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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.

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., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

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.- , 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., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Heme oxygenase-1 (HO-1), which catalyzes heme degradation releasing iron, regulates several processes related to breast cancer. Iron metabolism deregulation is also connected with several tumor processes. However the regulatory relationship between HO-1 and iron proteins in breast cancer remains unclear. Using human breast cancer biopsies, we found that high HO-1 levels significantly correlated with low DMT1 levels. Contrariwise, high HO-1 levels significantly correlated with high ZIP14 and prohepcidin expression, as well as hemosiderin storage. At mRNA level, we found that high HO-1 expression significantly correlated with low DMT1 expression but high ZIP14, L-ferritin and hepcidin expression. In in vivo experiments in mice with genetic overexpression or pharmacological activation of HO-1, we detected the same expression pattern observed in human biopsies. In in vitro experiments, HO-1 activation induced changes in iron proteins expression leading to an increase of hemosiderin, ROS levels, lipid peroxidation and a decrease of the growth rate. Such low growth rate induced by HO-1 activation was reversed when iron levels or ROS levels were reduced. Our findings demonstrate an important role of HO-1 on iron homeostasis in breast cancer. The changes in iron proteins expression when HO-1 is modulated led to the iron accumulation deregulating the iron cell cycle, and consequently, generating oxidative stress and low viability, all contributing to impair breast cancer progression., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Iron (Fe) isotopes can effectively unveil the Fe cycle mechanisms under redox and biological conditions during the weathering and pedogenic processes. Fe contents and Fe isotope compositions (defined as δ 56 Fe) in the soil profiles under secondary forest land, abandoned cropland and shrubland were investigated in a typical karst area in Southwest China. The results showed that the Fe content ranged from 23.92 to 38.56 g/kg, 21.92 to 33.02 g/kg and 12.98 to 27.93 g/kg, and the δ 56 Fe levels varied from -0.48 ‰ to 0.21 ‰, -0.24 ‰ to 0.11 ‰ and - 0.11 ‰ to 0.16 ‰ from the secondary forest land, abandoned cropland and shrubland, respectively. The correlation analysis results showed that Fe transportation and isotopic fractionation were regulated by the redox processes through soil pH and soil organic matter (SOM) in the abandoned cropland and shrubland. Heavier Fe isotope may be accumulated in the deeper soil of secondary forest land due to Fe-oxide precipitation. The Fe isotope fractionations were greatly altered by soil organic carbon (SOC) in surface soils due to negative surface charges. Soil pH also plays a key role in enriching lighter Fe in a medium-acidic environment (shrubland) by ligand-controlled dissolution and reductive dissolution. Long-term cultivation in abandoned cropland and grazing in shrubland reshaped the Fe cycle in soil profiles by changing soil pH and SOC contents. However, the similar values of δ 56 Fe in different land use soils indicated that the agricultural activities have no significant impact on the Fe transformation in karst soil ecosystems. The land utilization is reasonable in the Yinjiang County. This study provided effective data and insightful analysis to understand the Fe cycle processes in the karst soils under varied land uses., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022. Published by Elsevier B.V.)

Most glaciers worldwide are undergoing climate-forced recession, but the impact of glacier changes on biogeochemical cycles is unclear. This study examines the influence of proglacial sediment weathering on meltwater chemistry at the early stages of glacier recession in the High Arctic of Svalbard. Scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) in combination with a wide range of geochemical analyses were used in this study. The SEM-EDS analyses of sediments collected in front of Werenskioldbreen show general degradation of pyrite and carbonate grains with age. The outer parts of pyrite grains have a gradual decrease in sulphur and gradual increase in iron oxides due to pyrite oxidation. This process was less advanced in the proglacial zone younger than 100 years compared to older sites such as the terminal moraine from the Little Ice Age. In both the proglacial zone and the terminal moraine, physical weathering of mineral grains, including formation of microcracks and microfractures, clearly enhanced pyrite oxidation. A consequence of proglacial sediment weathering is that the river chemistry is strongly affected by carbonate dissolution driven by sulphuric acid from sulphide oxidation. Also, reactive iron oxides, a product of sulphide oxidation, are mobilized in the proglacial zone. The results of this study show that proglacial weathering in the High Arctic of Svalbard is strongly coupled to river geochemistry, especially during the early stages of proglacial exposure after glacier recession., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 The Authors. Published by Elsevier B.V. All rights reserved.)

Fe(II) regeneration from ferric sludge via a biocathode and citrate system has recently been proposed to avoid iron-sludge accumulation and iron consumption in homogeneous Fenton treatments. However, poor regeneration rate of Fe(II) from ferric sludge at a near-neutral pH, without an iron-complexing agent, limited its wider practical application. Here, a biocathode augmented with Geobacter sulfurreducens hosted by a microbial electrolysis cell was developed to efficiently regenerate dissolved Fe(II) from ferric sludge at near-neutral pH levels, without using iron-complexing agents. In the Geobacter sulfurreducens-rich biocathode without complexing agents, the regeneration rate of dissolved Fe(II) increased three-fold compared with the biocathode before inoculating Geobacter sulfurreducens. The highest concentration of dissolved Fe(II) increased from 45 mg Fe/L to 199 mg Fe/L at pH 6 when 0.5 V of voltage was applied. Furthermore, 84 mg Fe/L of dissolved Fe(II) was successfully regenerated from ferric sludge during the 123 days' operation of flow-through biocathode. Finally, the regenerated Fe(II) solution without organic matters was successfully applied in a near-neutral pH Fenton treatment to remove recalcitrant pollutants. This Geobacter sulfurreducens-rich biocathode, with its low chemical consumption, high regeneration rate and feasibility for continuous flow operation, offers a more efficient method to realize iron-free in homogeneous Fenton treatments., (Copyright © 2022 The Authors. Published by Elsevier B.V. All rights reserved.)

Ammonium removal in wastewater treatment plants demands large quantities energy input, such as aeration for wastewater and the addition of organics for nitrate reduction. Anaerobic ammonium oxidation coupled to Fe(III) reduction, called Feammox process play a crucial role in natural nitrogen cycle, which has been rarely investigated in the field of wastewater treatment. Besides, Iron-reducing bacteria (FeRB) as function bacteria of Feammox could transfer electrons to iron oxide by oxidizing organics. The possibility of anaerobic ammonium removal coupled with organics should be investigated to assess the potential of Feammox process for conventional wastewater treatment. In this study, five Fe(III) compounds, Fe 2 O 3 , Fe 3 O 4 , Fe(OH) 3 , Citrate-Fe and pyrite were supplemented to investigate the effect of iron oxides on ammonium removal in serum bottles with working volume of 100 mL. It was found that ammonium removal efficiency of the Fe 2 O 3 group was the highest. To simulate wastewater treatment process in sewage treatment plant, three Up-flow anaerobic sludge blanket reactors with volume of 250 mL adding Fe 2 O 3 were applied with influent of ammonium and carbon sources. It was found that the organics significantly inhibited the ammonium removal by Feammox process. This was attributed to that carbon sources and ammonium could be used as electron donors for Fe(III) reduction. In addition, this nitrogen removal was also likely related with the iron cycle, i.e., Fe(III) reduction with ammonium oxidation and Fe(II) oxidation with nitrate/nitrite reduction. This study provides a promising alternative technology for anaerobic ammonium removal in wastewater treatment. Optimizing nitrogen removal and carbon sources applied in conventional wastewater plants are required in future., Competing Interests: Declaration of competing interest The authors declared that they have no conflicts of interest to this work. We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted., (Copyright © 2021 Elsevier B.V. All rights reserved.)

To promote the reduction of Fe 3+ and improve the mineralization of organic pollutants, a novel electro-Fenton coupled with sulfite (Fe 3+ -EF/sulfite) process was constructed, which was superior to Fe 3+ -EF process in terms of carbamazepine (CBZ) degradation and mineralization with 5.99 times enhancement in degradation rate constant and 15.7 times enhancement on TOC removal. The complexation of Fe 3+ and sulfite prevented the precipitation of Fe 3+ , reduced Fe 3+ to Fe 2+ , and accelerated the iron cycle, so that H 2 O 2 utilization efficiency (0.051 mg TOC mg H2O2 -1 ) was greatly improved and electric energy consumption was greatly reduced (0.081 kWh g -1 TOC). The quenching experiments and EPR test confirmed that the reactive species, such as SO 3 •- , SO 4 •- , • OH, O 2 •- and 1 O 2 were responsible for the degradation of CBZ. This process also expanded the pH application range from 3 to 9 with satisfactory CBZ removal efficiency. This work verified the suitability of the Fe 3+ -EF/sulfite process for different sulfites (sulfite and bisulfite), typical pollutants (atrazine, sulfamethazine, rhodamine B) and real wastewater with 2.1-18.7 folds enhancement in degradation rate. The Fe 3+ -EF/sulfite process can achieve deep mineralization with low cost and simple operation, which has a broad and cost-effective application prospect in removal of refractory organic pollutants., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Although phosphate (PO 4 3- ) may play a decisive role in enriching toxic arsenic (As) in the groundwater of many Asian deltas, knowledge gaps exist regarding its interactions with As. This study investigates the simultaneous immobilisation of PO 4 3- and As in aquifer sediments at a redox transition zone in the Red River Delta of Vietnam. The majority of PO 4 3 - and As was found to be structurally bound in layers of Fe(III)-(oxyhydr)oxide precipitates, indicating that their formation represents a dominant immobilisation mechanism. This immobilisation was also closely linked to sorption. In the surface sorbed sediment pools, the molar ratios of total P to As were one order of magnitude higher than found in groundwater, reflecting a preferential sorption of PO 4 3- over As. However, this competitive sorption was largely dependent on the presence of Fe(III)-(oxyhydr)oxides. Ongoing contact of the aquifer sediments with iron-reducing groundwater resulted in the reductive dissolution of weakly crystalline Fe(III)-(oxyhydr)oxides, which was accompanied by decreased competition for sorption sites between PO 4 3- and As. Our results emphasise that, to be successful in the medium and long term, remediation approaches and management strategies need to consider competitive sorption between PO 4 3- and As and dynamics of the biogeochemical Fe-cycle., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Ammonium removal in wastewater treatment plants requires a large number of energy input, such as aeration and the addition of organics. Alternative, more economical technologies for nitrogen removal from wastewater are required. This study comprehensively investigated the feasible of microbial electricity coupled with Fe(III) reduction promoting the anaerobic ammonium removal. It was found that electrostimulation coupled with Fe(III) reduction (bioelectrochemical systems-Fe(III) (BES-Fe(III)) reactor) enhanced the anaerobic ammonium removal by 50.38% and 38.8% compared with the BES reactor and Fe(III) reactor, respectively. The ammonium removal rate reached the highest value of 80.62 ± 0.26 g N m -3 ·d -1 in the Fe(III)-BES reactor comparable to conventional wastewater treatment plants (WWWTPs). The improvement of ammonium removal might be the synergistic effect of BES and Feammox process on reaction process and microorganisms. Firstly, the addition of Fe 2 O 3 could improve the electrochemical characteristics by enriching iron-reducing bacterial (FeRB). Secondly, the improved ammonium removal could be due to nitrite generated from Feammox process driving the anodic ammonium oxidation. Additionally, the ammonium removal improvement might be the effect of BES on the Fe 2+ leaching so as to accelerate the Fe (II)/Fe(III) cycle. In agreement, higher abundance of FeRB and iron-oxidizing bacteria was detected in the Fe(III)-BES reactor. This study provides a lower energy consumption and operational cost technology compared with the conventional partial nitrification/denitrification, which was more than 800 times less than for the conventional wastewater treatment., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020. Published by Elsevier B.V.)

In rural domestic wastewater treatment using subsurface constructed wetland system (SFCWs), the lack of a carbon source for denitrification and limited phosphorus uptake are responsible for low removal of nitrogen and phosphorus, and a suitable substrate is therefore, necessary. Iron is an important component in nitrogen and phosphorus biogeochemical cycles. Few studies have addressed the application of iron in SFCWs. Therefore, we constructed SFCWs that used iron scraps as a substrate. Enhanced nitrification, denitrification and removal of phosphorus were observed. The large proportion of nitrite-oxidising bacteria present in CWs with iron scraps (CW-T) compared to gravel beds indicated that iron may enhance ammonium (NH 4 + ) oxidation. More nitrate-reducing bacteria related to Fe and autotrophic denitrifying bacteria were discovered in the back zone of CW-T and these enhanced denitrification process. Phosphate (PO 4 3- ) reacted with ferrous ion (Fe 2+ ) and ferric ion (Fe 3+ ) to generate the precipitant. Moreover, Fe 3+ reacted with water to generate iron oxide (FeOOH) that had a large adsorption capacity for phosphorus. After six months of operation, average NH 4 + -N, total nitrogen and total phosphorus removal rates were 66.98 ± 13.37 %, 71.26 ± 13.57 % and 93.54 ± 6.64 %, respectively. Iron scraps can potentially be utilised in SFCWs in rural domestic wastewater treatment., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

We used three stable reactors to investigate the rates of nitrate removal coupled with iron cycle and the subsequent influence of the reaction on bacterial communities. The iron-reducing bacterium Klebsiella sp. FC61 was immobilized on the reactor columns of the experimental groups B (only Klebsiella) and C (Klebsiella+magnetite). With the fluctuation of Fe 2+ to Fe3 + (iron cycle), the average nitrate removal efficiency increased from 73.22% to 93.91% and 86.92% to 97.84% in groups B and C, respectively, as the influent nitrate concentration decreased from 40 to 10mg/L. However, the average rate of nitrate removal showed the opposite trend (from 2.08mg/L/h to 0.67mg/L/h and 2.41mg/L/h to 0.69mg/L/h in groups B and C, respectively) as the influent nitrate concentration decreased. Analysis of microbial distribution and community structures indicated that the population of Klebsiella sp. increased in groups B (from 18.21% to 41.21%) and C (from 25.43% to 46.80%) and contributed to the effective removal of nitrate in the reactors., (Copyright © 2017 Elsevier Ltd. All rights reserved.)