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The treatment of metal‐laden industrial effluents by reverse osmosis is gaining in popularity worldwide due to its high performance. However, this process generates a polymetallic concentrate (retentate) stream in need of efficient post‐treatment prior to environmental discharge. This paper presents results on the bioremediation (in batch mode) of a metal‐laden, arsenic‐dominated retentate using Shewanella sp. O23S as inoculum. The incubation of the retentate for 14 days under anoxic conditions resulted in the following removal yields: As (8%), Co (11%), Mo (3%), Se (62%), Sb (30%), and Zn (40%). The addition of 1 mM cysteine increased the removal rate as follows: As (27%), Co (80%), Mo (78%), Se (88%), Sb (83%), and Zn (90%). The contribution of cysteine as a source of H2S to enhancing the removal yield was confirmed by its addition after seven days of incubations initially lacking it. Additionally, the cysteine‐sourced H2S was confirmed by its capture onto headspace‐mounted Pb‐acetate test strips that were analyzed by X‐ray diffraction. We show that real metal‐laden industrial effluents can be treated to medium‐to‐high efficiency using a biological system (naturally‐sourced inocula) and inexpensive reagents (yeast extract, lactate and cysteine).

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Microbes form biominerals via biologically-controlled mineralization (BCM) and biologically-induced mineralization (BIM) (Konhauser and Riding, 2012). BCM is commonly an intracellular process, where microbes employ genetic determinants and enzymes to induce mineralization. The end product (the biomineral) of BCM serves a biological function for its host. Some notable examples include magnetotactic bacteria (the magnetite chain helps target microaerophilic environments) and bacteria that biomineralize carbonates (intracellular carbonate contributes to buoyant density) (Uebe and Schüler, 2016; Görgen et al., 2021). Conversely, mineral formation in BIM does not have a regulatory control and the biomineralization product is generally located outside the cell. Numerous minerals are being formed via this process such as BaSO4, PbS or iron minerals. BIM-produced biominerals do not often have a clear biological function. For instance, respiratory-sourced biogenic Se0 may contribute to the buoyant density of sludge granules in upflow bioreactors (Staicu and Barton, 2021). However, with the renewed interest in microbial biominerals new biological functions may be acknowledged in the future.
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Acid mine drainage (AMD) still represents a huge environmental problem. Technical and scientific breakthroughs are still needed to decrease environmental damages, treatment cost, and waste production associated with AMD. The feasibility of combining continuously fed anaerobic sulfate-reducing bioreactor with downstream iron oxidation step was tested, at a laboratory scale, with two types of real arsenic-rich AMD waters from the site of Carnoulès (France), that differed in acidity (pH 3.3 and 4.0), arsenic (As, 18 and 174 mg.L⁻¹), and metal concentrations. Iron remained in solution, while up to 99% of As was precipitated as amorphous orpiment in the anaerobic sulfate-reducing bioreactor. Zinc (Zn) precipitation was also observed, up to 99%; however, the efficiency of Zn precipitation was less stable than that of As. The anaerobic bioreactor presented a stable bacterial community including a Desulfosporosinus-related sulfate reducer. When the effluents from the anaerobic process step were treated in a laboratory aerobic bioreactor, iron was oxidized efficiently. The feasibility of efficient orpiment bio-precipitation coupled with downstream iron oxidation was shown, thus opening the perspective of a low-cost combination of treatment steps for the removal of arsenic, zinc, and iron in As-rich AMDs.
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The production of cellular energy using the redox-state transformations of metals/metalloids is an ancient strategy some bacteria and archaea use to sustain growth under nutrient-poor and sometimes extreme conditions (Stolz and Oremland 1999; Gescher and Kappler 2012; Staicu and Barton 2017; Wells et al. 2020). Biominerals are synthesized by microbes to alleviate metal stress and to serve diverse ecological functions (e.g. magnetotactic bacteria synthesize particles of single-domain magnetite de novo, providing them the ability to sense and orient in the ambient geomagnetic field). Metals can be toxic and microbes have developed sophisticated resistance mechanisms to counteract this type of stress. Strategies include ion specific efflux pumps, sequestration in poorly soluble minerals and redox change reactions (Nies 1999; Ni et al. 2015). Metals are also key to human health, culture and industrialization. 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In contrast to the renewable energy, metals are not at a practical time scale, therefore their use should be sustainable. Further, there is growing concern over the proliferation of ‘e-waste’ (i.e. discarded electronic devices, computers and cell phones). This means new strategies have to be implemented for efficient recovery, reuse and for metal extraction from low-grade resources (e.g. metalliferous soils, metallurgical slags and mine waste; Vidal et al. 2017; Kisser et al. 2020). Microbes and their capacity to transport metals can be of great use in such a context as this approach offers a less energy-intensive and also a less environmentally-degrading alternative to processes such as hydro- and pyrometallurgy. Biomining and bioleaching, the recovery of metals using microbial metabolism, are successfully used in industrial operations for the extraction of copper, gold and uranium (Jerez 2017). This strategy can be applied to both metal-rich deposits as well as to low-grade metal wastes/slags resulted from past industrial activities and discarded in the environment (Potysz and Kierczak 2019). Another unexploited source is the metal-rich wastewater generated by numerous industrial activities. Such sources, in the framework of the growing circular economy paradigm shift, started to be regarded as a resource rather than a waste material. These industrial streams can be treated using a microbially-mediated bioremediation approach, coupled with metal recovery (Puyol et al. 2016). It may also be possible to recover metals from printed circuit boards of computers and cell phones (Argumedo-Delira, Diaz-Martinez and Gomez-Martinez 2020). Thus, we thought it timely to have a themed issue ‘Microbes vs Metals: Harvest and Recycle’. 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DOI:https://doi.org/10.1103/PhysRevB.14.1781
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Dowsing for danger Arsenic is a metabolic poison that is present in minute quantities in most rock materials and, under certain natural conditions, can accumulate in aquifers and cause adverse health effects. Podgorski and Berg used measurements of arsenic in groundwater from ∼80 previous studies to train a machine-learning model with globally continuous predictor variables, including climate, soil, and topography (see the Perspective by Zheng). The output global map reveals the potential for hazard from arsenic contamination in groundwater, even in many places where there are sparse or no reported measurements. The highest-risk regions include areas of southern and central Asia and South America. Understanding arsenic hazard is especially essential in areas facing current or future water insecurity. Science , this issue p. 845 ; see also p. 818
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Severe effects of selenium (Se) occurred among birds feeding and nesting at Kesterson Reservoir (San Joaquin Valley, California) in 1983‐1985. This paper describes the integration of site monitoring, risk assessment, and management actions conducted after the effects of Se were discovered. Selenium contamination of the site occurred over just a few years, but actions to resolve the contamination issues required >20 years. The Reservoir, a series of 12 ponds totaling about 1,280 acres (518 hectares), served for storage and evaporation of subsurface agricultural drainage. Selenium concentrations in Reservoir inflow in 1983 were about 300 µg/L, primarily as selenate; within the ponds it was biogeochemically reduced to other inorganic and organic forms and bioaccumulated by biota or deposited to sediments. An estimated 9000 kg of Se were delivered to Kesterson in 1981‐1986. A 1985 order required cleanup and abatement of the Reservoir, so Reclamation and the US Department of the Interior undertook actions and studies to reduce hazards to birds. In 1988, about one million cubic yards (764,500 cubic meters) of soil were used to fill portions of the Reservoir, transforming it into terrestrial habitat. Intensive monitoring began in 1989 to assess the impact of the Reservoir on wildlife, provide a basis for adjusting site management, verify the effectiveness of cleanup actions, and provide a basis for modifying future monitoring. Monitoring continued until 2014, with modifications and management actions based on results of two risk assessments (1993 and 2000). Monitoring results in 2013‐2014 showed that Se concentrations were relatively stable over time and risks to wildlife were low. From the initial problem discovery to the conclusion of actions taken to remediate the site, combining responsive, reactive, and adaptive monitoring; modeling; risk assessment, and mitigation actions proved effective in solving the problem so that risks to wildlife were reduced to minimal levels. This article is protected by copyright. All rights reserved. Because severe effects of selenium (Se) occurred in birds at Kesterson Reservoir, portions of the Reservoir were filled with soil, transforming it into terrestrial habitat; we describe the integration of subsequent site monitoring, ecological risk assessment, and management actions. Monitoring in 1989-2014 and two risk assessments (1993 and 2000) assessed impacts on wildlife and provided a basis for adjusting site management and modifying future monitoring; final results showed that Se concentrations were relatively stable over time and risks to wildlife were low. From the initial problem discovery to the conclusion of actions taken to remediate the site, combining responsive, reactive, and adaptive monitoring; modeling; and mitigation actions proved effective in solving the problem so that risks to wildlife were reduced to minimal levels. Selenium contamination of the site occurred over just a few years, but actions to resolve the contamination issues required more than 20 years.
Article
A significant amount of antimony (Sb) enters into the environment every year because of the wide use of Sb compounds in industry and agriculture. The exposure to Sb, either direct consumption of Sb or indirectly, may be fatal to the human health because both antimony and antimonide are toxic. Firstly, the introduction of Sb chemistry, distribution and health threats are presented in this review, which is essential to the removal techniques. Then, we provide the recent and common techniques to remove Sb, including adsorption, coagulation/flocculation, membrane separation, electrochemical methods, ion exchange and extraction. Removal techniques concentrate on the advantages, drawbacks, economical efficiency and the recent achievements of each technique. We also take an overall consideration of experimental conditions, comparison criteria, and economic aspects.
Article
Oxyanions of arsenic and selenium call be used in microbial anaerobic respiration as terminal electron accepters. The detection of arsenate and selenate respiring bacteria in numerous pristine and contaminated environments and their rapid appearance in enrichment culture suggest that they are widespread and metabolically active in nature. Although the bacterial species that have been isolated and characterized are still few in number, they are scattered throughout the bacterial domain and include Gram-positive bacteria, beta, gamma and epsilon Proteobacteria and the sole member of a deeply branching lineage of the bacteria, Chrysiogenes arsenatus. The oxidation of a number of organic substrates (i.e. acetate, lactate, pyruvate, glycerol, ethanol) or hydrogen can be coupled to the reduction of arsenate and selenate, but the actual donor used Varies from species to species. Both periplasmic and membrane-associated arsenate and selenate reductases have been characterized. Although the number of subunits and molecular masses differs, they all contain molybdenum. The extent of the environmental impact on the transformation and mobilization of arsenic and selenium by microbial dissimilatory processes is only now being fully appreciated.
Chapter
The chapter considers basic aspects of chemical thermodynamics as relevant for understanding microbial metabolisms in nature and for defining the chemical environments of the microbial world. The chapter describes enthalpy, entropy, and Gibbs free energy. All thermodynamically favorable chemical reactions proceed, barring kinetic barriers, until the distribution of reacting components in the system reaches equilibrium. The chapter discusses influence of temperature on thermodynamic properties, activity coefficient calculations, gas solubility and Henry's law, oxidation-reduction reactions. Cellular architecture and its relationship to show how organisms gain energy for their growth and metabolism are discussed. The chapter examines how catabolic (also called dissimilatory) processes and light provide the energy for the anabolic (also called assimilatory) synthesis of cellular material. It discusses some of the basic aspects of cellular metabolism and explains how different metabolisms are named. A vast array of different energy-providing metabolisms exist in nature, and a common nomenclature is adopted whereby these metabolisms are named based on their (1) energy source, (2) electron source, and (3) carbon source.
Infrared absorption and polarized Raman spectra of monoclinic As2O3 at 300K and 7K have been recorded. A vibrational analysis of the AsO bond stretching. OAsO angle deformation and of the rigid layer modes is reported. A complete valence force field calculation states precisely the assignments. The values of some force constants in crystalline and disordered phases of AS2O3 are compared.
Article
The molecular species of As(III) in aqueous solution have been studied by the Raman effect. Utilizing the Job method of continuous variation, solutions with [OH-]/[As(III)] between 3.5 and 15 have been shown to contain the four species As(OH)3, AsO(OH)2-, AsO2(OH)2-, and AsO33-. The Raman spectra are consistent with a C3v point group assignment for both As(OH)3 and AsO33-. Cs symmetry has been shown for AsO(OH)2- and probably for AsO2(OH)2-, although experimental data on the latter species were most difficult to obtain, since the spectra of all species are overlapped to a large extent. The As-O stretching vibrations, insensitive to D2O, are between 790 and 750 cm-1, whereas the symmetric As-OH stretching modes, all exhibiting an isotope effect, are at 710 cm-1 for As(OH)3 and 570 cm-1 for AsO(OH)2-. The species As(OH)3 is also identified from its Raman spectrum as the only major component in acidic aqueous solutions of As4O6(s). The existence of HAsO2 is ruled out. Furthermore, there is no evidence for polymerization in basic solutions within an [As(III)] range of 0.6-5.0 M.
Article
A 600 ml continuously stirred tank reactor was used to assess the performance of a zinc sulfide precipitation process using a biogenic sulfide solution (the effluent of a sulfate-reducing bioreactor) as sulfide source. In all experiments, a proportional-integral (PI) control algorithm was used to control the pH and the sulfide (S2-) concentration at the desired level in the precipitator. The pS (defined as: -log [S2-]) and pH were optimised using a chemical Na2S solution as sulfide source. A S2- concentration of 10(-15) M (i.e. pS 15) was found to be optimal for zinc sulfide precipitation, resulting in a residual zinc concentration of 0.07 mg/l from a 3 g/l Zn2+ influent, for both chemical Na2S and biogenic sulfide solutions. The mean particle size of the ZnS precipitates at pS 15 and pH 6.3 was 7.5 and 10.2 mu m when using biogenic sulfide and chemical Na2S, respectively, indicating that both sulfide sources are adequate for solid-liquid separation by sedimentation. When biogenic sulfide instead of chemical Na2S was used, the efficiency of the ZnS precipitation process slightly decreased both in terms of zinc effluent concentration (at pS 10 and 20) and particle size of the precipitate (at pS 10, 15 and 20). This was shown to be attributed to the presence of various substances (phosphate, micro-nutrients, acetate, EDTA) present in the sulfate-reducing reactor effluent. (C) 2006 Elsevier B.V. All rights reserved.
Article
Copper was continuously and selectively precipitated with Na(2)S to concentrations below 0.3 ppb from water containing around 600 ppm of both Cu and Zn in a Continuously Stirred Tank Reactor. The pH was controlled at 3 and the pS at 25 (pS=-log(S(2-))) by means of an Ag(2)S sulfide selective electrode. Copper's recovery and purity were about 100%, whereas the total soluble sulfide concentration was below 0.02 ppm. X-ray diffraction (XRD) analysis showed that copper precipitated as hexagonal CuS (covellite). The mode of the particle size distribution (PSD) of the CuS precipitates was around 36 microm. The PSD increased by high pS values and by the presence of Zn. Depending on the turbulence, the CuS precipitates can grow up to 200 microm or fragment in particles smaller than 3 microm in a few seconds. Zn precipitation with Na(2)S at pH 3 and 4, in batch, always lead to Zn concentrations above 1 ppm. Zn precipitated as cubic ZnS (spharelite).
Article
A newly discovered arsenate-reducing bacterium, strain OREX-4, differed significantly from strains MIT-13 and SES-3, the previously described arsenate-reducing isolates, which grew on nitrate but not on sulfate. In contrast, strain OREX-4 did not respire nitrate but grew on lactate, with either arsenate or sulfate serving as the electron acceptor, and even preferred arsenate. Both arsenate and sulfate reduction were inhibited by molybdate. Strain OREX-4, a gram-positive bacterium with a hexagonal S-layer on its cell wall, metabolized compounds commonly used by sulfate reducers. Scorodite (FeAsO42. H2O) an arsenate-containing mineral, provided micromolar concentrations of arsenate that supported cell growth. Physiologically and phylogenetically, strain OREX-4 was far-removed from strains MIT-13 and SES-3: strain OREX-4 grew on different electron donors and electron acceptors, and fell within the gram-positive group of the Bacteria, whereas MIT-13 and SES-3 fell together in the epsilon-subdivision of the Proteobacteria. Together, these results suggest that organisms spread among diverse bacterial phyla can use arsenate as a terminal electron acceptor, and that dissimilatory arsenate reduction might occur in the sulfidogenic zone at arsenate concentrations of environmental interest. 16S rRNA sequence analysis indicated that strain OREX-4 is a new species of the genus Desulfotomaculum, and accordingly, the name Desulfotomaculum auripigmentum is proposed.
Article
Oxyanions of arsenic and selenium can be used in microbial anaerobic respiration as terminal electron acceptors. The detection of arsenate and selenate respiring bacteria in numerous pristine and contaminated environments and their rapid appearance in enrichment culture suggest that they are widespread and metabolically active in nature. Although the bacterial species that have been isolated and characterized are still few in number, they are scattered throughout the bacterial domain and include Gram-positive bacteria, beta, gamma and epsilon Proteobacteria and the sole member of a deeply branching lineage of the bacteria, Chrysiogenes arsenatus. The oxidation of a number of organic substrates (i.e. acetate, lactate, pyruvate, glycerol, ethanol) or hydrogen can be coupled to the reduction of arsenate and selenate, but the actual donor used varies from species to species. Both periplasmic and membrane-associated arsenate and selenate reductases have been characterized. Although the number of subunits and molecular masses differs, they all contain molybdenum. The extent of the environmental impact on the transformation and mobilization of arsenic and selenium by microbial dissimilatory processes is only now being fully appreciated.
Article
Selenium pollution is a worldwide phenomenon and is associated with a broad spectrum of human activities, ranging from the most basic agricultural practices to the most high-tech industrial processes. Consequently, selenium contamination of aquatic habitats can take place in urban, suburban, and rural settings alike--from mountains to plains, from deserts to rainforests, and from the Arctic to the tropics. Human activities that increase waterborne concentrations of selenium are on the rise and the threat of widespread impacts to aquatic life is greater than ever before. Important sources of selenium contamination in aquatic habitats are often overlooked by environmental biologists and ecological risk assessors due to preoccupation with other, higher priority pollutants, yet selenium may pose the most serious long-term risk to aquatic habitats and fishery resources. Failure to include selenium in the list of constituents measured in contaminant screening/monitoring programs is a major mistake, both from the hazard assessment aspect and from the pollution control aspect. Once selenium contamination begins, a cascade of bioaccumulation events is set into motion which makes meaningful intervention nearly impossible. However, this cascade of events need not happen if adequate foresight and planning are exercised. Early evaluation and action are key. Prudent risk management based on environmentally sound hazard assessment and water quality goals can prevent biological impacts.