Photolytic ozonation for protection and rehabilitation of ground-water resources; a mechanistic study

The cleanup of ground-water resources which have been contaminated by anthropogenic organic compounds is difficult and expensive. Furthermore, most treatment methods merely transfer the contaminant to another phase, such as an adsorbant or the atmosphere. A treatment process which produces harmless by-products, could be set up on-site, and does not require the transport of hazardous materials is very desirable for such cleanup operations. Photolyticozonation, the combination of ozone treatment and ultraviolet irradiation, is an oxidative water treatment process which is capable of convert ing virtually any organic pollutant completely to carbon dioxide and water. Thus, it is potentially a very "clean" solution to many contamination problems. There has, however, been disagreement in the scientific literature concerning the effectiveness of the process, due largely to a lack of understanding of the chemistry which is involved. In this project, photolytic ozonation was studied at the laboratory scale, to better understand and, if possible, model the complex chemical reaction mechanism, so that the process can be more easily optimized from an economic stand point. It was shown that hydroxyl radical, the active species responsible for the destruction of organic pollutants, is not generated directly by ozone photolysisas has generally been speculated, but is produced by secondary reactions. A model has been developed which explains the behavior of the process under a variety of conditions and is useful for the prediction of process performance. The model includes parameters, the values of which may be inferred from the chemical structure of the organic pollutant. The reaction system is seen to be "versatile" in that it has alternate pathways by which pollutant destruction may proceed, depending on conditions in the water being treated.U.S. Department of the InteriorU.S. Geological Surve

Mechanisms of CCl4 Retention and Slow Release in Model Porous Solids and Sediments

This work is part of a larger collaborative project of the same title led by Robert Riley at PNNL. Our task goal is to use a state of the art microbalance and well-defined mesoporous silica particles to characterize the effects of pore size distribution on carbon tetrachloride release rate and sequestration. Mesoporous silicon dioxide (SiO2) particles with pore size distribution in the range of 20 to 70 Angstroms were synthesized under acidic conditions using nonionic surfactants as structure directing agents (Zhao et al., 1998). Siliceous particles (primarily silica dioxide) containing the template molecules are precipitated from solution, dried and the template is removed by combustion at 550 C. The particles obtained by this procedure were characterized using standard nitrogen adsorption at 77 K. Surface area and pore size distribution were calculated from the data coming from the nitrogen experiments. The particle size distribution was determined by using a centrifugal automatic particle size distribution analyzer, which employs a non-contact measuring method based on liquid-phase sedimentation and the change in particle concentrations on the basis of light transmission. To examine the effects of the pore size on CCl4 sequestration and release, a state-of-the-art microbalance was used to measure real-time desorption profiles of CCl4 released from these mesoporous materials. In addition, a gas chromatograph with flammable ionization detector (FID) and electron capture detector (ECD) was used to close the mass balances and confirm the observations made with the microbalance. Experiments with the microbalance include helium calibration (critical to the measurement of small amounts of CCl4 release), and CCl4 desorption rate experiments, to quantify release rates and residual sequestration of CCl4 in the mesoporous silica particles. Finally, a fully automated accelerated solvent extraction system was used to determine the actual mass of CT remaining in the samples immediately after finishing the desorption experiments

Subsurface Uranium Fate and Transport: Integrated Experiments and Modeling of Coupled Biogeochemical Mechanisms of Nanocrystalline Uraninite Oxidation by Fe(III)-(hydr)oxides - Project Final Report

Subsurface bacteria including sulfate reducing bacteria (SRB) reduce soluble U(VI) to insoluble U(IV) with subsequent precipitation of UO2. We have shown that SRB reduce U(VI) to nanometer-sized UO2 particles (1-5 nm) which are both intra- and extracellular, with UO2 inside the cell likely physically shielded from subsequent oxidation processes. We evaluated the UO2 nanoparticles produced by Desulfovibrio desulfuricans G20 under growth and non-growth conditions in the presence of lactate or pyruvate and sulfate, thiosulfate, or fumarate, using ultrafiltration and HR-TEM. Results showed that a significant mass fraction of bioreduced U (35-60%) existed as a mobile phase when the initial concentration of U(VI) was 160 µM. Further experiments with different initial U(VI) concentrations (25 - 900 M) in MTM with PIPES or bicarbonate buffers indicated that aggregation of uraninite depended on the initial concentrations of U(VI) and type of buffer. It is known that under some conditions SRB-mediated UO2 nanocrystals can be reoxidized (and thus remobilized) by Fe(III)-(hydr)oxides, common constituents of soils and sediments. To elucidate the mechanism of UO2 reoxidation by Fe(III) (hydr)oxides, we studied the impact of Fe and U chelating compounds (citrate, NTA, and EDTA) on reoxidation rates. Experiments were conducted in anaerobic batch systems in PIPES buffer. Results showed EDTA significantly accelerated UO2 reoxidation with an initial rate of 9.5M day-1 for ferrihydrite. In all cases, bicarbonate increased the rate and extent of UO2 reoxidation with ferrihydrite. The highest rate of UO2 reoxidation occurred when the chelator promoted UO2 and Fe(III) (hydr)oxide dissolution as demonstrated with EDTA. When UO2 dissolution did not occur, UO2 reoxidation likely proceeded through an aqueous Fe(III) intermediate as observed for both NTA and citrate. To complement to these laboratory studies, we collected U-bearing samples from a surface seep at the Rifle field site and have measured elevated U concentrations in oxic iron-rich sediments. To translate experimental results into numerical analysis of U fate and transport, a reaction network was developed based on Sani et al. (2004) to simulate U(VI) bioreduction with concomitant UO2 reoxidation in the presence of hematite or ferrihydrite. The reduction phase considers SRB reduction (using lactate) with the reductive dissolution of Fe(III) solids, which is set to be microbially mediated as well as abiotically driven by sulfide. Model results show the oxidation of HS– by Fe(III) directly competes with UO2 reoxidation as Fe(III) oxidizes HS– preferentially over UO2. The majority of Fe reduction is predicted to be abiotic, with ferrihydrite becoming fully consumed by reaction with sulfide. Predicted total dissolved carbonate concentrations from the degradation of lactate are elevated (log(pCO2) ~ –1) and, in the hematite system, yield close to two orders-of-magnitude higher U(VI) concentrations than under initial carbonate concentrations of 3 mM. Modeling of U(VI) bioreduction with concomitant reoxidation of UO2 in the presence of ferrihydrite was also extended to a two-dimensional field-scale groundwater flow and biogeochemically reactive transport model for the South Oyster site in eastern Virginia. This model was developed to simulate the field-scale immobilization and subsequent reoxidation of U by a biologically mediated reaction network

Center for Environmental Kinetics Analysis

Over the past two decades, numerous studies have produced high quality information on the rates at which bacteria can reduce metal oxides. The prototypical study--such as the one depicted to the right--focuses on only a few of the myriad variables affecting the rate. This approach allows for effective dissection of the mechanisms underlying DMRB activity, but, it also produces disjoint information that must be synthesized if we hope to predict the behavior of bacteria at the systems level

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

Sources and resources: importance of nutrients, resource allocation, and ecology in microalgal cultivation for lipid accumulation

Regardless of current market conditions and availability of conventional petroleum sources, alternatives are needed to circumvent future economic and environmental impacts from continued exploration and harvesting of conventional hydrocarbons. Diatoms and green algae (microalgae) are eukaryotic photoautotrophs that can utilize inorganic carbon (e.g., CO2) as a carbon source and sunlight as an energy source, and many microalgae can store carbon and energy in the form of neutral lipids. In addition to accumulating useful precursors for biofuels and chemical feed stocks, the use of autotrophic microorganisms can further contribute to reduced CO2 emissions through utilization of atmospheric CO2. Because of the inherent connection between carbon, nitrogen, and phosphorus in biological systems, macronutrient deprivation has been proven to significantly enhance lipid accumulation in different diatom and algae species. However, much work is needed to understand the link between carbon, nitrogen, and phosphorus in controlling resource allocation at different levels of biological resolution (cellular versus ecological). An improved understanding of the relationship between the effects of N, P, and micronutrient availability on carbon resource allocation (cell growth versus lipid storage) in microalgae is needed in conjunction with life cycle analysis. This mini-review will briefly discuss the current literature on the use of nutrient deprivation and other conditions to control and optimize microalgal growth in the context of cell and lipid accumulation for scale-up processes

Discovery of common and rare genetic risk variants for colorectal cancer.

To further dissect the genetic architecture of colorectal cancer (CRC), we performed whole-genome sequencing of 1,439 cases and 720 controls, imputed discovered sequence variants and Haplotype Reference Consortium panel variants into genome-wide association study data, and tested for association in 34,869 cases and 29,051 controls. Findings were followed up in an additional 23,262 cases and 38,296 controls. We discovered a strongly protective 0.3% frequency variant signal at CHD1. In a combined meta-analysis of 125,478 individuals, we identified 40 new independent signals at P < 5 × 10-8, bringing the number of known independent signals for CRC to ~100. New signals implicate lower-frequency variants, Krüppel-like factors, Hedgehog signaling, Hippo-YAP signaling, long noncoding RNAs and somatic drivers, and support a role for immune function. Heritability analyses suggest that CRC risk is highly polygenic, and larger, more comprehensive studies enabling rare variant analysis will improve understanding of biology underlying this risk and influence personalized screening strategies and drug development.Goncalo R Abecasis has received compensation from 23andMe and Helix. He is currently an employee of Regeneron Pharmaceuticals. Heather Hampel performs collaborative research with Ambry Genetics, InVitae Genetics, and Myriad Genetic Laboratories, Inc., is on the scientific advisory board for InVitae Genetics and Genome Medical, and has stock in Genome Medical. Rachel Pearlman has participated in collaborative funded research with Myriad Genetics Laboratories and Invitae Genetics but has no financial competitive interest

Mechanisms of CCl4 Retention and Slow Release in Model Porous Solids and Sediments

This work is part of a larger collaborative project of the same title led by Robert Riley at PNNL. Our task goal is to use a state of the art microbalance and well-defined mesoporous silica particles to characterize the effects of pore size distribution on carbon tetrachloride release rate and sequestration. Mesoporous silicon dioxide (SiO2) particles with pore size distribution in the range of 20 to 70 Angstroms were synthesized under acidic conditions using nonionic surfactants as structure directing agents (Zhao et al., 1998). Siliceous particles (primarily silica dioxide) containing the template molecules are precipitated from solution, dried and the template is removed by combustion at 550 C. The particles obtained by this procedure were characterized using standard nitrogen adsorption at 77 K. Surface area and pore size distribution were calculated from the data coming from the nitrogen experiments. The particle size distribution was determined by using a centrifugal automatic particle size distribution analyzer, which employs a non-contact measuring method based on liquid-phase sedimentation and the change in particle concentrations on the basis of light transmission. To examine the effects of the pore size on CCl4 sequestration and release, a state-of-the-art microbalance was used to measure real-time desorption profiles of CCl4 released from these mesoporous materials. In addition, a gas chromatograph with flammable ionization detector (FID) and electron capture detector (ECD) was used to close the mass balances and confirm the observations made with the microbalance. Experiments with the microbalance include helium calibration (critical to the measurement of small amounts of CCl4 release), and CCl4 desorption rate experiments, to quantify release rates and residual sequestration of CCl4 in the mesoporous silica particles. Finally, a fully automated accelerated solvent extraction system was used to determine the actual mass of CT remaining in the samples immediately after finishing the desorption experiments

FINAL REPORT - Mechanisms of CCl4 Retention and Slow Release in Model Porous Solids and Sediments

A magnetically coupled microbalance system has been used to measure adsorption and desorption isotherms and rates of desorption for carbon tetrachloride on dry prepared porous silica particles with narrow pore size distributions in the mesoporous range. Pore size distributions estimated from the carbon tetrachloride isotherms were found to be in close agreement with those determined using standard low temperature nitrogen adsorption. Three different types of particles were studied, with average pore diameters of 2.7 nm, 4.6 nm, and 5.9 nm. Prior to desorption rate studies, evacuated particulate samples were charged with volatile organic vapor at pressures sufficient to fill all mesopores with condensed fluid. Desorption rates into dry flowing helium were determined at 25 °C and atmospheric pressure, using the microbalance system combined with chromatographic analysis of the exit helium stream. Initial rates were found to decrease significantly, as mass adsorbed decreased. This residual mass was desorbing at such a low rate, that it can be considered a migration resistant fraction of the original mass adsorbed. Attempts to remove this residual mass at higher temperatures were partially successful; however, differences between the microbalance and gas chromatograph responses leave open uncertainty about whether the residual mass was pure carbon tetrachloride. To date, attempts at analysis of the residual mass using solvent extraction have not removed completely this uncertainty. For particles prepared using the same template surfactant, but with different average pore sizes, desorption rates were higher for the larger-pore particles, with correspondingly lower residual mass. Particles prepared with another template surfactant did not follow this pattern, exhibiting intermediate desorption rates and slightly lower residual mass, even though these particles had the smallest pores. These particles exhibited desorption isotherm behavior characteristic of larger pores connected by smaller openings. Except for peculiar behavior in the very early part of desorption experiments for one type of particles, the carbon tetrachloride desorption curves could be fit by a two-part model, employing a diffusion model for the bulk of the desorption, followed by a deactivation model as the mass adsorbed approached residual values. Simultaneous microbalance and gas chromatograph measurements were used to determine carbon tetrachloride and water desorption rates from silica particles initially containing both volatile components. Varying water to carbon tetrachloride ratios were loaded on two types of particles with different pore sizes, with water always loaded first. With water on the particles, pore volumes were significantly reduced. When compared at the same mass adsorbed values, total desorption rates consistently decreased with increasing water content. Total residual mass was found to be a strong function of initial water content, increasing nonlinearly from as initial water content increased from 0 % to 100 %. As expected, during the first few hours of all desorption rate experiments, the rates of carbon tetrachloride desorption were larger than for water. At low initial water contents, total desorption rates were controlled throughout by the carbon tetrachloride rates. For higher water contents, the water rates became larger than the carbon tetrachloride rates for at least some period of intermediate times, after the bulk of the carbon tetrachloride had been desorbed. Although the compositions of the residual mass have not been independently measured, there is evidence that both components were retained, but that water was the major component when there was significant initial water on the particles