Reduction of chlorinated hydrocarbons using nano zero-valent iron supported with an electric field. Characterization of electrochemical processes and thermodynamic stability.

Electric field assisted remediation using nano iron has shown outstanding results as well as economic benefits during pilot applications (Cerníková et al., 2020). This method is based on donating electrons to the zero-valent iron that possess an inherently strong reductive capacity. The reduction of chlorinated hydrocarbons may be characterized by a decrease in contaminants or better still by the evolution of ethene and ethane originating from the reduction of chlorinated ethenes. The evolution of ethene and ethane was observed predominantly in the vicinity of the anode despite reduction processes being expected near the cathode - the electron donor. The reduction near the anode occurred due to dissolved Fe2+ ions, whose presence was suggested by a Pourbaix diagram that combines Eh/pH values to characterize electrochemical stabilities between different species. No products of dechlorination were observed in the area of the cathode due to presence of oxidized Fe in the form of Fe3+ or Fe(OH)4-. The experimental work described in this research provides a deeper view of the processes of electrochemical reductive dechlorination using zero-valent iron and DC. It also showed an increase in the efficiency compared to the method using zero-valent iron only.

Dissolution of Cu and Zn-bearing ore by indigenous iron-oxidizing bacterial consortia supplemented with dried bamboo sawdust and variations in bacterial structural dynamics: A new concept in bioleaching.

Disposing of low-grade ores involves numerous environmental issues. Bioleaching with acidophilic bacteria is the preferred solution to process these ores for metals recovery. In this study, indigenous iron-oxidizing bacteria Acidithiobacillus ferrooxidans, Leptospirillum ferriphilum, and Leptospirillum ferrooxidans were used in consortia supplemented with acid-treated bamboo sawdust (BSD) for copper and zinc recovery. Findings showed the extreme catalytic response of BSD with the best recovery of metals. Maximum of 92.2 ± 4.0% copper (0.35%) and 90.0 ± 5.4% zinc (0.33%) were recovered after 8 days of processing in the presence of 2 g/L BSD. Significant variations were reported in physicochemical parameters during bioleaching in the presence of a different concentration of BSD. Fourier Transform Infrared spectroscopy results of bioleached residues showed significant variations in spectral pattern and maximum variations were reported in 2.0 g/L BSD, which indicates maximum metals dissolutions. The impact of bacterial consortia and BSD on iron speciation of bioleached ores was analyzed by using Mössbauer spectroscopy and clear variations in iron speciation were reported. Furthermore, the bacterial community structure dynamics revealed significant variations in the individual bacterial proportion in each experiment. This finding shows that the dosage concentration of BSD influenced the microenvironment, which effect the bacterial abundance and these variations in the bacterial structural communities were not associated with the initial proportion of bacterial cells inoculated in the bioleaching process. Moreover, the mechanism of chemical reactions was proposed by explaining the possible role of BSD as a reductant under micro-aerophilic conditions that facilitates the bacterial reduction of ferric iron. This type of bioleaching process with indigenous iron-oxidizing bacteria and BSD has significant potential to further upscale the bioleaching process for recalcitrant ore bodies in an environment friendly and cost-effective way.

Engineered in situ biogeochemical transformation as a secondary treatment following ISCO - A field test.

ISCO using activated sodium persulphate is a widely used technology for treating chlorinated solvent source zones. In sensitive areas, however, high groundwater sulphate concentrations following treatment may be a drawback. In situ biogeochemical transformation, a technology that degrades contaminants via reduced iron minerals formed by microbial activity, offers a potential solution for such sites, the bioreduction of sulphate and production of iron sulphides that abiotically degrade chlorinated ethenes acting as a secondary technology following ISCO. This study assesses this approach in the field using hydrochemical and molecular tools, solid phase analysis and geochemical modelling. Following a neutralisation and bioaugmentation, favourable conditions for iron- and sulphate-reducers were created, resulting in a remarkable increase in their relative abundance. The abundance of dechlorinating bacteria (Dehalococcoides mccartyi, Dehalobacter sp. and Desulfitobacterium spp.) remained low throughout this process. The activity of iron- and sulphate-reducers was further stimulated through application of magnetite plus starch and microiron plus starch, resulting in an increase in ferrous iron concentration (from

Can Sulfate Be the First Dominant Aqueous Sulfur Species Formed in the Oxidation of Pyrite by Acidithiobacillus ferrooxidans?

According to the literature, pyrite (FeS2) oxidation has been previously determined to involve thiosulfate as the first aqueous intermediate sulfur product, which is further oxidized to sulfate. In the present study, pyrite oxidation by Acidithiobacillus ferrooxidans was studied using electrochemical and metabolic approaches in an effort to extend existing knowledge on the oxidation mechanism. Due to the small surface area, the reaction rate of a compact pyrite electrode in the form of polycrystalline pyrite aggregate in A. ferrooxidans suspension was very slow at a spontaneously formed high redox potential. The slow rate made it possible to investigate the oxidation process in detail over a term of 100 days. Using electrochemical parameters from polarization curves and levels of released iron, the number of exchanged electrons per pyrite molecule was estimated. The values close to 14 and 2 electrons were determined for the oxidation with and without bacteria, respectively. These results indicated that sulfate was the dominant first aqueous sulfur species formed in the presence of bacteria and elemental sulfur was predominantly formed without bacteria. The stoichiometric calculations are consistent with high iron-oxidizing activities of bacteria that continually keep the released iron in the ferric form, resulting in a high redox potential. The sulfur entity of pyrite was oxidized to sulfate by Fe3+ without intermediate thiosulfate under these conditions. Cell attachment on the corroded pyrite electrode surface was documented although pyrite surface corrosion by Fe3+ was evident without bacterial participation. Attached cells may be important in initiating the oxidation of the pyrite surface to release iron from the mineral. During the active phase of oxidation of a pyrite concentrate sample, the ATP levels in attached and planktonic bacteria were consistent with previously established ATP content of iron-oxidizing cells. No significant upregulation of three essential genes involved in energy metabolism of sulfur compounds was observed in the planktonic cells, which represented the dominant biomass in the pyrite culture. The study demonstrated the formation of sulfate as the first dissolved sulfur species with iron-oxidizing bacteria under high redox potential conditions. Minor aqueous sulfur intermediates may be formed but as a result of side reactions.

Selected mechanical paremeters of women's hair in the Caucasian population.

OBJECTIVE: More parameters have been used for more detailed description of mechanical properties of human hair as a fibre than in analogous studies. All measured samples were taken from five different locations on the heads of 60 women of varied age. METHODS: For each hair, the diameter was determined optically and then the test in the Deform Type 2 testing machine was carried out. Deformation curves were obtained by testing 10 mm long samples up to the rupture point at constant temperature, humidity and constant crossbar speed of 2 mm/min. The curves were processed with software for the calculation of mechanical parameters of the hairs. This specialized software has been designed by us for that purpose. Resulting values were arranged into tables and figures. RESULTS: As far as hair cross-section is concerned, it has been found that for the European population it appears to be rather higher - 86 µm - than indicated in formerly published texts. The 56 µm mentioned in the work of other authors has been observed only utterly exceptionally, in 0.3 % of the population. All quantities studied (except extensibility) display moderate to strong positive skewness in comparison to Gauss distribution. The most marked skewness is seen in the resilience. At the same time, this quantity displays the highest value of non-Gaussian distribution. The elasticity module of 2.3±0.6 GPa is three times lower than the one reported by other authors, yet according to the fact published in our work - which shows unambiguously that the thinner the hair, the higher elasticity module it displays - the value of 7.2 GPa for the 56 µm thick hairs is comparable and it confirms the hypothesis that the cortex, which is responsible for the mechanical strength of the hair, is contained in a higher ratio in thinner hairs. This similarly applies to the ultimate strength; the linearity limit is hard to compare with literature, as it almost does not appear there. CONCLUSION: By measuring 886 samples from the heads of 60 adult women of European type, it was possible to ascertain the current norm for a larger number of mechanical parameters of the hairs. Further merit of this work is the fact that the hairs were taken systematically from five well-defined places of the studied heads in equal count, which is an aspect formerly published works do not respect and they do not present the location of sampling.

Evaluation of rheological parameters of the axial system using the Transfer Vibration through Spine (TVS) method.

OBJECTIVE: The human motion system reacts to both hypo and hyperactivity loads by changes to the rheological properties of tissues. This study deals with changes to the axial system (AS) compartment. Using the appropriate methodologies and mathematical-physical methods, these changes can be identified and quantified. METHODS: This study describes the noninvasive TVS (Transfer Vibration through Spine) method, which was applied to assess the AS selected mechanical properties in various modes. A pilot study was conducted on a top-level twelve-year-old girl-gymnast. The data detection was carried out in three cycles, before and after a peak 3.5 hour training session and the next day, after resting, just before the next training. RESULTS: Specifically, the values of selected rheological parameters, the AS damping coefficient b and viscosity µ, were obtained. The dynamics of their changes, in the stated load cycles, has also been shown. The damping coefficient b fell from the value of 0.626 to 0.324 before training and increased to 0.394 after resting. The viscosity coefficient µ showed a similar trend, namely falling from the value of 9.85 [Pa.s] to 2.15 [Pa.s] and then increasing to 3.8 [Pa.s] . CONCLUSIONS: With its computational solution, the TVS method,is a diagnostic apparatus making it possible to classify AS properties, both quantitatively and qualitatively, or its chosen segments and their changes, respectively. It can be used in classifying, preventing and treating the consequences of extreme motion and relaxing modes. The TVS application also makes it possible to control AS states over therapeutic, recovery, ergonomic and other loading modes of the human locomotion system.

Changes in the mechanical parameters of hair in a group of women in reproductive age.

OBJECTIVE: Hair quality and scalp characteristics are considered to be a significant marker of health. This marker is reflected in mechanical properties of hair. To investigate these properties, hair samples have been collected among women of different age and then analyzed. The thickness, Young's modulus of elasticity and ultimate strength limit were the main observed parameters. METHODS: The diameter of each hair has been measured using an optical microscope equipped with a digital camera. The hair was then clipped into the uniaxial tensile testing device. Each sample has been stretched to failure at a speed of 2 mm/min and force vs. elongation was recorded. The mechanical results were converted with respect to the diameter and Stress-Strain curve was obtained for each sample. In addition, all the analyzed samples were divided into two groups in dependence on the age, namely samples from women younger than 35 and over 35 years of age. All the measured parameters were statistically evaluated. RESULTS: Young's modulus, yield and elongation parameters showed no significant difference among samples. On the other hand there was a significant difference among the samples in ultimate strength values. Findings from group analysis showed that women under 35 years show about 5 times greater variability in hair strength than that of women above that age. CONCLUSION: The results of our study indicate that hair tendency to grow persists up to 30 years of age, then slowly decreases and then achieves a steady state around 60 years of age.

Changes in attenuation characteristics of axial system of pregnant drivers detected by the TVS method.

OBJECTIVES: During a longer car drive there are changes in rheological properties of driver's or passenger's connective tissues taking place as a consequence of monotonous and vibration load. These changes show more among the pregnant drivers, whose motion system is under heavier demands due to pregnancy. To asses these changes we have used the TVS (transfer vibration through the spine) method. METHODS: The TVS is based on application of γ excitation pulses with half-length 5 ms and then harmonic excitation continuously periodically changing from 5 Hz to 160 Hz on C7 and L5 vertebrae. This wave is transferred along the axial system and the acceleration of all the spinous tips of the vertebrae, along which the waves spread between C7 and S1, is detected by accelerometric sensors. The measurement was carried out on three drivers before and after a 4-hours driving. The same measurements of wave transfer along the spine with just one pregnant woman were carried out in th 16th, 26th and 32nd week of pregnancy. Consequently we constructed a simplified model of the spine in order to analyze gathered data by discovering elementary properties of the measured system. RESULTS: After both vibration and physical load there is a more significant dampening of the spinal tissues apparent, i.e. lower acceleration amplitude and the tissues resonance frequency also shifts towards the lower frequencies. On the other hand after long lasting relaxation on a bed an opposite tendency showed, the acceleration amplitude was higher, tissues were relaxed and dampening was lower. The same tendency manifested among the pregnant women. The influence of progressing pregnancy on the spinal segment transfer function showed through a shifting of peaks above 20Hz. Their size also changes monotonously. An absorption area moves towards higher frequencies, rigidity of axial system connections grows. CONCLUSION: The results say that drivers, including pregnant women, show changes in mechanical properties of examined tissues before and after vibration or other type of load. Or conversely before and after relaxation on a bed. Results of this work will be further analyzed, verified and evaluation procedures will be improved. We expect to find dependencies between excitation and resonance frequencies during the transfer via the axial system, the rheological properties of the axial system components and the physical nature of the load of the axial system. They are then going to be applicable for the prevention of injuries of the axial system, physiotherapy practices in the rehabilitation of post-operative conditions, the dosage of training loads of athletes, in determining the effects of job stress regimes and their prevention.

Stoichiometry of bacterial anaerobic oxidation of elemental sulfur by ferric iron.

The conventional stoichiometry of the oxidation of elemental sulfur by ferric iron in Acidithiobacillus ferrooxidans was not in agreement with our experimental data in terms of ferrous iron and proton formation. Reaction modelling under the actual conditions of bacterial activity resulted in a different stoichiometry, where additional iron species participate in the process to affect the number of released protons. The suggested reaction equation may more accurately predict the intensity of environmental acidification during the anaerobic bioprocess.

Kinetic bacterial bioluminescence assay for contact sediment toxicity testing: relationships with the matrix composition and contamination.

The present study represents the first broader evaluation of the rapid 30-s kinetic bioluminescence assay with Vibrio fisheri (microplate format modification) for contact toxicity testing of whole sediments. The present study focused on river sediments from the Morava River basin, Czech Republic, repeatedly sampled during 2005 to 2006 and analyzed for geological and geochemical parameters, content of toxic metals, major organic pollutants, and toxicity. High natural variation in toxicity (50% inhibitory concentration [IC50] values ranging from 0.8 to >80 mg sediment dry wt/ml) was found (among different sampling periods and years, among sites), and this could be related to the sediment dynamics affected by spring high flows and summer droughts. From the 46 sediment descriptors, exchangeable protons (H(+)) was the only parameter that consistently correlated with toxicity. Three other descriptors (i.e., content of organic carbon plus two parameters from the detailed silicate analysis of sediments: percentage of SO(3) representing total sulfur content, structural water H(2)O+) also significantly correlated with toxicity. There were only minor and variable correlations with contamination. We propose sediment safety guideline categories for the V. fisheri kinetic test with severe toxicity threshold of IC50 < 1 mg dry wt/ml. Although sediments are considered a rather stable matrix in comparison with river water, we confirmed high variability and dynamics that should be reflected in monitoring plans and field studies.

Alteration of arsenopyrite in soils under different vegetation covers.

The weathering of arsenopyrite (FeAsS) has been monitored in soils using an in situ experimental approach. Arsenopyrite in nylon experimental bags was placed in individual horizons in soils in spruce (litter, horizons A, B, and C), beech (litter, horizons A, B, and C) and unforested (horizons A, B, and C) areas and left in contact with the soil for a period of 1 year. The individual areas on the ridge of the Krusné hory Mts., Czech Republic, had the same lithology, climatic and environmental conditions. Scorodite (FeAsO(4).2H(2)O) was identified as a principal secondary mineral of arsenic (As) formed directly on the surface of the arsenopyrite. Scorodite was formed in all the areas in all soil horizons. The amount of scorodite formed decreased in the series beech, spruce and unforested areas. In forested areas, there was a larger amount of scorodite on arsenopyrites exposed in organic horizons (litter, A horizon). The greater rate of arsenopyrite alteration in organic horizons in the beech stand compared to spruce stand is probably a result of faster mineralization of organic material with resulting production of nitrate and better seepage conditions of soil in this area. Speciation of As determined using the sequential extraction technique demonstrated that As was bonded in the soils primarily in the residual fractions prior to the experiment. The As content in the mobile fractions increased in the organic horizon in the forested areas after the experiments.

Identification of viscoelastic parameters of skin with a scar in vivo, influence of soft tissue technique on changes of skin parameters.

The goal of the experiment was to develop an identification method capable of objective detection of changes of viscoelastic properties of skin with a scar remaining after a modified radical mastectomy. We compared the intact skin and the skin with a scar, a scar before and after physiotherapy. We used two methods. The first one is based on measurements of the local dynamic deformation response of the skin and the second one is the matrix identification of static deformation that identifies properties of the whole tested region of the explored tissues. We identified the skin stretchability, shiftability against deeper layers and deeply analysed both the methods. In some patients, we found statistically proven difference. In all these cases the measurement methods have detected changes of the observed tissue condition. We found both methods to be potentially applicable after further improvements as a diagnostic tool, which can contribute to the improvement of postoperative care of patients.

The influence of temperature and hydration on the sorption properties of bentonite.

The effects of exposure to synthetic groundwater at elevated temperature gradients on the sorption properties of bentonite were investigated using the Mock-Up-Cz experiment. This experiment simulated the vertical placement of a container of radioactive waste according to the Swedish KBS-3 system for a period of more than 3 years. The mineralogical composition, as well as its chemical and physico-chemical properties, including the uptake of (99)TcO(4)(-) and (134)Cs(+), was used to evaluate the chemical changes caused by the long-term exposure of bentonite buffer to thermal and hydration gradients. It was found that the bentonite material was predominantly stable. No more than 2% of the montmorillonite was transformed due to thermal and moisture gradients. It was concluded that the new-formed mineral phases have no significant influence on the ion exchange and sorption properties of bulk bentonite samples.

Environmental applications of chemically pure natural ferrihydrite.

Fresh precipitates, deposited from seepage waters of complex-ore mine-tailing impoundment at Zlaté Hory, Czech Republic, were characterized by means of X-ray diffraction, transmission electron microscopy, low temperature and in-field Mössbauer spectroscopy, and Brunauer-Emmett-Teller surface area measurements. The prevailing phases (approximately 96 wt %) found in precipitates are poorly crystalline, 2-6 nm sized two-line ferrihydrite, forming globular aggregates of about 150 nm in diameter, rimmed by acicular irregular nanocrystals of goethite. These nanocrystalline ferrihydrite-goethite precipitates are of a relatively high chemical purity (approximately 3% SiO2, Zn approximately 1300 ppm, trace and rare earth elements < 100 ppm) and thus applicable in various nanotechnologies. With a surface area of 270 m2 g(-1), precipitate possesses a high catalytic activity in the decomposition of hydrogen peroxide, which is comparable with that found for commercially accessible FeO(OH) catalyst. Another superior aspect of such natural nanoparticles presents a cheap and suitable precursor for a thermally induced solid-state synthesis of the stable core-shell alpha-Fe-FeO nanoparticles that are well applicable in reductive technologies of groundwater treatment. Just the possibility of using the undesirable waste contaminating the environment in further environmental technologies is the key practical benefit discussed in this paper.

Geochemical and Pb isotopic evidence for sources and dispersal of metal contamination in stream sediments from the mining and smelting district of Príbram, Czech Republic.

Stream sediments from the mining and smelting district of Príbram, Czech Republic, were studied to determine the degree, sources and dispersal of metal contamination using a combination of bulk metal and mineralogical determinations, sequential extractions and Pb isotopic analyses. The highest metal concentrations were found 3-4 km downstream from the main polymetallic mining site (9800 mg Pb kg(-1), 26 039 mg Zn kg(-1), 316.4 mg Cd kg(-1), 256.9 mg Cu kg(-1)). The calculated enrichment factors (EFs) confirmed the extreme degree of contamination by Pb, Zn and Cd (EF>40). Lead, Zn and Cd are bound mainly to Fe oxides and hydroxides. In the most contaminated samples Pb is also present as Pb carbonates and litharge (PbO). Lead isotopic analysis indicates that the predominant source of stream sediment contamination is historic Pb-Ag mining and primary Pb smelting (206Pb/207Pb=1.16), while the role of secondary smelting (car battery processing) is negligible.