal processes using anammox bacteria are expected to achieve high-rate removal while remaining economical, and their practical applications have been investigated. However, anammox bacteria still have unfavorable characteristics for practical use, including susceptibility to a change in environmental conditions. In this study, with an aim of exploring the adaptability of mixed anammox bacteria to environmental conditions, the shift of nitrogen-removal performance and bacterial community in a mixed culture comprising freshwater anammox bacteria (FAB) and marine anammox bacteria (MAB) were investigated by a continuously stirred tank reactor (CSTR). The CSTR inoculated with the mixed anammox bacteria was operated for 180 days under an averaged condition between freshwater and marine conditions with a temperature of 27.5 °C and a synthetic medium with 15 g/L NaCl was used. Nitrogen-removal performance became stable after 114 days and more than 90% of nitrogen that was loaded into the reactor was removed in the range of nitrogen loading rate 0.07-0.42 kg N/m³/d. After operating at 0.42 kg N/m³/d for one month, a biomass sample was taken and its bacterial community was analyzed by clone-library analysis using a partial sequence of 16S rRNA. Among the clones of anammox bacteria that were made by an anammox-bacteria-specific primer, 97% of them were MAB and only 3% were FAB. These results indicate that the bacterial community including anammox bacteria was evidently changed due to environmental conditions and that the averaged condition in this study was suitable for marine bacteria rather than freshwater bacteria.

Anammox bacteria exhibit capacity to withstand long-term starvation stress: A proteomic-based investigation of survival mechanisms

Although anammox bacteria are commonly exposed to long-term starvation during transportation and preservation process, physiological changes in these organisms during long-term starvation are not well understood, nor are the molecular bases of their starvation survival strategies. To reveal survival mechanisms during long-term anaerobic and anoxic starvation (60 days at 20 ± 1 °C), metaproteomic technology was utilized to identify differentially expressed proteins in Candidatus Kuenenia stuttgartiensis. Our results showed that Candidatus Kuenenia stuttgartiensis exhibits a capacity to withstand long-term starvation stress. Although activity decay rates of 0.0129 d^-1 and 0.0049 d^-1 were observed for anammox sludge in anoxic and anaerobic starvation, the relative abundance of Candidatus Kuenenia stuttgartiensis, the shape of anammox granules, and the fraction of viable cells remained constant under both anaerobic and anoxic starvation conditions. Metaproteomics results illustrated that Candidatus Kuenenia stuttgartiensis maintained stable levels of most intracellular proteins, especially enzymes involved in principal metabolic pathways after 60-d of anaerobic or anoxic starvation, thereby allowing cells to regain metabolic activities once substrates became available. Induction of starvation proteins could be a survival strategy employed by Candidatus Kuenenia stuttgartiensis to resist long-term starvation stresses. During anaerobic starvation, 34 proteins were upregulated, five of which were associated with carbohydrate catabolism and oxidation of organic compounds, thereby increasing potential for utilization of endogenous carbon sources to produce energy. During anoxic starvation, only two proteins were upregulated, which may be attributed to insufficient energy for the synthesis of starvation-induced proteins.

Enhancement of the adaptability of anammox granules to zinc shock by appropriate organic carbon treatment

Heavy metals, which are commonly present in high ammonia-containing wastewater, can cause inhibitory effects to anammox reaction. This study proposes a novel approach to enhance the adaptability of anammox granules to heavy metal [Zn(II)] shock by organic carbon (sodium acetate, NaAc) treatment, paying special attention to optimization of the treatment dosage and duration. For granules treated with 200 mg chemical oxygen demand (COD)/L NaAc for 2 d, the activity recovery (six cycles) efficiency after Zn(II) (40 mg/L) shock reached 127.4%. The extracellular polymeric substance (EPS) production increased by 168% and heterotrophic bacteria mildly proliferated (increased by 14%) in such granules compared with the control. The dramatic recovery capacity was likely due to the entrapment and barrier function of EPS and the outer-layer proliferated heterotrophic bacteria. This finding offers a useful process to enable maximum adaptability of anammox granules from heavy metals shocks, allowing anammox technology to be more widely applied.

Aggregation ability of three phylogenetically distant anammox bacterial species

Anaerobic ammonium-oxidizing (anammox) bacteria are well known for their aggregation ability. However, very little is known about cell surface physicochemical properties of anammox bacteria and thus their aggregation abilities have not been quantitatively evaluated yet. Here, we investigated the aggregation abilities of three different anammox bacterial species: "Candidatus Brocadia sinica", "Ca. Jettenia caeni" and "Ca. Brocadia sapporoensis". Planktonic free-living enrichment cultures of these three anammox species were harvested from the membrane bioreactors (MBRs). The physicochemical properties (e.g., contact angle, zeta potential, and surface thermodynamics) were analyzed for these anammox bacterial species and used in the extended DLVO theory to understand the force-distance relationship. In addition, their extracellular polymeric substances (EPSs) were characterized by X-ray photoelectron spectroscopy and nuclear magnetic resonance. The results revealed that the "Ca. B. sinica" cells have the most hydrophobic surface and less hydrophilic functional groups in EPS than other anammox strains, suggesting better aggregation capability. Furthermore, aggregate formation and anammox bacterial populations were monitored when planktonic free-living cells were cultured in up-flow column reactors under the same conditions. Rapid development of microbial aggregates was observed with the anammox bacterial population shifts to a dominance of "Ca. B. sinica" in all three reactors. The dominance of "Ca. B. sinica" could be explained by its better aggregation ability and the superior growth kinetic properties (higher growth rate and affinity to nitrite). The superior aggregation ability of "Ca. B. sinica" indicates significant advantages (efficient and rapid start-up of anammox reactors due to better biomass retention as granules and consequently stable performance) in wastewater treatment application.

Practical applications of PCR primers in detection of anammox bacteria effectively from different types of samples

Research on anammox (anaerobic ammonium oxidizing) bacteria is important due to their biogeochemical and industrial application significance since the first discovery made over two decades ago. By coupling NH₄⁺ and NO₂^- biochemically to form N₂ gas, anammox bacteria contribute significantly to global marine and terrestrial nitrogen balance (responsible for 50, 9~40, and 4~37% of the nitrogen loss for marine, lakes, and paddy soil) and are also useful in energy-conserving nitrogen removal in wastewater treatment. PCR-based detection and quantification of anammox bacteria are an easy, essential, and widely accessible technique used ubiquitously for studying them in many environmental niches. In this article, we make a summary on practical applications of 16S rRNA and functional gene PCR primers, including hydrazine dehydrogenase (Hzo), nitrite reductase (NirS), hydrazine synthase (Hzs), and cytochrome c biogenesis proteins (Ccs) in detection of them. PCR primer performances in both practical applications and tests in silico are also presented for comparison. For detecting general and specific anammox bacterial groups, selection of appropriate PCR primers for different environmental samples and practical application guidance on choice of appropriate primer pairs for different purposes are also offered. This article provides practical information on selection and application of PCR technique in detection of anammox bacteria from the diverse environments to further promote convenient applications of this technique in research and other purposes.

Microbial competition among anammox bacteria in nitrite-limited bioreactors

Phylogenetically diverse anammox bacteria have been detected in most of anoxic natural and engineered ecosystems and thus regarded as key players in the global nitrogen cycle. However, ecological niche differentiation of anammox bacteria remains unresolved despite its ecological and practical importance. In this study, the microbial competitions for a common substrate (nitrite) among three anammox species (i.e. "Candidatus Brocadia sinica", "Candidatus Jettenia caeni" and "Candidatus Kuenenia stuttgartiensis") were systematically investigated in nitrite-limited gel-immobilized column reactors (GICR) and membrane bioreactors (MBRs) under different nitrogen loading rates (NLRs). 16 S rRNA gene-based population dynamics revealed that "Ca. J. caeni" could proliferate only at low NLRs, whereas "Ca. B. sinica" outcompeted other two species at higher NLRs in both types of reactors. Furthermore, FISH analysis revealed that "Ca. J. caeni" was mainly present as spherical microclusters at the inner part (low NO₂^- environment), whereas "Ca. B. sinica" was present throughout the gel beads and granules. This spatial distribution supports the outcomes of the competition experiments. However, the successful competition of "Ca. J. caeni" at low NLR could not be explained with the Monod model probably due to inaccuracy of kinetic parameters such as half saturation constant (K_s) for nitrite and a difference in the maintenance rate (m). In addition, the growth of "Ca. K. stuttgartiensis" could not be observed in any experimental conditions, suggesting possible unknown factor(s) is missing. Taken together, NLR was one of factors determining ecological niche differentiation of "Ca. B. sinica" and "Ca. J. caeni".

Role of c-di-GMP in anammox aggregation and systematic analysis of its turnover protein in Candidatus Jettenia caeni

The anaerobic ammonium oxidation (anammox) process has been recognized as a promising sewage treatment approach. Considering the susceptibility, it is meaningful to study the behaviors of anammox bacteria under the unfavorable conditions. Here, we found that anammox bacteria more probably tended to aggregation by the regulation of c-di-GMP against the unfavorable environmental stresses (low temperature, aerobic condition and low pH). Further using multiple protein sequence alignment, we systematically examined the functionality of thirteen genes encoding putative c-di-GMP metabolic enzymes in anammox organism Candidatus Jettenia caeni, revealing most of the predicted enzymes were predicted to be active. Particularly, ectopic expression of jcaA, a gene encoding a protein with both GGDEF domain and EAL domain, suggested that it encoded a functional enzyme capable of both synthesizing and degrading c-di-GMP, which was clearly confirmed by in vitro enzymatic assays and reverse transcription polymerase chain reaction (RT-PCR). Furthermore, the catalytic mechanism was simulated by the means of three-dimensional homology modeling and molecular docking. The identification of c-di-GMP turnover and its role in granulation for anammox organism provides a new perspective for regulation of its aggregation capability and further promotion of anammox performance in the application of wastewater treatment process.

Anammox-zeolite system acting as buffer to achieve stable effluent nitrogen values

For a successful nitrogen removal, Anammox process needs to be established in line with a stable partial nitritation pretreatment unit since wastewater influent is mostly unsuitable for direct treatment by Anammox. Partial nitritation is, however, a critical bottleneck for the nitrogen removal since it is often difficult to maintain the right proportions of NO₂-N and NH₄-N during long periods of time for Anammox process. This study investigated the potential of Anammox-zeolite biofilter to buffer inequalities in nitrite and ammonium nitrogen in the influent feed. Anammox-zeolite biofilter combines the ion-exchange property of zeolite with the biological removal by Anammox process. Continuous-flow biofilter was operated for 570 days to test the response of Anammox-zeolite system for irregular ammonium and nitrite nitrogen entries. The reactor demonstrated stable and high nitrogen removal efficiencies (approximately 95 %) even when the influent NO₂-N to NH₄-N ratios were far from the stoichiometric ratio for Anammox reaction (i.e. NO₂-N to NH₄-N ranging from 0 to infinity). This is achieved by the sorption of surplus NH₄-N by zeolite particles in case ammonium rich influent came in excess with respect to Anammox stoichiometry. Similarly, when ammonium-poor influent is fed to the reactor, ammonium desorption took place due to shifts in ion-exchange equilibrium and deficient amount were supplied by previously sorbed NH₄-N. Here, zeolite acted as a preserving reservoir of ammonium where both sorption and desorption took place when needed and this caused the Anammox-zeolite system to act as a buffer system to generate a stable effluent.

Expression of the nirS, hzsA, and hdh Genes in Response to Nitrite Shock and Recovery in Candidatus Kuenenia stuttgartiensis

In this study, Candidatus Kuenenia stuttgartiensis were subjected to distinct nitrite shocks (66 (control), 200, 300, 400, and 500 mg N/L), and the responses of mRNA levels of cytochrome cd1 nitrite/nitric oxide oxidoreductase (nirS), hydrazine synthase (hzsA), and hydrazine dehydrogenase (hdh) were assessed. Changes in the hydrazine dehydrogenase (HDH) protein level were monitored. At 200 mg NO2(-)-N/L, the normalized specific anaerobic ammonium-oxidizing activity (nSAA) slightly increased relative to the control despite a significant decrease in nirS, hzsA, and hdh mRNA levels. When nitrite increased to 300 and 400 mg N/L, increased nirS, hzsA, and hdh mRNA levels were observed, but the nSAA decreased, relative to the 200 mg NO2(-)-N/L exposure. HDH protein detection revealed that Candidatus Kuenenia stuttgartiensis attempted to yield high enzyme levels by stimulating mRNA synthesis to resist the nitrite-induced stress. On 500 mg NO2(-)-N/L shock, the nirS, hzsA, and hdh mRNA levels decreased, alongside decreased nSAA and HDH levels. Although the mRNA levels did not always coincide with activities, our findings advance understanding of the mechanisms that anammox bacteria use to cope with nitrite inhibition at the transcriptional and translational levels, which will improve the diagnostic accuracy of bioreactor failures when nitrite accumulation occurs.

Effects of substrates on N2O emissions in an anaerobic ammonium oxidation (anammox) reactor

N2O emission in the anaerobic ammonium oxidation (anammox) process is of growing concern. In this study, effects of substrate concentrations on N2O emissions were investigated in an anammox reactor. Extremely high N2O emissions of 1.67 % were led by high NH4-N concentrations. Results showed that N2O emissions have a positive correlation with NH4-N concentrations in the anammox reactor. Reducing NH4-N concentrations by recycling pump resulted in decreasing N2O emissions. In addition, further studies were performed to identify a key biological process that is contributed to N2O emissions from the anammox reactor. Based on the results obtained, Nitrosomonas, which can oxidize ammonia to nitrite, was deemed as the main sources of N2O emissions.

Kinetic models for nitrogen inhibition in ANAMMOX and nitrification process on deammonification system at room temperature

In this study were fitted the best kinetic model for nitrogen removal inhibition by ammonium and/or nitrite in three different nitrogen removal systems operated at 25 °C: a nitrifying system (NF) containing only ammonia oxidizing bacteria (AOB), an ANAMMOX system (AMX) containing only ANAMMOX bacteria, and a deammonification system (DMX) containing both AOB and ANAMMOX bacteria. NF system showed inhibition by ammonium and was best described by Andrews model. The AMX system showed a strong inhibition by nitrite and Edwards model presented a best system representation. For DMX system, the increased substrate concentration (until 1060 mg NH3-N/L) tested was not limiting for the ammonia consumption rate and the Monod model was the best model to describe this process. The AOB and ANAMMOX sludges combined in the DMX system displayed a better activity, substrate affinity and excellent substrate tolerance than in nitrifying and ANAMMOX process.

Comparative analysis of two 16S rRNA gene-based PCR primer sets provides insight into the diversity distribution patterns of anammox bacteria in different environments

Due to the high divergence among 16S rRNA genes of anammox bacteria, different diversity pattern of the community could be resulted from using different primer set. In this study, the efficiencies and specificities of two commonly used sets, Amx368F/Amx820R and Brod541F/Amx820R, were evaluated by exploring the diversity characteristics of anammox bacteria in sediments from marine, estuary, and freshwater wetland. Statistical analysis indicated that the base mispairing rate between bases on 16S rRNA gene sequences retrieved by Amx368F/Amx820R and their corresponding ones on primer Brod541F was quite high, suggesting the different efficiency and specificity of Amx368F/Amx820R and Brod541F/Amx820R. Further experimental results demonstrated that multiple genera of anammox bacteria, including Ca. Scalindua, Ca. Brocadia, and Ca. Kuenenia, were able to be detected by Amx368F/Amx820R, but only Ca. Scalindua could be retrieved by Brod541F/Amx820R. Moreover, the phylogenetic clusters of Ca. Scalindua by Amx368F/Amx820R were different completely from those by Brod541F/Amx820R, presenting a significant complementary effect. By joint application of these two primer sets, the diversity distribution patterns of anammox bacteria in different environments were analyzed. Almost all retrieved sequences from marine sediments belonged to Ca. Scalindua. Sequences from freshwater wetland were affiliated to Ca. Brocadia and two new clusters, while high diversity of anammox bacteria was found in estuary, including Ca. Scalindua, Ca. Brocadia, and Ca. Kuenenia, corresponding to the river-sea intersection environmental feature. In total, these two prime sets have different characteristic for anammox bacteria detecting from environmental samples, and their combined application could achieve better diversity display of anammox community.

Concurrence of Anaerobic Ammonium Oxidation and Organotrophic Denitrification in Presence of p-Cresol

This study was carried out to evaluate the capacity of anaerobic granular sludge for oxidizing ammonium and p-cresol with nitrate as terminal electron acceptor. Kinetics for the anaerobic oxidation of ammonium and p-cresol is described in this paper. The phenolic compound was very efficiently consumed, achieving 65 % of mineralization. Ammonium and nitrate were also consumed at 83 and 92 %, respectively, being the main product N2. Anaerobic ammonium oxidation was promoted owing to accumulation of nitrite, and it allowed the synergy of anaerobic ammonium oxidation and organotrophic denitrification for the simultaneous removal of ammonium, nitrate, and p-cresol. A carbonaceous intermediate partially identified was transiently accumulated, and it transitorily truncated the respiratory process of denitrification. These experimental results might be considered for defining strategies in order to remove nitrate, ammonium, and phenolic compounds from wastewaters.

Consequence of altered nitrogen cycles in the coupled human and ecological system under changing climate: The need for long-term and site-based research

Anthropogenically derived nitrogen (N) has a central role in global environmental changes, including climate change, biodiversity loss, air pollution, greenhouse gas emission, water pollution, as well as food production and human health. Current understanding of the biogeochemical processes that govern the N cycle in coupled human-ecological systems around the globe is drawn largely from the long-term ecological monitoring and experimental studies. Here, we review spatial and temporal patterns and trends in reactive N emissions, and the interactions between N and other important elements that dictate their delivery from terrestrial to aquatic ecosystems, and the impacts of N on biodiversity and human society. Integrated international and long-term collaborative studies covering research gaps will reduce uncertainties and promote further understanding of the nitrogen cycle in various ecosystems.

Appropriate Fe (II) addition significantly enhances anaerobic ammonium oxidation (Anammox) activity through improving the bacterial growth rate

The application of anaerobic ammonium oxidation (Anammox) process is often limited by the slow growth rate of Anammox bacteria. As the essential substrate element that required for culturing Anammox sludge, Fe (II) is expected to affect Anammox bacterial growth. This work systematically studied the effects of Fe (II) addition on Anammox activity based on the kinetic analysis of specific growth rate using data from batch tests with an enriched Anammox sludge at different dosing levels. Results clearly demonstrated that appropriate Fe (II) dosing (i.e., 0.09 mM) significantly enhanced the specific Anammox growth rate up to 0.172 d(-1) compared to 0.118 d(-1) at regular Fe (II) level (0.03 mM). The relationship between Fe (II) concentration and specific Anammox growth rate was found to be well described by typical substrate inhibition kinetics, which was integrated into currently well-established Anammox model to describe the enhanced Anammox growth with Fe (II) addition. The validity of the integrated Anammox model was verified using long-term experimental data from three independent Anammox reactors with different Fe (II) dosing levels. This Fe (II)-based approach could be potentially implemented to enhance the process rate for possible mainstream application of Anammox technology, in order for an energy autarchic wastewater treatment.

Effect of zero-valent iron on the start-up performance of anaerobic ammonium oxidation (anammox) process

The long start-up time of anaerobic ammonium oxidation (anammox) process hinders the widespread application of anammox technology in practical wastewater treatment when anammox seed sludge is not available. Meanwhile, the production of nitrate cannot meet the increasingly more strict discharge standards. To combine the chemical nitrate reduction to ammonium with biological nitrogen removal, two anammox upflow anaerobic sludge blanket reactors packed with different types of zero-valent iron (ZVI), microscale ZVI (mZVI) and nanoscale ZVI (nZVI), were developed to accelerate the start-up of anammox process. The results revealed that anammox start-up time shortened from 126 to 105 and 84 days with the addition of mZVI and nZVI. The nitrogen removal performance was also improved remarkably by adding ZVI, especially in the start-up stage. The value of dissolved oxygen showed that ZVI could be regarded as a useful deoxidant to create anaerobic condition for the proliferation of anammox bacteria. ZVI was favorable for the secretion of EPS, which would represent the activity of anammox bacteria. The result of real-time quantitative PCR (qPCR) further confirmed that the proliferation of anammox bacteria was enhanced by ZVI.

Enhancement of anammox performance in a novel non-woven fabric membrane bioreactor (nMBR)

As well as a membrane separator, a non-woven fabric module could be employed as a biomass carrier to enhance microorganism proliferation and nitrogen removal.

Physiological characterization of anaerobic ammonium oxidizing bacterium 'Candidatus Jettenia caeni'

To date, six candidate genera of anaerobic ammonium-oxidizing (anammox) bacteria have been identified, and numerous studies have been conducted to understand their ecophysiology. In this study, we examined the physiological characteristics of an anammox bacterium in the genus 'Candidatus Jettenia'. Planctomycete KSU-1 was found to be a mesophilic (20-42.5°C) and neutrophilic (pH 6.5-8.5) bacterium with a maximum growth rate of 0.0020 h(-1) . Planctomycete KSU-1 cells showed typical physiological and structural features of anammox bacteria; i.e. (29) N2 gas production by coupling of (15) NH4 (+) and (14) NO2 (-) , accumulation of hydrazine with the consumption of hydroxylamine and the presence of anammoxosome. In addition, the cells were capable of respiratory ammonification with oxidation of acetate. Notably, the cells contained menaquinone-7 as a dominant respiratory quinone. Proteomic analysis was performed to examine underlying core metabolisms, and high expressions of hydrazine synthase, hydrazine dehydrogenase, hydroxylamine dehydrogenase, nitrite/nitrate oxidoreductase and carbon monoxide dehydrogenase/acetyl-CoA synthase were detected. These proteins require iron or copper as a metal cofactor, and both were dominant in planctomycete KSU-1 cells. On the basis of these experimental results, we proposed the name 'Ca. Jettenia caeni' sp. nov. for the bacterial clade of the planctomycete KSU-1.

Nitrate removal in shallow, open-water treatment wetlands

The diffuse biomat formed on the bottom of shallow, open-water unit process wetland cells contains suboxic zones that provide conditions conducive to NO3(-) removal via microbial denitrification, as well as anaerobic ammonium oxidation (anammox). To assess these processes, nitrogen cycling was evaluated over a 3-year period in a pilot-scale wetland cell receiving nitrified municipal wastewater effluent. NO3(-) removal varied seasonally, with approximately two-thirds of the NO3(-) entering the cell removed on an annual basis. Microcosm studies indicated that NO3(-) removal was mainly attributable to denitrification within the diffuse biomat (i.e., 80 ± 20%), with accretion of assimilated nitrogen accounting for less than 3% of the NO3(-) removed. The importance of denitrification to NO3(-) removal was supported by the presence of denitrifying genes (nirS and nirK) within the biomat. While modest when compared to the presence of denitrifying genes, a higher abundance of the anammox-specific gene hydrazine synthase (hzs) at the biomat bottom than at the biomat surface, the simultaneous presence of NH4(+) and NO3(-) within the biomat, and NH4(+) removal coupled to NO2(-) and NO3(-) removal in microcosm studies, suggested that anammox may have been responsible for some NO3(-) removal, following reduction of NO3(-) to NO2(-) within the biomat. The annual temperature-corrected areal first-order NO3(-) removal rate (k20 = 59.4 ± 6.2 m yr(-1)) was higher than values reported for more than 75% of vegetated wetlands that treated water in which NO3(-) was the primary nitrogen species (e.g., nitrified secondary wastewater effluent and agricultural runoff). The inclusion of open-water cells, originally designed for the removal of trace organic contaminants and pathogens, in unit-process wetlands may enhance NO3(-) removal as compared to existing vegetated wetland systems.

Floatation of flocculent and granular sludge in a high-loaded anammox reactor

The floatation of flocculent and granular sludge was investigated in this study. An anaerobic ammonium oxidation (anammox) upflow anaerobic sludge blanket (UASB) reactor was operated for 665 days. During this time, the maximum nitrogen removal rate was 52.6 kg Nm(-3) d(-1). Floccule floatation occurred between days 100 and 140, which potentially resulted from the sudden increase in gas yield and the poor settling ability of the floccules. Increasing the shear rate from 0.084 to 0.135 s(-1) was effective at eliminating floccule floatation. In addition, granule floatation occurred between days 572 and 665, which likely resulted from the formation of hollows within the granules. Floatation may be effectively prevented by maintaining a shear rate of more than 0.778 s(-1). Furthermore, the mechanisms of granule floatation and the floatation processes were proposed. Overall, controlling the shear force may effectively overcome sludge floatation.

Biogeography of anaerobic ammonia-oxidizing (anammox) bacteria

Anaerobic ammonia-oxidizing (anammox) bacteria are able to oxidize ammonia and reduce nitrite to produce N₂ gas. After being discovered in a wastewater treatment plant (WWTP), anammox bacteria were subsequently characterized in natural environments, including marine, estuary, freshwater, and terrestrial habitats. Although anammox bacteria play an important role in removing fixed N from both engineered and natural ecosystems, broad scale anammox bacterial distributions have not yet been summarized. The objectives of this study were to explore global distributions and diversity of anammox bacteria and to identify factors that influence their biogeography. Over 6000 anammox 16S rRNA gene sequences from the public database were analyzed in this current study. Data ordinations indicated that salinity was an important factor governing anammox bacterial distributions, with distinct populations inhabiting natural and engineered ecosystems. Gene phylogenies and rarefaction analysis demonstrated that freshwater environments and the marine water column harbored the highest and the lowest diversity of anammox bacteria, respectively. Co-occurrence network analysis indicated that Ca. Scalindua strongly connected with other Ca. Scalindua taxa, whereas Ca. Brocadia co-occurred with taxa from both known and unknown anammox genera. Our survey provides a better understanding of ecological factors affecting anammox bacterial distributions and provides a comprehensive baseline for understanding the relationships among anammox communities in global environments.