Abundance Of Anammox Bacteria Research Articles

Adaptation of anammox granules in swine wastewater treatment to low temperatures at a full-scale simultaneous partial nitrification, anammox, and denitrification plant

In the anammox process, maintaining a high anammox activity at low water temperatures for stable nitrogen removal is a challenge. In this study, to verify the adaptability of anammox to low water temperatures, we investigated effects of annual temperature fluctuations on nitrogen removal in a full-scale swine wastewater treatment plant, where anammox bacteria accumulated. Annual quarters were defined as L-1 (November–January), L-2 (February–April), H-1 (April–July), and H-2 (July–October). The total nitrogen removal rate was stable at 0.08–0.11 kg-N/m3/d, even during temperature fluctuations. Removal efficiencies of biochemical oxygen demand and total nitrogen were consistently high at 95–99% and 69–81%, respectively. The anammox activity and abundance of anammox bacteria were highest in granule L-1 and lowest in granule H-2. The optimal temperature for anammox activity shifted from 35 °C in granules H-1 and H-2 to 30 °C in granules L-1 and L-2, while the latter maintained a moderate activity compared to the former at low temperature. Candidatus Jettenia asiatica was predominant, especially in granule L-2, accounting for up to 54% of the microbial community composition at the genus level. The high specific anammox activity in granule L-2 was considered to be due to the abundance of anammox bacteria and the adaptation of Ca. Jettenia asiatica to low temperature. The anammox granules adapted well to low temperatures and demonstrated high efficiency in the simultaneous partial nitrification anammox and denitrification process without heating. Thus, constructing an energy-saving and cost-effective nitrogen removal system can be considered.

Carrier type induces anammox biofilm structure and the nitrogen removal pathway: Demonstration in a full-scale partial nitritation/anammox process

In this study, two typical carrier types, microporous and macroporous carriers, were collected from a full-scale partial nitritation/anammox reactor for analysis and comparison of the biofilm structure characteristics, performance and removal nitrogen pathway. For microporous carriers, a thicker biofilm (>5 mm) was obtained with higher biomass and abundance of anammox bacteria as well as a higher nitrogen removal efficiency due to the integration of denitrifying and anammox bacteria. In addition, higher microbial community stability can be expected under varying environmental conditions. In comparison, macroporous carrier biofilm exhibited a lower thickness (0.4–2.3 mm) and lower microbial richness, with a strong network correlation among genera. Analysis showed that the mainly positive correlation between anammox bacteria and ammonium oxidizing bacteria, enhancing coupling partial nitritation and anammox. These findings help further our understanding of the mechanisms of anammox biofilm nitrogen removal and provide a baseline for optimization of the design of carrier structures.

Unveiling performance stability and its recovery mechanisms of one-stage partial nitritation-anammox process with airlift enhanced micro-granules

The performance stability and its recovery mechanisms of a partial nitritation-anammox process were investigated. A one-stage airlift enhanced micro-granules (AEM) system was operated for 650 days continuously to treat 50 mg-NH4/L wastewater. During the stable stage, a high nitrogen removal efficiency of 72.7 ± 8.4% lasting for 230 days was successfully achieved under 0.28 L/min aeration rate and 0.10–0.20 mg/L dissolved oxygen (DO) concentration. A microbial consortium with good granularity appeared in red. The specific activity of anammox and ammonia oxidation increased to 1.02 and 0.93 g-N/g-VSS/d, respectively. Meanwhile, the microbial analysis showed the AEM system shifted the dominant microflora from Proteobacteria to Planctomycetes in which Candidatus Brocadia abundance reached a high of 35.0%. The results reveal that the long-term airlift-aeration promoted granulation and further enhanced activities, the abundances of anammox bacteria, and suppressed nitrite-oxidizing bacteria. Optimizing the DO control is also critical for stability increment and process recovery.

Successful enhancement and related characteristics of anammox bacterial activity by hydraulic supply strategy under limited inoculum

Two EGSB (expanded granular sludge bed) reactors (R0 and R1) with 2 g-VSS L−1 anammox sludge were established to intensify specific anammox activity (SAA) and biomass growth under limited inoculum, and in response to a hydraulic strategy. During the start-up period, HRT (hydraulic retention time) was set at 12h in R0, while sharply decreased from 12h to 4h in R1. The sludge characteristics, abundance, and community shifts were also investigated to explore their correlations with SAA enhancement. The results showed that after 120 days, SAA of R1 finally reached 1.6 kg-N kg-VSS−1 per day, which was 1.8- times that of R0. The initial shortened HRT in R1 changed the assembly mode of granulation, and unlike the flocculant sludge in R0, the formation and growth of small granules played a more critical role in improving SAA in R1. Also, the tightly bound layer of extracellular polymeric substances promoted a rapid increase in the proportion of particles larger than 0.6 mm in size, which significantly enhanced SAA. QPCR showed the corresponding abundance of anammox bacteria was gradually saturated to 5.72E+10 copies g-SS−1 when the SAA tended to be stable. While the increase in “saturated abundance” particles (>1.0 mm) speeded up the proliferation of anammox bacteria. The corresponding doubling time was shortened from 36.8–10.0 d in R1, which made up for the disadvantage of the initial biomass loss. The high-throughput analysis revealed Candidatus Kuenenia stuttgartiensis was the dominant genus (34.22 %) in R1.

Nitrogen removal from low COD/TIN real municipal sewage by coupling partial denitrification with anammox in mainstream

The application of partial denitrification coupling with anammox (PD/A) in municipal sewage treatment is one of the most promising research field, and it has just begun. In 548 days of experiment treating real domestic sewage, the continuous flow reactor was started up by adding biocarriers containing anammox bacteria and operated stably after acclimatization. The PD/A was successfully achieved in the step-feed AO system. Furthermore, mass balance of ammonium revealed that anammox could contribute 32–47% to nitrogen loss. Compared with no biocarriers addition phase, the nitrogen removal efficiency (NRE) increased to 77.8 ± 4.3% and the effluent total inorganic nitrogen (TIN) decreased to 11.0 ± 2.1 mg/L at the COD/TIN ratio of 2.9 from day 428 to day 548 under the condition of anammox biocarriers addition and without external carbon source. Quantitative polymerase chain reaction (qPCR) and high-throughput sequencing analysis showed that anammox bacteria on the biological carrier accounted for 3.06% of the total bacteria in the stable phase, which was much higher than the reported <0.003% in wastewater treatment plants (WWTPs). After 247 days of operation with anammox biocarriers addition, the abundance of anammox bacteria on the carriers tended to be stable at 3.36 × 1010 gene copies g−1 dry sludge. The activity of anammox decreased and maintained at 13.14 g NH4+-N m−3 d−1 under the biocarriers-only condition, while increased from 11.71 g NH4+-N m−3 d−1 to 25.65 g NH4+-N m−3 d−1 in the hybrid condition of biocarriers and flocs. This study indicated that PD/A is effective to strengthen nitrogen removal with low COD/TIN ratio.

Fouling behavior and mechanism of hydrophilic modified membrane in anammox membrane bioreactor: Role of gel layer

Membrane hydrophilic modification has been applied as an effective antifouling strategy for aerobic and anaerobic heterotrophic membrane bioreactors (MBRs), while its antifouling performance remains unclear for anaerobic ammonium oxidation (anammox) MBR. Herein, hydrophilic membranes (Mh) modified from pristine nylon fabric meshes (Mp, pore size of 20 μm), were applied in long-term operation of an anammox MBR. Although the average flux of Mh was 90.7% higher than that of Mp (p < 0.05) filtered with model foulant (bovine serum albumin) in a dead-end filtration test, the average filtration cycle of Mh in the anammox MBR was 37.9% shorter than that of Mp filtered with synthesized wastewater, in spite of the comparable total nitrogen removal efficiency (over 80%) achieved. A thin and compact gel layer was formed on Mh by adsorption of hydrophilic polysaccharide and further gelation of protein and colloidal biomass. The bound water wrapped in the gel layer on Mh brought about 32.8% higher filtration resistance, and caused 81.3% higher contribution rate of the flux decline caused by concentration polarization, compared with Mp. Moreover, more microbial metabolites, especially protein (23.9% vs. 17.7%), was rejected by Mh than Mp, providing organic matters for the proliferation of heterotrophic bacteria, and leading to the decreased relative abundance of anammox bacteria (from 63.2% to 35.2%). We proposed the formation process of the gel layer and revealed the membrane fouling mechanism on Mh in the anammox MBR, providing significant theoretical foundation for the membrane fouling control of anammox MBR systems.

The simultaneous recruitment of anammox granules and biofilm by a sequential immobilization and granulation approach

Anaerobic ammonium oxidation (anammox) is an important pathway in the nitrogen cycle and for autotrophic nitrogen removal of wastewater. However, the slow granulation or biofilm formation of anammox bacteria in a continuous-flow reactor without anammox inoculum is still a challenge. To accelerate granulation or biofilm formation, an approach of sequential immobilization and granulation of anammox (SIGA) and an internal circulation immobilized blanket (ICIB) with non-granular activated sludge inoculum was investigated. Pre-immobilizing the biofilm with carriers showed higher efficiencies of nitrite removal and enrichment of Candidatus Kuenenia than anaerobic sludge without immobilization. An ICIB with pre-immobilized anaerobic biofilm and an up-flow anaerobic sludge bed (UASB) with pre-acclimated anaerobic sludge were operated for 180 d. The ICIB reactor achieved a nitrogen removal rate of 1.11 kg·N/(m3·d) whereas the UASB reactor only obtained 0.29 kg·N/(m3·d). Illumina HiSeq sequencing of 16S rRNA gene amplicons indicated that the relative abundance of anammox bacteria (Candidatus Kuenenia, Candidatus Brocadia, and Candidatus Jettenia) achieved 42.5–50.6% in biofilm and 45.3–47.1% in granules in the ICIB reactor. By contrast, no anammox bacteria were enriched in the sludge of the UASB reactor. These findings showed that the granulation and the biofilm formation of abundant anammox bacteria occurred in a single ICIB. The anammox biofilm and internal circulation facilitate the granulation of anammox bacteria, as the planktonic anammox cells escaped from the biofilm on the carrier provides parent cells for the formation of anammox granules under suitable hydraulic shear conditions. This study provides a new strategy for a faster start-up of anammox using activated sludge inoculum based on ICIB and SIGA.

Geochemical transition zone powering microbial growth in subsurface sediments

No other environment hosts as many microbial cells as the marine sedimentary biosphere. While the majority of these cells are expected to be alive, they are speculated to be persisting in a state of maintenance without net growth due to extreme starvation. Here, we report evidence for in situ growth of anaerobic ammonium-oxidizing (anammox) bacteria in ∼80,000-y-old subsurface sediments from the Arctic Mid-Ocean Ridge. The growth is confined to the nitrate-ammonium transition zone (NATZ), a widespread geochemical transition zone where most of the upward ammonium flux from deep anoxic sediments is being consumed. In this zone the anammox bacteria abundances, assessed by quantification of marker genes, consistently displayed a four order of magnitude increase relative to adjacent layers in four cores. This subsurface cell increase coincides with a markedly higher power supply driven mainly by intensified anammox reaction rates, thereby providing a quantitative link between microbial proliferation and energy availability. The reconstructed draft genome of the dominant anammox bacterium showed an index of replication (iRep) of 1.32, suggesting that 32% of this population was actively replicating. The genome belongs to a Scalindua species which we name Candidatus Scalindua sediminis, so far exclusively found in marine sediments. It has the capacity to utilize urea and cyanate and a mixotrophic lifestyle. Our results demonstrate that specific microbial groups are not only able to survive unfavorable conditions over geological timescales, but can proliferate in situ when encountering ideal conditions with significant consequences for biogeochemical nitrogen cycling.

The effects of undulating seasonal temperature on the performance and microbial community characteristics of simultaneous anammox and denitrification (SAD) process

The effects of undulating seasonal temperature change (USTC) (10.1 °C–31.8 °C) on the N and carbon removal efficiency of simultaneous anammox and denitrification (SAD) were investigated, and the recovery performance of SAD was simulated. Results showed that 15 °C was the critical temperature of SAD for N and carbon removal under USTC from summer to winter. The removal efficiency of NH4+-N was improved in the final stage after temperature rise, but still lower than that in summer after long-term low temperature inhibition. The contribution of anammox to N removal was more than denitrification. The abundance of anammox bacteria (AnAOB) in SAD reactor was 8.8%–11.7% from summer to autumn. Candidatus Kuenenia replaced Candidatus Brocadia as the main AnAOB gradually. Finally, AnAOB abundance increased from 4.2% to 6.6% after recovery, and the abundance of denitrifying bacteria (DB) became the highest, which mainly includes Thauera and Hydrogenophaga.

Fixed nitrogen removal mechanisms associated with sulfur cycling in tropical wetlands

Wetland ecosystems play an important role in nitrogen cycling, yet the role of anaerobic ammonium oxidation (anammox) in tropical wetlands remains unclear. In the current study the anammox process accounted for 29.8 ~ 57.3% of nitrogen loss in ex situ activity batch tests of microcosms established from anoxic sediments of different tropical wetlands, with the highest activity being 17.95±0.51 nmol-N/g dry sediment/h. This activity was most likely driven by sulfide oxidation with dissimilatory nitrate reduction to ammonium (sulfide-driven DNRA). Microbial community analyses revealed a variety of anammox bacteria related to several known lineages, including Candidatus Anammoximicrobium, Candidatus Brocadia and Candidatus Kuenenia, at different wetlands. Metagenome predictions, batch tests, and isotope-tracing suggested that the high level of anammox activity was due to sulfide-driven DNRA. This was corroborated by a strong correlation (through Pearson's analysis) between the abundance of anammox bacteria and the nrfA (a dissimilatory nitrate reduction to ammonium gene) and dsrA (a sulfate reductase gene) genes, as well as sulfate, ammonium and nitrate concentrations. These correlations suggest syntrophic interactions among sulfate-reducing, sulfide-driven DNRA, and anammox bacterial populations. A better understanding of the role of sulfur in nitrogen loss via the anammox reaction in natural systems could inform development of a viable wastewater treatment strategy that utilizes sulfate to minimize the activity of denitrifying bacteria and thus to reduce nitrous oxide emissions from wastewater treatment plants.

Simultaneous occurrence and analysis of both anammox and n-damo bacteria in five full-scale wastewater treatment plants

Anaerobic ammonium oxidation (anammox) and nitrite-dependent anaerobic methane oxidation (n-damo) processes are two newly discovered biochemical pathways for removal of reactive nitrogen species and methane. An investigation was initiated to investigate the simultaneous removal of ammonium and methane and the corresponding microorganisms in a full-scale sewage treatment plant and four landfill leachate treatment plants. In this study, hzsB and pmoA genes were used to amplify the genomic DNA of these samples to reveal the diversity of anammox bacteria and n-damo bacteria in these WWTPs. Both anammox bacteria and n-damo bacteria were detected successfully in all samples. The hzsB gene-based PCR amplified sequences featured three genera of Candidatus (Ca.) Brocadia, Ca. Kuenenia and Ca. Jettenia in these WWTPs, while the pmoA gene amplification showed two species of Ca. Methylomirabilis oxyfera and Ca. Methylomirabilis sinica. It was observed that after inoculation of anammox sludge, Brocadia becomes more dominant from the initial co-existing consortium of Kuenenia and Brocadia, and the community diversity decreased accordingly. Based on quantitative 16S rRNA gene PCR, the abundance of anammox bacteria ranged from 2.64 × 106 to 1.73 × 1013 copies per gram dry sludge in the five plants, particularly high on the carriers of landfill leachate wastewaters and the abundance of n-damo bacteria ranged from 2.52 × 107 to 2.19 × 108 copies per gram dry sludge in the five plants. Results shows that abundances of anammox bacteria and AOB (ammonium oxidizing bacteria) were limited by the lower ammonium in the sewage treatment plant, but were higher corresponding to ammonium concentration. Successful inoculation of anammox bacteria was achieved in practical engineering systems and the co-occurrence of anammox bacteria and n-damo bacteria plays an important role in N and C removal in WWTPs.

Achieving fast start-up of anammox process by promoting the growth of anammox bacteria with FeS addition

The effects of FeS on nitrogen removal performance and microbial community of anammox process were studied. During the start-up period, the removal efficiencies of nitrite and total nitrogen were significantly improved by FeS. The addition of FeS increased the content of iron ions in the reactor and promoted the synthesis of heme c, which was involved in the formation of various enzymes. Compared with the control, the abundance of anammox bacteria in the FeS reactor was increased by 29%, and the expression level of the nirS gene (encoding cd1 type nitrite reductase containing heme) was nearly doubled. The content of nitrite reductase (ammonia-forming) in the community was increased by 26.4%. The difference in functional bacteria and enzyme contents in the microbial community resulted in a difference in nitrogen removal rate (NRR) between the two reactors. High-throughput results indicated that FeS increased the richness and diversity of microbial community and enhanced the metabolic function of the microbial community. The addition of FeS did not change the dominant position of Ca. Kuenenia in both reactors. But the relative abundance of heterotrophic denitrifying bacteria was reduced with FeS, which may be related to the inhibition effect of S2− produced by FeS.

Insight into the benefits of anammox bacteria living as aggregates

This work tried understanding aggregation preference of anammox bacteria from benefit-driven perspective. Aggregated anammox sludge (AGS) gained benefits in specific anammox activity (SAA) (increased by 40.47 ± 12.64%) and in toxicity resistance (enhanced by 65.41%) than scattered anammox sludge (SCS), which were verified by kinetics. The increased heme c content by 35.67 ± 5.77% and enhanced relative abundance of anammox bacteria by 9.29% supported the benefits in biological activity and improved EPS content by 1097.59 ± 43.06% (622.16 ± 61.73% for protein (PN), 2403.47 ± 162.75% for humic acid (HA) and 1145.34 ± 97.33% for polysaccharide (PS)) justified the benefits in toxicity resistance. The diverse microbial communities and organized spatial structures owned by AGS promoted interactions between species, as the intrinsic justification for obtaining the benefits. We expect our findings to provide theoretical guidance for promotions and applications of the anammox process with excellent nitrogen removal capacity and stability.

Characteristics of rapid-biofiltering anammox reactor (RBAR) for low nitrogen wastewater treatment

This research provides an important approach for rapid treatment of low nitrogen wastewater through anaerobic ammonium oxidation (anammox), which was realized in a rapid-biofiltering anammox reactor (RBAR). The operation mode of continuous upward flow and gradually shortened hydraulic retention time (HRT) accumulated anammox bacteria effectively in RBAR, where carmine anammox granular sludge and thick biofilm were co-existed, leading the biomass concentration and the specific anammox activity to reach 21.61 gSS/L and 0.82 gN/gVSS·d in the main functional zone. Moreover, the relative abundance of anammox bacteria in the whole reactor was more than 50%, and the relative abundance of Candidatus Brocadia in the biofilm of 20–47 cm zone reached 71.10%. Results showed that the removal rate and effluent concentration of total nitrogen remained stable at 86.24% and 14.20 mg/L (below 15 mg/L) averagely, under HRT of 32 min when the the nitrogen loading rate was 4.86 kgN/m3·d.

Build the expressway for the salt-tolerant anammox process: Acclimation strategy tells the story

The wide existence of saline wastewater has attracted public attention due to its environmental destructiveness. The potential of anammox to treat saline wastewater was systematically evaluated in this study. Three bioreactors with different salinity increasing strategies (R1: inhibition kinetic; R2: gradient increasing; R3: pulsed increasing) were operated to identify the optimal acclimation mode. The results showed that the inhibition of anammox activity by salinity was mainly caused by the loss of enzyme activity. Under the condition of 25.0 g NaCl L−1, the highest nitrogen removal rate of R3 (2.36 ± 0.14 kg N m−3 d−1) indicated that the pulsed strategy might be optimal. Changes in microbial community might be the primary reason lead to different acclimatization results. The relative abundance of anammox bacteria increased by 37.19% in R1 and by 46.81% in R3, but remained stable in R2 with increasing salinity. Dynamic varations in bacterial interactions, proteins, and functional genes revealed the potential resistance mechanisms of bacteria to salinity. The present work provides a novel approach and guidance for the treatment of nitrogen-rich saline wastewater by the anammox process.

Improving Efficiency and Stability of Anammox through Sequentially Coupling Nitritation and Denitritation in a Single-Stage Bioreactor.

This study developed an innovative process for the treatment of low-ammonium wastewater in a single-stage bioreactor over 250 days. Partial nitritation-anammox and partial denitritation-anammox (PN/A-PDN/A) processes were combined under aerobic/anoxic operation, and a high nitrogen removal efficiency (94.6%) was obtained at a nitrogen removal rate of 0.54 kg N m-3 d-1 and a chemical oxygen demand to total inorganic nitrogen (COD/TIN) ratio of 0.28. Mass balance analysis identified anammox as the dominant nitrogen removal pathway, achieving 88.3% nitrogen loss. The abundance of anammox bacteria and their bioactivity rapidly increased and were effectively maintained, as indicated by qPCR and bioactivity tests. The PN/A-PDN/A process provided two pathways of nitrite production for anammox, which favored the enrichment of anammox bacteria and stable processing. In addition, the enrichment of anammox bacteria was promoted by selective floc discharge since anammox bacteria are mainly located in granules (relative abundance of 29.64 ± 7.89%). Competitive organisms (including heterotrophic bacteria and nitrite oxidizing bacteria), enriched in flocs, were washed out. Overall, these findings confirmed anammox, sequentially combined with PN and PDN via aerobic/anoxic strategy, as a promising alternative for mainstream anammox.

Comparing nitrite-limited and ammonium-limited anammox processes treating low-strength wastewater: Functional and population heterogeneity

Biomass segregation between granules/biofilm and flocs is widespread in anammox-based processes. The segregation of biomass allows for easy control of processes stability. The goal of this study is to understand the biomass segregation in two anoxic anammox reactors respectively operated in nitrite-limited (RNO2) and ammonium-limited (RNH4) modes treating low-strength wastewater at 20 °C. Results showed that size-based biomass segregation was developed in both reactors. But the functional and population heterogeneity was more significant in the ammonium-limited anammox reactor. The activity and abundance of anammox bacteria in large granules were significantly higher than that in flocs under the ammonium-limited conditions. The large granules played a major role in nitrogen removal in RNH4. By contrast, both large granules and small flocs contributed significantly to the nitrogen loss in the nitrite-limited anammox reactor, since a large number of anammox bacteria existed in both granules and flocs. Besides, a number of Nitrospira-like NOB were also detected in both anoxic anammox reactors, which primarily inhabited in flocs seemingly droved by the availability of oxygen. But the abundance of Nitrospira in RNH4 was much higher than that in RNO2. All these results suggested that selective flocs removal would be necessary for RNH4 to improve its anammox performance but non-essential for RNO2. The two anammox reactors shared the predominant anammox species with the closest relative to Ca. Brocadia sp. 40 (98%). Unexpectedly, the anammox species grew faster in RNH4. But the microbial diversity and evenness was much greater in RNO2, suggesting its higher functional stability.

Wastewater Treatment using the “Sulfate Reduction, DenitrificationAnammox and Partial Nitrification (SRDAPN)” Process

Although nitrogen removal from wastewater is essential to prevent eutrophication, the biological processes employed to this end are characterized by several disadvantages, including high energy consumption and the production of large quantities of sludge. Thus, in this study, the organic matter and nitrogen removal efficiencies of the new sulfate reduction, denitrification/anammox and partial nitrification (SRDAPN) process were examined using an anaerobic-anoxic-oxic biofilter reactor. The results showed that the organic matter removal efficiency of the new process at loading rate 1.0 kg COD/m3 per day was 97%. With a circulation flow from the oxic to the anoxic column that was 3 times influent, the nitrogen removal efficiency of the sulfur denitrification and nitrification (SRDN) process without anammox, was 66%, while that of the SRDAPN process with anammox was 76%. Additionally, nitrogen consumption by the anammox reaction in the anoxic column was 13.8% for nitrite-nitrogen and 10.5% for ammonium-nitrogen, and the withdrawal of excess sludge was not required throughout the 170 days of operation. Microbial community analysis showed that acetogenic sulfate reducing bacteria and acetoclastic methanogens coexisted in the anaerobic column, and in the anoxic column, the total relative abundance of anammox bacteria, including Candidatus Brocadia, which coexisted with heterotrophic denitrifying bacteria and sulfur denitrifying bacteria, was 17-18%. Thus, this study established the SRDAPN process as an energy saving and high removal efficiency process.

Anammox bacterial abundance and biodiversity in greenhouse vegetable soil are influenced by high nitrate content

The anaerobic ammonium oxidizing (anammox) process has been found to play an important role in terrestrial ecosystems in recent years. However, the diversity and abundance of anammox bacteria in nitrogen (N)-rich agricultural soils under high fertilizer greenhouse conditions are still unclear. Two greenhouse fields with different N fertilizer input levels were chosen, and their soil profiles were studied with molecular technologies, including quantitative polymerase chain reaction assay, a clone library, and phylogenetic analysis based on hzsB (encoding anammox hydrazine synthase β-subunit) gene. Molecular analyses suggested that anammox bacteria were at their highest density at 10–20 cm soil depth, and that the anammox bacterial abundance was significantly lower at high N than at low N. Candidatus Brocadia was the sole anammox bacterial genus throughout the soil depth profiles. The highest diversity of anammox bacteria was found at 30–40 cm soil depth, and different phylotypic clusters of Candidatus Brocadia were associated with specific soil environmental factors, such as nitrates, soil depth, and total N. Correlation analyses and redundancy analyses confirmed that high nitrate content associated with high N fertilizer input had a significant negative influence on the abundance and biodiversity of anammox bacteria. These results imply that excessive use of N fertilizer would affect arid land soil N loss to the atmosphere by the anammox pathway.

Evolution of microbial dynamics with the introduction of real seawater portions in a low-strength feeding anammox process

The salinity effect on anammox bacteria has been widely reported; however, rare studies describe the microbial dynamics of anammox-based process response to the introduction of real seawater at mainstream conditions. In this study, an anammox process at mainstream conditions without pre-enriching anammox bacteria was shifted to the feeds of a synthetic wastewater with a portion of seawater mixture. It achieved over 0.180 kg-N/(m3 day) of nitrogen removal rate with an additional seawater proportion of 20% in the influent. The bacterial biodiversity was significantly increased with the increase of seawater proportions. High relative abundance of anammox bacteria (34.24–39.92%) related to Ca. Brocadia was enriched and acclimated to the saline environment. However, the introduction of seawater caused the enrichment of nitrite-oxidizing Ca. Nitrospira, which was responsible for the deterioration of nitrogen removal efficiency. Possible adaptation metabolisms in anammox bacteria and other nitrogen transforming bacteria are discussed. These results highlight the importance of microbial diversity for anammox process under the saline environments of 20% and 40% seawater composition.