Feammox Process Research Articles

Ferrihydrite optimizing Feammox inoculum to enhance ammonia removal from concentrate wastewater through continuous upflow anaerobic sludge blanket (UASB)

The manuscript discusses Feammox reaction from aspects of Feammox inoculum from five soil sources (paddy soil, forest soil, pond sediment, planting red soil, and planting black soil), optimization by 0–50 mmol ferrihydrite and application to ammonia removal by continuous upflow anaerobic sludge blanket (UASB). The results demonstrated that Feammox enrichment from pond sediment had the highest NH4+-N removal rate of 45.92 %, which was used as the seed sludge of ferrihydrite optimization. Under the optimal concentration of ferrihydrite (10 mmol L−1), Feammox enrichment removed 79.09 % NH4+-N and comparably removed 80 % phosphorus. In UASB reactor, the predominant bacteria of Anaerolineaceae, Candidatus Brocadia, Denitratisoma, Terrimonas, and Nitrosomonas involved conversion of Fe3+/Fe2+ and ammonia removal (66.05 % NH4+-N removal rate) within 154 days at pH 6, comparably facilitating over 40 % of TP removal. In the interacting process of NH4+, NO2- and NO3-, the theoretical calculation results signify that ferrihydrite exhibits a significant affinity for NH4+ adsorption over NO2- and NO3-. These findings enhance our understanding of the Feammox process under various environmental conditions and provide insights into the Fe/N transformation process.

Performances and mechanisms of anaerobic nitrogen removal through Fe (III)/Fe (II) cycle with sponge iron biofilm without external iron addition

Anaerobic ammonia oxidation coupled to Fe (III) reduction (Feammox) plays an important role in the natural nitrogen cycle. However, for its application in wastewater treatment process, the source of iron is a major limitation. In this study, Feammox process was successfully achieved without external iron addition using sponge iron biofilm. The products of Feammox process, nitrate and Fe (II), provided substrates for nitrate dependent ferrous oxidation (NDFO). Therefore, nitrogen removal and Fe (II)/Fe (III) cycle were achieved in reactor and nitrogen removal efficiency by Feammox and NDFO pathways was up to 58.4 %. The X-ray diffraction indicated the sludge contained magnetite and lepidocrocite, which provided Fe (III) for the occurrence of Feammox. Microorganisms related to Feammox process were dominated by Geothrix. It was found Feammox activity was similar at pH of 8 and 7, while inhibited at pH of 6, which was caused by the decrease of Feammox bacteria. And Feammox activity decreased with the decrease of temperature, in which the ammonia removal rate was 2 times faster at 30 °C than at 10 °C. Under micro‑oxygen aeration, the ammonia removal rate improved and Feammox and NDFO processes still played roles in system, nevertheless, under high dissolved oxygen condition, Feammox bacteria-Geothrix and NDFO bacteria Thiobacillus would be gradually eliminated from the system.

Feammox bacterial biofilm formation in HFMB

Nitrogen pollution has been increasing with the development of industrialization. Consequently, the excessive deposition of reactive nitrogen in the environment has generated the loss of biodiversity and eutrophication of different ecosystems. In 2005, a Feammox process was discovered that anaerobically metabolizes ammonium. Feammox with the use of hollow fiber membrane bioreactors (HFMB), based on the formation of biofilms of bacterial communities, has emerged as a possible efficient and sustainable method for ammonium removal in environments with high iron concentrations. This work sought to study the possibility of implementing, at laboratory scale, an efficient method by evaluating the use of HFMB. Samples from an internal circulation reactor (IC) incubated in culture media for Feammox bacteria. The cultures were enriched in a batch reactor to evaluate growth conditions. Next, HFMB assembly was performed, and Feammox parameters were monitored. Also, conventional PCR and scanning electron microscopy (SEM) analysis were performed to characterize the bacterial communities associated with biofilm formation. The use of sodium acetate presented the best performance for Feammox activity. The HFMB operation showed an ammonium (NH4+) removal of 50%. SEM analysis of the fibers illustrated the formation of biofilm networks formed by bacteria, which were identified as Albidiferax ferrireducens, Geobacter spp, Ferrovum myxofaciens, Shewanella spp., and Anammox. Functional genes Archaea/Bacteria ammonia monooxygenase, nrxA, hzsB, nirS and nosZ were also identified. The implementation of HFMB Feammox could be used as a sustainable tool for the removal of ammonium from wastewater produced because of anthropogenic activities.

Asynchronous characteristics of Feammox and iron reduction from paddy soils in Southern China

Recently, the newly discovered anaerobic ammonium oxidation coupled with iron reduction (i.e., Feammox) has been proven to be a widespread nitrogen (N) loss pathway in ecosystems and has an essential contribution to gaseous N loss in paddy soil. However, the mechanism of iron-nitrogen coupling transformation and the role of iron-reducing bacteria (IRB) in Feammox were poorly understood. This study investigated the Feammox and iron reduction changes and microbial community evolution in a long-term anaerobic incubation by 15N isotope labeling combined with molecular biological techniques. The average rates of Feammox and iron reduction during the whole incubation were 0.25 ± 0.04 μg N g−1 d−1 and 40.58 ± 3.28 μg Fe g−1 d−1, respectively. High iron oxide content increased the Feammox rate, but decreased the proportion of Feammox–N2 in three Feammox pathways. RBG-13-54-9, Brevundimonas, and Pelomonas played a vital role in the evolution of microbial communities. The characteristics of asynchronous changes between Feammox and iron reduction were found through long-term incubation. IRB might not be the key species directly driving Feammox, and it is necessary to reevaluate the role of IRB in Feammox process.

Nitrogen loss in coastal sediments driven by anaerobic ammonium oxidation coupled to microbial reduction of Mn(IV)-oxide

Coastal sediments play a central role in regulating the amount of land-derived reactive nitrogen (Nr) entering the ocean, and their importance becomes crucial in vulnerable ecosystems threatened by anthropogenic activities. Sedimentary denitrification has been identified as the main sink of Nr in marine environments, while anaerobic ammonium oxidation with nitrite (anammox) has also been pointed out as a key player in controlling the nitrogen pool in these locations. Collected evidence in the present work indicates that the microbial biota in coastal sediments from Baja California (northwestern Mexico) has the potential to drive anaerobic ammonium oxidation linked to Mn(IV) reduction (manganammox). Unamended sediment showed ammonification, but addition of vernadite (δMnO2 with nano-crystal size ∼15 Å) as terminal electron acceptor fueled simultaneous ammonium oxidation (up to ∼400 μM of ammonium removed) and production of Mn(II) with a ratio ∆[Mn(II)]/∆[NH4+] of 1.8, which is very close to the stoichiometric value of manganammox (1.5). Additional incubations spiked with external ammonium also showed concomitant ammonium oxidation and Mn(II) production, accounting for ∼30 % of the oxidized ammonium. Tracer analysis revealed that the nitrogen loss associated with manganammox was 4.2 ± 0.4 μg 30N2/g-day, which is 17-fold higher than that related to the feammox process (anaerobic ammonium oxidation linked to Fe(III) reduction, 0.24 ± 0.02 μg 30N2/g-day). Taxonomic characterization based on 16S rRNA gene sequencing revealed the existence of several clades belonging to Desulfobacterota as potential microorganisms catalyzing the manganammox process. These findings suggest that manganammox has the potential to be an additional Nr sink in coastal environments, whose contribution to total Nr losses remains to be evaluated.

Anaerobic ammonium oxidation coupled to iron(III) reduction catalyzed by a lithoautotrophic nitrate-reducing iron(II) oxidizing enrichment culture.

The last two decades have seen nitrogen/iron-transforming bacteria at the forefront of new biogeochemical discoveries, such as anaerobic ammonium oxidation coupled to ferric iron reduction (feammox) and lithoautotrophic nitrate-reducing ferrous iron-oxidation (NRFeOx). These emerging findings continue to expand our knowledge of the nitrogen/iron cycle in nature and also highlight the need to re-understand the functional traits of the microorganisms involved. Here, as a proof-of-principle, we report compelling evidence for the capability of an NRFeOx enrichment culture to catalyze the feammox process. Our results demonstrate that the NRFeOx culture predominantly oxidizes NH4+ to nitrogen gas, by reducing both chelated nitrilotriacetic acid (NTA)-Fe(III) and poorly soluble Fe(III)-bearing minerals (γ-FeOOH) at pH 4.0 and 8.0, respectively. In the NRFeOx culture, Fe(II)-oxidizing bacteria of Rhodanobacter and Fe(III)-reducing bacteria of unclassified_Acidobacteriota coexisted. Their relative abundances were dynamically regulated by the supplemented iron sources. Metagenomic analysis revealed that the NRFeOx culture contained a complete set of denitrifying genes along with hao genes for ammonium oxidation. Additionally, numerous genes encoding extracellular electron transport-associated proteins or their homologs were identified, which facilitated the reduction of extracellular iron by this culture. More broadly, this work lightens the unexplored potential of specific microbial groups in driving nitrogen transformation through multiple pathways and highlights the essential role of microbial iron metabolism in the integral biogeochemical nitrogen cycle.

Use of soluble iron salt as an electron acceptor to provide Fe(III) for Feammox process: Ammonium removal performance and mechanism

Fe(III) reduction coupled with anaerobic ammonium oxidation (Feammox) is a newly discovered biological ammonium removal technology. Compared to anaerobic ammonium oxidation (anammox) process, Feammox does not require NO2−-N as a reaction substrate and is more tolerant to heavy metals. In this study, soluble iron salts FeCl3 was added to anaerobic sequencing batch reactor (ASBR) to start Feammox process. The effects of Fe/N, pH and temperature on the Feammox performance were investigated. Optimal working conditions were determined by combining the variation law of nitrogen and iron elements. The results showed that the best NH4+-N removal efficiency when Fe/N, pH and temperature were 0.15, 6.5 and 30 °C, respectively. The modified Boltzmann model fitted better in Feammox kinetic analysis (R2 = 0.9789), which could clearly explain that the degradation of substrate and the generation of product. Microbial analysis showed that in addition to the typical iron-reducing bacteria, the dominant genus Candidatus_Brocadia of anammox was also enriched in the system with relative abundance of 3.16 %, implying that both Feammox and anammox contributed to the transformation of NH4+-N. Overall, optimizing the operating conditions of Feammox is important significance to maintain the stability of NH4+-N removal performance and provide theoretical basis for constructing a novel wastewater treatment process.

Nitrogen loss through anaerobic ammonium oxidation coupled with ferric iron reduction in the Yellow River Wetland, Sanmenxia, China

Anaerobic ammonium oxidation coupled with iron(III) reduction (Feammox) is a recently discovered pathway of nitrogen removal. However, little is known about the pathways of N transformation via Feammox in the Yellow River wetland. In this study, the difference between Feammox in a natural wetland (site YJW) and a crop rotation wetland (site TEH) was researched using isotope tracing and metagenome techniques. The results revealed that Feammox occurred in TEH but not in YJW. The Feammox rates in the TEH samples were 0.02–0.13 mg N kg−1 d−1 in different depth intervals (0–5 cm, 5–10 cm, 10–20 cm, and 20–30 cm), and the maximum value for TEH occurred in the 5–10 cm depth interval. Iron reducing bacteria play an essential role in Feammox. Rotational tillage reduced the microbial diversity of the iron-reducing bacteria, but it increased the abundance of iron-reducing bacteria at the genus level, and the dominate iron-reducing bacteria responsible for the Feammox process were Anaeromyxobacter and Geobacter. The Feammox rate was less than the denitrification rate (0.55–1.09 mg N kg−1 d−1), an estimated nitrogen loss of 1.1–7.1 t N km−2 a−1 was associated with the Feammox in the wetland. However, the correlation between the functional genes of the iron-reducing bacteria and the rate remains unclear.

Impacts of storm disturbance and the role of the Feammox process in high nutrient riparian sediments

The extensive agricultural feedlot operations in the Neuse River Watershed (NRW) in North Carolina result in high nutrient loading, particularly of ammonium (NH4+). In September 2018, Hurricane Florence devastated large portions of the NRW, creating a unique opportunity to study the impact of such hydrological events on the biogeochemistry of riverine and riparian sediments. The high NH4+ concentrations, naturally acidic conditions, and elevated levels of ferric iron [Fe(III)] in Neuse River sediments and soils provide an ideal environment for Acidimicrobium sp. A6 (referred to hereon as A6), a bacterium capable of conducting the Feammox process in which NH4+ is oxidized while iron is reduced. A6 was observed in all sediment samples obtained from the Neuse River, and it is therefore predicted that this process may be an important mechanism for NH4+ removal in this river system. Incubations of NRW samples indicate that the NH4+ oxidation potential via the Feammox process in the NRW is comparable with aerobic NH4+ oxidation by heterotrophic microorganisms. Given the high demand for Fe(III) by the Feammox process, it has been unclear how such a process may occur in sedimentary environments where ferric iron [Fe(III)] might be depleted. The results presented here show that a major hydrologic storm event can result in an increase in Fe(III) and in an increase in the abundance of Fe-reducing bacteria, including Acidimicrobium sp. A6. These findings indicate that major hydrologic storm events may, via the delivery of Fe(III), be capable of enhancing Feammox activity in riverine sediments that favor the Feammox process.

Quinone electron shuttle enhanced ammonium removal performance in anaerobic ammonium oxidation coupled with Fe(III) reduction

Anaerobic ammonium oxidation coupled with Fe(III) reduction (Feammox) is a newly discovered ammonium removal process, but the low ammonium removal efficiency restricts its application in practical wastewater treatment. In this study, iron compounds Fe2O3, Fe(OH)3 and Fe3O4 were added to anaerobic sequencing batch reactors (ASBR) to explore the effect of different iron sources for the Feammox reaction on ammonium removal performance. The removal efficiencies of ammonium in Fe2O3, Fe(OH)3 and Fe3O4 groups were 34.02%, 22.8% and 7.58%, respectively. Additionally, to investigate electron shuttle effect of the quinone compound anthraquinone-2,6-disulfonate (AQDS) between Fe2O3, Fe(OH)3, Fe3O4 and ammonium and whether AQDS can improve the efficiency of Feammox, batch experiments were carried out in 250 mL serum bottles. The ammonium removal efficiency of the AQDS-Fe2O3 group was 48.53%, while those of the AQDS-Fe(OH)3 and AQDS-Fe3O4 groups were 35.63% and 15.46%, respectively. This implied that AQDS enhanced the ammonium removal performance of Feammox, especially accelerating the electron shuttle rate between Fe2O3 and ammonium. X-ray diffraction showed new iron minerals appear in the system. Moreover, modified Boltzmann model was more suitable to describe the removal of NH4+-N and showed a good correlation(R2 >0.99). This study demonstrates the significant influence of AQDS on Feammox process, which provides a theoretical basis for the application of Feammox in practical sewage treatment.

Feammox Bacterial Biofilms as an Alternative Biological Process for the Removal of Nitrogen from Agricultural Wastewater

The excessive deposition of ammonium (reactive nitrogen) in the environment has led to losses of biodiversity and the eutrophication of ecosystems. Anthropogenic sources contribute twice the natural rate of terrestrial reactive nitrogen and provide about 45% of the total amount of it produced annually on Earth. Recently, a biological process that anaerobically metabolizes ammonium and facilitates iron reduction, termed Feammox, was discovered. The use of Feammox activity together with hollow fiber membrane bioreactors (HFMB), for which the latter are based on the formation of biofilms of bacterial communities, constitutes an efficient and sustainable method for the removal of ammonium from agriculturally derived wastewater. To implement the use of HFMB with Feammox activity, the formation of Feammox bacterial biofilms from wastewater sludge samples from a brewery was evaluated. The cultures were enriched with two different carbon sources, namely, sodium acetate and sodium bicarbonate; then, ferrous iron and ammonium concentrations, which were used as indicators of reactive nitrogen removal, were measured. The measurements revealed that the ammonium removal level reaches 20.4% when sodium acetate is used as carbon source. Moreover, an increase in the ferrous iron concentration of +Δ84.6 mg/L was observed, indicating that Feammox activity had been generated. Biofilm formation was observed under Feammox conditions on the hollow fibers. These results showed that Feammox bacteria can form biofilms and efficiently remove ammonium from wastewater, constituting an essential feature with which to scale up the process to HFMBs. Overall, these results contribute to a better understanding of the Feammox process that can be used to implement these processes in agriculture and thus progress towards a more sustainable industry.

Modeling the kinetics of perfluorooctanoic and perfluorooctane sulfonic acid biodegradation by Acidimicrobium sp. Strain A6 during the feammox process

Per- and polyfluoroalkyl substances (PFAS) are emerging contaminants of concern due to their health effects and persistence in the environment. Although perfluoroalkyl acids (PFAAs), such as perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) are very difficult to biodegrade because they are completely saturated with fluorine, it has recently been shown that Acidimicrobium sp. A6 (A6), which oxidizes ammonium under iron reducing conditions (Feammox process), can defluorinate PFAAs. A kinetic model was developed and tested in this study using results from previously published laboratory experiments, augmented with results from additional incubations, to couple the Feammox process to PFAS defluorination. The experimental results show higher Feammox activity and PFAS degradation in the A6 enrichment cultures than in the highly enriched A6 cultures. The coupled experimental and modeling results show that the PFAS defluorination rate is proportional to the rate of ammonium oxidation. The ammonium oxidation rate and the defluorination rate increase monotonically, but not linearly, with increasing A6 biomass. Given that different experiments had different level of Feammox activity, the parameters required to simulate the Feammox varied between A6 cultures. Nonetheless, the kinetic model was able to simulate an anaerobic incubation system and show that PFAS defluorination is proportional to the Feammox activity.

Volatile fatty acids changed the microbial community during feammox in coastal saline-alkaline paddy soil.

In order to indicate the effect of volatile fatty acids (VFAs) on the characteristics of feammox and dissimilatory iron reducing bacteria (DIRB) in paddy soils, different VFAs were selected with paddy soils for anaerobic cultivation. Five treatments were set up, respectively, only adding N and both adding N and C (formate + NH4+ (Fo-N), acetate + NH4+ (Ac-N), propionate + NH4+ (Pr-N), and butyrate + NH4+ (Bu-N)) treatments. The concentration of Fe(II), Fe(III), NH4+, and VFAs was assessed within 45 d, and the bacterial community was determined after cultivation. The oxidation rates of NH4+ were the highest in N treatment, while it was the lowest in Fo-N treatment. Under the four C treatments, the consumption of NH4+ and Fe(III) was the fastest in Pr-N treatment, which was consumed by 31.2% and 76.3%, respectively. Different VFAs selected for distinct DIRB. Compared with N treatment, Ac-N and Bu-N treatment increased the relative abundance of DIRB, such as Geobacter and Clostridia, which increased the consumption of VFAs during incubation. Overall, VFAs, especially formate, could promote Fe(III) reduction and compete with the feammox process for the electron acceptors to decrease the feammox reaction, and prohibited soil NH4+ loss. Therefore, VFAs, which was released from organic fertilizer, could reduce NH4+ loss in feammox process of saline-alkaline paddy soils.

Nitrogen and carbon removal from anaerobic digester effluents with low carbon to nitrogen ratios under feammox conditions

Removal of nitrogen and carbon from anaerobic digester (AD) effluents is challenging for currently available technologies. Herein, effective treatment for real AD effluents was achieved via the feammox process by using a Multistage Feammox Bioreactor (MSFB). The reactor achieved the best performance with AD effluent of a low carbon to nitrogen (C/N) ratio of 2.5. A 6-day retention time reached removal efficiencies for NH4+ and COD at 99 % and 97 %, respectively, with a thorough conversion of NH4+ to N2. Accordingly, the MSFB achieved removal rates for N and C of 14 and 34 mg L−1 d−1, respectively. The C/N ratio of 2.5 is regarded to be the critical point above which the feammox is shifted to conventional iron reduction with organic carbon. Iron-reducing bacteria of the γ- Proteobacteria (Pseudomonas and Acinetobacter), and δ- Proteobacteria (Geobacter) were dominant in the MSFB and were supposed to drive the feammox process.

Enhancement of N removal by electrification coupled by Feammox and Fe(II)/Fe(III) cycle in wastewater treatment

Ammonium (NH4+) is a known toxic nitrogen pollutant in wastewater, and will result in serious water quality deterioration when discharged without treatment. Feammox is a promising new pathway to remove NH4+ by its oxidization coupling with the reduction of Fe(III) mediated by ferric reducing bacteria (FeRB). However, the low efficiency of Feammox limits the application in wastewater treatment. In this study, NH4+ removal efficiency by Feammox was promoted by introduction of Fe2O3 and AQDS (Anthraquinone-2,6-disulfonic acid) as electron shuttling molecules with and without electrification in two batch experiments Rn (Fe2O3+AQDS) and Re (Fe2O3+AQDS + electrification). Results from this study showed that NH4+ removal was significantly enhanced under electrification, with the efficiency increased up to 74.3% by day of 34. The high efficiency of NH4+ removal was discussed to be accelerated by the Fe(II)/Fe(III) cycling under electrification. Further clues were provided by the microbial community analysis by high throughput sequencing. Both the FeRB and denitrification bacteria were promoted in their relative abundance under electrification. Genus of denitrification bacteria Citrifermentans, Klebsiella, Legionella, Clicycliphilus and Ciaphorobacter were confirmed by their Feammox potential for the first time since they were clustered closely with Feammox bacteria in the phylogenetic tree. Based on the above, the combination of FeRB, NDFO and denitrifying bacteria coupled with Feammox process in the reactors all contributed to the NH4+ removal. This study provided new evidence and revealed insightful functional microbial groups for ammonium-rich wastewater treatment with amendment of AQDS under electrification.

Nitrogen loss from anaerobic ammonium oxidation coupled to Iron(III) reduction activity across estuarine and coastal wetlands of China: Spatial variations, controlling factors, and environmental implications

Anaerobic ammonium oxidation coupled with ferric iron reduction (Feammox) is a newly identified microbial nitrogen (N) removal process in natural ecosystems. However, little is known about the distributions of Feammox activity and their environmental drivers across estuarine and coastal wetlands at a continental scale. In this study, we determined the potential Feammox rates and related microbial diversities and abundances along the estuarine and coastal wetlands of China encompassing subtropical to temperate climate zones. Measured potential Feammox activity ranged from 0.05 to 0.23 mg N kg−1 d-1, and the process rates at the subtropical sites were generally higher than at the temperate sites. Partial least squares path model (PLS-PM) showed that the abundance of Fe reducing bacteria significantly and directly affected the potential Feammox rates, while sediment characteristics (mainly including sediment water content, Fe(III), TOC and NO3–) and geographical factors (longitude and latitude) had an indirect effect on the process rates. The N loss via the Feammox was approximately 1.72–7.89 kg N ha−1 year−1, accounting for 0.41–1.91 % of multi-annual average land-based inorganic N transported into the estuarine and coastal wetlands of China. Overall, this study reveals the distribution patterns and controlling factors of the Feammox process in estuarine and coastal wetlands of China, and provides a valuable database for N management in estuarine and coastal ecosystems.

Feammox in alluvial-lacustrine aquifer system: Nitrogen/iron isotopic and biogeochemical evidences

Groundwater nitrogen contamination is becoming increasingly serious worldwide, and natural nitrogen attenuation processes such as anaerobic ammonium oxidation coupled to iron reduction (“Feammox”) play an important role in mitigating contamination. Although there has been intensive study of Feammox in soils and sediments, still lacks research on this process in groundwater. This study makes effort to demonstrate the occurrence of Feammox in groundwater by combining information from Fe/N isotope composition, the quantitative polymerase chain reaction (qPCR) assay, and 16S rRNA gene sequencing. Poyang Lake Plain of Yangtze River in central China was selected as the case study area. The critical evidences that indicate Feammox in groundwater include favorable hydrogeochemical conditions of the alluvia-lacustrine aquifer systems, the simultaneous enrichment of 15N in ammonium and 56Fe, the relative high abundance of Acidimicrobiaceae bacterium A6, and the joint elevation of the abundance of the Feammox bacteria and the concentration of Fe(III). Redundancy analysis (RDA) indicated that Geothrix and Rhodobacter may participate directly or cooperatively in the Feammox process. Ammonium-oxidizing archaea (AOA) involved in ammonium-oxidizing or Feammox process may be stimulated by Fe(III) under a low oxygen concentration and weakly acidic condition. Anammox may be indirectly enhanced by products of the nitrogen transformation processes involving Feammox bacteria and AOA. Fe(III) concentration is an important environmental factor affecting the abundance of functional microorganisms related to nitrogen cycling and the composition of ammonium-oxidizing and iron-reducing microbes. Specific geological background (such as the widespread red soils) and anthropogenic input of ammonium, iron, and acidic substances may jointly promote Feammox in groundwater.

Achieving Ammonium Removal Through Anammox-Derived Feammox With Low Demand of Fe(III).

Feammox-based nitrogen removal technology can reduce energy consumption by aeration and emission of carbon dioxide. However, the huge theoretical demand for Fe(III) becomes a challenge for the further development of Feammox. This study investigated an anammox-derived Feammox process with an intermittent dosage of Fe2O3 and proposed a novel approach to reduce the Fe(III) consumption. The results showed that anammox genera Candidatus Brocadia and Candidatus Kuenenia in the seed anammox sludge significantly decreased after cultivation. The formation of N2 was the dominating pathway in Feammox while that of nitrite and nitrate could be neglected. Batch tests showed that specific Feammox activity of ammonium oxidation was 1.14–9.98 mg N/(g VSS·d). The maximum removal efficiency of ammonium reached 52.3% in the bioreactor with a low dosage of Fe(III) which was only 5.8% of the theoretical demand in Feammox. The removal of ammonium was mainly achieved through Feammox, while partial nitrification/anammox also played a role due to the non-power and unintentional oxygen leakage. The super-low oxygen also responded to the low demand of Fe(III) in the bioreactor because it could trigger the cycle of Fe(III)/Fe(II) by coupling Feammox and chemical oxidation of Fe(II) to Fe(III). Therefore, anammox-derived Feammox can achieve the removal of ammonium with low Fe(III) demand at super-low oxygen.

Genome-Resolved Metagenomic Analysis of Groundwater: Insights into Arsenic Mobilization in Biogeochemical Interaction Networks

High-arsenic (As) groundwaters, a worldwide issue, are critically controlled by multiple interconnected biogeochemical processes. However, there is limited information on the complex biogeochemical interaction networks that cause groundwater As enrichment in aquifer systems. The western Hetao basin was selected as a study area to address this knowledge gap, offering an aquifer system where groundwater flows from an oxidizing proximal fan (low dissolved As) to a reducing flat plain (high dissolved As). The key microbial interaction networks underpinning the biogeochemical pathways responsible for As mobilization along the groundwater flow path were characterized by genome-resolved metagenomic analysis. Genes associated with microbial Fe(II) oxidation and dissimilatory nitrate reduction were noted in the proximal fan, suggesting the importance of nitrate-dependent Fe(II) oxidation in immobilizing As. However, genes catalyzing microbial Fe(III) reduction (omcS) and As(V) detoxification (arsC) were highlighted in groundwater samples downgradient flow path, inferring that reductive dissolution of As-bearing Fe(III) (oxyhydr)oxides mobilized As(V), followed by enzymatic reduction to As(III). Genes associated with ammonium oxidation (hzsABC and hdh) were also positively correlated with Fe(III) reduction (omcS), suggesting a role for the Feammox process in driving As mobilization. The current study illustrates how genomic sequencing tools can help dissect complex biogeochemical systems, and strengthen biogeochemical models that capture key aspects of groundwater As enrichment.

Kinetics of Perfluorooctanoic and Perfluorooctane Sulfonic Acid Biodegradation by Acidimicrobium Sp. Strain A6 During the Feammox Process

Kinetics of Perfluorooctanoic and Perfluorooctane Sulfonic Acid Biodegradation by Acidimicrobium Sp. Strain A6 During the Feammox Process