R-3 Repository :: Browsing by Author "Alvarez, Pedro J."

Browsing by Author "Alvarez, Pedro J."

Now showing 1 - 20 of 34

1, 4-Dioxane biodegradation at low temperatures in Arctic groundwater samples
(2010) Li, Mengyan; Alvarez, Pedro J.
1,4-Dioxane is an emerging groundwater contaminant and a probable human carcinogen. Its biodegradation was investigated in microcosms prepared with groundwater and soil from an impacted site in Alaska. In addition to natural attenuation conditions (i.e., no amendments), the following treatments were tested: (a) biostimulation by addition of 1-butanol (a readily available auxiliary substrate) and inorganic nutrients; and (b) bioaugmentation with Pseudonocardia dioxanivorans CB1190, a well-characterized dioxane degrading bacterium, or with Pseudonocardia antarctica DVS 5a1, a bacterium isolated from Antarctica. Biostimulation enhanced the degradation of 50 mg L-1 dioxane by indigenous microorganisms (about 0.01 mg dioxane d-1 mg protein-1) at both 4 and 14°C, with a simultaneous increase in biomass. A more pronounced enhancement was observed through bioaugmentation. Microcosms with 50 mg L -1 initial dioxane (representing source zone contamination) and augmented with CB1190 degraded dioxane fastest (0.155 +/- 0.038 mg dioxane d-1 mg protein-1) at 14°C, and the degradation rate decreased dramatically at 4°C (0.021 +/- 0.007 mg dioxane d-1 mg protein-1). In contrast, microcosms with DVS 5a1 degraded dioxane at similar rates at 4 and 14°C (0.018 +/- 0.004 and 0.015 +/- 0.006 mg dioxane d-1 mg protein-1, respectively). DVS 5a1 outperformed CB1190 when the initial dioxane concentration was low (500 microg L-1). This indicates differences in competitive advantages of these two strains. Natural attenuation microcosms also showed significant degradation over 6 months when the initial dioxane concentration was 500 microg L-1. This is the first study to report the potential for dioxane bioremediation and natural attenuation of contaminated groundwater in sensitive cold-weather ecosystems such as the Arctic.
Addition of a Magnetite Layer onto a Polysulfone Water Treatment Membrane to Enhance Virus Removal
(2012) Raciny, Isabel; Alvarez, Pedro J.
The applicability of low-pressure membranes systems in distributed (point of use) water treatment is hindered by, among other things, their inability to remove potentially harmful viruses and ions via size exclusion. According to the USEPA and the Safe Drinking Water Act, drinking water treatment processes must be designed for 4-log virus removal. Batch experiments using magnetite nanoparticle (nano-Fe 3 O 4 ) suspensions and water filtration experiments with Polysulfone (PSf) membranes coated with nano-Fe 3 O 4 were conducted to assess the removal of a model virus (bacteriophage MS2). The membranes were coated via a simple filtration protocol. Unmodified membranes were a poor adsorbent for MS2 bacteriophage with less than 0.5-log removal, whereas membranes coated with magnetite nanoparticles exhibited a removal efficiency exceeding 99.99% (4-log). Thus, a cartridge of PSf membranes coated with nano-Fe 3 O 4 particles could be used to remove viruses from water. Such membranes showed negligible iron leaching into the filtrate, thus obviating concern about colored water. Further research is needed to reduce the loss of water flux caused by coating.
Antibiotic Resistance Gene (ARG) maintenance: Aerobic versus anaerobic conditions and the correlation of plasmid loss to the intracellular redox environment
(2010) Mansfield, William R.; Alvarez, Pedro J.
Antibiotic resistance genes (ARGs) have become emerging contaminants through the overuse and misuse of antibiotics in animal agriculture. Propagation, development, and maintenance of such a contaminant through bacterial reservoirs are not well understood. Identifying environments to which ARGs are attenuated due to an inability to meet the metabolic burden of maintaining the plasmids that carry the ARGs, will give insight to possible solutions. An anaerobic environment was shown to cause the loss of tetracycline resistant (Tet R) gene TetC which is carried on the pSC101 plasmid within the tested strain Escherichia coli c600. Fluctuation and attenuation of the ARG harboring plasmid was also correlated with the intracellular reduction potential of the cells, which was measured as the NADH/NAD+ ratio. This suggests a relationship between ARG plasmid maintenance and the energy state of the cells, possibly reflecting that the energy burden of ARG and associated plasmid maintenance is more difficult to meet under anaerobic conditions that are less favorable from an energy harvesting perspective. These results suggest that the use of anaerobic barriers (e.g., permeable anaerobic mulch barriers or anaerobic lagoons) to intercept ARG-laden drainage from confined animal feeding operations may attenuate the propagation of ARGs into the environment.
Antibiotic resistance vector transport, reservoir amplification and attenuation
(2008) Rysz, Michal; Alvarez, Pedro J.; Ward, C. H.; Gonzalez, Ramon
Microbial antibiotic resistance is an emerging environmental pollution problem with deleterious effects on water supplies and human health. Currently, little is known about the role of environmental factors in the maintenance, propagation and attenuation of antibiotic resistance. This study investigated the effects of antibiotic exposure concentrations, nutrient availability, and microbial growth rate on resistance dynamics, as well as, the porous medium transport characteristics of antibiotic resistance vectors. Exposure to high antibiotic concentrations increased, (1) the percentage of resistant bacterial strains in soil, (2) the persistence of resistant strains in soil and (3) the relative abundance of resistance genes in bacteria; and decreased the Shannon Weaver diversity index. Rich growth medium enhanced resistance plasmid maintenance and stability even in the absence of selective pressure of the antibiotic possibly be alleviating the metabolic burden imparted on the carrier bacteria by the resistance plasmids. The growth rate exerted a strain-specific response on resistance dynamics, with higher plasmid instability (i.e., increased loss) observed at higher growth rates (Pseudomonas aeruginosa), but no such effect observed for an Eschericha coli strain. Resistance vector plumes may be enhanced by: (1) groundwater conditions conducive to plasmid coagulation and colloid formation of approximately 1 mum, and (2) high concentrations of resistant bacteria that exhibit fast initial deposition, and strong blocking behavior after matrix deposition. The results of this research suggest that decreasing environmental antimicrobial concentrations will be conducive to the attenuation of microbial antibiotic resistance, but may not be sufficient in completely eliminating the resistance reservoirs, thus additional control methods may be needed to minimize the impact of these pollutants. The results should also provide insight to improve regulatory and sustainability decision-making processes related to the use of antibiotic in animal agriculture.
Application of Foam for Mobility Control in Enhanced Oil Recovery (EOR) Process
(2014-04-24) Cui, Leyu; Hirasaki, George J.; Miller, Clarence A.; Biswal, Sibani Lisa; Alvarez, Pedro J.
This thesis focuses on the application of foam for mobility control in enhanced oil recovery (EOR) process. The performance of foam and surfactants was evaluated by systematic laboratory study. This includes the screening and evaluation of surfactant formulations for foam EOR process and the investigation of foam for mobility control at reservoir conditions. The adsorption of cationic surfactants on natural minerals was discussed in a separate chapter, although it is one aspect for evaluating surfactant formulations. A numerical model was used to fit the foam strength for foam flooding at reservoir conditions. The solubility, thermal and chemical stability and foaming ability of surfactant formulations were investigated in the screening and evaluation step. A qualified surfactant formulation for foam EOR should be soluble and stable from injection to reservoir conditions. The foaming ability of surfactant formulations needs to be verified in a porous media with crude oil. The bulk foam tests, i.e., foam height, equilibrium foam volume and foam half-life, are not suggested to be used for evaluating foaming ability of surfactant formulations, because of the poor correlation with foam tests in porous media. The detrimental effect of oil, especially for light crude oil, for foam stability was demonstrated. Foam boosters, e.g., betaine surfactants, can be used to stabilize the foam in the presence of crude oil. The mobility control ability of foam was evaluated in Silurian dolomite cores at reservoir conditions after screening and evaluation step. The apparent viscosity of foam was used to describe the mobility control ability. The higher apparent viscosity indicates the stronger foam and better mobility control ability. The strength of foam depends on foam quality, salinity and temperature. The influence of each parameter was investigated and illustrated by controlled experiments. Ethomeen C12 in formation brine and CO2 can generate strong foam at 120 °C and 3400 psi in a wide range of foam quality after the pressure gradient exceeded the minimum pressure gradient. The adsorption of cationic surfactant on the pure carbonate minerals is low owing to the repulsion of the electrostatic force. However, the natural carbonate minerals contain negatively charged impurities, e.g., silica and clays. The adsorption of cationic surfactants on these impurities was significant. Multivalent cations, i.e., Mg2+, Ca2+ and Al3+, can compete with cationic surfactants on the negatively charged binding sites to reduce the adsorption. The adsorption of Ethomeen C12 on silica was reduced from 5.33 mg/m2 in DI water to 3.31 mg/m2 in synthetic brine with 1.51×10-3 mol/L Al3+. The adsorption of Ethomeen C12 was measured at 2 atm CO2 to keep the solution clear. The method of methylene blue (MB) two-phase titration was improved to determine the cationic surfactant concentrations in high salinity brine. In summary, this study demonstrates the methodology to screen the surfactant formulations for the foam EOR process, elucidates the application of the foam for mobility control at reservoir conditions, improves the MB two-phase titration for cationic surfactant in high salinity brine and illuminates the reducing of the adsorption for cationic surfactants on natural carbonate minerals.
Assessing Biological Interactions and Potential Impacts of Emerging Carbonaceous Materials to Terrestrial Organisms
(2011) Li, Dong; Alvarez, Pedro J.
This research addresses the potential ecotoxicity of two emerging carbonaceous materials: C 60 and biochar. The use of these materials is rapidly increasing, as well as their potential for widespread applications. Thus, information about unintended consequences associated the widespread use, incidental or accidental release, and disposal of these emerging materials is needed. The environmental impacts of C 60 , its stable water suspension (nC 60 ), and biochar are assessed here using bacteria and earthworms as model receptors. The antibacterial activity of nC 60 can be mitigated by the presence of natural organic matter as a soil constituent or dissolved in the water column. Sorption to soil might decrease the bioavailability of nC 60 and thus its toxicity to bacteria. Aqueous organic matter also may mitigate nC 60 toxicity. Pristine C 60 showed toxicity to the earthworm's reproduction and was rapidly bioaccumulated by earthworms, although to a lower extent than smaller phenanthrene molecules that are more hydrophobic; thus, the large molecular size of C 60 hinders its bioaccumulation. Less bioaccumulation occurred at higher C 60 concentration in soil, which is counterintuitive and reflects that higher C 60 concentrations that exceed the soil sorption capacity exist as larger precipitates that are less bioavailable. Earthworms avoided soils amended with high concentrations of dry biochar, and experienced significant weight loss after 28-day exposure. The avoidance response was likely to avert desiccation rather than to avoid potential toxicants (i.e., PAHs formed during biochar production by pyrolysis) or nutrient scarcity. By wetting the biochar to field capacity before exposing the worms, this adverse effect can be completely mitigated. Overall, this research provides a foundation for ecotoxicity assessment associated with exposure to C 60 or biochar, and establishes a method by which other emerging materials can be evaluated for their potential environmental impacts.
Assessing Photocatalytic Oxidation Using Modified TiO2 Nanomaterials for Virus Inactivation in Drinking Water: Mechanisms and Application
(2013-06-05) Liga, Michael; Li, Qilin; Alvarez, Pedro J.; Barron, Andrew R.; Tao, Yizhi Jane
Photocatalytic oxidation is an alternative water treatment method under consideration for disinfecting water. Chlorine disinfection can form harmful byproducts, and some viruses (e.g. adenoviruses) are resistant to other alternative disinfection methods. Photocatalytic oxidation using nano-sized photocatalytic particles (e.g. TiO2, fullerene) holds promise; however, it is limited by its low efficiency and long required treatment times. This research focuses on improving virus inactivation by photocatalytic oxidation by modifying catalysts for improved activity, by analyzing virus inactivation kinetics, and by elucidating the inactivation mechanisms of adenovirus serotype 2 (AdV2) and bacteriophage MS2. Modifying TiO2 with silver (nAg/TiO2) or silica (SiO2-TiO2) improves the inactivation kinetics of bacteriophage MS2 by a factor of 3-10. nAg/ TiO2 increases hydroxyl radical (HO•) production while SiO2 increases the adsorption of MS2 to TiO2. These results suggest that modifying the photocatalyst surface to increase contaminant adsorption is an important improvement strategy along with increasing HO• production. The inactivation kinetics of AdV2 by P25 TiO2 is much slower than the MS2 inactivation kinetics and displays a strong shoulder, which is not present in the MS2 kinetics. nAg/TiO2 initially improves the inactivation rate of AdV2. SiO2-TiO2 reduces the AdV2 inactivation kinetics since adsorption is not significantly enhanced, as it is with MS2. Amino-C60 is highly effective for AdV2 inactivation under visible light irradiation, making it a good material for use in solar disinfection systems. The efficacy of amino-fullerene also demonstrates that singlet oxygen is effective for AdV2 inactivation. When exposed to irradiated TiO2, AdV2 hexon proteins are heavily damaged resulting in the release of DNA. DNA damage is also present but may occur after capsids break. With MS2, the host interaction protein is rapidly damaged, but not the coat protein. The kinetics of MS2 inactivation are rapid since it may quickly lose its ability to attach to host cells, while AdV2 kinetics are slower since the entire capsid must undergo heavy oxidation before inactivation occurs. Adenovirus inactivation likely occurs through breaching the capsid followed by radical attack of DNA and core proteins.
Bacteria and fullerene: The microbial response to fullerene water suspensions
(2008) Lyon, Delina Yvonne-Marie de Souza; Alvarez, Pedro J.
The current nanotechnology boom necessitates timely research into the health and environmental impacts of nanomaterials to enhance their eco-responsible manufacture, use, and disposal. Using the water-insoluble C60 as a model nanomaterial, the potential environmental impacts of a C60 water suspension, termed nC60, are here assessed with bacteria as a receptor. nC60 was evaluated for antibacterial activity, antibacterial mechanisms, impact on natural microbial systems, and potential disinfection applications. nC60 is a potent antibacterial agent when tested against pure cultures of different bacteria. Whereas neither light nor oxygen affects its potency, toxicity is increased by smaller particle size and mitigated by salts which promote precipitation. In complex environments, toxicity was lessened by salts or by natural organic matter that sorbed or coated nC60, reducing its bioavailability. The applicability of nC60 as a disinfectant is thus limited to situations with limited organic matter and debris (e.g., drinking water disinfection); it is not recommended for antibiofouling coatings where precipitating debris occluded the nC60 coating and promoted biofilm formation. In contrast to literature showing nC60 -generated reactive oxygen species damaging eukaryotic systems, this research shows that nC60 behaves as an oxidant upon direct contact with the cell, leading to uncoupled respiration and/or damaged respiratory proteins. The methods that were previously used to detect ROS-mediated damage are shown to be ambiguous and susceptible to interference by nC60, implying that the evidence of ROS-mediated oxidative stress needs to be re-evaluated. Overall, this research reflects an overall image of preventable or negligible environmental impact of nC60, and provides a methodology by which the potential environmental impacts of other nanomaterials can be evaluated.
Bench-scale studies of natural attenuation, biostimulation, and bioaugmentation for remediation of groundwater contaminated with benzene and toluene in the Piceance Basin, CO
(2010) Monier, Amy L.; Alvarez, Pedro J.
The US EPA requires direct evidence of contaminant removal before bioremediation or natural attenuation can be used for site remediation. Microcosm studies are commonly used to provide this line of evidence; however, molecular biology tools may provide a better approach for biological forensic analysis of contaminated sites. DNA biomarker technology and laboratory scale microcosms were used to assess the feasibility of natural attenuation, biostimulation, and bioaugmentation for the remediation of a benzene and toluene (B/T) contaminated aquifer. Detection and subsequent increase of target aerobic catabolic and phylogenetic gene biomarkers corroborated aerobic B/T degradation observed in laboratory scale microcosms. Anaerobic biomarker and microcosm studies failed to produce evidence of anaerobic B/T biodegradation potential. Biostimulation (nitrate and sulfate addition) and bioaugmentation with a known anaerobic benzene degrading culture both failed to stimulate B/T removal. However, the addition of benzoate slightly stimulated the removal of benzene under anaerobic conditions. Collectively these results suggest this petroleum hydrocarbon aquifer is not strictly anaerobic and has the potential for natural attenuation processes under aerobic conditions. This research demonstrated the value of using DNA biomarkers as a tool for biological and abiotic forensic site investigations.
Effect of geosorbents on the antibacterial activity of nC60
(2008) Li, Dong; Alvarez, Pedro J.
The rapid development of nanotechnology calls for a timely assessment of the impact of manufactured nanoparticles on environmental settings. This study investigated the association between a C 60 water suspension (nC 60 ) and geosorbents, and their effects on the antibacterial activity of C 60 . The presence of geosorbents reduced the bioavailability of nC 60 and thus its antibacterial activity. Adsorption of humic acid onto nC 60 was also found to eliminate nC 60 toxicity, probably due to coating of nC 60 , which hinders its direct contact with bacteria. These findings indicate the toxicity of nC 60 is controlled by its bioavailability in natural soil settings.
Effects of fuel alcohols on BTEX plume dynamics: An assessment of natural attenuation using RT3D with a general substrate interaction module
(2010) Gomez, Diego E.; Alvarez, Pedro J.
A numerical model was developed to evaluate the effect of fuel alcohols present in reformulated gasoline on BTEX natural attenuation and groundwater plume elongation. The model, developed as a module for the RT3D (Reactive Transport in 3-Dimensions) model, includes commonly considered fate and transport processes (advection, dispersion, adsorption, biodegradation and depletion of electron acceptors during biodegradation) and substrate interactions previously not considered (e.g., a decrease in the specific benzene utilization rate due to metabolic flux dilution and/or catabolite repression) as well as microbial populations shifts, cosolvency effects, alcohol toxicity and source zone depletion dynamics that affect groundwater concentrations of gasoline constituents. The model was used to (1) evaluate the relative importance of benzene plume-elongation mechanisms, (2) how the concentration of ethanol in reformulated gasoline affects the length and longevity of benzene plumes, and (3) the effects of five fuel alcohols (methanol, ethanol, 1-propanol, iso-butanol and n-butanol) on the natural attenuation of benzene in fuel contaminated groundwater. Model simulations showed that all fuel alcohols can hinder the natural attenuation of benzene, due mainly to accelerated depletion of dissolved oxygen during their biodegradation (leading to strongly anaerobic methanogenic conditions) and a decrease in the specific degradation rate for benzene (due to catabolite repression and metabolic flux dilution). Thus, releases of alcohol-blended gasoline should result in longer benzene plumes compared to regular gasoline. However, the simulated lifespan of benzene plumes was shorter for blends with higher alcohol contents, due to a lower mass of benzene released, and increased microbial activity associated with fortuitous growth of BTEX degraders on fuel alcohols. Benzene plume elongation and longevity were more pronounced in the presence of alcohols that biodegrade slower (e.g., propanol and n-butanol), forming longer and more persistent alcohol plumes. In general, our model indicates that higher alcohols blends have a lower impact on BTEX natural attenuation, while more recalcitrant alcohols have a higher impact. Thus, E85 (85% Ethanol) had the lowest impact on BTEX plume elongation and B10 (10% n-Butanol) had the highest impact. However, simulations were highly sensitive to site-specific biokinetic coefficients for alcohol degradation, which forewarns against generalizations about the level of impact of specific fuel alcohols on benzene plume dynamics, and calls for further pilot-scale and field research to validate the assumptions and results from this model.
Environmental Factors Associated With Natural Methane Occurrence in the Appalachian Basin
(Wiley, 2016) Molofsky, Lisa J.; Connor, John A.; McHugh, Thomas E.; Richardson, Stephen D.; Woroszylo, Casper; Alvarez, Pedro J.
The recent boom in shale gas development in the Marcellus Shale has increased interest in the methods to distinguish between naturally occurring methane in groundwater and stray methane associated with drilling and production operations. This study evaluates the relationship between natural methane occurrence and three principal environmental factors (groundwater redox state, water type, and topography) using two pre-drill datasets of 132 samples from western Pennsylvania, Ohio, and West Virginia and 1417 samples from northeastern Pennsylvania. Higher natural methane concentrations in residential wells are strongly associated with reducing conditions characterized by low nitrate and low sulfate ([NO3−] < 0.5 mg/L; [SO42−] < 2.5 mg/L). However, no significant relationship exists between methane and iron [Fe(II)], which is traditionally considered an indicator of conditions that have progressed through iron reduction. As shown in previous studies, water type is significantly correlated with natural methane concentrations, where sodium (Na) -rich waters exhibit significantly higher (p<0.001) natural methane concentrations than calcium (Ca)-rich waters. For water wells exhibiting Na-rich waters and/or low nitrate and low sulfate conditions, valley locations are associated with higher methane concentrations than upland topography. Consequently, we identify three factors (“Low NO3− & SO42−” redox condition, Na-rich water type, and valley location), which, in combination, offer strong predictive power regarding the natural occurrence of high methane concentrations. Samples exhibiting these three factors have a median methane concentration of 10,000 µg/L. These heuristic relationships may facilitate the design of pre-drill monitoring programs and the subsequent evaluation of post-drill monitoring results to help distinguish between naturally occurring methane and methane originating from anthropogenic sources or migration pathways.
Genetic Catabolic Probes to Assess the Natural Attenuation of 1,4-Dioxane
(2013-12-06) Li, Mengyan; Alvarez, Pedro J.; Li, Qilin; Bennett, George N.; Fiorenza, Stephanie
Remediation of aquifers contaminated with 1,4-dioxane (dioxane) is a difficult task because dioxane can be recalcitrant to biodegradation, is not easily removed by volatilization or adsorption, and is highly mobile in groundwater. Monitored natural attenuation (MNA), which relies primarily on biodegradation, is often the most cost-effective approach to manage large and dilute groundwater plumes of priority pollutants, such as those formed by dioxane. However, the burden of proof that MNA is an appropriate solution lies on the proponent, which requires demonstration of the presence and expression of relevant biodegradation capabilities. Therefore, an innovative micro-extraction of aqueous samples coupled with gas chromatography/mass spectrometry (GC/MS) was developed to monitor dioxane attenuation with low part-per-billion detection sensitivity. Soluble di-iron monooxygenases (SDIMOs), especially group-5 SDIMOs (e.g., tetrahydrofuran [THF]/dioxane monooxygenases), are of significant interest due to their potential role in the initializing the cleavage of cyclic ethers. In this study, seven gene clusters encoding SDIMOs were annotated in the genome of Pseudonocardia dioxanivorans CB1190, a well-characterized bacterial dioxane degrader. Reverse transcription quantitative polymerase chain reaction (RT-qPCR) results revealed that only the dxmA gene encoding the large hydroxylase of the putative dioxane monooxygenase was significantly up-regulated when fed with dioxane and its structural analog, THF, compared to controls fed with acetate. This is in accordance with previous evidence implicating the key role of dioxane/THF in initiating the oxidation of cyclic ethers. Additional efforts to evaluate the presence of SDIMO genes in groundwater samples were undertaken using advanced molecular tools, such as functional gene array (i.e. GeoChip) and PCR-DGGE. Both assays demonstrated the widespread distribution of various dioxane-degrading SDIMO genes at a dioxane-impacted site in Alaska. Notably, a group-5 thmA-like gene was enriched in source-zone samples with higher dioxane concentrations, suggesting selective pressure by dioxane. Microcosm assays with 14C-labeled dioxane showed that the highest mineralization capacity corresponded to the source area, which was presumably more acclimated and contained a higher abundance of SDIMO genes. Thus, converging lines of evidence based on both pure bacterial cultures and complex environmental samples corroborate the usefulness of THF/dioxane monooxygenases as biomarkers of dioxane natural attenuation. A primer/probe set was then developed to target bacterial genes encoding the large hydroxylase subunits of THF/dioxane monooxygenases using Taqman (5’-nuclease) chemistry. The probe targets conserved regions surrounding the active site, thus enabling detection of multiple dioxane degraders. Real-time PCR using reference strain genomic DNA demonstrated the high selectivity (no false positives) and sensitivity of this probe. Microcosm tests prepared with groundwater samples from 16 monitoring wells at five different dioxane-impacted sites showed that enrichment of this catabolic gene (up to 114-fold) was significantly correlated to the amount of dioxane degraded. A significant correlation was also found between biodegradation rates and the abundance of thmA/dxmA genes, suggesting them as reliable indicators of dioxane biodegradation activity. Furthermore, pyrosequencing-based metagenomics and 16S rDNA profiling was used to understand how dioxane contamination incidents along with chlorinated solvents and other hydrocarbons have affected the indigenous microbial communities and the microbes that are critical to carbon cycling at the site in Alaska. Actinobacteria and Proteobacteria were the dominant bacterial phyla. However, shifting of the microbial communities structures among various sampling locations was significantly related to the types and presence of external carbon sources (e.g., synthetic chemicals and naturally released gases) at the site. This indicates that the indigenous microbes have adapted to the local environment probably due to long term of acclimation, and may be contributing to the presence of natural attenuation. This study comprehensively evaluated the essential roles of THF/dioxane monooxygenases in dioxane degradation in dioxane-degrading bacterial strains and environment samples. This is the first report to elicit the impact from dioxane and other co-contaminants on shaping functional and phylogenetic structures of microbial communities at a dioxane-impacted site. The development of the novel catabolic biomarker (thmA/dxmA) is of great research and engineering value to unequivocally characterize both dioxane biodegradation potential and activity for enhanced MNA forensics.
Heteroaggregation of Multiwall Carbon Nanotubes and Naturally Occurring Colloids in Aquatic Systems
(2013-12-05) Coogan, Patricia; Li, Qilin; Alvarez, Pedro J.; Tomson, Mason B.
The heteroaggregation of engineered nanoparticles (ENPs) with naturally occurring colloids (NOCs) plays an important role in determining the ultimate fate and transport of nanomaterials in the environment. The objective of this research was to characterize the potential for heteroaggregation between functionalized multiwall carbon nanotubes (MWCNTs) with NOCs in the aquatic environment. Carboxylated MWCNTs (COOH-MWCNTs) and amine functionalized MWCNTs (NH2-MWCNTs) were studied. The natural clay kaolinite was chosen as a model NOC due to its widespread presence in the natural environment and unique charge heterogeneity. In this study, the aggregation between CNTs and kaolinite was analyzed for a range of CNT:NOC ratios and pH as well as in different source waters in a series of sedimentation and aggregation experiments. Sedimentation was monitored using ultraviolet-visible (UV-VIS) spectroscopy, while aggregation was characterized by dynamic light scattering. The heteroaggregation of the COOH-MWCNTs was found to be heavily dependent on pH and the CNT:NOC ratio. The sedimentation rate of the CNT-NOC mixture indicated by UV-VIS spectroscopy and average particle size measured by DLS both increased at low pH while the CNT solution remained stable over time when tested at the same solution chemistry. As the CNT:NOC ratio decreased, the CNT-NOC mixture demonstrated enhanced sedimentation behavior at pH 3. The enhanced sedimentation coupled with increasing particle size of the mixture indicated the presence of CNT-NOC heteroaggregates. At higher pH, no enhanced sedimentation occurred for the range of ratios tested. The NH2-MWCNTs were not dispersible at neutral pH were therefore only tested at pH 3. All solutions regardless of ratio indicated no significant evidence of enhanced sedimentation due to heteroaggregation for the NH2-MWCNTs in this study. Filtered and unfiltered natural water samples from Lake Houston and the Trinity River were also analyzed and found to significantly enhance the sedimentation of the CNTs at neutral pH. The unfiltered samples exhibited enhanced sedimentation of the COOH-MWCNTs compared to the filtered samples. There was also evidence of enhanced removal of other particles present in the natural water sample due to the addition of CNTs. This indicates that the presence of CNTs could affect the transport of other contaminants in aquatic systems, altering the distribution of contaminants particularly at the sediment-water interface. These results suggest that NOCs enhance the sedimentation of CNTs in the natural environment and are highly dependent on pH and the ratio of carbon nanotube to natural colloid.
How understanding and harnessing the microaerobic metabolism of glycerol in Escherichia coli can revitalize the biodiesel industry
(2009) Durnin, Guyton; Alvarez, Pedro J.
Governments want to replace fossil fuels with biofuels like ethanol and biodiesel due to concerns about pollution and price instability. However, the biodiesel industry must find a market for glycerol to be profitable. The large quantities and reduced state of its carbon have made glycerol an attractive choice for ethanol production. While Escherichia coli can produce ethanol anaerobically, cell growth requires expensive complex nutrients. To bypass this issue, we used microaerobic conditions and maintained 91% recovery of carbon into products. We identified the pathways involved in the microaerobic metabolism of glycerol using genetic and biochemical tools and further engineered the optimized anaerobic E. coli strains for microaerobic conditions. Greater cell growth and product synthesis were achieved by overexpressing glycerol dehydrogenase and dihydroxyacetone kinase. The final strain DeltafrdADeltaptaDeltaldhA (EH05) pZSKLMg1dA was tested at high glycerol levels where it produced almost exclusively ethanol in minimum media at superior volumetric rates.
Impact of Sunlight and Natural Organic Matter on the Fate, Transport, and Toxicity of Carbon Based Nanomaterials
(2013-09-16) Qu, Xiaolei; Li, Qilin; Alvarez, Pedro J.; Zhong, Weiwei; Weisman, R. Bruce
The fast growing production of carbon based nanomaterials (CNMs) and their potential widespread use in consumer products raise concerns regarding their potential risks to human health and ecosystems. The present study investigated the role of photochemical transformation and natural organic matter (NOM) in the fate, transport, and toxicity of fullerenes and carbon nanotubes (CNTs) in natural aquatic systems, providing fundamental information for risk assessment and management. Photochemical transformation of aqueous fullerene nanoparticles (nC60) and CNTs occurs at significant rates under UVA irradiation at intensity similar to that in sunlight. The transformation processes are mediated by self-generated ROS, resulting in changes of surface structure depending on the initial surface oxidation state of CNMs. UVA irradiation leads to oxygenation of nC60 surface and decarboxylation of carboxylated multi-walled carbon nanotubes (COOH-MWNTs). The environmental transport of CNMs is significantly affected by their surface chemistry, concentration and species of electrolytes, and concentration and properties of co-existing NOM. In electrolyte solutions without NOM, the mobility of CNMs is largely decided by their surface chemistry, primarily the oxygen-containing functional groups. In NaCl solutions, UVA irradiation remarkably enhanced the mobility of nC60; conversely, it reduced nC60 stability in CaCl2 solutions. The mobility of COOH-MWNTs in NaCl solutions correlated well with the abundance of surface carboxyl groups. Humic acid, once adsorbed on the nC60 surface, can significantly enhance its stability through steric hindrance. The extent of stabilization depends on the amount and properties of humic acid adsorbed. Humic acid has limited adsorption on UVA-irradiated nC60. Soil humic acid is more efficient in stabilizing nC60 than aquatic humic acid due to its higher molecular weight. Humic acid immobilized onto the silica surface can potential enhance or hinder nC60 deposition, depending on the complex interplay of attractive and repulsive forces. MWNTs are more toxicity to bacteria, Escherichia coli, than COOH-MWNTs due to their higher bioavailability and oxidative capacity. Surface oxidation induced by •OH reduced the toxicity of MWNT while reactions with •OH have little effect on the COOH-MWNT toxicity. Antioxidants such as glutathione can effectively inhibit the antibacterial activity of MWNTs.
Improvement of thermodynamic modeling of calcium carbonate and calcium sulfates at high temperature and high pressure in mixed electrolytes
(2013-12-05) Dai, Zhaoyi; Tomson, Mason B.; Alvarez, Pedro J.; Li, Qilin
Pitzer theory is used to predict the solubility of gypsum, anhydrite and calcite over wide ranges of temperature, pressure, and ionic strength with mixed electrolytes, which usually occurs in deep water oil and gas production. Gypsum solubility was measured from 0 to 40 oC, from 14.7 to 20000 psi, with 0 to 4 mol NaCl/kg H2O. Anhydrite solubility in literature was confirmed and adopted in this study. The equilibrium constants of gypsum and anhydrite were incorporated by temperature and pressure dependent parts from different researches. Along with other virial coefficients, virial coefficients for Ca2+-SO42- interactions were fitted, based on which solubility of gypsum/anhydrite is precisely predicted. They are also applied to accurately predict calcite solubility with mixed electrolytes from 0 to 250 oC (except for 100 oC) up to 21000 psi. The Kassoc for CaSO4(0) derived from b2(CaSO4) in this study matches well with other experimental data at 1 atm 25 oC.
Iron: From Synthesis, Characterization, and Application of Sulfide Green Rust to Viability in Arsenic Water Treatment
(2013-09-16) Jones, Christopher; Colvin, Vicki L.; Wilson, Lon J.; Alvarez, Pedro J.
Iron chemistry plays an important role in our world. At the nanoscale, iron oxide nanoparticles (nanomagnetite) have many inherent physical or chemical characteristics that drive potential solutions to real-world problems; appropriation of nanomagnetite’s properties as a “scaffold” for chemistry would further enhance its effectiveness in applications. In an effort to make use of nanomagnetite’s physical properties, a new “Sulfide Green Rust” (sGR) has been synthesized from magnetic iron nanoparticles. The material is crystalline, reactive due to high iron(II) content, and dissolves in the aqueous phase. Nanomagnetite’s magnetic properties were also observed to persist after sGR synthesis. X-ray absorption spectroscopy (XAS) confirmed the synthesis of this new FeS2-like material. The crystallinity, composition, and various physical characteristics were examined using a host of techniques including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), Mössbauer spectroscopy, CRYO-TEM, Raman spectroscopy, and ultraviolet-to-visible (UV-Vis) spectroscopy. To demonstrate its use, the material was then subjected to a test of its reactive potential, namely water remediation of an orange dye contaminant. Iron serves a function at the macroscale as well regarding water treatment, since iron coagulation-filtration is the industry standard for arsenic treatment. Determining a technology’s merit as a solution goes beyond technical concern, however, as environmental and economic aspects also play important roles. Life Cycle Analysis, or LCA, methodology works to holistically compare each of these facets from cradle to grave. To address the current arsenic drinking water requirements at a case setting in Hungary, the LCA technique was applied on two example arsenic removal technologies, both coagulation-filtration and adsorption. 9 out of 10 considered impact categories tended to favour coagulation-filtration in this small municipality study, however realistic variations in water chemistry and product characteristics led to some overlap of their environmental impact. Electricity did not have a large direct impact, regeneration of the adsorption technology was very costly, and adsorption’s hazardous waste was not reduced compared to coagulation-filtration. Coagulation-filtration is also the cheaper of the two technologies; its highest cost is that of waste disposal, while the highest single expense modeled is that of adsorption media cost.
Microbial processes influencing the attenuation and impacts of ethanol-blended fuel releases
(2013-12-05) Ma, Jie; Alvarez, Pedro J.; Li, Qilin; Bennett, George N.; Rixey, Bill
Fuel releases that impact groundwater are a common occurrence, and the growing use of ethanol as a transportation biofuel is increasing the likelihood of encountering ethanol in such releases. Therefore, it is important to understand how such releases behave and affect public safety and environmental health, and how indigenous microorganisms respond and affect their migration, fate, and overall impacts. Vapor intrusion risk (i.e., methane explosion and enhanced fuel hydrocarbon vapor intrusion) associated with ethanol blend releases is a potential concern. Using both experimental measurements and mathematical model simulations, this thesis shows that methane is unlikely to build up to pose an explosion hazard (5% v:v) if diffusion is the only mass transport pathway through the unsaturated zone. However, if methanogenic activity near the source zone is sufficiently high to cause advective gas transport, the methane indoor concentration may exceed the flammable threshold. As a group of widely distributed microorganisms, methanotrophs can significantly attenuate methane migration through the vadose zone, and thus alleviate the associated explosion risk. However, methane biodegradation could consume soil oxygen that would otherwise be available to support biodegradation of volatile hydrocarbons, and increase their vapor intrusion potential. The release of an ethanol blend solution (10 % v:v ethanol solution mixed with 50 mg/L benzene and 50 mg/L toluene) experiment into a pilot-scale (8 m3) aquifer tank produced a large amount of volatile fatty acids (VFAs). The accumulation of VFAs (particularly butyric acid) exceeded the secondary maximum contaminant level value for odor, which represents a previously unreported aesthetic impact. After the release was shut off, ethanol anaerobic degradation was temporarily stimulated when the dissolved ethanol concentration decreased below its toxicity threshold (~2,000 mg/L for this system). Methane generation persisted for more than 100 days after the disappearance of dissolved ethanol. The persistent methane was likely generated from ethanol degradation byproducts (e.g., acetate) and solid organic carbon in aquifer materials. Ethanol blend releases stimulate the microbial growth and increased the organic carbon content in the aquifer. Microorganisms play a critical role in the fate of ethanol-blended fuel releases, often determining their region of influence and potential impacts. This thesis used advanced molecular tools including 454 pyrosequencing and real-time PCR (qPCR) to characterize changes in structure of indigenous microbial communities in response to 1) a pilot-scale ethanol blend release and to 2) the shut-off of such release. This thesis shows that the ethanol blend release stimulated microbial growth and significantly changed the microbial community structure by enriching microbial groups involved in the fermentative degradation process. The growth of putative hydrocarbon degraders and commensal anaerobes, and increases in degradation rates suggest an adaptive response that increases the potential for natural attenuation of ethanol blend releases. After the release was shut off, the microbial community returned towards the pre-contaminated state; however, restoration was relatively slow and far from complete even one year later. Overall, this thesis advanced current understanding of vapor intrusion risks and groundwater quality impacts associated ethanol blend releases and microbial ecology in the impacted aquifer. The integration of this knowledge with site-specific information on pertinent hydrogeological processes will undoubtedly enhance engineering practices such as site investigation, risk assessment, and bioremediation implementation and maintenance to deal with releases of current and future biofuel blends.
Microcosm Assessment of Aerobic Intrinsic Bioremediation and Mineralization Potential for three 1,4-Dioxane Impacted Sites
(2013-11-19) Van Orden, Elisa; Alvarez, Pedro J.; Ward, C. H.; Tomson, Mason B.
1,4-Dioxane (dioxane) is a potential carcinogen widely used as a stabilizer for chlorinated solvents, and it exhibits high mobility in groundwater. Dioxane is recalcitrant to biodegradation, and its physicochemical properties preclude effective removal by volatilization or adsorption. Through this long-term microcosm study, we have assessed the natural attenuation potential of dioxane for multiple sediment and groundwater samples collected from three sites located in Los Angeles, CA. Groundwater and sediment samples were taken from three locations at each plume, representing the source zone, middle and leading edge. A total of 13 monitoring wells were sampled to prepare the microcosms and subsequently assess the indigenous potential to biodegrade dioxane. The microcosms were spiked with 14C-labeed dioxane to assess mineralization potential (per 14CO2 recovery). No dioxane loss and less than 8% CO2 recovery was observed in the negative controls, indicating that dioxane removal (and mineralization) was due to biodegradation. Positive control microcosms amended with the dioxane degrader Pseudonocardia dioxivorans CB1190 exhibited dioxane degradation activity statistically indistinguishable from observed batch incubations prepared with mineral media, indicating an absence of inhibitory compounds in source zone samples. Complete dioxane removal, exhibiting linear (zero-order) kinetics (indicative of saturated enzymes), was observed during 24 weeks incubation in all biologically active, unaugmented microcosms. Up to 43% mineralization as CO2 and 5% to 7% biomass growth was observed in unaugmented microcosms experiencing rapid dioxane loss. Degradation activity decreased with increasing distance from the contaminant source zone, presumably due to less acclimation. Source-zone microcosms from Site 1 exhibited relatively high biodegradation activity (323.9 ± 7.6 µg/L/day) and were respiked with dioxane for confirmatory purposes. The respike (2 ppm dioxane) was degraded faster within four weeks, suggesting a higher level of acclimation (possibly due to the growth of indigenous dioxane degraders) after the initial 24 week study. Source-zone microcosms from Site 2 and 3 exhibited biodegradation activities of 1.4 ± 0.09 µg/L/day and 47.1 ± 1.8 µg/L/day, respectively. Overall, these results show that indigenous microorganisms capable of degrading dioxane are present at the three sites considered, and suggest that monitored natural attenuation should be considered as a remedial response.

Browsing by Author "Alvarez, Pedro J."

Results Per Page

Sort Options