Anaerobic ammonia-oxidation coupled with Fe3+ reduction by an anaerobic culture from a piggery wastewater acclimated to NH4 +/Fe3+ medium

Enhancing total nitrogen removal in constructed wetlands: A Comparative study of iron ore and biochar amendments

Efficient nitrogen removal in constructed wetlands (CWs) remains challenging when treating agricultural runoff with a low carbon-to-nitrogen ratio (C/N). However, using biochar, iron ore, and FeCl3-modified biochar (Fe-BC) as amendments could potentially improve total nitrogen (TN) removal efficiency in CWs, but the underlying mechanisms associated with adding these substrates are unclear. In this study, five CWs: quartz sand constructed wetland (Control), biochar constructed wetland, Fe-BC constructed wetland, iron ore constructed wetland, and iron ore + biochar constructed wetland, were built to compare their treatment performance. The rhizosphere microbial community compositions and their co-occurrence networks were analyzed to reveal the underlying mechanisms driving their treatment performance. The results showed that iron ore was the most efficient amendment, although all treatments increased TN removal efficiency in the CWs. Ammonia-oxidizing, heterotrophic denitrifying, nitrate-dependent anaerobic ferrous oxidizing (NAFO), and Feammox bacteria abundance was higher in the iron ore system and led to the simultaneous removal of NH4+-N, NO3--N, and NO2--N. Visual representations of the co-occurrence networks further revealed that there was an increase in cooperative mutualism (the high proportion of positive links) and more complex interactions among genera related to the nitrogen and iron cycle (especially ammonia-oxidizing bacteria, heterotrophic denitrifying bacteria, NAFO bacteria, and Feammox bacteria) in the iron ore system, which ultimately contributed to the highest TN removal efficiency. This study provides critical insights into how different iron ore or biochar substrates could be used to treat agricultural runoff in CWs.

Potential electron acceptors for ammonium oxidation in wastewater treatment system under anoxic condition: A review

Anaerobic ammonium oxidation has been considered as an environmental-friendly and energy-efficient biological nitrogen removal (BNR) technology. Recently, new reaction pathway for ammonium oxidation under anaerobic condition had been discovered. In addition to nitrite, iron trivalent, sulfate, manganese and electrons from electrode might be potential electron acceptors for ammonium oxidation, which can be coupled to traditional BNR process for wastewater treatment. In this paper, the pathway and mechanism for ammonium oxidation with various electron acceptors under anaerobic condition is studied comprehensively, and the research progress of potentially functional microbes is summarized. The potential application of various electron acceptors for ammonium oxidation in wastewater is addressed, and the N2O emission during nitrogen removal is also discussed, which was important greenhouse gas for global climate change. The problems remained unclear for ammonium oxidation by multi-electron acceptors and potential interactions are also discussed in this review.

Effects of Fe oxides and their redox cycling on Cd activity in paddy soils: A review

Cadmium (Cd) contamination of soils is a global problem, particularly in paddy soils. Fe oxides, as a key fraction of paddy soils, can significantly affect the environmental behavior of Cd, which is controlled by complicated environmental factors. Therefore, it is necessary to systematically collect and generalize relevant knowledge, which can provide more insight into the migration mechanism of Cd and a theoretical basis for future remediation of Cd contaminated paddy soils. This paper summarized that (1) Fe oxides influence Cd activity through adsorption, complexation, and coprecipitation during transformation; (2) compared with the flooded period, the activity of Cd during the drainage period is stronger in paddy soils, and the affinity of different Fe components for Cd was distinct; (3) Fe plaque reduced Cd activity but was associated with plant Fe²⁺ nutritional status; (4) the physicochemical properties of paddy soils have the greatest impact on the interaction between Fe oxides and Cd, especially with pH and water fluctuations.

New insight and enhancement mechanisms for Feammox process by electron shuttles in wastewater treatment - A systematic review

Ammonium oxidation coupled to Fe(III) reduction (Feammox) is a newly discovered iron-nitrogen cycle process of microbial catalyzed NH₄⁺ oxidation coupled with iron reduction. Fe(III) often exists in the form of insoluble iron minerals resulting in reduced microbial availability and low efficiency of Feammox. Electron shuttles(ESs) can be reversibly oxidized and reduced which has the potential to improve Feammox efficiency. This review summarizes the discovery process, electron transfer mechanism, influencing factors and driven microorganisms of Feammox, ang expounds the possibility and potential mechanism of ESs to enhance Feammox efficiency. Based on an in-depth analysis of the current research situation of Feammox for nitrogen removal, the knowledge gaps and future research directions including how to apply ESs enhanced Feammox to promote nitrogen removal in practical wastewater treatment have been highlighted. This review can provide new ideas for the engineering application research of Feammox and strong theoretical support for its development.

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.

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.

Anaerobic ammonium oxidation coupled to Fe(III) reduction: Discovery, mechanism and application prospects in wastewater treatment

Fe(III) reduction coupled with anaerobic ammonium oxidation is known as Feammox. Feammox, which was first discovered in wetland ecosystems, has the potential to be used in wastewater treatment systems due to its ability to remove ammonium. Feammox can produce N₂, NO₂^- or NO₃^- through the reduction of Fe(III) and oxidation of ammonium, which is a potential process to nitrogen loss from aquatic ecosystems and terrestrial ecosystems. The Acidimicrobiaceae sp. A6 was the first Feammox functional bacteria that was successfully isolated from wetlands. The nitrogen removal effect of Feammox can be influenced by many environmental factors, such as pH, organic matter, and different sources of Fe(III). Feammox has broad application prospects, but more exploration is needed to apply this principle to wastewater treatment. This review introduces the development, mechanism, functional microbes and factors affecting the Feammox process, and discusses its potential applications.

The effects of Fe(III) and Fe(II) on anammox process and the Fe-N metabolism

This study aims to compare the effects of different Fe stress on anammox (anaerobic ammonium oxidation) process, therefore seven identical reactors were operated under different Fe(II)/Fe(III) concentrations. After 38 days of operation, the anammox activity was highest (10.49 ± 0.41 mg-TN/(g-VSS·h)) under conditions of 5 mg/L-Fe(II), while under 30 mg/L-Fe(III) displayed severe inhibition. The results showed that continuous addition of 30 mg/L-Fe(III) would damage the composition of EPS (extracellular polymeric substances) and make anammox bacteria more sensitive to environmental stress. While high Fe(II) concentrations could result in precipitates encasing granular sludge, affecting substrate utilization. Moreover, the results of ΔNO₃^--N/ΔNH₄⁺-N indicated that Fe(II)-dependent nitrate reduction was induced in reactors added with Fe(II). OM27_clade and norank_f__Burkholderiaceae might be candidates for this process according to the correlation of genera and functional genes (based on the PICRUSt 2 functional prediction). Overall, this research is expected to provide new ideas to the effects of Fe(II)/Fe(III) on anammox and to the practical application of coupled system based on anammox in wastewater treatment.

A promising destiny for Feammox: From biogeochemical ammonium oxidation to wastewater treatment

Ammonium is one of the most common forms of nitrogen that exists in wastewater, and it can cause severe pollution when it is discharged without treatment. New technologies must be developed to effectively remove ammonium because conventional nitrification-denitrification methods are limited by the lack of organic carbon. Anaerobic ammonium oxidation coupled to Fe(III) reduction is known as Feammox, and is a recently discovered nitrogen cycling process. Feammox can proceed under autotrophic or anaerobic conditions and effectively transforms ammonium to stable, innocuous dinitrogen gas, using the ferric iron as an electron acceptor. This method is cost-effective, environmentally friendly, and conducive to joint application with other nitrogen removal reactions in low-C/N municipal wastewater treatments. This review provides a comprehensive survey of Feammox mechanistic investigations and presents studies regarding the functional microorganism colonies. The potential for Feammox to be applied for the removal of nitrogen from various polluted water sources and the combination of the Feammox process with other frontier environmental technologies are also discussed. In addition, future perspectives for removing ammonium using Feammox are presented.

Functional Interrelationships of Microorganisms in Iron-Based Anaerobic Wastewater Treatment

This study explicated the functional activities of microorganisms and their interrelationships under four previously reported iron reducing conditions to identify critical factors that governed the performance of these novel iron-dosed anaerobic biological wastewater treatment processes. Various iron-reducing bacteria (FeRB) and sulfate reducing bacteria (SRB) were identified as the predominant species that concurrently facilitated organics oxidation and the main contributors to removal of organics. The high organic contents of wastewater provided sufficient electron donors for active growth of both FeRB and SRB. In addition to the organic content, Fe (III) and sulfate concentrations (expressed by Fe/S ratio) were found to play a significant role in regulating the microbial abundance and functional activities. Various fermentative bacteria contributed to this FeRB-SRB synergy by fermenting larger organic compounds to smaller compounds, which were subsequently used by FeRB and SRB. Feammox (ferric reduction coupled to ammonium oxidation) bacterium was identified in the bioreactor fed with wastewater containing ammonium. Organic substrate level was a critical factor that regulated the competitive relationship between heterotrophic FeRB and Feammox bacteria. There were evidences that suggested a synergistic relationship between FeRB and nitrogen-fixing bacteria (NFB), where ferric iron and organics concentrations both promoted microbial activities of FeRB and NFB. A concept model was developed to illustrate the identified functional interrelationships and their governing factors for further development of the iron-based wastewater treatment systems.

Anaerobic degradation of xenobiotic organic contaminants (XOCs): The role of electron flow and potential enhancing strategies

In groundwater, deep soil layer, sediment, the widespread of xenobiotic organic contaminants (XOCs) have been leading to the concern of human health and eco-environment safety, which calls for a better understanding on the fate and remediation of XOCs in anoxic matrices. In the absence of oxygen, bacteria utilize various oxidized substances, e.g. nitrate, sulphate, metallic (hydr)oxides, humic substance, as terminal electron acceptors (TEAs) to fuel anaerobic XOCs degradation. Although there have been increasing anaerobic biodegradation studies focusing on species identification, degrading pathways, community dynamics, systematic reviews on the underlying mechanism of anaerobic contaminants removal from the perspective of electron flow are limited. In this review, we provide the insight on anaerobic biodegradation from electrons aspect - electron production, transport, and consumption. The mechanism of the coupling between TEAs reduction and pollutants degradation is deconstructed in the level of community, pure culture, and cellular biochemistry. Hereby, relevant strategies to promote anaerobic biodegradation are proposed for guiding to an efficient XOCs bioremediation.

Effect of organic matter derived from algae and macrophyte on anaerobic ammonium oxidation coupled to ferric iron reduction in the sediment of a shallow freshwater lake

As a recently discovered process of nitrogen cycling, anaerobic ammonium oxidation coupled to ferric iron reduction (Feammox) has attracted more attentions. This study investigated the spatial variation of Feammox in the sediment of different zones of a shallow freshwater lake and the effect of organic matter derived from algae and macrophyte on Feammox process. The potential Feammox rates showed significant differences among sediments from algae-dominated area (ADA), transitional area in the center of the lake (TDA), and macrophyte-dominated area (MDA), and in a descending order, ADA, MDA, and TDA. The potential Feammox rate ranged from 0.14 to 0.34 mg N kg^-1day^-1 in the freshwater lake sediment. The potential Feammox rates of the sediment with algae or macrophyte amendment were 12.29% and 15.31% higher than the control test without algae and macrophyte amendment. The addition of algae or macrophyte to the sediment from TDA could improve the amount of HCl-extractable total Fe, Fe(III) reduction rate, and the abundance of FeRB. These results demonstrated that organic matter is one of the key regulators of Feammox process.

Anaerobic biodegradation of pharmaceutical compounds coupled to dissimilatory manganese (IV) or iron (III) reduction

Pharmaceuticals in water have adverse effects on aquatic environment. Anaerobic pharmaceutical biodegradation coupled to dissimilatory manganese(Mn) (IV)- or iron(Fe) (III)-oxides reduction is potentially efficient but unexplored. In this study, batch experiments were performed using different Mn(IV) and Fe(III) species with a microbial inoculum pre-cultivated with 15 mM chemically-synthesized Mn(IV) and 10 mg L^-1 metoprolol. Results show 26% caffeine and 52% naproxen are degraded with Mn(IV) as terminal electron acceptor and insignificant biodegradation for other pharmaceuticals tested. Reduction of Mn(IV) from drinking water treatment is coupled to anaerobic biodegradation of metoprolol and propranolol, resulting in removal efficiencies of 96% and 31%, respectively. The results indicate that adsorption contributes to the pharmaceutical removal during the first 10 days of incubation, while biodegradation is the main removal mechanism in the whole period. Fe(III) can also be used as electron acceptor in anaerobic pharmaceutical biodegradation. Over half of the added metoprolol is degraded with both chemically-synthesized Fe(III) and Fe(III)-citrate as terminal electron acceptors. However, this process did not occur when using Fe(III) from drinking water treatment or Fe(III)-based sorbents. This study indicates that anaerobic pharmaceutical biodegradation coupled to dissimilatory Mn(IV) or Fe(III) reduction is possible, and promising for application to cleaning wastewater treatment plant effluents.

Anaerobic ammonium oxidation coupled to ferric iron reduction in the sediment of a eutrophic lake

Anaerobic ammonium oxidation coupled to ferric iron reduction (Feammox) has been assumed to play an important role in nitrogen removal from ecosystems. This study assessed the potential role of Feammox in nitrogen transformation in eutrophic lake sediment using an isotope tracing technique in sediment slurry incubation experiments. Feammox was discovered in eutrophic lake sediment. A significant correlation was found between Feammox rates and iron-reducing rates. Furthermore, the positive correlations between the abundance of iron-reducing bacteria (FeRB), such as Geobacteraceae spp. and Shewanella spp., and Feammox rates indicate that Feammox was mediated by FeRB. The potential rate of Feammox in the isotopic tracer incubation treatment was 0.23-0.43 mg N kg^-1 day^-1. The estimated nitrogen loss caused by Feammox accounts for 5.0-9.2% of the human-induced N input annually into the eutrophic lake. Feammox alone or coupled with anaerobic ammonium oxidation (anammox) and/or denitrification may have an essential role in the nitrogen cycle within eutrophic lake sediment.

Role and application of iron in water treatment for nitrogen removal: A review

It is crucial to have a review on the role of iron in water treatment for the guidance towards the selection of appropriate processes, content of iron, and application conditions, as there are few reviews available at present and the systematic information is lacking for both researchers and engineers. The objectives of this review are to summarize the state of arts with respect to iron applied in nitrogen removal, discuss chemical and biological or bio-chemical combined nitrogen removal pathways and processes coupled with iron, and to reveal reaction mechanisms as well as providing references or even solutions to pertinent the practical engineering application of nitrate removal coupling with iron. The following information have been summarized and discussed in details: (1) iron based materials with varieties of preparations and forms, (2) major coupling ways of nitrogen removal methods or processes with iron application, (3) chemical reaction equations about a variety of chemical and biological or bio-chemical combined processes and the main mechanisms. In addition, challenges and/or drawbacks during the nitrogen removal processes will also be discussed in this paper, which is aimed to seek better practical engineering applications of nitrate removal coupling with iron.

Simultaneous Fe(III) reduction and ammonia oxidation process in Anammox sludge

In recent years, there have been a number of reports on the phenomenon in which ferric iron (Fe(III)) is reduced to ferrous iron [Fe(II)] in anaerobic environments, accompanied by simultaneous oxidation of ammonia to NO₂^-, NO₃^-, or N_2. However, studies on the relevant reaction characteristics and mechanisms are rare. Recently, in research on the effect of Fe(III) on the activity of Anammox sludge, excess ammonia oxidization has also been found. Hence, in the present study, Fe(III) was used to serve as the electron acceptor instead of NO₂^-, and the feasibility and characteristics of Anammox coupled to Fe(III) reduction (termed Feammox) were investigated. After 160days of cultivation, the conversion rate of ammonia in the reactor was above 80%, accompanied by the production of a large amount of NO₃^- and a small amount of NO₂^-. The total nitrogen removal rate was up to 71.8%. Furthermore, quantities of Fe(II) were detected in the sludge fluorescence in situ hybridization (FISH) and denaturated gradient gel electrophoresis (DGGE) analyses further revealed that in the sludge, some Anammox bacteria were retained, and some microbes were enriched during the acclimatization process. We thus deduced that in Anammox sludge, Fe(III) reduction takes place together with ammonia oxidation to NO₂^- and NO₃^- along with the Anammox process.

Novel simultaneous Fe(iii) reduction and ammonium oxidation of Klebsiella sp. FC61 under the anaerobic conditions

A simultaneous Fe(iii) reduction and ammonium oxidation of strain FC61 was isolated from the Tang Yu oligotrophic reservoir of Xi'an (China).

The enhancement of ammonium removal from ethanolamine wastewater using air-cathode microbial fuel cells coupled to ferric reduction

A microbial fuel cell (MFC) with biological Fe(III) reduction was implemented for simultaneous ethanolamine (ETA) degradation and electrical energy generation. In the feasibility experiment using acetate as a substrate in a single-chamber MFC with goethite and ammonium at a ratio of 3.0(mol/mol), up to 96.1% of the ammonium was removed through the novel process related to Fe(III). In addition, the highest voltage output (0.53V) and maximum power density (0.49Wm(-2)) were obtained. However, the ammonium removal and electrical performance decreased as acetate was replaced with ETA. In the long-term experiment, the electrical performance markedly decreased where the voltage loss increased due to Fe deposition on the membranes.