The influence of single and combined effects of Zn, Cu and temperature on microbial growth

© 2014 Global NEST Printed in Greece. All rights reserved.The purpose of the present study is to investigate the single and joint effect of zinc and copper to the growth pattern of the metal tolerant species of Arthrobacter sp. JM018. The results showed that, both, Zn and Cu at concentrations between 1 to 10 µM stimulated the growth of the above microorganism at 35 °C. Stimulation was reduced with the increase of Zn concentration, while the opposite phenomenon was observed for copper. On the other hand, similar concentrations of joint Zn and Cu resulted to slight growth inhibition, indicating antagonism between the studied heavy metals. Experiments with the same microorganism at 20 °C and 35 °C, at metal free and 10 µM Zn, indicated that the stimulatory effect of zinc was significantly more pronounced at lower temperatures. The latter is indicative of the strong role of temperature on the expression of heavy metals to microorganisms

ZnO quantum dots-graphene composites: Formation mechanism and enhanced photocatalytic activity for degradation of methyl orange dye

The current study demonstrates homogenous decorating of zinc oxide quantum dots (QDs) onto graphene oxide (GO) surface via simple chemical method. The AFM image exhibited that the prepared graphene was 0.8 nm thick and hence practically monolayer. Average size of the ZnO QDs was estimated by transmission electron microscopy around 3 nm. Instrumental and chemical analyses demonstrated formation of a strong bond between ZnO QDs and GO, through C-O-Zn and C-Zn bridges. The UV-visible spectra displayed that the introduction of graphene sheets to ZnO QDs resulted in higher absorption intensity of UV as well as widening of adsorption window toward visible light for ZnO-Graphene due to chemical bond between ZnO QDS and graphene surface. Results showed that adding of graphene up to 30% can improve resistance of ZnO against acids however for keeping the activity of catalyst, the recommended pH is near neutral (pH approximate to 6-7.2). In addition, the presence of graphene on the surface of the ZnO could significantly suppress the photocorrosion effect. The ZnO-Graphene hybrids indicated enhanced photocatalytic activity for degradation of methyl orange (MO) with the following order: ZnO-5% Graphene > ZnO-10% Graphene > ZnO QDs > ZnO30%-Graphene. This enhancement of photocatalytic activity may be attributed to the extended absorption of visible light, reducing of electronehole recombination rate, and adsorption of MO molecules onto the huge surface area of graphene, where they are kept at vicinity of ZnO for decomposition. (C) 2015 Elsevier B.V. All rights reserved

Impact of different environmental conditions on the aggregation of biogenic U(IV) nanoparticles synthesized by Desulfovibrio alaskensis G20

This study investigates the impact of specific environmental conditions on the formation of colloidal U(IV) nanoparticles by the sulfate reducing bacteria (SRB, Desulfovibrio alaskensis G20). The reduction of soluble U(VI) to less soluble U(IV) was quantitatively investigated under growth and non-growth conditions in bicarbonate or 1,4-piperazinediethanesulfonic acid (PIPES) buffered environments. The results showed that under non-growth conditions, the majority of the reduced U nanoparticles aggregated and precipitated out of solution. High resolution transmission electron microscopy revealed that only a very small fraction of cells had reduced U precipitates in the periplasmic spaces in the presence of PIPES buffer, whereas in the presence of bicarbonate buffer, reduced U was also observed in the cytoplasm with greater aggregation of biogenic U(IV) particles at higher initial U(VI) concentrations. The same experiments were repeated under growth conditions using two different electron donors (lactate and pyruvate) and three electron acceptors (sulfate, fumarate, and thiosulfate). In contrast to the results of the non-growth experiments, even after 0.2 mu m filtration, the majority of biogenic U(IV) remained in the aqueous phase resulting in potentially mobile biogenic U(IV) nanoparticles. Size fractionation results showed that U(IV) aggregates were between 18 and 200 nm in diameter, and thus could be very mobile. The findings of this study are helpful to assess the size and potential mobility of reduced U nanoparticles under different environmental conditions, and would provide insights on their potential impact affecting U(VI) bioremediation efforts at subsurface contaminated sites

Synthesis of graphene oxide/magnesium oxide nanocomposites with high-rate adsorption of methylene blue

A series of graphene oxide/magnesium oxide nanocomposites (GO/MgO NCs) were and applied for the removal of Methylene Blue (MB) from aqueous solutions. The prepared NCs were characterized using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectrum, X-ray photoelectron spectroscopy, and thermogravimetric analysis. The results showed that MgO particles was successfully decorated on GO. The impacts of different experimental variables on the removal of MB including GO/MgO NCs dosage, pH, contact time, and initial MB concentration were investigated. The experimental analysis of adsorption isotherms indicated that adsorption data was best fit with the Langmuir isotherm model. Among the three different synthesized weight ratios of GO/MgO (5:1, 1:1, and 1:5), 5:1 ratio showed the maximum adsorption capacity as 833 mg/g, which is higher than any previously reported GO-based composites. The synthesized GO/MgO NC is also observed to have higher adsorption capacity for MB removal, in comparison with pure GO and MgO. The kinetic adsorption data was best described by pseudo-second-order kinetic model. The pH of point of zero charge (pH(pzc)) of GO/MgO NCs was determined to be 9.7, 10.5, and 10.5 for ratios 5:1, 1:1, and 1:5, respectively. The results revealed that electrostatic attraction can be the dominant mechanism of adsorption between GO/MgO NCs and MB for pH above pH(pzc); whereas for pH below pH(pzc), other adsorption mechanisms such as hydrogen bonding and pi-pi interaction may attribute to adsorption. The high adsorption capacity of GO/MgO composites, thus makes it a promising adsorbent for water and wastewater treatment. (C) 2016 Elsevier B.V. All rights reserved

Graphene oxide/magnesium oxide nanocomposite: A novel catalyst for ozonation of phenol from wastewater

© ASCE.Catalytic ozonation is a promising advanced oxidation technique for the removal of contaminants from water and wastewater. Graphene oxide (GO) is an oxidized derivative of graphene which contains epoxide, hydroxyl, and carboxyl groups with high surface area, and is being recently used for effective adsorption of pollutants in aquatic environments. In our previous work, we modified GO with magnesium oxide (MgO) and demonstrated the high-rate adsorption of methylene blue (MB) by the synthesized nanocomposite (NC). In this study, our synthesized NC is applied as a catalyst for catalytic ozonation of phenol in a laboratory scale batch reactor. The results showed that the catalytic ozonation significantly improved the mineralization of phenol compared to that of ozonation without the catalyst. The impact of experimental variables on oxidation of phenol, particularly GO/MgO NC dosage and reaction time is investigated. A possible mechanism for the catalytic ozonation of phenol is also proposed. Our results show promising application of the proposed technology for the removal of various organic contaminants from wastewater

Single and joint effects of Zn and Cu to ATP pool and microbial recovery in continuous growth systems

BACKGROUND Four parallel continuous stirred tank reactors were used to investigate the single and joint exposure of Zn and Cu to Arthrobacter sp. JM018, in terms of the impact on the adenosine triphosphate (ATP) pool and microbial tolerance. RESULTS ATP, optical density (OD), and substrate concentration measurements indicated that Cu was more toxic than Zn under all conditions studied. The results showed that although both OD and ATP measurements individually reflected a decrease in microbial growth rate after the addition of metals for the reactors exposed to Cu, specific ATP (i.e. ATP/OD) showed only a temporary reduction followed by a monotonic return to pre-exposure levels within 100 h. The latter implied tolerance and recovery in the energy status of these cells, after the initial shock due to the exposure to Cu. CONCLUSION Specific ATP is an important quantity to be considered as a measure of the activity or energy status of microbial biomass surviving after exposure to toxic metals or other unfavorable conditions. The study provides insights for maintaining metal-tolerant microbial communities and to explore both quantitatively and experimentally the dynamics of ATP pool and microbial tolerance in metal-contaminated environments. (c) 2018 Society of Chemical Industr

A uranium bioremediation reactive transport benchmark

A reactive transport benchmark problem set has been developed based on in situ uranium bio-immobilization experiments that have been performed at a former uranium mill tailing site in Rifle, CO, USA. Acetate-amended groundwater stimulates indigenous microorganisms to catalyze the reduction of U(VI) to a sparingly soluble U(IV) mineral. The interplay between the flow, acetate loading periods and rates, and microbially mediated and geochemical reactions leads to dynamic behavior in metal- and sulfate-reducing bacteria, pH, alkalinity, and reactive mineral surfaces. The benchmark is based on an 8.5 m long one-dimensional model domain with constant saturated flow and uniform porosity. The 159-day simulation introduces acetate and bromide through the upgradient boundary in 14- and 85-day pulses separated by a 10 day interruption. Acetate loading is tripled during the second pulse, which is followed by a 50 day recovery period. Terminal electron-accepting processes for goethite, phyllosilicate Fe(III), U(VI), and sulfate are modeled using Monod-type rate laws. Major ion geochemistry modeled includes mineral reactions as well as aqueous and surface complexation reactions for UO, Fe2+, and H+. In addition to the dynamics imparted by the transport of the acetate pulses, U(VI) behavior involves the interplay between bioreduction, which is dependent on acetate availability, and speciation-controlled surface complexation, which is dependent on pH, alkalinity, and available surface complexation sites. The general difficulty of this benchmark is the large number of reactions (74), multiple rate law formulations, a multisite uranium surface complexation model, and the strong interdependency and sensitivity of the reaction processes. Results are presented for three simulators: HYDROGEOCHEM, PHT3D, and PHREEQC

Emerging Technologies in Environmental Bioremediation

This book describes the state-of-the-art and possibilities of emerging technologies in environmental bioremediation, and reviews its various areas together with their related issues and implications. Considering the number of problems that define and concretize the field of environmental microbiology or bioremediation, the role of some bioprocesses and biosystems for environmental protection, control, and health based on the utilization of living organisms are analyzed. The book aims to provide a comprehensive view of advanced emerging technologies with environmental approaches for wastewater treatment, heavy metal removal, pesticide degradation, dye removal, waste management, microbial transformation of environmental contaminants, etc. With advancements in the area of environmental bioremediation, researchers are looking for new opportunities to improve quality standards and the environment. Recent technologies have given an impetus to the possibility of using renewable raw materials as a potential source of energy. Cost-intensive and ecofriendly technologies for producing high-quality products and efficient ways to recycle waste to minimize environmental pollution are the needs of hour. The use of bioremediation technologies through microbial communities is another viable option to remediate environmental pollutants, such as heavy metals, pesticides, and dyes. Since physicochemical technologies employed in the past have many potential drawbacks including their high cost and low sustainability, efficient biotechnological alternatives to overcome increasing environmental pollution are needed. Hence, environment-friendly technologies that can reduce the pollutants causing adverse hazards to humans and the surrounding environment are required. Environmental remediation, pollution prevention, detection, and monitoring are evaluated by considering the achievements, as well as the future prospects, in the development of biotechnology. Various relevant topics have been chosen to illustrate each of the main areas of environmental biotechnology: wastewater treatment, soil treatment, solid waste treatment, and waste gas treatment, dealing with both microbiological and processengineering aspects. The distinct role of emerging technologies in environmental bioremediation in the future is emphasized by considering the opportunities to contribute to new solutions and directions in the remediation of contaminated environments, as well as minimizing future waste release and creating pollution-preventing alternatives. To take advantage of these opportunities, innovative new strategies, which advance the use of molecular biological methods and genetic engineering technologies, are examined. These methods would improve the understanding of existing biological processes in order to increase their efficiency, productivity, and flexibility. Examples of the development and implementation of such strategies are included. Also, the contributions of environmental biotechnology to the progress of a more sustainable society are revealed

Pressure-driven water flow through hydrophilic alumina nanomembranes

We present an experimental study that focuses on pressure-driven flow of distilled water through. alumina membranes with 5, 10 and 20 nm pore radii. The nanopore geometry, pore size and porosity are characterized using scanning electron microscopy images taken pre- and post-flow experiments. Comparisons of these images have shown reduction in the pore size, which is attributed to precipitation of hydroxyl groups on alumina surfaces. Measured flowrates compared with the Hagen-Poiseuille flow relations consistently predict 2.2 nm reductions in the pore size for three different membranes. This behavior can be explained by the formation of a thick stick layer of water molecules over hydroxylated alumina surfaces, evidenced by water droplet contact angle measurements that exhibit increased hydrophilicity of alumina surfaces. Other possible effects of the mismatch between theory and experiments such as unaccounted pressure losses in the system or the streaming potential effects were also considered, but shown to be negligible for current experimental conditions