Anammox Process Research Articles

Adaptation of anammox process for nitrogen removal from acidic nitritation effluent in a low pH moving bed biofilm reactor.

Acidic partial nitritation (PN) has emerged to be a promisingly stable process in wastewater treatment, which can simultaneously achieve nitrite accumulation and about half of ammonium reduction. However, directly applying anaerobic ammonium oxidation (anammox) process to treat the acidic PN effluent (pH 4-5) is susceptible to the inhibition of anammox bacteria. Here, this study demonstrated the adaptation of anammox process to acidic pH in a moving bed biofilm reactor (MBBR). By feeding the laboratory-scale MBBR with acidic PN effluent (pH=4.6±0.2), the pH of an anammox reactor was self-sustained in the range of pH 5-6. Yet, a high total nitrogen removal efficiency of over 80% at a practical loading rate of up to 149.7±3.9mg N/L/d was achieved. Comprehensive microbial assessment, including amplicon sequencing, metagenomics, cryosection-FISH, and qPCR, identified that Candidatus Brocadia, close to known neutrophilic members, was the dominant anammox bacteria. Anammox bacteria were found present in the inner layer of thick biofilms but barely present in the surface layer of thick biofilms and in thin biofilms. Results from batch tests also showed that the activity of anammox biofilms could be maintained when subjected to pH 5 at a nitrite concentration of 10mg N/L, whereas the activity was completely inhibited after disturbing the biofilm structure. These results collectively indicate that the anammox bacteria enriched in the present acidic MBBR could not be inherently acid-tolerant. Instead, the achieved stable anammox performance under the acidic condition is likely due to biofilm stratification and protection. This result highlights the biofilm configuration as a useful solution to address nitrogen removal from acidic PN effluent, and also suggests that biofilm may play a critical role in protecting anammox bacteria found in many acidic nature environments.

Effects of benthic bioturbation on anammox in nitrogen removal at the sediment-water interface in eutrophic surface waters.

Anaerobic ammonium oxidation (anammox) significantly contributes to nitrogen loss in freshwater ecosystems. The sediment-water interface (SWI), known as a "hot spot" for anammox, also harbors numerous macroinvertebrates. However, the impact of their bioturbation on anammox has generally been overlooked. This study compared the effects of three representative macroinvertebrates (i.e., Propsilocerus akamusi, Branchiura sowerbyi and Radix swinhoei) with different bioturbation modes on anammox and the N-removal processes at the SWI by using a microcosmic system. The results demonstrated that all three benthic macroinvertebrates promoted anammox in addition to denitrification processes. The highest N-removal was achieved in the presence of P. akamusi considered as a gallery-diffuser, where the relative abundance of Planctomycetes (to which the anammox bacteria belong) increased by 70%. P. akamusi increased the abundance of anammox hzsB gene by 2.58-fold and promoted potential anammox rate by 12.79nmol N g-1 h-1, which in turn facilitated total N-removal mass increased by 2.42-fold. In the presence of B. sowerbyi and R. swinhoei, the potential anammox rates increased by 4.81 and 5.57nmol N g-1 h-1, respectively. These results underscore the substantial impact of macroinvertebrates on anammox and N-removal processes, highlighting their crucial role in N pollution control, and sustaining the overall health and stability of eutrophic water bodies.

Rapid achievement of partial nitrification in domestic sewage treatment by in-site fermentation coupled with sludge discharge: Performance and mechanisms

Rapid achievement and stabilization of partial nitrification (PN) are the key bottlenecks for the application of anaerobic ammonia oxidization (anammox) process. In this study, a novel combined strategy was proposed to achieve PN in domestic sewage by in-site fermentation coupled with sludge discharge. Experiencing fermentation and reactivation period for 13 days, PN was rapidly established. Nitrite accumulation rate (NAR) on average maintained at 98.4 ± 2.0 % with sludge retention time (SRT) of 12 days. The quantitative real-time PCR (qPCR) and bioactivities of nitrifying bacteria shown that fermentation damaged on AOB less than on NOB, leading to the appearance of nitrite accumulation after fermentation period. PN remained stable for 114 days under rich‑oxygen environment (DO of 1.7–2.7 mg/L). High-throughput sequencing shown the abundance of Nitrospira decreased from 1.06 % to 0.003 %, while that of Nitrosomonas increased from 0.54 % to 1.03 %, suggesting that elimination of NOB was important reason for stabilization of PN. In-site fermentation coupled sludge discharge proved to be feasible for providing stable nitrite source, facilitating anammox operation in mainstream wastewater treatment.

"Candidatus Subterrananammoxibiaceae," a New Anammox Bacterial Family in Globally Distributed Marine and Terrestrial Subsurfaces.

Bacteria specialized in anaerobic ammonium oxidation (anammox) are widespread in many anoxic habitats and form an important functional guild in the global nitrogen cycle by consuming bio-available nitrogen for energy rather than biomass production. Due to their slow growth rates, cultivation-independent approaches have been used to decipher their diversity across environments. However, their full diversity has not been well recognized. Here, we report a new family of putative anammox bacteria, "Candidatus Subterrananammoxibiaceae," existing in the globally distributed terrestrial and marine subsurface (groundwater and sediments of estuary, deep-sea, and hadal trenches). We recovered a high-quality metagenome-assembled genome of this family, tentatively named "Candidatus Subterrananammoxibius californiae," from a California groundwater site. The "Ca. Subterrananammoxibius californiae" genome not only contains genes for all essential components of anammox metabolism (e.g., hydrazine synthase, hydrazine oxidoreductase, nitrite reductase, and nitrite oxidoreductase) but also has the capacity for urea hydrolysis. In an Arctic ridge sediment core where redox zonation is well resolved, "Ca. Subterrananammoxibiaceae" is confined within the nitrate-ammonium transition zone where the anammox rate maximum occurs, providing environmental proof of the anammox activity of this new family. Phylogenetic analysis of nitrite oxidoreductase suggests that a horizontal transfer facilitated the spreading of the nitrite oxidation capacity between anammox bacteria (in the Planctomycetota phylum) and nitrite-oxidizing bacteria from Nitrospirota and Nitrospinota. By recognizing this new anammox family, we propose that all lineages within the "Ca. Brocadiales" order have anammox capacity. IMPORTANCE Microorganisms called anammox bacteria are efficient in removing bioavailable nitrogen from many natural and human-made environments. They exist in almost every anoxic habitat where both ammonium and nitrate/nitrite are present. However, only a few anammox bacteria have been cultured in laboratory settings, and their full phylogenetic diversity has not been recognized. Here, we present a new bacterial family whose members are present across both the terrestrial and marine subsurface. By reconstructing a high-quality genome from the groundwater environment, we demonstrate that this family has all critical enzymes of anammox metabolism and, notably, also urea utilization. This bacterium family in marine sediments is also preferably present in the niche where the anammox process occurs. These findings suggest that this novel family, named "Candidatus Subterrananammoxibiaceae," is an overlooked group of anammox bacteria, which should have impacts on nitrogen cycling in a range of environments.

Hydroxyapatite (HAP) formation in acetate-driven partial denitrification process: Enhancing sludge granulation and phosphorus removal

Partial denitrification/anammox (PD/A) processes have emerged as a promising technology for efficient nitrogen removal from wastewater. However, these processes fail to remove phosphorus (P), a key pollutant that contributes to water eutrophication. To address this issue, the potential of inducing hydroxyapatite (HAP) precipitation in PD processes to achieve simultaneous P removal was investigated for the first time. Specifically, three SBRs (R1-R3) for PD were operated with adding varying concentrations of external Ca (30, 60, and 120 mg/L, respectively). Results demonstrated significant P reduction in all three SBRs, particularly in R3 with high Ca, which achieved an 80 % removal efficiency. Notably, sludge granulation was observed during operation, with the granule size in R3 with high Ca reaching 906.1 μm during the stable period, exceeding those in R2 (788.7 μm) and R1 (707.1 μm). This led to good settle ability of the PD sludge, as demonstrated by the lowest SVI5 (20 mL/g MLSS). Moreover, the decrease in the MLVSS/MLSS ratio suggested that the inorganic content accumulated, as observed by confocal laser scanning microscopy in the interior of the granules. Elemental composition analysis suggested that PD granules contained high P and Ca, while the X-ray diffraction (XRD) results confirmed the formation of HAP. Overall, this study demonstrated that PD-HAP coupled granular sludge process has potential as a robust and efficient method for nitrite production, as well as effective P removal and recovery, thereby advancing the application of anammox processes in wastewater treatment.

Enhancing mainstream anammox process by adding Fe3O4 nanoparticles

In order to further promote the application of mainstream anammox, magnetic field enhancing technology was applied to improve the anammox start-up and operation performance under the conditions of low temperature and substrates concentrations. Two UASBs were adopted as anammox reactors and run in parallel. The controlling group and the magnetic field enhancing group (with 2.4 g/L Fe3O4 NPs) were recorded as UASBC and UASBM. The results showed that UASBC and UASBM successfully took 37 days and 33 days to start mainstream anammox with TNRE of 90.03% and 85.05%, respectively. The maximum TNLR of UASBC and UASBM reached 0.54 mg N(m3·d)−1 and 0.82 mg N(m3·d)−1 with the maximum TNRE of 86.41% and 85.50% during 121 days operation. The results showed that magnetic filed could change morphological characteristics of AnAOB and strengthen sludge granulation by adjusting the composition of EPS. Microbial high-throughput sequencing analysis results showed the phylum of Planctomycetes dominated in UASBC and UASBM with the relative abundance of 26.41% and 32.68% on 121 d. Candidatus Kuenenia was cultured as the dominant bacteria, and it was speculated that magnetic filed had the ability to promoting the enrichment of Candidatus Kuenenia. These findings were interesting and meaningful, and could provide new ideas for long-term application of mainstream anammox.

Pilot-scale demonstration of self-enrichment of anammox bacteria in a two-stage nitrification-denitrification suspended sludge system treating municipal wastewater under extremely low nitrogen loading rate

In suspended sludge system, efficient enrichment and retention of anammox bacteria are crucial obstacles in mainstream wastewater treatment by anammox process. In this study, anammox bacteria was self-enriched in a pilot-scale suspended sludge system of two-stage nitrification–denitrification process serving municipal wastewater treatment. With the low ammonia (NH4+-N) of 9.3 mg/L, nitrate (NO3–-N) of 15.6 mg/L and COD/NO3–-N of 2.2 under extremely low nitrogen loading rate of 0.012 kg N/m3/d, anammox activity bloomed after its abundance increasing from 5.9 × 107 to 4.6 × 109 copies/g dry sludge. Significant NH4+-N removal was occurred and maintained stably in the denitrification reactor with anammox bacteria accounting for 1.13%, even under temperature decreasing to 20.0℃. The adequately anoxic environment, efficient retention with the static settlement, and NO2– production via NO3– reduction provided favorable environment for anammox bacteria. This study demonstrated the feasibility and great potential in mainstream anammox application without seeding specific sludge.

Efficient nitrogen removal from municipal wastewater by an autotrophic-heterotrophic coupled anammox system: The up-regulation of key functional genes

The metabolic pathways based on key functional genes were innovatively revealed in the autotrophic-heterotrophic coupled anammox system for real municipal wastewater treatment. The nitrogen removal performance of the system was stabilized at 88.40 ± 3.39 % during the treatment of real municipal wastewater. The relative abundances of the nitrification functional genes ammonia oxidase (amoA/B/C), hydroxylamine oxidoreductase (hao), and nitrite oxidoreductases (nxrA/B) were increased by 1.2–2.4 times, and these three nitrification functional genes were mostly contributed by Nitrospira that dominated the efficient nitrification of the system. The relative abundance of anammox bacteria Candidatus Brocadia augmented from 0.35 % to 0.75 %, accompanied with the increased expression of hydrazine synthase (hzs) and hydrazine dehydrogenase (hdh), resulting in the major role of anammox (81.24 %) for nitrogen removal. The expression enhancement of the functional genes nitrite reductase (narG/H, napA/B) that promoted partial denitrification (PD) of the system weakened the adverse effects of the sharp decline in the population of PD microbe Thauera (from 5.7 % to 2.2 %). The metabolic module analysis indicated that the carbon metabolism pathways of the system mainly included CO2 fixation and organic carbon metabolism, and the stable enrichment of autotrophic bacteria ensured stable CO2 fixation. Furthermore, the enhanced expression of the glucokinases (glk, GCK, HK, ppgk) and the abundant pyruvate kinase (PK) achieved stable hydrolysis ability of organic carbon metabolism function of the system. This study offers research basics to practical application of the mainstream anammox process.

Insights into the response of anammox process to oxytetracycline: Impacts of static magnetic field

The long-term effects of oxytetracycline (OTC) with a high concentration on the anaerobic ammonium oxidation (Anammox) process were evaluated, and the role of static magnetic field (SMF) was further explored. The stress of OTC at 50 mg/L had little effect on the nitrogen removal of anammox process at the first 16 days. With the continuous addition of OTC and the increase of nitrogen loading, the OTC inhibited the nitrogen removal and anammox activity severely. During the 32 days of recovery period without OTC addition, the nitrogen removal was further deteriorated, indicating the inhibition of OTC on anammox activity was irreversible and persistent. The application of SMF alleviated the inhibition of OTC on anammox to some extent, and the specific anammox activity was enhanced by 47.1% compared to the system without SMF during the OTC stress stage. Antibiotic efflux was the major resistance mechanism in the anammox process, and tetA, tetG and rpsJ were the main functional antibiotic resistance genes. The addition of OTC weakened the metabolic interactions between the anammox bacteria and the symbiotic bacteria involved in the metabolism of cofactors and secondary metabolites, leading to the poor anammox activity. The adaptability of microbes to the OTC stress was improved by the application of SMF, which can enhance the metabolic pathways related to bacterial growth and resistance to environmental stress.

Metagenomics insights into high-rate nitrogen removal from municipal wastewater by integrated nitrification, partial denitrification and Anammox at an extremely short hydraulic retention time

To achieve high-rate nitrogen removal in municipal wastewater treatment through anaerobic ammonia oxidation (Anammox), the nitrification, partial denitrification, and Anammox processes were integrated by a step-feed strategy. An exceptional nitrogen removal load of 0.224 kg N/(m3·d) was achieved by gradient-reducing the hydraulic retention time (HRT) to 5 h. Metagenomic analysis demonstrated that Nitrosospira could express all genes encoding ammonia oxidation under low nitrogen and dissolved oxygen conditions (less than 0.5 mg/L), enabling complete nitrification. With the short of HRT, the relative abundance of Thauera increased from 2.8 % to 6.4 %. Frequent substrate exchanges at such extremely short HRT facilitated enhanced synergistic interactions among Nitrosospira, Thauera, and Candidatus Brocadia. These findings provide a comprehensive understanding of the utilization of Anammox combined processes for high-speed nitrogen removal in municipal wastewater treatment and the microbial interactions involved.

Microbial driving mechanism for nitrogen removal performance of anammox with combined fillers addition: Microbial community dynamics, metabolic function and network analysis

Microbial community is vital for efficient nitrogen removal in an anaerobic ammonium oxidation (anammox) system. However, the mechanisms of microbially driven anammox denitrification are far from clear. The results showed that the nitrogen removal efficiency (especially the removal rate of NH4+-N, which reached 85.6 ± 3.1 %) significantly increased (p < 0.05) by combined fillers addition. Scanning electron microscope (SEM) images showed the microflora changed gradually from short rod-shaped to spherical aggregates, improving shock loading resistance in the system. The dominant microflora shifted from Proteobacteria and Bacteroidetes to Chloroflexi and Planctomycetes, in which Candidatus Jettenia reached a maximum abundance of 30.7 %. Meanwhile, the abundance of denitrifying bacteria (Denitratisoma and Thiobacillus) was significantly diminished. Significant enhancements in the energy metabolic capacity of microorganisms, especially nitrogen metabolism, were observed in the anammox process. Moreover, the increase in abundance of hzo gene suggested the enhancement of the anammox process. Co-occurrence network analysis demonstrated that the genera Longilinea, Thiobacillus, Candidatus Jettenia, Dokdonella, and Candidatus Brocadia were the keystones, and complex microbial interactions (stronger symbiotic than competitive relationships) enhanced the nitrogen removal capability. Overall, the results of this study provided more comprehensive information regarding community succession, coexistence and collaboration in anammox process for nitrogen removal.

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

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

Characterization of Anammox Bacteria from Marine Water and Sediment Samples

Anammox activity of water and sediment taken from marine ecosistem around Semarang were investigated in anammox media agar and batch reactor. Effect of increasing salinities (3% to 5%, 7% and 9%) and decreasing salinities (3% to 2%, 1% and 0%) were investigated. Water and sediment taken from marine ecosistem around Semarang city showed a positive result. Increasing salinity up to 9% will have a positive influence on the activity of anammox bacteria. Whereas, the decrease in salinity will negatively affect anammox bacteria. The ratio of ammonium:nitrite for anammox process ranges from 0.89 to 1.22 and ammonium removal rate varies from 0.08 to 0.59 mg-N/liter hour.

Study on the mechanism of enhanced anaerobic ammonia oxidation performance by extracellular electron acceptor biochar

ABSTRACT Anaerobic ammonia oxidation process has the advantages of energy and cost reduction, therefore, it has been considered as one of the main alternatives to conventional biological denitrification process in recent years. Biochar has been applied in the anammox process for nitrogen removal efficiency. But, due to its extracellular electron transfer capacity and abundance of redox-specific functional groups, which served as extracellular electron acceptor to anaerobically oxidize NH4 + is still controversy. In this study, the anaerobic ammonia oxidation was investigated when biochar was used as electron acceptor in the wastewater. According to the optimal process variables determined in the batch tests, when the influent NH4 +-N concentration in the anaerobic ammonia oxidation reaction was 30–50 mg/L and the biochar dosing was at 10 g/L, it showed some promotion in the long-term experiments. The anaerobic ammonia oxidation process with biochar as the electron acceptor reached more than 60% NH4 +-N removal efficiency in the system, and the ΔNO3 --N/ΔNH4 +-N ratio reached 0.19 which tended to the theoretical value. After 20 days, the voltage in the system keeps fluctuating about 4 mV, indicated that the functional bacteria using biochar as the electron acceptor gradually dominated the system. In addition, the abundance of norank_f__norank_o__SBR1031 in the Chloroflexi phylum has increased significantly at 29.92%, while the abundance of the major genus Candidatus_Kuenenia in AnAOB has decreased slightly at 11.47%.

Effective abatement of ammonium and nitrate release from sediments by biochar coverage

Inorganic forms of N from sediments and runoff water, among others, remain some of the key sources of pollution of water bodies. However, the release of NH4+-N from sediment to water can be effectively reduced by biochar coverage due to high adsorption capacity, unlike NO3—N, where biochar has a low affinity. The feasibility of biochar coverage to abate NO3−-N release needs to be evaluated. This study collected four sediments from Lake Taihu (China). Three types of biochar pyrolyzed from ordinary wastes, coconut shell (coBC), algal and excess sludge, were prepared to cover them and were incubated for 90 days. Results showed that the terminal total nitrogen (TN) and NO3−-N concentrations decreased from 5.35 to 2.31–3.04 mg/L, 3.05 to 0.34–1.11 mg/L, respectively. CoBC coverage showed the best performance for reducing NO3−-N release flux from 26.99 ± 0.19 to 9.30 ± 0.02 mg/m2·d (63.6 %). Potential denitrifiers, such as Flavobacterium and Exiguobacterium, were enriched in the biochar-coverage layer, and the absolute abundance of N-related functional genes (narG, nirS, nosZ and anammox) was increased by 1.76–4.21 times (p < 0.05). Jar tests by 15N isotope labeling further indicated that biochar addition increased the denitrification and anammox rates by 53.5–83.4 %. Experiments combining exogenous organic‑carbon addition and 15N labeling demonstrated that biochar's key role was regulating organic matter's bioavailability. Analysis with partial least square path modeling (PLS-PM) implied biochar with higher adsorption enhanced the denitrification and anammox processes in sediments via modifying the niche with suitable DOC, TN, and pH. This study suggested that biochar coverage could effectively abate NO3−-N release from sediments by affecting the denitrification and anammox processes.

Towards intensified preservation technology of anammox granular sludge: Insights into the role of energy support

Anammox is an advanced biotechnology for nitrogen removal and has been widely applied in wastewater treatment. Preservation of anammox granular sludge (AnGS) is an essential approach to support the sustainable development of anammox processes. In this study, the activity descent and its mechanism of AnGS during long-term cryopreservation were investigated. The results showed that the cryopreservation process of AnGS could be divided into plummeting stage, maintaining stage and descending stage in terms of activity index, namely three-stage activity descent. A significant positive correlation was observed between the ATP pool and the three-stage activity descent (by hzo-mRNA/hzo-gene ratio) of AnGS (R2 = 0.944). The ATP pool was found to be replenished by the sequential consumption of endogenous energy substances, leading to the stationary activity of AnGS. The consumption of essential cell components as an energy source was revealed to cause damage and even death of functional bacteria, and the energy stress could be mitigated by the regular exogenous substrate supply. Consequently, the energy support in terms of ATP could be a feasible way to innovate the preservation technology and promote the sustainable development of anammox processes.

Coupling membrane electro-bioreactor with anammox process to treat wastewater at low temperatures

Membrane bioreactors (MBRs)have been extensively applied to municipal wastewater treatment. Nevertheless, MBRs cannot eliminate nutrients to an adequate level without extra operation units and intensive chemical supplies. Furthermore, low temperatures destroy the performance of the MBR process. In this work, a pioneering anammox membrane electro-bioreactor (MEBR/anammox) system was designed and operated at a constant flow rate of 7L/d with continuous monitoring of sludge liquor temperature (8–22 °C). The MEBR/anammox worked with a sludge retention time (SRT) of 20 days and a hydraulic retention time (HRT) of 24 h. It was found that temperature variations did not significantly influence the effluents quality in terms of nutrients and COD. At lower operating temperatures, the effluent concentrations of NH4-N, TN, PO4-P, and COD in the MEBR-anammox were 0.77 mg/L, 6.42 mg/L, 0.80 mg/L, and 24.95 mg/L, respectively. The corresponding removal efficiencies were 94.46%, 88.62%, 95.60%, and 90.76%, respectively. Taken together, the implementation of a low/periodic direct current (DC) of 14.85 A/m2 and anammox process inside the MBR, achieving a MEBR/anammox, was found to enhance the efficacy of the treatment system, improve sludge properties and increase membrane fouling control in low-temperature milieus compared to traditional MBR. The MEBR/anammox system, introduced in this work, establishes an innovative wastewater technology that minimizes the footprint, capital and operating expenditures of the plant. In addition, this system could open new prospects for the treatment of municipal sewage in cold regions.

Long-term effect of light rare earth element neodymium on Anammox process

During the mining of rare earth minerals, the application of neodymium-containing manures, and the treatment of spent neodymium iron boron magnet, the generation of ammonia wastewater containing neodymium is increasing. Thus, the effects of neodymium (Nd(III)) on anaerobic ammonium oxidation (Anammox) were investigated from the aspects of performance, kinetics, statistics, microbial community and sludge morphology, and the recovery strategy of EDTA-2Na wash was discussed. The nitrogen removal efficiency of the Anammox reactor decreased significantly and eventually collapsed at the Nd(III) dosing levels of 20 and 40 mg L−1, respectively. And the toxicity of Nd(III) to AnAOB was determined by the amount internalized into the cells. The EDTA-2Na wash successfully increased the total nitrogen removal rate (TNRR) of Nd(III)-inhibited Anammox to 41.60% of its initial value within 30 days, and the modified Boltzmann model accurately simulated this recovery process. The transient and extended effects of Nd(III), self-recovery, and EDTA-2Na wash on Anammox were effectively assessed using a one-sample t-test. 16S rRNA gene sequencing indicated that Nd(III) remarkably decreased the relative abundance of Planctomycetes and Candidatus Brocadia. The scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) revealed crystal-like neodymium particles on the surface of Anammox sludge. The above-mentioned results demonstrate that the concentration of Nd(III) should be below the toxicity threshold (20 mg L−1) when treating ammonia wastewater containing neodymium by Anammox, and also emphasize the importance of an appropriate recovery strategy.

Coupled systems of pre-denitrification and partial nitritation/anammox improved functional microbial structure and nitrogen removal in treating swine manure digestate

This study evaluated the functional activity and microbial structure of a pre-denitrification and single-stage partial nitritation/anammox process (DB-SNAP) coupled system for effectively treating swine manure digestate (SMD). At influent ammonium concentrations of (1000 to 1500) mg/L, the pre-denitrification reactor increased the nitrogen removal efficiency (NRE) by 5%, resulting in an average NRE of 96%. The DB-SNAP and nitrogen-limited strategy facilitated the rapid adoption of anammox bacteria (AnAOB) in the SMD, maintaining a high specific rate of 0.3gN/gVSS/d. A high secretion of tightly bound extracellular polymeric substances (76 mg/gVSS to 102 mg/gVSS) promoted micro-granule aggregation and stability. Moreover, Ca. Kuenenia, an AnAOB genus, was highly enriched from 21% to (27 to 30) %, whereas Nitrospira, a nitrite-oxidizing bacteria, was significantly suppressed to (0 to 0.05) %. These findings will provide valuable guidance in implementing the anammox process in swine wastewater treatment.

Anammox with alternative electron acceptors: perspectives for nitrogen removal from wastewaters.

In the context of the anaerobic ammonium oxidation process (anammox), great scientific advances have been made over the past two decades, making anammox a consolidated technology widely used worldwide for nitrogen removal from wastewaters. This review provides a detailed and comprehensive description of the anammox process, the microorganisms involved and their metabolism. In addition, recent research on the application of the anammox process with alternative electron acceptors is described, highlighting the biochemical reactions involved, its advantages and potential applications for specific wastewaters. An updated description is also given of studies reporting the ability of microorganisms to couple the anammox process to extracellular electron transfer to insoluble electron acceptors; particularly iron, carbon-based materials and electrodes in bioelectrochemical systems (BES). The latter, also referred to as anodic anammox, is a promising strategy to combine the ammonium removal from wastewater with bioelectricity production, which is discussed here in terms of its efficiency, economic feasibility, and energetic aspects. Therefore, the information provided in this review is relevant for future applications.