Search

Feammox, one of the potential pathways for nitrogen loss in the environment, plays an essential role in nitrogen cycling and provides new ideas for the biological denitrification of wastewater. However, the Feammox reaction has low nitrogen removal efficiency and stagnates due to insufficient Fe(III) sources. It strongly depends on an Fe(III) source supply, significantly limiting its development. In this study, a synergistic nitrogen removal system using Feammox and Nitrate-Dependent Fe(II) Oxidation (NDFO) driven by NO3−-N was constructed within an organic carbon environment. It uses the synergy between Feammox and NDFO to improve nitrogen removal. The removal efficiency of NH4+-N reaches over 70% in stages III-V, with a maximum removal efficiency of 89.4%. NH4+-N oxidation and Fe(III) reduction are positively coupled in the Feammox reaction. The Fe(II)/Fe(III) cycle process driven by Feammox and NDFO improves the utilization of the iron source, thus guaranteeing the sustainability of the NH4+-N oxidation reaction. In addition, the organic carbon environment also enriched NDFO bacteria (Thermomonas and Acinetobacter) and increased the reaction rate of NDFO, which enhanced the transformation of Fe(II). We improved the nitrogen removal efficiency of Feammox and provided a new approach for nitrogen removal in wastewater treatment. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: The saline and buffered environment in actual wastewater imposes higher demands on Fenton and Fenton‐like catalytic systems. This study developed a MoS2 co‐catalytic Fe2O3 Fenton‐like system with controllable Lewis acid‐base sites, achieving efficient treatment of various model pollutants and actual industrial wastewater under neutral buffered environment. The acidic microenvironment structured by the edge S sites (Lewis basic sites) in the MoS2/Fe2O3 catalyst is susceptible to the influence of Lewis acidic sites constructed by Mo and Fe element, affecting catalytic performance. Optimizing the ratio of precursor amounts ensures the stable presence of the acidic microenvironment on the surface of catalyst, enabling the beneficial co‐catalytic effect of Mo sites to be realized. Furthermore, it transcends the rigid constraints imposed by the Fenton reaction on reaction environments, thereby expanding the applicability of commonplace oxides such as Fe2O3 in actual industrial water remediation. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: The saline and buffered environment in actual wastewater imposes higher demands on Fenton and Fenton‐like catalytic systems. This study developed a MoS2 co‐catalytic Fe2O3 Fenton‐like system with controllable Lewis acid‐base sites, achieving efficient treatment of various model pollutants and actual industrial wastewater under neutral buffered environment. The acidic microenvironment structured by the edge S sites (Lewis basic sites) in the MoS2/Fe2O3 catalyst is susceptible to the influence of Lewis acidic sites constructed by Mo and Fe element, affecting catalytic performance. Optimizing the ratio of precursor amounts ensures the stable presence of the acidic microenvironment on the surface of catalyst, enabling the beneficial co‐catalytic effect of Mo sites to be realized. Furthermore, it transcends the rigid constraints imposed by the Fenton reaction on reaction environments, thereby expanding the applicability of commonplace oxides such as Fe2O3 in actual industrial water remediation. [ABSTRACT FROM AUTHOR]

Constructed wetlands (CWs) are widely applied for decentralized wastewater treatment. However, achieving efficient removal of ammonia ( NH 4 + − N ) has proven challenging due to insufficient oxygen. In this study, natural hematite (Fe2O3) was employed as a CW substrate (H-CWs) for the first time to drive anaerobic ammonia oxidation coupled with iron(III) reduction (Feammox). Compared to gravel constructed wetlands (G-CWs), ammonia removal was enhanced by 38.14% to 54.03% and nitrous oxide (N2O) emissions were reduced by 34.60% in H-CWs. The synergistic removal of ammonia and nitrate by H-CWs also resulted in the absence of ammoxidation by-products. Inhibitor and 15N isotope tracer incubations showed that Feammox accounting for approximately 40% of all ammonia removal in the H-CWs. The enrichment of iron phosphate (Fe3Fe4(PO4)6) promoted the accumulation of the Feammox intermediate compound FeOOH. Microbial nanowires were observed on the surface of H-CW substrates as well, suggesting that the observed biological ammoxidation was most likely related to extracellular electron transfer (EET). Microbial and metagenomics analysis revealed that H-CWs elevated the integrity and enhanced the abundance of functional microorganisms and genes associated with nitrogen metabolism. Overall, the efficient ammonia removal in the absence of O2 together with a reduction in N2O emissions as described in this study may provide useful guidance for hematite-mediated anaerobic ammonia removal in CWs. [ABSTRACT FROM AUTHOR]

Impaired water quality in Mediterranean climate reservoirs is mainly associated with eutrophication and internal nutrient loading. To improve water quality in hypereutrophic Hodges Reservoir, California, United States, a hypolimnetic oxygenation system (HOS), using pure oxygen gas, was implemented in 2020. This study encompasses 3 years of pre-oxygenation data (2017-2019) and 2 years of post-oxygenation data (2020-2021) to understand the cycling of nutrients, metals, and mercury in the reservoir. During the wet year of 2017, mildly reduced conditions lasted until mid-summer in the enlarged reservoir. Nutrients and metals were seen in the hypolimnion including ammonia (~2 mg-N/L), manganese (~0.5 mg/L), phosphate (~0.5 mg-P/L), and sulfide (~10 mg/L). Production of methylmercury (MeHg), an important bioaccumulative toxin, was favored from April to June with a hypolimnetic accumulation rate of around 200 ng/m2·d. In contrast, the dry year of 2018 exhibited higher hypolimnetic concentrations of ammonia (~4 mg-N/L), manganese (~1 mg/L), phosphate (>0.5 mg-P/L), and sulfide (>15 mg/L). The rapid onset of highly reduced conditions in 2018 corresponded with low MeHg hypolimnetic accumulation (~50 ng/m2·d). It seems that mildly reduced conditions were associated with higher MeHg accumulation, while sulfidic, reduced conditions impaired inorganic mercury bioavailability for MeHg production and/or promoted microbial demethylation. Sulfide also appeared to act as a sink for iron via FeS precipitation, and potentially for manganese via MnS precipitation or manganese coprecipitation with FeS. Mass flux estimates for 2017-2019 indicate that much of the nutrients that accumulated in the hypolimnion moved via turbulent diffusion into the epilimnion at loading rates far exceeding thresholds predicting eutrophic conditions. After oxygenation in 2020-2021, the reservoir water column was highly oxidized but showed a lack of thermal stratification, suggesting reservoir operations in combination with HOS implementation inadvertently mixed the water column in this relatively shallow reservoir. Postoxygenation, concentrations of ammonia, phosphate, manganese, and mercury in bottom waters all decreased, likely in response to oxidized conditions. Oxygenated bottom waters exhibited elevated nitrate, a byproduct of ammonia nitrification, and iron, a byproduct of FeS oxidation, indicating a lake-wide response to oxygenation. [ABSTRACT FROM AUTHOR]

Release of iron (Fe) from continental shelves is a major source of this limiting nutrient for phytoplankton in the open ocean, including productive Eastern Boundary Upwelling Systems. The mechanisms governing the transport and fate of Fe along continental margins remain poorly understood, reflecting interaction of physical and biogeochemical processes that are crudely represented by global ocean biogeochemical models. Here, we use a submesoscale‐permitting physical‐biogeochemical model to investigate processes governing the delivery of shelf‐derived Fe to the open ocean along the northern U.S. West Coast. We find that a significant fraction (∼20%) of the Fe released by sediments on the shelf is transported offshore, fertilizing the broader Northeast Pacific Ocean. This transport is governed by two main pathways that reflect interaction between the wind‐driven ocean circulation and Fe release by low‐oxygen sediments: the first in the surface boundary layer during upwelling events; the second in the bottom boundary layer, associated with pervasive interactions of the poleward California Undercurrent with bottom topography. In the water column interior, transient and standing eddies strengthen offshore transport, counteracting the onshore pull of the mean upwelling circulation. Several hot‐spots of intense Fe delivery to the open ocean are maintained by standing meanders in the mean current and enhanced by transient eddies and seasonal oxygen depletion. Our results highlight the importance of fine‐scale dynamics for the transport of Fe and shelf‐derived elements from continental margins to the open ocean, and the need to improve representation of these processes in biogeochemical models used for climate studies. Plain Language Summary: Iron is an essential nutrient that supports the life of marine organisms. In the ocean, large quantities of iron are released by sediments found along the continents. However, this iron is not very soluble, and it tends to precipitate back to the sediments close to where it is released. In fact, we still struggle to understand how enough of this iron makes its way to the open ocean, where it fertilizes phytoplankton and sustains fisheries. In this study, we use a sophisticated computer simulation of the ocean currents and chemistry of the northern U.S. West Coast to study the transport of iron released along the continent to the open ocean. This computer simulation is able to reproduce the currents observed along the coast with high realism, including small swirls, eddies, and meanders that constantly mix coastal waters with open ocean waters. We found that about one‐fifth of all the iron released by sediments along the coast is transported offshore, where it can sustain the life of marine organisms. This transport from the coast to the open ocean mostly takes place near the surface, reflecting upwelling caused by winds in the summer, and near the bottom, reflecting transport caused by the friction of the poleward California Undercurrent with the seafloor. We also found that episodic swirls, eddies, and meanders reinforce this delivery of iron to the open ocean, in particular along several "hot‐spots" of intense transport along the coast. Our results suggest that global computer simulations used to study how marine ecosystems respond to climate change should improve how they represent small‐scale currents and their effects on the cycle of iron, in particular along the ocean's coastlines. Key Points: Shelf‐to‐basin transport is a major source of iron to the North East Pacific OceanHalf of this transport occurs year‐round by downslope Ekman flow in the bottom boundary layer, sustained by the poleward California UndercurrentRegional hot‐spots of iron transport are sustained by meanders in the poleward undercurrent and local bottom oxygen depletion [ABSTRACT FROM AUTHOR]

The Amarillo River in Famatina, La Rioja, Argentina, is a natural acidic river with distinctive yellow-ochreous iron precipitates along its course. While mining activities have occurred in the area, the river's natural acidity is influenced by environmental factors beyond mineralogy, where microbial species have a crucial role. Although iron-oxidising bacteria have been identified, a comprehensive analysis of the entire microbial community in this extreme environment has not yet been conducted. In this study, we employ high-throughput sequencing to explore the bacterial and fungal diversity in the Amarillo River and Cueva de Pérez terraces, considered prehistoric analogues of the current river basin. Fe(II)-enrichment cultures mimicking different environmental conditions of the river were also analysed to better understand the roles of prokaryotes and fungi in iron oxidation processes. Additionally, we investigate the ecological relationships between bacteria and fungi using co-occurrence and network analysis. Our findings reveal a diverse bacterial community in the river and terraces, including uncultured species affiliated with Acidimicrobiia, part of an uncharacterised universal microbial acidic diversity. Acidophiles such as Acidithiobacillus ferrivorans, the main iron oxidiser of the system, and Acidiphilium, which is unable to catalyse Fe(II) oxidation but has a great metabolic flexibility,, are part of the core of the microbial community, showing significant involvement in intraspecies interactions. Alicyclobacillus, which is the main Fe(II) oxidiser in the enrichment culture at 30 °C and is detected all over the system, highlights its flexibility towards the iron cycle. The prevalence of key microorganisms in both rivers and terraces implies their enduring contribution to the iron cycle as well as in shaping the iconic yellow landscape of the Amarillo River. In conclusion, this study enhances our understanding of microbial involvement in iron mineral precipitation, emphasising the collaborative efforts of bacteria and fungi as fundamental geological agents in the Amarillo River. [ABSTRACT FROM AUTHOR]

Impaired water quality in Mediterranean climate reservoirs is mainly associated with eutrophication and internal nutrient loading. To improve water quality in hypereutrophic Hodges Reservoir, California, United States, a hypolimnetic oxygenation system (HOS), using pure oxygen gas, was implemented in 2020. This study encompasses 3 years of pre-oxygenation data (2017–2019) and 2 years of post-oxygenation data (2020–2021) to understand the cycling of nutrients, metals, and mercury in the reservoir. During the wet year of 2017, mildly reduced conditions lasted until mid-summer in the enlarged reservoir. Nutrients and metals were seen in the hypolimnion including ammonia (~2 mg-N/L), manganese (~0.5 mg/L), phosphate (~0.5 mg-P/L), and sulfide (~10 mg/L). Production of methylmercury (MeHg), an important bioaccumulative toxin, was favored from April to June with a hypolimnetic accumulation rate of around 200 ng/m2·d. In contrast, the dry year of 2018 exhibited higher hypolimnetic concentrations of ammonia (~4 mg-N/L), manganese (~1 mg/L), phosphate (>0.5 mg-P/L), and sulfide (>15 mg/L). The rapid onset of highly reduced conditions in 2018 corresponded with low MeHg hypolimnetic accumulation (~50 ng/m2·d). It seems that mildly reduced conditions were associated with higher MeHg accumulation, while sulfidic, reduced conditions impaired inorganic mercury bioavailability for MeHg production and/or promoted microbial demethylation. Sulfide also appeared to act as a sink for iron via FeS precipitation, and potentially for manganese via MnS precipitation or manganese coprecipitation with FeS. Mass flux estimates for 2017–2019 indicate that much of the nutrients that accumulated in the hypolimnion moved via turbulent diffusion into the epilimnion at loading rates far exceeding thresholds predicting eutrophic conditions. After oxygenation in 2020–2021, the reservoir water column was highly oxidized but showed a lack of thermal stratification, suggesting reservoir operations in combination with HOS implementation inadvertently mixed the water column in this relatively shallow reservoir. Post-oxygenation, concentrations of ammonia, phosphate, manganese, and mercury in bottom waters all decreased, likely in response to oxidized conditions. Oxygenated bottom waters exhibited elevated nitrate, a byproduct of ammonia nitrification, and iron, a byproduct of FeS oxidation, indicating a lake-wide response to oxygenation.

In the present study, we demonstrated that the presence of cysteine could remarkably enhance the degradation of atrazine by Fe3O4/persulfate system. The results of electron paramagnetic resonance (EPR) spectra confirmed the combination of cysteine and Fe3O4 exhibited much higher activity on activation of persulfate to generate more SO4•- and •OH than Fe3O4 alone. At pH of 3.0, SO4•- and •OH contributed to about 58.2 % and 41.8 % of atrazine removal respectively, while •OH gradually dominated the oxidation of atrazine from neutral condition to alkaline condition. The co-existing Cl− and HCO3− could quench SO4•-, resulting in the inhibition of atrazine degradation. The presence of low natural organic matters (NOM) concentration (0–2 mg L−1) could enhance the atrazine removal, and high concentration (>5 mg L−1) of NOM restrained the atrazine degradation. During the Cysteine/Fe3O4/Persulfate process, cysteine served as a complexing reagent and reductant. Through acidolysis and complexation, Fe3O4 could release dissolved and surface bound Fe2+, both of which contributed to the activation of persulfate together. Meanwhile, cysteine was not rapidly consumed due to a regeneration process, which was beneficial for maintaining Fe2+/Fe3+ cycle and constantly accelerating the activation of persulfate for atrazine degradation. The reused Fe3O4 and cysteine in the Cysteine/Fe3O4/Persulfate process exhibited high stability for the atrazine degradation after three cycles. The degradation pathway of atrazine included alkylic-oxidation, dealkylation, dechlorination-hydroxylation processes. The present study indicates the novel Cysteine/Fe3O4/Persulfate process might be a high potential for treatment of organic polluted water.

Link for citation: Soldatova E.A., Sidkina E.S., Kiriukhin B.A., Maximov P.N., Krivenok L.A., Ivanov V., Tananaev N.I. Geochemical conditions of Sullar spring: formation of authigenic minerals and methane fluxes. Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 10, рр. 16-33. In Rus. Relevance and the research object. Interpermafrost aquifers and areas of their discharge with seasonal ice covers are special permafrost-hydrogeological and hydrochemical systems that are not typical for the thick continuous permafrost zone of Central Yakutia. Differences in chlorofluorocarbon content indicate the anaerobic conditions of some springs suggesting microbial degradation of these compounds by methanogenic bacteria. In the discharge area of such springs, a sharp change in the geochemical conditions takes place leading to a transformation in the water chemical composition and boosting the processes of authigenic mineral formation in this buffer area. In current work we considered the geochemical system of the Sullar spring – the most northern and the least studied among interpermafrost groundwater discharge zones of the Lena River right bank. Intensive accumulation of authigenic minerals was found in the Sullar discharge area during field research. It was Fe compounds with bacterial mats as an opalescent film. Some researchers state the connection between the transformation of Fe compounds during permafrost melting and the migration and transformation of organic matter, including its consumption by microorganisms with further methane emission. We assumed that there is a relationship between the authigenic mineral formation and the content and emission of methane in the discharge area of the spring. This research is the first comprehensive description of the hydrochemistry of the interpermafrost water of the Sullar spring. The aim of the research was to explore influence of geochemical conditions and microbial communities on formation of authigenic minerals and methane fluxes, in particular the effect of the change of geochemical conditions due to groundwater discharge on Fe precipitation and to analyze the relation of that process with methane fluxes. For this purpose, we study water chemical composition of the Sullar spring, measure methane fluxes from water surface and analyze mineral and microbial composition of secondary mineral crusts and bottom eluvium collected near water sampling points. Methods. The main element content was determined by ion chromatography. The concentrations of the bicarbonate ion and dissolved carbon dioxide were calculated by the equilibrium modeling method based on the pH and Eh values of the system. The content of trace elements was measured by mass spectrometry with inductively coupled plasma. To identify seasonal and annual variability, a retrospective analysis of the water chemical composition of the Sullar spring for the period from 1962 to 2020 was carried out. Methane fluxes were measured using the chamber method. The methane concentration was determined by gas chromatography with a flame ionization detector. The features of the secondary mineral crusts and bottom eluvium were determined using a petrographic microscope. The chemical composition of individual mineral phases was evaluated using a scanning electron microscope equipped with a detector for energy dispersive X-ray spectral microanalysis. The DNA concentration was measured on a fluorimeter. Amplicon libraries were generated by polymer chain reaction with universal primers for the V4 region. Equilibrium modeling was carried out using the HCh software.

The Amarillo River in Famatina, La Rioja, Argentina, is a natural acidic river with distinctive yellow-ochreous iron precipitates along its course. While mining activities have occurred in the area, the river’s natural acidity is influenced by environmental factors beyond mineralogy, where microbial species have a crucial role. Although iron-oxidising bacteria have been identified, a comprehensive analysis of the entire microbial community in this extreme environment has not yet been conducted. In this study, we employ high-throughput sequencing to explore the bacterial and fungal diversity in the Amarillo River and Cueva de Pérez terraces, considered prehistoric analogues of the current river basin. Fe(II)-enrichment cultures mimicking different environmental conditions of the river were also analysed to better understand the roles of prokaryotes and fungi in iron oxidation processes. Additionally, we investigate the ecological relationships between bacteria and fungi using co-occurrence and network analysis. Our findings reveal a diverse bacterial community in the river and terraces, including uncultured species affiliated with Acidimicrobiia, part of an uncharacterised universal microbial acidic diversity. Acidophiles such as Acidithiobacillus ferrivorans, the main iron oxidiser of the system, and Acidiphilium, which is unable to catalyse Fe(II) oxidation but has a great metabolic flexibility,, are part of the core of the microbial community, showing significant involvement in intraspecies interactions. Alicyclobacillus, which is the main Fe(II) oxidiser in the enrichment culture at 30 °C and is detected all over the system, highlights its flexibility towards the iron cycle. The prevalence of key microorganisms in both rivers and terraces implies their enduring contribution to the iron cycle as well as in shaping the iconic yellow landscape of the Amarillo River. In conclusion, this study enhances our understanding of microbial involvement in iron mineral precipitation, emphasising the collaborative efforts of bacteria and fungi as fundamental geological agents in the Amarillo River.

[Display omitted] • The use of the Fe 3 O 4 @C 3D electrode for efficient degradation of the MB. • Na 2 S 2 O 3 electrolyte optimised the Fe2+/Fe3+ cycle and extended the applicable pH range of the electrode. • The presence of Na 2 S 2 O 3 reduces iron dissolution and improves the cyclic degradation properties of the material. The cycling rate of iron ions has been reported to limit the Fenton reaction rate. It is, therefore, vital to enhance the cycling rate of iron ions. A composite three-dimensional electrode (FOC) was synthesized using glucose, ammonium carbonate, and FeCl 3 through a combination of hydrothermal synthesis and calcination. The electrode's conditions were subsequently optimized for the applicable pH range and the concentration of methylene blue (MB) that could be effectively degraded. At an FOC-800 dosage of 0.5 g/L, a supply voltage of 4 V, and an initial pH of 4, a degradation rate of 98 % for 10 mg/L MB was achieved, with a 67.5 % reduction in total organic carbon using 2 g/L Na 2 S 2 O 3 as the electrolyte. The material also demonstrated efficacy in degrading both chemical and pharmaceutical wastewater. A comparative analysis using Na 2 SO 4 as the electrolyte confirmed that Na 2 S 2 O 3 effectively promoted the cycling of iron ions, enhancing the degradation performance of FOC and expanding its effective pH range. High-performance liquid chromatography (HPLC) was employed to monitor the concentration changes of S 2 O 3 2- and SO 4 2- during the reaction, while LC-MS was used to identify the degradation products of MB, and ECOSAR was utilized to assess the toxicity of these products. Burst experiments and EPR analysis identified ●OH as the primary active species responsible for degradation, with O 2 ∙ - playing a supporting but not dominant role. [ABSTRACT FROM AUTHOR]

• Synergy between S2−and vivianite enhances immobilization of cationic heavy metals. • Vivianite structure remains stable throughout the sulfidation-reoxidation process. • Sulfidation targets Fe(II) sites at the corners of the PO4 tetrahedron in vivianite. • Reoxidation of CdS and S sites in vivianite thermodynamically favors Cd fixation. • Cd is sequestered within the vivianite structure via the Cd-O-P and Cd-O-Fe bonds. Iron minerals in nature are pivotal hosts for heavy metals, significantly influencing their geochemical cycling and eventual fate. It is generally accepted that, vivianite, a prevalent iron phosphate mineral in aquatic and terrestrial environments, exhibits a limited capacity for adsorbing cationic heavy metals. However, our study unveils a remarkable phenomenon that the synergistic interaction between sulfide (S2−) and vivianite triggers an unexpected sulfidation−reoxidation process, enhancing the immobilization of heavy metals such as cadmium (Cd), copper (Cu), and zinc (Zn). For instance, the combination of vivianite and S2− boosted the removal of Cd2+ from the aqueous phase under anaerobic conditions, and ensured the retention of Cd stabilized in the solid phase when shifted to aerobic conditions. It is intriguing to note that no discrete FeS formation was detected in the sulfidation phase, and the primary crystal structure of vivianite largely retained its integrity throughout the whole process. Detailed molecular-level investigations indicate that sulfidation predominantly targets the Fe(II) sites at the corners of the PO4 tetrahedron in vivianite. With the transition to aerobic conditions, the exothermic oxidation of CdS and the S sites in vivianite initiates, rendering it thermodynamically favorable for Cd to form multidentate coordination structures, predominantly through the Cd-O-P and Cd-O-Fe bonds. This mechanism elucidates how Cd is incorporated into the vivianite structure, highlighting a novel pathway for heavy metal immobilization via the sulfidation−reoxidation dynamics in iron phosphate minerals. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • The oxidation of thiophene derivatives by Fe(III)/H 2 O 2 systems addresses autocatalytic features. • Thiophene derivatives facilitated the removal of coexisting pollutants in Fe(III)/H 2 O 2 treatment systems. • The primary HO•-addition radicals rapidly reduced Fe(III) to foster iron cycling. The sluggish reduction of Fe(III) to Fe(II) restricts the decontamination efficiency of Fenton reactions. New strategy development toward enhancing Fe(II) regeneration and decontamination efficiency relies primarily on the well-established inorganic Fenton chemistry, yet the involvement of organic contaminants and its potential role in the Fenton reactions have been insufficiently concerned. Here, using 2,5-thiophene carboxylic acid (TDA) as a representative sulfur-containing heterocyclic contaminant and atrazine as a coexisting contaminant, we uncovered the promoting effect of thiophene derivatives on Fenton oxidation. The degradation of TDA and coexisting refractory contaminants was highly efficient in the sluggish Fe(III)/H 2 O 2 oxidation process with autocatalytic features. Spin trapping and chemical scavenging results underpinned the crucial contribution of hydroxyl radicals (HO•) to organic oxidation. Analysis of iron cycling combined with theoretical calculations revealed that the enhancement of TDA on Fenton oxidation originated from the rapid reduction of Fe(III) by the primary radicals generated from addition of HO• to the thiophene ring. [ABSTRACT FROM AUTHOR]

Biodegradation, while cost-effective, is hindered by the requirement for specialized microorganisms and co-contaminants. Innovative biological technologies like the microbially driven Fenton reaction, hold promise for enhancing degradation efficiency. However, the intricate biochemical processes and essential steps for effective degradation in such systems have remained unclear. In this study, we harnessed the potential of the microbially driven Fenton reaction by employing Shewanella oneidensis MR-1 (MR-1). Our approach showcased remarkable efficacy in degrading a range of contaminants, including sulfadimethoxine (SDM), 4,4'-dibromodiphenyl ether (BDE-15) and atrazine (ATZ). Using SDM as a model contaminant of emergent contaminants (ECs), we unveiled that biodegradation relied on the generation of hydroxyl radicals (•OH) and involvement of oxidoreductases. Transcriptomic analysis shed light on the pivotal components of extracellular electron transfer (EET) during both anaerobic and aerobic periods. The presence of reactive oxidizing species induced cellular damage and impeded DNA repair, thereby affecting the Mtr pathway of EET. Moreover, the formation of vivianite hindered SDM degradation, underscoring the necessity of maintaining iron ions in the solution to ensure sustainable and efficient degradation. Overall, this study offers valuable insights into microbial technique for ECs degradation, providing a comprehensive understanding of degradation mechanisms during aerobic/anaerobic cycling. [Display omitted] • Microbially driven Fenton reaction can effectively degrade SDM, BDE-15, and ATZ. • Biodegradation process relies on hydroxyl radicals and oxidoreductases. • Extracellular electron transfer plays a vital role in anaerobic/aerobic cycles. • The production of vivianite and ROS restrained the biodegradation process. [ABSTRACT FROM AUTHOR]

In the Western Tropical South Pacific, a hotspot of dinitrogen‐fixing organisms has been identified. The survival of these species depends on the availability of dissolved iron (DFe); however, the source of this DFe is still unclear. DFe was measured along a transect from 175°E to 166°W near 19–21°S. The distribution of DFe showed high spatial variability: low concentrations (∼0.2 nmol kg−1) in the South Pacific gyre and high concentrations (up to 50 nmol kg−1) in the west of the Tonga arc, indicating that this arc is a clear boundary between iron‐poor and iron‐rich waters. An optimal multiparameter analysis was used to distinguish the relative importance of physical transport relative to non‐conservative processes on the observed distribution. This analysis demonstrated that the shallow hydrothermal sources present along the Tonga‐Kermadec arc are responsible for the high concentrations observed in the photic layer. Nevertheless, in contrast to what has been observed for deep hydrothermal plumes, our results highlighted the rapid decrease in DFe concentrations near shallow hydrothermal sources. This is likely due to a shorter residence time of surface water masses combined with several biogeochemical processes at play (precipitation, scavenging, biological uptake, and photoreduction). This study clearly highlights the role of shallow hydrothermal sources on the DFe cycle within the Tonga‐Kermadec arc where a strong link to biological activity in surface waters can be assessed, despite the small but significant fraction of DFe ultimately stabilized. It also emphasizes the need to consider the impact of these sources for a better understanding of the global iron cycle. Key Points: Shallow hydrothermal plumes are not transported over long distances, in contrast to what has been previously reported for deep plumesSpecific surface ocean conditions and chemical processes are primarily responsible for the low dispersion of shallow hydrothermal ironNevertheless, the cumulative impact of multiple sources along the Tonga arc could fertilize the entire Lau Basin with dissolved iron [ABSTRACT FROM AUTHOR]

Iron deficiency (ID), with or without anemia, is commonly found worldwide and affects the health and wellbeing of pregnant and nonpregnant women. Symptoms of ID- which include fatigue, pica (ice craving), restless legs syndrome, poor concentration and work function, increased susceptibility to infection, and cardiovascular stress- can cause significant morbidity and reduced quality of life. The etiologies of iron deficiency in women are usually specific to each community. In the developing world, iron deficiency is usually associated with poor iron intake and parasitic infections, whereas in higher income regions, iron deficiency is typically the result of heavy, abnormal uterine bleeding, and pregnancy. Iron-poor diets and poor iron absorption resulting from gut disorders can also play a role. Diagnosis of iron deficiency is usually straightforward and characterized by a low ferritin level; however, the diagnosis can be challenging in women with concomitant inflammatory disorders, in which case a low percent transferrin saturation, performed after an overnight fast, can inform on the need for iron. Therapy is frequently initiated with oral iron salts; however, use of these oral regimens is commonly associated with adverse events, mostly gastrointestinal in nature, that have been shown to adversely impact compliance, continuation, and the achievement of therapeutic goals. A further impediment to the effectiveness of oral iron is its poor absorption because of comorbidity (i.e., celiac disease, gastritis, etc.), surgery (bariatric), or physiologic inhibitory mechanisms. As such, intravenous (IV) iron regimens are increasingly being used to treat ID, as such regimens have been shown to avoid the gastrointestinal adverse events commonly associated with oral regimens. Indeed, IV iron has been shown to provide adequate iron replacement in women with functional iron deficiencies as well as those with ID resulting from inflammatory disorders- patients often resistant to oral iron therapy. More recent IV iron regimens have been shown to provide iron replacement in a safe and effective manner, being associated with more salutary adverse event profiles than earlier IV iron regimens. In fact, these iron regimens can provide a complete replacement dose in a single 15–60-min visit. [ABSTRACT FROM AUTHOR]

Volatile organic compounds (VOCs) need to be treated urgently, which are easily produced in the production process of chemical and printing industries・ The gaseous toluene, one of the typical VOCs pollutants, was treated by UV/Fenton coupled with wet scrubbing technology・ The influences of concentrations of H202, Fe2+ and initial pH on the degradation efficiency of toluene were investigated・ The trends of toluene, CO2, H202, Fe2 + and • OH concentrations were analyzed. The results show that the optimal condition was： H2 O2 50 mmol/L, Fe2+ 2. 5 mmol/L, initial pH = 3, gaseous toluene concentration 670 mg/m3, flow rate 900 mL/min. In this condition, the degradation and mineralization efficiency of gaseous toluene reached 72% and 69%, respectively・ UV irradiation can effectively promote the reduction from Fe3 + to Fe2+ and produce more • OH, which can effectively improve the degradation and mineralization efficiency of gaseous toluene. [ABSTRACT FROM AUTHOR]

In this paper, three groups of controlled variable experiments were compared for 64 d, which was based on the coupling reaction of Feammox (NH4+ oxidation with Fe(III) reduction) and NDFO (NO3 –-dependent Fe(II) oxidation), to explore the nitrogen removal effect of Feammox and NDFO coupling technology on livestock wastewater and iron recycling mechanism under anaerobic conditions. Through the analysis of transformation in the contents of various nitrogen and iron in the experimental operation system, it was found that the simultaneous nitrogen removal occurred with the presence of interconversion between Fe(II) and Fe(III). The Fe(III) added in the C2 group advanced the progress of Feammox and realized the iron cycle to remove nitrogen under the combination of Feammox and NDFO. However, after 50 d of operation, due to the insufficient NO3 – content, the nitrogen removal was weakened, and the final ammonia nitrogen removal rate was 65.1%, and the total nitrogen removal rate was 71.2%. Comparatively, the C3 group added NO3– regularly based on the C2 group which promoted the NDFO reaction and further realized the circle of Feammox and NDFO. The final NH4+ removal rate reached 88.9%, and the total nitrogen removal rate reached 84.6%, which was significantly better than the C2 group and the blank group. The analysis of the microbial community by 16S rRNA high-throughput sequencing technology concluded that the main functional microorganism under the system was Ignavibacteria. This study provides a new theoretical basis for the exploration of Fe/N cycling mechanism under Feammox-NDFO coupling technology and nitrogen treatment in livestock wastewater in the future. [ABSTRACT FROM AUTHOR]

Oolitic ironstones are iron-rich and chert-poor sedimentary rocks containing concentrically coated grains composed of iron (oxyhydr)oxides and iron phyllosilicates that offer a unique window into iron cycling in ancient coastal environments. These enigmatic deposits are common in the Phanerozoic stratigraphic record yet lack clear modern analogues, and curiously are thought to be absent from Precambrian strata, suggesting a secular control on their deposition. Here we describe a previously unreported ironstone from the middle Tonian (ca. 850 Ma) Katherine Group in the Wernecke Inlier (Yukon, Canada), and show that similar deposits can be found—albeit rarely—throughout the Proterozoic. We investigate the origin of this unit and evaluate its palaeoenvironmental significance, and in light of an extensive literature review, present a holistic model for Precambrian ironstone deposition. The Katherine ironstone occurs in multiple horizons in the McClure and Abraham Plains formations and contains iron ooids and oncoids composed dominantly of authigenic hematite and berthierine, with detrital quartz grains. Textural relationships demonstrate that these coated grains formed on the seafloor with synsedimentary reworking, and the fine interlamination of these phases in grain coatings suggests redox and pH fluctuation during ironstone genesis. Facies associations indicate that the ironstones accumulated in a range of low-energy, shallow marine environments (tidal mudflats and coastal embayments). Geochemical analyses offer insights into genetic processes, and the radiogenic Nd isotope composition and negative Eu anomalies of the Katherine ironstone suggest a continental iron source. We present a model whereby abundant iron, cations, and silica—requisite for the authigenesis of iron phyllosilicates—were supplied from chemical weathering and preferentially enriched in coastal environments due to gradients in pH, Eh and salinity. This continental input would have led to intense iron cycling coupled to organic matter respiration, iron phyllosilicate authigenesis (i.e., reverse weathering). The enrichment of authigenic Fe(III) (oxyhydr)oxides and Fe(II) phyllosilicates took place on a broad coastal plain influenced by both autogenic and allogenic fluctuations in relative sea level, likely in a humid, tropical climate. The lenticular and episodic nature of ironstones in the Proterozoic stratigraphic record suggests that a unique combination of environmental conditions fostered ironstone accumulation. By reviewing the literature on oolitic ironstones, we re-evaluate the temporal distribution of these deposits compared to Archaean–Palaeoproterozoic iron formations, and show that the Great Oxidation Event may have been a prerequisite for ironstone deposition, which may implicate oxidative chemical weathering or suboxic, marine iron cycling. In general, we suggest that the Precambrian record of oolitic ironstones represents an important deep-time archive of iron and nutrient cycling in coastal settings. • Ironstones have a distinct texture and mineralogy to iron formations. • The Tonian Katherine Group ironstone was deposited in low-energy coastal settings. • Diagenesis of weathering products led to redox cycling and phyllosilicate authigenesis. • Common in the Phanerozoic record, ironstones also span the Proterozoic Eon. • Ironstones can provide valuable constraints on biogeochemical cycles in deep time. [ABSTRACT FROM AUTHOR]

• Hydrogel cross-linking creates a 3D network structure for S-Fe particles. • Amorphous Fe substrate can deeply remove N and P simultaneously in SAD. • Iron-rich media promoted Fe circulation and nitrogen removal by enriching FRB. • Clostridium_sensu_stricto_1 and Geobacter were the keystone species of FRB. • The low effluent pH (<4) of the biofilter did not limit denitrification. The autotrophic denitrification of coupled sulfur and natural iron ore can remove nitrogen and phosphorus from wastewater with low C/N ratios. However, the low solubility of crystalline Fe limits its bioavailability and P absorption capacity. This study investigated the effects of amorphous Fe in drinking water treatment residue (DWTR) and crystalline Fe in red mud (RM) on nitrogen and phosphorus removal during sulfur autotrophic processes. Two types of S-Fe cross-linked filler particles with three-dimensional mesh structures were obtained by combining sulfur with the DWTR/RM using the hydrogel encapsulation method. Two fixed-bed reactors, sulfur-DWTR autotrophic denitrification (SDAD) and sulfur-RM autotrophic denitrification (SRAD), were constructed and stably operated for 236 d Under a 5–8-h hydraulic retention time, the average NO 3 −–N, TN, and phosphate removal rates of SDAD and SRAD were 99.04 %, 96.29 %, 94.03 % (SDAD) and 97.33 %, 69.97 %, 82.26 % (SRAD), respectively. It is important to note that fermentative iron-reducing bacteria, specifically Clostridium_sensu_stricto_1 , were present in SDAD at an abundance of 58.17 %, but were absent from SRAD. The presence of these bacteria facilitated the reduction of Fe (III) to Fe (II), which led to the complete denitrification of the S-Fe (II) co-electron donor to produce Fe (III), completing the iron cycle in the system. This study proposes an enhancement method for sulfur autotrophic denitrification using an amorphous Fe substrate, providing a new option for the efficient treatment of low-C/N wastewater. [Display omitted] [ABSTRACT FROM AUTHOR]

The Fe(II)/Fe(III) cycle is an important driving force for dissolution and transformation of jarosite. Divalent heavy metals usually coexist with jarosite; however, their effects on Fe(II)-induced jarosite transformation and different repartitioning behavior during mineral dissolution-recrystallization are still unclear. Here, we investigated Fe(II)-induced (1 mM Fe(II)) jarosite conversion in the presence of Cd(II), Mn(II), Co(II), Ni(II) and Pb(II) (denoted as Me(II), 1 mM), respectively, under anaerobic condition at neutral pH. The results showed that all co-existing Me(II) retarded Fe(II)-induced jarosite dissolution. In the Fe(II)-only system, jarosite first rapidly transformed to lepidocrocite (an intermediate product) and then slowly to goethite; lepidocrocite was the main product. In Fe(II)–Cd(II), -Mn(II), and -Pb(II) systems, coexisting Cd(II), Mn(II) and Pb(II) retarded the above process and lepidocrocite was still the dominant conversion product. In Fe(II)–Co(II) system, coexisting Co(II) promoted lepidocrocite transformation into goethite. In Fe(II)–Ni(II) system, jarosite appeared to be directly converted into goethite, although small amounts of lepidocrocite were detected in the final product. In all treatments, the appearance or accumulation of lepidocrocite may be also related to the re-adsorption of released sulfate. By the end of reaction, 6.0 %, 4.0 %, 76.0 % 11.3 % and 19.2 % of total Cd(II), Mn(II), Pb(II) Co(II) and Ni(II) were adsorbed on the surface of solid products. Up to 49.6 %, 44.3 %, and 21.6 % of Co(II), Ni(II), and Pb(II) incorporated into solid product, with the reaction indicating that the dynamic process of Fe(II) interaction with goethite may promote the continuous incorporation of Co(II), Ni(II), and Pb(II). [Display omitted] • The coexisting divalent metals retarded Fe(II)-induced jarosite dissolution. • In treatments with Cd(II), Mn(II) and Pb(II), lepidocrocite was dominant product. • In treatments with Co(II) and Ni(II), the main converted product was goethite. • Released sulfate may play an important role in the accumulation of lepidocrocite. • Fe(II) induced continuous incorporation of Co(II), Ni(II) and Pb(II) into goethite. [ABSTRACT FROM AUTHOR]

• Fe(Ⅲ)/ Fe(Ⅱ) cycle enables nitrate bio-reduction to ammonium at low C/N ratios. • Insoluble iron serves as the electron carrier. • Fe(Ⅲ)/ Fe(Ⅱ) cycle stimulated the upregulation of nrfA and downregulation of nirK. • Geobacter reserved by the Fe cycle exerted a vital role in ammonium production. The recovery of reactive nitrogen from industrial wastewater by biological ammoniation is a promising strategy of sustainable wastewater treatment. However, the low C/N ratio of pickling wastewater restricts nitrate towards ammonium, resulting in nitrogen loss. Here, we have proven the feasibility of nitrate ammoniation utilizing the Fe(Ⅲ)/Fe(Ⅱ) cycle at low C/N ratios, where partial organic electrons were employed to reduce Fe(Ⅲ) and the regenerated Fe(Ⅱ) facilitated ammoniation. It achieved the nitrate reduction efficiency of 96 ± 2 % and ammoniation efficiency of 49 ± 2 % for 3 cycles. Iron cycle enhanced the DNRA, demonstrated by the upregulation of nrfA and the downregulation of nirK. Electroactive Geobacter spp. with DNRA capability was sustained at high abundance (∼23 %) by the electron exchange process with extracellular iron. These findings provided a novel approach to recover active N using the iron cycle from wastewater, which has broader implications for sustainable circular economy and the ecology of carbon, iron and nitrogen cycle. [Display omitted] [ABSTRACT FROM AUTHOR]

The present work revises hypotheses to explain the molecular hydrogen genesis in Earth's crust based on iron cycle under water and sulfur environment. Indeed, known reactions are usually associated to minerals reacting with water under oxidizing conditions, such as the serpentinization. From geological observations, other gases have been identified in mid-oceanic ridges, in ophiolitic sites and in Proterozoic continental rocks (more than 550 million years) such as CH 4 , N 2 and He in various proportions. We use thermodynamic simulations to predict the direction of a range of possible metamorphic reactions regarding Gibbs free energies as a function of depth in Earth's crust, temperatures up to 1500 °C, pressure up to 10 kbar and including the relative partial pressures of the gases expressed by the reaction quotient Qr. While the oxidation of ferrous into ferric iron forming molecular hydrogen has been already extensively studied through the serpentinization and siderite decomposition, the role of pyritization has been significantly underestimated. We show that iron-based oxide precursors under hydrogen sulfide lead to H 2 formation and pyrite FeS 2 down to the middle level of the crust (down to 12 km in the crust-using the thermal gradient of 30 °C, at ΔG = ΔG0, Qr = 1). As the crust can be considered as a semi-open system (with H 2 leaking), its genesis is likely to appear also at deeper levels. The slow cooling of continental rocks through time in cratonic area is also compatible with the enhancement of pyritization reactions. The serpentinization is favored at lower temperatures. Those complementary processes can co-exist in black and white smokers and are key indices for hydrogen prospection as they involve redox reactions, impacting pH, with magnetic changes (through magnetite formation), thermal gradient changes and pyrite formation. The 'olivinization' of serpentinites (without hydrogen involved in the reaction), i.e. the inversion of serpentinization in order to close the iron cycle in the mantle, is evaluated to occur from 10 to 12 km using a normal thermal gradient. We find then that the iron cycle can be completed as the ferrous ion can be regenerated from the ferric iron via different mechanisms. It implies that natural hydrogen appears as a renewable raw matter on Earth, with clear interest in terms of industrial valorization. [Display omitted] • Combining iron and sulfur redox cycles for H 2 genesis. • Pyritization and serpentinization reactions as a function of crust's depth using thermodynamic simulations. • Renewable Hydrogen prospection and BIF. • Metamorphic reactions regarding geological events and thermal gradient (craton evolution, convection, subduction). • Methanation from siderite decomposition. [ABSTRACT FROM AUTHOR]

Microorganisms and burrowing animals exert a pronounced impact on the cycling of redox sensitive metals in coastal sediments. We hypothesized that the iron biogeochemical cycle and associated sedimentary microbial community will respond to seasonal changes in a bioturbated intertidal mudflat. In this study, we monitored the spatiotemporal dynamics of porewater and highly reactive solid phase iron with the corresponding prokaryotic and eukaryotic sedimentary microbial communities over one annual cycle from November 2015 to November 2016. Continuous and seasonally variable pools of both porewater Fe(II) and highly reactive iron (FeHR) were observed throughout the seasons with significant increases of Fe(II) and FeHR in response to increased sediment temperature in summer months. Maximum concentrations of Fe(II) and FeHR were predominantly confined to the upper 5 cm of sediment throughout the year. Iron-oxidizing and -reducing microorganisms were present and stable temporally, and exhibited a depth-dependent stratification likely due to availability of Fe(II) and FeHR pools, respectively. Zetaproteobacteria, presumptive lithotrophic iron-oxidizing bacteria, were present at abundances around 0.5–1% in the top 5 cm of sediment with decline abundance with depth. As a whole the microbial community was relatively stable across the seasons, and showed strongest separation with depth, probably driven by changes in oxygen availability and organic matter. The Deltaproteobacteria, principally taxa known to be associated with sulfur and iron cycling, were prevalent, especially at >5 cm depth. Gammaproteobacteria and Bacteroidetes were also abundant, with putatively aerobic members especially prevalent in the cm of the sediment. The relative abundance of diatoms, estimated from abundance of 18S rRNA gene counts, showed evidence of a seasonal signal possibly tied to spring and fall blooms. Overall, analysis of phytoplankton found significant abundance at depth, likely due to the feeding and bio-mixing activity of marine worms. Macro-, and meiofauna, consistent with expected taxa, were detected throughout the year via 18S gene counts, and showed some seasonal variations that may influence sedimentary iron transformations by active microbial grazing. In summary, this analysis revealed relatively consistent temporal and spatial trends in iron geochemistry and microbial and macrobial community composition, while also indicating a complex dynamic of microbial and macrobial interactions are responsible for maintaining these processes.

Shallow-water hydrothermal vents are widespread, especially in the Mediterranean Sea, owing to the active volcanism of the area. Apart free microbial communities’ investigations, few biological studies have been leaded yet. Investigations of microbial communities associated with Nematoda, an ecologically important group in sediments, can help to improve our overall understanding of these ecosystems. We used a multidisciplinary-approach, based on microscopic observations (scanning electron microscopy: SEM and Fluorescence In Situ Hybridization: FISH) coupled with a molecular diversity analysis using metabarcoding, based on the 16S rRNA gene (V3-V4 region), to characterize the bacterial community of a free-living marine nematode and its environment, the shallow hydrothermal vent near Naples (Italy). Observations of living bacteria in the intestine (FISH), molecular and phylogenetic analyses showed that this species of nematode harbors its own bacterial community, distinct from the surrounding sediment and water. Metabarcoding results revealed the specific microbiomes of the sediment from three sites of this hydrothermal area to be composed mainly of sulfur oxidizing and reducing related bacteria.

The limitation of iron (Fe) makes the North Pacific a typically high-nitrate, low-chlorophyll (HNLC) region in comparison with other oceanic regions of the world. Iron inputs from land via river discharge and atmospheric dust deposition are the primary processes introducing Fe into the ocean. Also, subsequent physical processes are crucial in transporting biologically available Fe into the upper ocean. As anthropogenic dust increases, the Fe from anthropogenic activities is expected to become more important in terms of impacting marine ecosystems. To investigate the Fe cycle and its impact on ecosystems, a project entitled ‘The sources and transport of Fe in the North Pacific and its impact on marine ecosystems’ has been funded by the National Natural Science Foundation of China. The project will focus on three major scientific questions: (1) What are the major sources of Fe in the North Pacific? (2) What is the influence of the Fe-binding ligand cycle on marine ecosystems? (3) What is the likely influence of global change in the future? The distribution of Fe and its corresponding impact on the marine ecosystem in current and future environmental conditions will be investigated. The results of the project are expected to improve our understanding of the marine ecosystem in the North Pacific.

Shallow-water hydrothermal vents are widespread, especially in the Mediterranean Sea, owing to the active volcanism of the area. Apart free microbial communities' investigations, few biological studies have been leaded yet. Investigations of microbial communities associated with Nematoda, an ecologically important group in sediments, can help to improve our overall understanding of these ecosystems. We used a multidisciplinary-approach, based on microscopic observations (scanning electron microscopy: SEM and Fluorescence In Situ Hybridization: FISH) coupled with a molecular diversity analysis using metabarcoding, based on the 16S rRNA gene (V3-V4 region), to characterize the bacterial community of a free-living marine nematode and its environment, the shallow hydrothermal vent near Naples (Italy). Observations of living bacteria in the intestine (FISH), molecular and phylogenetic analyses showed that this species of nematode harbors its own bacterial community, distinct from the surrounding sediment and water. Metabarcoding results revealed the specific microbiomes of the sediment from three sites of this hydrothermal area to be composed mainly of sulfur oxidizing and reducing related bacteria. [ABSTRACT FROM AUTHOR]

Iron can be a growth‐limiting nutrient for phytoplankton, modifying rates of net primary production, nitrogen fixation, and carbon export ‐ highlighting the importance of new iron inputs from the atmosphere. The bioavailable iron fraction depends on the emission source and the dissolution during transport. The impacts of anthropogenic combustion and land use change on emissions from industrial, domestic, shipping, desert, and wildfire sources suggest that Northern Hemisphere soluble iron deposition has likely been enhanced between 2% and 68% over the Industrial Era. If policy and climate follow the intermediate Representative Concentration Pathway 4.5 trajectory, then results suggest that Southern Ocean (>30°S) soluble iron deposition would be enhanced between 63% and 95% by 2100. Marine net primary productivity and carbon export within the open ocean are most sensitive to changes in soluble iron deposition in the Southern Hemisphere; this is predominantly driven by fire rather than dust iron sources. Changes in iron deposition cause large perturbations to the marine nitrogen cycle, up to 70% increase in denitrification and 15% increase in nitrogen fixation, but only modestly impacts the carbon cycle and atmospheric CO2 concentrations (1–3 ppm). Regionally, primary productivity increases due to increased iron deposition are often compensated by offsetting decreases downstream corresponding to equivalent changes in the rate of phytoplankton macronutrient uptake, particularly in the equatorial Pacific. These effects are weaker in the Southern Ocean, suggesting that changes in iron deposition in this region dominates the global carbon cycle and climate response. Key Points: Human activity significantly modifies the magnitude and location of atmospheric soluble iron deposition to the oceansMarine carbon cycle responses to Anthropocene iron flux changes are modest but more sensitive to varying fire than dust iron emissionsIncreasing the iron flux produces offsetting patterns in phytoplankton macronutrient uptake and productivity rates at the basin scale [ABSTRACT FROM AUTHOR]

This study introduces the UV/glucose-oxidase@Kaolin (GOD@Kaolin) coupled organic green rust (OGR) system (UV/OGR/GOD@Kaolin) to investigate the promotion of glucose oxidase activity by UV light and its synergistic degradation mechanism for photosensitive pollutants, specifically targeting the efficient degradation of 4-chlorophenol (4-CP). The enzyme system demonstrates its ability to overcome drawbacks associated with traditional Fenton systems, including a narrow pH range and high localized concentration of H 2 O 2 , by gradually releasing hydrogen peroxide in situ within a neutral environment. In the presence of UV radiation under specific conditions, enhanced enzyme activity is observed, resulting in increased efficiency in pollutant removal. The gradual release of hydrogen peroxide plays a crucial role in preventing unwanted reactions among active substances. These unique features facilitate the generation of highly reactive species, such as Fe(IV) O, •OH, and •O 2 −, tailored to efficiently target the organic components of interest. Additionally, the system establishes a positive iron cycle, ensuring a sustained reactive capability throughout the degradation process. The results highlight the UV/OGR/GOD@Kaolin system as an effective and environmentally friendly approach for the degradation of 4-CP, and the resilience of the enzyme extends the system's applicability to a broader range of scenarios. [Display omitted] • UV irradiation enhances the enzymatic activity through irritating GOD photosensitivity. • UV irradiation reduces Fe3+ to Fe2+, promoting the iron cycle. • The in-situ release of hydrogen peroxide improves its utilization efficiency. • The in-situ release of hydrogen peroxide improves its utilization efficiency. • GOD loading on kaolin enhances enzyme structure and activity and can also be recycled. [ABSTRACT FROM AUTHOR]

• CaSO 3 was introduced into the PS-AOPs system. • The Fe(III)/CaSO 3 /PDS system degraded 96.5 % of 2,4-DCP. • The conversion pathway of SO 3 − to SO 4 − and to 1O 2 was first proposed. • Oxidation of Fe(IV) and 1O 2 in the Fe(III)/CaSO 3 /PDS system was verified. S(IV)-based advanced oxidation processes (S(IV)-AOPs) have been gradually developed in groundwater organic contamination remediation. However, conventional Na 2 SO 3 is extremely soluble and prone to produce high concentrations of SO 3 2− to quench reactive oxide species (ROS), which seriously hinders the practical application of S(IV)-AOPs. In this work, a novel homogeneous iron-based AOPs system consisting of Fe(III), CaSO 3 , and peroxydisulfate (PDS) was proposed by using CaSO 3 instead of Na 2 SO 3 as a slow-released source of SO 3 2−. With the synergistic of PDS, the generated Fe(II) continuously converted to Fe(III), and the k obs of the constructed Fe(III)/CaSO 3 /PDS system was 8.8 times higher than that of the Fe(III)/CaSO 3 system. 96.5 % of 2,4-dichlorophenol (2,4-DCP) was durably degraded by Fe(III)/CaSO 3 /PDS system at a dose ratio of 1:5:15. ROS quenching experiments, electron paramagnetic resonance (EPR) tests, and probe tests indicated that Fe(IV), SO 4 −, and 1O 2 played a major role in the degradation of 2,4-DCP. The conversion of SO 4 − to 1O 2 in the system was demonstrated. Possible degradation pathways were proposed based on the density functional theory (DFT) calculations combined with LC-MS and GC–MS analysis. The results confirmed that the Fe(III)/CaSO 3 /PDS system exhibited strong stability and broad-spectrum applicability, which laid the foundation for the future engineering application of homogeneous iron-based AOP systems. [ABSTRACT FROM AUTHOR]

• Iron-mediated autotrophic microgranules were formed. • Iron was trapped effectively under microaerobic conditions. • AOB and anammox bacteria coexisted in microgranules for N removal. • Iron redox cycle coupled with N removal could be achieved in microgranules. • Synergy between Feammox and anammox could be responsible for N removal. Granule-based partial nitritation and anaerobic ammonium oxidation (PN/A) is an energy-efficient approach for treating ammonia wastewater. When treating low-strength ammonia wastewater, the stable synergy between PN and anammox is however difficult to establish due to unstable dissolved oxygen control. Here, we proposed, the PN/A granular sludge formed by a micro-oxygen-driven iron redox cycle with continuous aeration (0.42 ± 0.10 mg-O 2 /L) as a novel strategy to achieve stable and efficient nitrogen (N) removal. 240-day bioreactor operation showed that the iron-involved reactor had 37 % higher N removal efficiency than the iron-free reactor. Due to the formation of the microaerobic granular sludge (MGS), the bio(chemistry)-driven iron cycle could be formed with the support of anaerobic ammonium oxidation coupled to Fe3+ reduction. Both ammonia-oxidizing bacteria and generated Fe2+ could scavenge the oxygen as a defensive shield for oxygen-sensitive anammox bacteria in the MGS. Moreover, the iron minerals derived from iron oxidation and Fe-P precipitates were also deposited on the MGS surface and/or embedded in the internal channels, thus reducing the size of the channels that could limit oxygen mass transfer inside the MGS. The spatiotemporal assembly of diverse functional microorganisms in the MGS for the realization of stable PN/A could be achieved with the support of the iron redox cycle. In contrast, the iron-free MGS could not optimize oxygen mass transfer, which led to an unstable and inefficient PN/A. This work provides an alternative iron-related autotrophic N removal for low-strength ammonia wastewater. [Display omitted] [ABSTRACT FROM AUTHOR]

Copyright of Journal of Agro-Environment Science is the property of Journal of Agro-Environment Science Editorial Board and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract The cycling of iron (Fe) is often closely linked with that of carbon, nitrogen, phosphorus and manganese. Therefore, alterations in the Fe cycle may be indicative of concurrent overall changes in the biogeochemistry of terrestrial and aquatic ecosystems. Biogeochemical processes taking part in the Fe cycle frequently fractionate stable Fe isotopes, leaving soil, plant and other compartments of the ecosystems with varied Fe isotopic signatures. In this work, we reviewed the Fe isotope fractionation processes that have been reported so far for terrestrial ecosystems. While parent materials vary in Fe isotope compositions, pedogenic processes can further fractionate Fe isotope signatures, resulting in soil profiles with δ56Fe values (relative to isotope standard IRMM-014) from −0.52 to +0.72‰. Different soil Fe pools, as a result of cycling processes, show an even broader range of δ56Fe values, with secondary Fe oxides being isotopically the lightest, and with Fe sequestered in silicate minerals being the heaviest, due to preferential release of light Fe isotopes during dissolution of minerals. Actually and potentially plant-available Fe in soil can be extracted by 0.5 M HCl, which includes pools of water-extractable and exchangeable Fe, organically bound or adsorbed Fe, and poorly crystalline Fe oxides, altogether showing a depletion of heavy Fe isotopes with δ56Fe values down to −1.08‰. Depending on the Fe speciation and concentration present in the growth medium, plants can adapt their uptake strategy for Fe. Plants of the strategy I type especially take up light iron isotopes, while strategy II plants fractionate less towards light isotopes. Aboveground tissues usually show lighter Fe isotope signatures than the roots, with flowers (δ56Fe: −2.15 to −0.23‰) being isotopically the lightest. In freshwater systems, the most distinct Fe isotope fractionation is usually found at the oxic-anoxic interface, where redox conditions change and thus Fe speciation controls the degree of Fe isotope fractionation. Similar to soils, the δ56Fe values of unfiltered water mainly reflect averaged Fe isotope compositions across fractions with different particle sizes. In filtered freshwater (<0.45 μm), isolated colloid-sized fractions can exhibit either positive or negative δ56Fe values, depending on the chosen size fraction and the origin of the (nano) particles, with δ56Fe values up to +2.79‰ for fractions smaller than 0.003 μm from an arctic stream or down to −1.73‰ for dissolved Fe (<0.02 μm) from a boreal forested catchment. Most freshwater studies showed that rivers with elevated contents of dissolved organic carbon (DOC) tend to be isotopically heavier than those with lower DOC contents, while some studies also showed that rivers with high DOC can display light Fe isotopic signatures owing to the input of groundwater- and/or soil water-derived Fe. Finally, anthropogenic impacts can contribute to Fe isotope fractionation in freshwaters and may widen the range of δ56Fe values in the environment, with the lowest records found down to −5.29‰. Overall, our compilation reveals that Fe pools in different terrestrial system compartments vary in stable Fe isotope compositions, although the current database is still small. In order to use stable Fe isotopes as proxies to reconstruct the biogeochemical processes, future works should not solely rely on bulk δ56Fe assessments, but also involve the assessment of different fractionation factors for all biogeochemical pathways, which includes isotopic analyses among various pools of the terrestrial Fe cycle. [ABSTRACT FROM AUTHOR]

• Higher nitrate removal was achieved in ZVI-plant biomass coupled EFB. • Plant biomass promoted the enrichment of autotrophic and heterotrophic denitrifiers. • Increased iron cycle and glycolysis genes ensured electron donors supply in EFB-IB. • Enhanced autotrophic–heterotrophic denitrification led to more N loss in EFB-IB. In this study, the ecological floating bed supporting with zero-valent iron (ZVI) and plant biomass (EFB-IB) was constructed to improve nitrogen removal from low-polluted water. The effects of ZVI coupling with plant biomass on microbial community structure, metabolic pathways and functional genes were analyzed by metagenomic sequencing, and the mechanism for nitrogen removal was revealed. Results showed that compared with mono-ZVI system (EFB-C), the denitrification efficiencies of EFB-IB were effectively enhanced, with the higher average NO 3 −-N removal efficiencies of 22.60–59.19%. Simultaneously, the average NH 4 +-N removal efficiencies were 73.08–91.10%. Metagenomic analyses showed that EFB-IB enriched microbes that involved in iron cycle, lignocellulosic degradation and nitrogen metabolism. Plant biomass addition simultaneously increased the relative abundances of autotrophic and heterotrophic denitrifying bacteria. Network analysis showed the cooperation between autotrophic and heterotrophic denitrifying bacteria in EFB-IB. Moreover, compared with EFB-C, plant biomass addition increased the relative abundances of genes related to iron cycle, lignocellulose degradation and glycolysis processes, ensuring the production of autotrophic and heterotrophic electron donors. Therefore, the relative abundances of key enzymes and functional genes related to denitrification were higher in EFB-IB, being beneficial to the NO 3 −-N removal. Additionally, the correlation analysis of nitrogen removal and functional genes verified the synergistic mechanism of iron-based autotrophic denitrification and plant biomass-mediated heterotrophic denitrification in EFB-IB. In summary, plant biomass has excellent potential to improve the nitrogen removal of iron-based EFB from low-polluted water. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • A low cost and eco-friendly tannin product TE was used as a reductant to improve Fe(Ⅱ)/H 2 O 2 system. • TE successfully broadened the pH range of Fe(Ⅱ)/H 2 O 2 system by enhancing iron cycle and promoting ROS generation. • OH and O 2 − were both identified in Fenton system, and OH played a dominant role in Met degradation. • The complexes formed by TE and iron species showed reaction activity with O 2 −, and converted O 2 − into OH. In this study, a low-cost natural biomass extracted from higher plants - Tannin - was used to improve the Fenton system by promoting iron cycling due to the abundant phenolic hydroxyl groups in the molecular structure. Tannin extract (TE) of black wattle was combined with Fe(Ⅱ)/H 2 O 2 system at room temperature and under pH 3 to 8. Methionine (Met) was chosen as a target pollutant, as its critical role in the global sulfur cycle and algae-induced black bloom events. The results found that TE could significantly promote Fe(Ⅱ)/H 2 O 2 system, Met degradation increased from 44 % to 86 % under pH 6.0, and the mineralization increased from 14.86 % to 38.96 %. Both quenching experiments and electron paramagnetic resonance (EPR) analysis confirmed that OH and O 2 − contributed to Met degradation, and OH played a key role in TE/Fe(Ⅱ)/H 2 O 2 system. The reducibility of TE at different pH values was evaluated, the highest Fe(Ⅲ) reducing rate of TE was obtained at pH of 4.5 (k = 22.48 M−1min−1) based on the formation model. TE and its complex catalyzed the dismutation of O 2 − to form OH. The degradation rate constant of TE/Fe(Ⅱ)/H 2 O 2 system was 3.63 min−1, and the intermediates of Met degradation was proved to be non-toxic. In conclusion, TE could facilitate the iron recycle in Fenton system, consequently to strengthen H 2 O 2 activation, and it offered an energy-saving and eco-friendly way for organic pollutants treatment. [ABSTRACT FROM AUTHOR]