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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]

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. [Display omitted] • Iron consumption and discharge of iron sludge can be reduced in Fenton treatments. • Dissolved Fe(II) can be obtained at pH 6, without iron complexation agents. • External voltage and Geobacteraceae enhance the Fe(II) regeneration rate. • Dissolved Fe(II) production is realized in a flow-through biocathode. [ABSTRACT FROM AUTHOR]

Abstract: Heterogeneous photodegradation of pentachlorophenol (PCP) in the goethite (α-FeOOH) and hematite (α-Fe2O3) systems with oxalate under UVA illumination was investigated. The PCP degradation, dechlorination and detoxification, in terms of Microtox acute toxicity, were all achieved to the higher efficiency in the hematite suspension than in the goethite suspension. The optimal initial concentration of oxalic acid () for the PCP degradation with goethite and hematite under the experimental conditions was found to be 1.2mM, since sufficient Fe(III) as Fe(C2O4)3 3− and Fe(II) as Fe(C2O4)2 2− can be formed at . The main intermediates of PCP degradation were identified by GC–MS, HPLC and IC analyses. It was found that the cycling process between Fe(III) and Fe(II) in both the goethite and hematite systems occurred more vigorously at the initial stage and gradually became gentle, while the rate of PCP photodegradation varied from fast to slow during the reaction time. Furthermore, the formation of H2O2 during photoreaction was studied to explore its relationship with the photodegradation efficiency and the iron cycling process. [Copyright &y& Elsevier]

To promote the reduction of Fe3+ and improve the mineralization of organic pollutants, a novel electro-Fenton coupled with sulfite (Fe3+-EF/sulfite) process was constructed, which was superior to Fe3+-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 Fe3+ and sulfite prevented the precipitation of Fe3+, reduced Fe3+ to Fe2+, 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 1O 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 Fe3+-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 Fe3+-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. [Display omitted] • Fe3+-EF/sulfite greatly enhanced the removal and mineralization of carbamazepine (CBZ). • Fe3+-EF/sulfite reduced Fe3+ to Fe2+, improved iron cycle and H 2 O 2 utilization efficiency. • This process expanded the applicable pH range (3−9) with greatly reduced energy consumption. • Reactive species including SO 3 •-, SO 4 •-, •OH, O 2 •- and 1O 2 were responsible for CBZ degradation. • The process had good applicability to different sulfites, different pollutants and real wastewater. [ABSTRACT FROM AUTHOR]

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. [Display omitted] • PO 4 3- and As retention in aquifer sediments controlled by redox properties. • competition between PO 4 3- and As for sorption sites reflected in P/As ratios. • PO 4 3- and As retention by sorption and subsequent incorporation in Fe-oxides. • changing sedimentary P and As pools due to influence of Fe-reducing groundwater. • Fe-reduction lowers sorption sites and competitive sorption of PO 4 3- and As. [ABSTRACT FROM AUTHOR]

• Iron scraps enhance simultaneous total nitrogen and total phosphorus removal. • Iron scraps enhanced nitrification and autotrophic denitrification process. • Main phosphorus removed by FeOOH adsorption. 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 (Fe2+) and ferric ion (Fe3+) to generate the precipitant. Moreover, Fe3+ 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. [ABSTRACT FROM AUTHOR]