Biogenesis of Magnetite Nanoparticles Using Shewanella Species Isolated from Diverse Regions.

The objective of this study was to synthesize magnetite (Fe3O4) nanoparticles using diverse Shewanella species isolated from different environments. Magnetite formation experiments were performed with 11 species of Shewanella using akaganeite (ß-FeOOH) as an electron acceptor and lactate (C3H6O3) as an electron donor under a N2 atmosphere at room temperature. Magnetites and other products formed by the bacteria were characterized by XRD and TEM-EDS analyses. In this study, all the strains of Shewanella species produced magnetite nanoparticles with 2.5 to 20 nm in size. However, the size of the magnetite varied with the species of Shewanella, and a few species formed Fe(III) oxide as secondary minerals such as goethite and lepidocrocite. These results indicate that different species of iron-reducing bacteria belonging to the genus Shewanella exhibit different rates of Fe(III) reduction resulting in magnetite nanocrystals of varying size and formation of secondary mineral species.

Mixed Contaminants Removal Efficiency Using Bio-FeS Nanoparticles.

Advances in nanotechnology has provided diverse industrial applications including an environmental remediation field. In particular, bio-nanotechnology gives extended eco-friendly remediation practice. Among diverse bio-nanoparticles synthesized by microorganisms, the iron based nanoparticles (NPs) are of great interest because of their availability, low cost and toxicity to human health and the environment. In this study, iron based nanoparticles were biologically synthesized and mineralogically identified. Also, the removal efficiency of mixed contaminants, high As(III)-low Cr(VI) and high As(V)-low Cr(VI), using these bio-nanoparticles were conducted. As a result, biologically synthesized NPs were identified as FeS complex and their catalytic capacity showed highly effective to immobilize more than 97% of mixed contaminants by adsorption/mineralization.

Microbially Induced Formation of Fe Carbonates by Metal-Reducing Bacteria Enriched from a CO2 Repository Candidate Site.

The objectives of this research were to study the microbial diversity of metal-reducing bacteria enriched from sedimentary rock collected from a CO2 repository candidate site and to examine the effect that the bicarbonate concentration had on the iron reduction and biomineralization by the cultures. The enriched metal-reducing bacteria (i.e., JG-3) consisted mostly of Exiguobacterium sp. and Shewanella sp., and the microbial reduction of akaganeite (ß-FeOOH), an Fe(III) oxyhydroxide, was examined over 7 days of bacterial cultivation at 30 °C under different concentrations of bicarbonate (0~210 mM). The akaganeite (ß-FeOOH) transformed into goethite (α-FeOOH) and magnetite (Fe3O4) in low HCO-3 buffered medium (<70 mM) and was transformed to magnetite and siderite (FeCO3) in high HCO-3 buffered medium (>140 mM). These results indicate that metal- reducing bacteria from a deep subsurface environment reduce and transform an iron oxyhydroxide to siderite (FeCO3) in HCO-3 buffered medium and that microbial iron reduction may accelerate the mineral trapping of CO2 for deep geologic sequestration.

Effects of Aging on Transformation of Biogenic Magnetite Nanoparticles.

This study examined the microbial synthesis of magnetite and Pd/Zn-substituted magnetite using metal-reducing bacteria (Clostridium sp.), and the mineralogical characteristics of various types of magnetite formed initially and transformed minerals aged for 5 years. XRD, SXRD, and TEM-EDS analyses were used to characterize the mineralogy, crystal structure, chemistry, shape, and size distribution of the magnetites and transformed minerals. The metal-reducing bacteria reduced akaganeite and Pd/Zn-akaganeite to magnetite and Pd/Zn-substituted magnetite using glucose as an electron donor, respectively. Metal substitution of Pd and Zn within the magnetite structure resulted in a decrease in the unit-cell parameter of the magnetite crystals. After 5 years, the biogenic magnetite showed changes in unit-cell parameters and transformation to siderite during prolonged cultivation under anaerobic conditions. These results indicate that long-term aging may affect the mineralogical transformation and alter the nano-sized crystal structure.

Iron Oxyhydroxide Nanoparticle-Coated Carbon Cloth Electrode for Remediation of Cr(VI)-Contaminated Wastewater.

Among in situ and ex situ groundwater technologies, electrochemical treatment has been successfully employed to remediate water heavily contaminated with metals. Electrochemical treatment of Cr(VI)-contaminated wastewater has been attempted using various factors such as electrode materials, surfactants, and electrolytes. In this study, inexpensive carbon cloth was selected and coated with iron oxyhydroxide nanoparticles to enhance electrochemical remediation of Cr(VI)-contaminated wastewater. Iron oxyhydroxide nanoparticles (INP) synthesized by chemical precipitation were coated on carbon cloth electrodes by immersion to examine Cr(VI) removal. The efficiency of Cr(VI) reduction/immobilization was compared between carbon cloth (CC) and carbon cloth coated with iron oxyhydroxide nanoparticles (INP-CC) with/without DC application at a constant potential of 5.0 V to treat water contaminated with 100 mg/L Cr(VI) for 48 h. The removal rate of Cr(VI) was as follows: 10% for CC electrodes and 32% for INP-CC electrodes, compared to >90% for both CC and INP-CC electrodes with DC application for 48 h. In the INP-CC + EC group the pH-Eh condition tended to acidic oxidizing condition due to oxidative substances, O2(g) and hydrogen ions generated on anodic reaction during 12~24 h when Cr(VI) removal reached at 80%, but the CC + EC group remained with minor change for 36 h resulting less reduction efficiency of Cr(VI), despite a successful removal efficiency after 48 h which is similar to the INP-CC + EC group. These results indicated that multiple interactions (C/Cr6+­Cr3+/Fe3+­Fe2+/H+­OH−) on the surface of CC and INP-CC enhanced by EC might contribute to reduction of Cr(VI) and adsorption/precipitation of chromate ions. In particular, INP-CC+ EC might perform dual roles as an electron donor for Fe2+ and/or as an absorbent with DC application in Cr(VI) immobilization. INP-CC enhanced-EC technology could be an economic and efficient approach to remediation of wastewater heavily contaminated with Cr(VI).

Biomineralization of Mg-Enriched Calcium Carbonates by Aerobic Microorganisms Enriched from Rhodoliths.

The objective of this study was to investigate the effect of Mg:Ca ratio in the medium on the formation of low- and high-Mg calcite by aerobic microorganisms enriched from rhodoliths (mainly Proteus mirabilis, Wu Do-1). XRD analyses showed that both low- and high-Mg calcites were formed depending on the Mg:Ca ratio in the medium. Calcite was formed at Ca:Mg ratios of 6:0 and 3:1 and high-Mg calcite was formed at Ca:Mg ratios of 1:1 and 1:3 in the medium. Huntite was formed with a Ca:Mg ratio of 0:6. SEM-EDS analyses showed that the low- and high-Mg calcite crystals had a rhombohedron shape and consisted of Ca, Si and Mg with extracellular polymeric substances (EPS). These results indicate that Wu Do-1 induced precipitation of low- and high-Mg calcite crystals depending on the Ca:Mg ratio in the medium. The carbonate minerals were precipitated on the cell walls and EPS via the accumulation of Ca and/or Mg ions. Therefore, microbial formation of carbonate minerals may play an important role in Ca, Mg, and carbon biogeochemistry as well as CO2 fixation in the natural environments.

Microbial Precipitation of Cr(III)-Hydroxide and Se(0) Nanoparticles During Anoxic Bioreduction of Cr(VI)- and Se(VI)-Contaminated Water.

This study examined the microbial precipitations of Cr(III)-hydroxide and Se(0) nanoparticles during anoxic bioreductions of Cr(VI) and Se(VI) using metal-reducing bacteria enriched from groundwater. Metal-reducing bacteria enriched from groundwater at the Korea Atomic Energy Research Institute (KAERI) Underground Research Tunnel (KURT), Daejeon, S. Korea were used. Metal reduction and precipitation experiments with the metal-reducing bacteria were conducted using Cr(VI)- and Se(VI)-contaminated water and glucose as a carbon source under an anaerobic environment at room temperature. XRD, SEM-EDX, and TEM-EDX analyses were used to characterize the mineralogy, crystal structure, chemistry, shape, and size distribution of the precipitates. The metal-reducing bacteria reduced Cr(VI) of potassium chromate (K2CrO4) to Cr(III) of chromium hydroxide [Cr(OH)3], and Se(VI) of sodium selenate (Na2SeO4) to selenium Se(0), with changes of color and turbidity. XRD, SEM-EDX, and TEM-EDX analyses revealed that the chromium hydroxide [Cr(OH)3] was formed extracellularly with nanoparticles of 20­30 nm in size, and elemental selenium Se(0) nanoparticles had a sphere shape of 50­250 nm in size. These results show that metal-reducing bacteria in groundwater can aid or accelerate precipitation of heavy metals such as Cr(VI) and Se(VI) via bioreduction processes under anoxic environments. These results may also be useful for the recovery of Cr and Se nanoparticles in natural environments.

Synthesis of Nano-Sized Silicon Oxide, Iron Oxide and Carbonates from Chrysotile Asbestos.

The objectives of this study were to investigate the physicochemical dissolution of chrysotile asbestos and to synthesize nano-sized materials and carbonate minerals from the asbestos via acid dissolution and pH changes. Chrysotile asbestos powder was dissolved in 3 different acids, HCl, HThe objectives of this study were to investigate the physicochemical dissolution of chrysotile asbestos and to synthesize nano-sized materials and carbonate minerals from the asbestos via acid dissolution and pH changes. Chrysotile asbestos powder was dissolved in 3 different acids, HCl, H2SO4, and HNO3, and the solutions were then titrated using NH4OH and reacted with CO2. The residual material and precipitates were examined with XRD and TEM-EDS. ICP-AES analysis was also used to investigate the chemical makeup of the solution. The concentration of Mg in the solution was about 1,280 mg/L. The chrysotile became noncrystalline silica after acid treatment (pH = 0). At pH 8.6 and 9.5, the precipitates were amorphous iron oxide and nesquehonite [Mg(HCO3)(OH)·2(H2O)] after reaction with CO2. The particle size of the precipitates ranged from 2 to 500 nm. These results indicate that dissolution of chrysotile asbestos using HCl, H2SO4, and HNO3 can chemically alter chrysotile fibers. Also, the dissolved materials can be used as precursors for other materials such as silica, iron oxide, and carbonates. This process may be useful for the synthesis of silica and iron oxides and for mineral carbonation for carbon sequestration. SO4, and HNO3, and the solutions were then titrated using NH4OH and reacted with CO2. The residual material and precipitates were examined with XRD and TEM-EDS. ICP-AES analysis was also used to investigate the chemical makeup of the solution. The concentration of Mg in the solution was about 1,280 mg/L. The chrysotile became noncrystalline silica after acid treatment (pH = 0). At pH 8.6 and 9.5, the precipitates were amorphous iron oxide and nesquehonite [Mg(HCO3)(OH)·2(H2O)] after reaction with CO2. The particle size of the precipitates ranged from 2 to 500 nm. These results indicate that dissolution of chrysotile asbestos using HCl, H2SO4, and HNO3 can chemically alter chrysotile fibers. Also, the dissolved materials can be used as precursors for other materials such as silica, iron oxide, and carbonates. This process may be useful for the synthesis of silica and iron oxides and for mineral carbonation for carbon sequestration.

Microbially-Mediated Precipitation of Calcium Carbonate Nanoparticles.

The objective of this study was to investigate the biomineralization of carbonate minerals using microorganisms (Wu Do-1) enriched from rhodoliths. A 16S rRNA sequence analysis showed that Wu Do-1 mainly contained Proteus mirabilis. The pH decreased from 6.5 to 5.3 over the first 4 days of incubation due to microbial oxidation of organic acids, after which it increased to 7.8 over the remaining incubation period. XRD analysis showed that the precipitates were Mg-rich cal- cite (MgxCa(1-x)CO3), whereas no precipitates were formed without the addition of Wu Do-1 in D-1 medium. SEM-EDS analyses showed that the Mg-rich calcite had a rhombohedron shape and consisted of Ca, Si and Mg with an extracelluar polymeric substance (EPS). In addition, TEM-EDS analyses revealed they were hexagon in shape, 500-700 nm in size, and composed of Ca, Mg, C, and O. These results indicated that Wu Do-1 induced precipitation of Mg-rich calcite on the cell walls and EPS via the accumulation of Ca and/or Mg ions. Therefore, microbial precipitation of carbonate nanoparticles may play an important role in metal and carbon biogeochemistry, as well as in carbon sequestration in natural environments.

Biotransformation and Its Application: Biogenic Nano-Catalyst and Metal-Reducing-Bacteria for Remediation of Cr(VI)-Contaminated Water.

The use of ubiquitous metal-reducing bacteria (MRB) and the synthesis and transforming capability of nano-sized catalysts (BNC) provide enormous potential for the transformation of environmental waste to environmental catalysts, such as abandoned mine precipitates that are transformed into nontoxic and inexpensive catalysts for remediating contaminated groundwater. In this study, BNC from acid mine drainage (AMD) precipitates are transformed to nm-sized siderite after a fermenting process under anaerobic conditions, and MRB enriched from inter-tidal flat sediments were examined for efficiency in the Cr(VI) reduction and immobilization in upward flow-through sand column tests. As a result, BNC and MRB proved to have excellent Cr(VI) reducing/immobilizing capacity independently and when used in conjunction. In addition the combination of BNC+MRB showed to have a capacity enhanced with 20% more capability of Cr(VI) reduction and immobilization in flow-through column test for 168 h.

Microbial Synthesis and Characterization of Superparamagnetic Zn-Substituted Magnetite Nanoparticles.

The objective of this study is to examine microbial synthesis of magnetite and Zn-substituted magnetite nanoparticles by iron-reducing bacteria (Clostridium sp.) enriched from intertidal flat sediments. The magnetite nanoparticles were synthesized by the bacteria under anaerobic conditions at room temperature using akaganeite (ß-FeOOH) or Zn-substituted akaganeite (ß-ZnxFe1-xOOH) as a magnetite precursor during glucose fermentation. This research indicates that fermentation processes can establish the microbial synthesis of magnetite and Zn-substituted magnetite when conditions are at room temperature, ambient pressure, and pH values near neutral to slightly basic (pH < 8).

Remediation of chromium-contaminated water using biogenic nano-sized materials and metal-reducing bacteria.

As an environmental nanotechnology, nano-sized materials have the potential to create novel and effective in-situ and ex-situ treatments for contaminated groundwater due to its high catalytic reactivity, large surface area, and dispersibility. In this study the efficiency of Cr(VI) reduction and immobilization using biotic and abiotic nano-sized materials (NSMs) and metal-reducing bacteria (MRB) was evaluated to remediate Cr(VI)-contaminated groundwater in batch and column tests. The results of this study revealed that the combination of the mixed MRB and bio-FeS/siderite performed the highest efficiency of Cr(VI) reduction and immobilization. Cr(VI) reduction by MRB and NSMs could impact on solubility of Cr(VI) and geochemical changes favorable for precipitation and adsorption.

Microbially induced synthesis of cubic and hexagonal selenium nanoparticles.

Nanobiotechnology represents an economic alternative for chemical and physical methods of nanoparticles formation. The objectives of this study were to synthesize selenium nanoparticles by microbial processes using anaerobic metal-reducing bacteria as well as to characterize mineralogical properties of the nanoparticles. The selenium nanoparticles were about 200 nm in size and ball shaped. Microbial processes for elemental selenium synthesis may be useful for recovery of natural selenate in the natural environments and immobilization of selenium isotope in the high level nuclear waste disposal sites.

Microbial synthesis of silver nanoparticles.

The objectives of this research were to study biogenic synthesis of Ag(0) nanoparticles and to determine the effects of various experimental conditions such as silver nitrate concentrations, pHs and temperatures controlling for the optimal biosynthesis of Ag(0) nanoparticles. The metal-reducing bacteria formed 5-15 nm-sized Ag(0) nanoparticles by reduction of 0.5-1 mM silver nitrate under the conditions around 15-25 degrees C and medium pH 7.5-8.5 within 3 days of incubation. These results not only show that the bacteria enzymatically reduced Ag(I), but also offer methods for microbial synthesis of homogeneous silver nanoparticles and silver recovery from the natural environments.

Spatial modeling for radon concentrations in subway stations in Seoul, Korea.

This study examined the environmental and geological determinants of radon concentration in subway stations by applying a spatial statistical model to the integrated GIS database. The data were collected for 237 underground subway stations located inside the city of Seoul, South Korea and used for mapping to illustrate the spatial distribution of airborne radon exposure and analysis of potential contribution of station-specific and geological determinants. A Bayesian conditional autoregressive regression (CAR) model was developed to explain the radon concentrations, and the predicted radon surface was generated and visualized to identify hotspot regions where elevated radon exposure is likely to be present in underground settings. The findings include: (1) subway stations located within granite bedrock maintained relatively higher radon concentrations; (2) underground radon emanation is not only controlled by lithology and the associated uranium content of the rocks and soil, but also by structural factors which facilitate easy migration of radon from deeper parts of the earth's crust; (3) radon risks would be elevated if the underground facility is constructed too deep without any control measure; and (4) not only the foundation of an underground facility but also the nature of the soil and rocks in the vicinity helps determine whether or not dangerous levels of radon gas are likely to accumulate inside. This modeling effort is expected to provide guidelines regarding the identification of future station locations with a lower radon risk and the mandatory installation of adequate radon reduction systems for the underground space where people stay or commute for long periods of time.

Influence of deglaciation on microbial communities in marine sediments off the coast of Svalbard, Arctic Circle.

Increases in global temperatures have been shown to enhance glacier melting in the Arctic region. Here, we have evaluated the effects of meltwater runoff on the microbial communities of coastal marine sediment located along a transect of Temelfjorden, in Svalbard. As close to the glacier front, the sediment properties were clearly influenced by deglaciation. Denaturing gradient gel electrophoresis profiles showed that the sediment microbial communities of the stations of glacier front (stations 188-178) were distinguishable from that of outer fjord region (station 176). Canonical correspondence analysis indicated that total carbon and calcium carbonate in sediment and chlorophyll a in bottom water were key factors driving the change of microbial communities. Analysis of 16S rRNA gene clone libraries suggested that microbial diversity was higher within the glacier-proximal zone (station 188) directly affected by the runoffs than in the outer fjord region. While the crenarchaeotal group I.1a dominated at station 176 (62%), Marine Benthic Group-B and other Crenarchaeota groups were proportionally abundant. With regard to the bacterial community, alpha-Proteobacteria and Flavobacteria lineages prevailed (60%) at station 188, whereas delta-Proteobacteria (largely sulfate-reducers) predominated (32%) at station 176. Considering no clone sequences related to sulfate-reducers, station 188 may be more oxic compared to station 176. The distance-wise compositional variation in the microbial communities is attributable to their adaptations to the sediment environments which are differentially affected by melting glaciers.

Characterization of magnetite-organic complex nanoparticles by metal-reducing bacteria.

Magnetite nanoparticles exhibit clear technological potential for biomedical applications. The objectives of this study were to synthesize magnetite-organic complex nanoparticles through the use of metal-reducing bacteria and characterize the mineralogical and surface chemical properties of these nanoparticles as well as to test their potential applications in biomedical technology with regards to their protein immobilization capacity. The microbially formed magnetite nanoparticles had a size of around 10 nm with a spherical shape and were coated with organics containing an abundance of reactive carboxyl groups without any chemical process for functionalizing them. These microbial processes may lead to a simple preparation of functional magnetite-organic complex nanoparticles which have benefits for biomedical applications.

Environmental application of nanomaterials and metal-reducing bacteria to remediate arsenic-contaminated groundwater.

The objective of this study was to remediate As-contaminated groundwater using both nanomaterials and metal-reducing bacteria. In the batch experiment, a set of Pd-akaganeite in combination with the bacteria removed 95% of the arsenic from the contaminated groundwater. This result suggested that nanotechnology and biotechnology has the potential to create novel and effective treatment technologies for arsenic-contaminated groundwater.

Remediation of TCE-contaminated groundwater using nanocatalyst and bacteria.

The objective of this study was to develop and evaluate the remediation of trichloroethene (TCE)-contaminated groundwater using both a nanocatalyst (bio-Zn-magnetite) and bacterium (similar to Clostridium quinii) in anoxic environments. Of the 7 nanocatalysts tested, bio-Zn-magnetite showed the highest TCE dechlorination efficiency, with an average of ca. 90% within 8 days in a batch experiment. The column tests confirmed that the application of bio-Zn-magnetite in combination with the bacterium achieved high degradation efficiency (ca. 90%) of TCE within 5 days compared to the nanocatalyst only, which degraded only 30% of the TCE. These results suggest that the application of a nanocatalyst and the bacterium have potential for the remediation of TCE-contaminated groundwater in subsurface environments.

Simultaneous leaching and carbon sequestration in constrained aqueous solutions.

The behavior of metal ions' leaching and precipitated mineral phases of metal-rich fly ash (FA) was examined in order to evaluate microbial impacts on carbon sequestration and metal immobilization. The leaching solutions consisted of aerobic deionized water (DW) and artificial eutrophic water (AEW) that was anaerobic, organic- and mineral-rich, and higher salinity as is typical of bottom water in eutrophic algae ponds. The Fe- and Ca-rich FAs were predominantly composed of quartz, mullite, portlandite, calcite, hannebachite, maghemite, and hematite. After 86 days, only Fe and Ca contents exhibited a decrease in leaching solutions while other major and trace elements showed increasing or steady trends in preference to the type of FA and leaching solution. Ca-rich FA showed strong carbon sequestration efficiency ranging up to 32.3 g CO(2)/kg FA after 86 days, corresponding to almost 65% of biotic carbon sequestration potential under some conditions. Variations in the properties of FAs such as chemical compositions, mineral constituents as well as the type of leaching solution impacted CO(2) capture. Even though the relative amount of calcite increased sixfold in the AEW and the relative amount of mineral phase reached 37.3 wt% using Ca-rich FA for 86 days, chemical sequestration did not accomplish simultaneous precipitation and sequestration of several heavy metals.