Abstract Silicate glasses are an accepted option for immobilizing nuclear waste and waste glass can be disposed in near-surface environments. It is important to understand glass alteration mechanisms under site-relevant conditions to predict glass corrosion rates upon disposal. Microbial activity near the glass surface may influence glass alteration. However, waste glass chemical durability is currently evaluated without consideration of microbial alteration. Here, four glass compositions were tested in three solutions, with and without a subsurface Paenibacillus bacterium, to compare the extent of glass leaching. Results indicate that the Paenibacillus cells increased glass alteration, resulting in higher concentrations of boron, iron, sodium, and silicon released into solution. The combination of microbially mediated organic acid production, which decreased pH, and glass dissolution, which increased pH, resulted in a net neutral or slightly acidic solution that could promote further glass alteration. The amount of each element released depended on glass composition and solution chemistry. This study revealed the dynamic relationship between microbial metabolism, elemental release, and corresponding changes to solution pH, showing that microbial processes can indirectly accelerate glass alteration. This work supports a greater understanding of microbially-influenced glass alteration and informs development of standardized durability tests to assess microbial influence at disposal facilities.

A fundamental understanding of processes that slow divalent metal silicate carbonation is important for developing effective strategies to durably store carbon dioxide and mitigate atmospheric CO2. This study presents a detailed investigation of a passivation effect unique to low-water conditions during the carbonation of forsterite (Mg2SiO4) and highlights the importance of hygroscopicity in influencing metal silicate carbonation. Integrated in situ and ex situ experimental results showed that the decrease in the carbonation rate of forsterite observed after ∼10 h in humid supercritical CO2 (50 °C, 90 bar) correlates with a reduction in water film thickness, and in particular, weakly hydrogen bonded adsorbed water that facilitates ion transport. We attribute the decrease in thickness to a drop in the concentrations of hygroscopic Mg2+, MgHCO3+, and HCO3- ions within the film as the predominate forsterite carbonation product evolves from amorphous magnesium carbonate (AMC) to magnesite (MgCO3). When more soluble AMC is present, hygroscopic ion concentrations are higher, drawing more water from the supercritical phase to the forsterite surface. Carbonation rates are faster because thicker water films can better mobilize ions to growing carbonates. In contrast, when less soluble magnesite predominates, hygroscopic ion concentrations are lower, water films are thinner, and carbonate rates are slower.

Soil organic matter (SOM) has attracted a great deal of interest; particularly for its potential to mitigate human derived CO2 emissions. Studies have demonstrated that SOM plays a critical role in carbon storage and COQ sequestration. However, the sorption properties of SOM, which influence its transport in pore water and stabilization within the soil, remain poorly understood. This study develops a workflow to: (1) examine compound-specific advective and diffusive transport and desorption behaviors, (2) quantify desorption rates through stop-flow and continuous-flow column experiments, and (3) evaluate the impact of soil microporosity on SOM mobility using high-resolution imaging and extractions. Intact core column experiments were conducted on Uncultivated (Natural) and Cultivated soil samples, both were arid soils, collected in Washington State. X-ray computed tomography was employed to measure porosity and pore connectivity, while Fourier-transform ion cyclotron resonance mass spectrometry was used to analyze SOM composition. The findings revealed that cultivation increased total carbon and nitrogen levels due to irrigation and fertilization, enhancing carbon capture potential in arid soils. In contrast, the Natural soil, characterized by higher porosity and connectivity, contained more oxidized carbon. Pore network analysis indicated that soil compaction in the Cultivated soil may lead to longer diffusion pathways, significantly influencing SOM transport and stability.

Mineral-organic matter (OM) studies have predominantly focused on acidic soils that are abundant in iron (Fe) oxides and aluminum (Al) oxides. We have probed mineral-OM interactions in an alkaline or calcareous soil of the Aridisols class. Unlike the role of Fe and Al, the role of Ca-minerals (particularly calcite), which are ubiquitous in alkaline soils, in OM sequestration is not well understood. Multiple recent model studies with aqueous Ca2+ or synthetic calcite and a suite of OM compounds have shown Ca-OM assemblages to be spatially correlated with calcite at the microscale. To study the chemical state of both Ca and Fe and their competing role in soil organic matter (SOM) stabilization, we performed laboratory characterization using x-ray diffraction, Mossbauer spectroscopy, x-ray photoelectron spectroscopy, scanning electron microscopy, and scanning transmission electron microscopy, alongside synchrotron-based microscale chemical imaging using scanning transmission xray microscopy combined with near-edge x-ray absorption fine structure. Ca mineral-organic associations were found to be ubiquitous in this system and are likely critical for understanding SOM stabilization/degradation in alkaline soils. From our findings on mineralogy, speciation, and the nature of Ca-OM bridging, we identified differences in C and Ca chemistry based on the relative location of OM to Ca minerals. The OM near the calcite crystal was enriched in lipid and protein moieties, Ca-OM next to Fe minerals displayed a strong contribution from aromatic compounds, while on the surface of microbes, the carbonate was believed to be of microbial in origin, as also suggested by preliminary works reporting on the formation of amorphous calcite or nano-calcite. In Ca-OM admixed with carbonate, it was difficult to distinguish Ca-associated OM from amorphous calcite or nano-calcite.

This study examines how greenhouse gas (GHG) production and organic matter (OM) transformations in coastal wetland soils vary with the availability of oxygen and other terminal electron acceptors. We also evaluated how OM and redox-sensitive species varied across different size fractions: particulates (0.45-1μm), fine colloids (0.1-0.45μm), and nano particulates plus truly soluble (<0.1μm; NP+S) during 21-day aerobic and anaerobic slurry incubations. Soils were collected from the center of a freshwater coastal wetland (FW-C) in Lake Erie, the upland-wetland edge of the same wetland (FW-E), and the center of a saline coastal wetland (SW-C) in Washington state. Anaerobic methane production for FW-E soils were 47 and 27,537 times greater than FW-C and SW-C soils, respectively. High particulate Fe2+ and dissolved sulfate concentrations in FW-C and SW-C soils suggest that iron and/or sulfate reduction inhibited methanogenesis. Aerobic CO2 production was highest for both freshwater soils, which had a higher proportion of OM in the NP+S fraction (64±28% and 70±10% for FW-C and FW-E, respectively) and C:N ratios reflective of microbial detritus (1.7±0.2 and 1.4±0.3 for FW-E and FW-C, respectively) compared to SW-C, which had a higher fraction of particulate (58±9%) and fine colloidal (19±7%) OM and C:N ratios reflective of vegetation detritus (11.2 ± 0.5). The variability in GHG production and shifts in OM size fractionation and composition observed across freshwater and saline soils collected within individual and across different sites reinforce the high spatial variability in the processes controlling OM stability, mobility, and bioavailability in coastal wetland soils.

Coastal wetlands, including freshwater systems near large lakes, rapidly bury carbon, but less is known about how they transport carbon either to marine and lake environments or to the atmosphere as greenhouse gases (GHGs) such as carbon dioxide and methane. This study examines how GHG production and organic matter (OM) mobility in coastal wetland soils vary with the availability of oxygen and other terminal electron acceptors. We also evaluated how OM and redox-sensitive species varied across different size fractions: particulates (0.45-1μm), fine colloids (0.1-0.45μm), and nano particulates plus truly soluble (<0.1μm; NP+S) during 21-day aerobic and anaerobic slurry incubations. Soils were collected from the center of a freshwater coastal wetland (FW-C) in Lake Erie, the upland-wetland edge of the same wetland (FW-E), and the center of a saline coastal wetland (SW-C) in the Pacific Northwest, USA. Anaerobic methane production for FW-E soils were 47 and 27,537 times greater than FW-C and SW-C soils, respectively. High Fe2+ and dissolved sulfate concentrations in FW-C and SW-C soils suggest that iron and/or sulfate reduction inhibited methanogenesis. Aerobic CO2 production was highest for both freshwater soils, which had a higher proportion of OM in the NP+S fraction (64±28% and 70±10% for FW-C and FW-E, respectively) and organic C:N ratios reflective of microbial detritus (5.3±5.3 and 5.3±7.0 for FW-E and FW-C, respectively) compared to SW-C, which had a higher fraction of particulate (58±9%) and fine colloidal (19±7%) OM and organic C:N ratios reflective of vegetation detritus (11.4 ± 1.7). The variability in GHG production and shifts in OM size fractionation and composition observed across freshwater and saline soils collected within individual and across different sites reinforce the high spatial variability in the processes controlling OM stability, mobility, and bioavailability in coastal wetland soils.

Soil organic matter (SOM) persistence in aridic soils is primarily attributed to SOM stabilization through Ca-complex-ation. In addition, SOM stabilization by calcite, a common mineral in aridic environments, was recently attributed to adsorption and occlusion on calcite voids. We present a systematic study that investigates SOM compounds interaction, individually or as part of a mixture, with calcite using molecular level dynamics and kinetic batch sorption experiments. Four SOM compounds, representing major classes in dissolved SOM, e.g., fatty acids, amino acids, carbohydrates, and lignin, were used in this study. In the single compound system, adsorption to calcite is compound specific as follows: fatty acid >> amino acid congruent to lignin and no adsorption of carbohydrate. Fatty acid selective adsorption is attributed to its carboxyl group strong affinity for Ca-coordinated sites of calcite. Amino acid weaker adsorption is attributed to the combined effects of carboxylate and ammonium multifunctionalities, resulting in frequent liquid partitioning of amino acid. Meanwhile, findings suggest that lignin may deprotonate and subsequently adsorb to calcite. In the competing mixed compounds system, fatty acid adsorbs to calcite similarly to the single system, while carbohydrate yet again does not adsorb. The amino acid and lignin behavior however is driven by calcite dissolution and Ca(aq) release. Evidence suggests the formation of aqueous Ca-organo associations, Ca-complexes, or Ca mixed cross-linkages, which surprisingly are not bound to mineral Ca-surface sites. Although Ca-organo associations are not adsorbed, they have limited mobilities, which dictate their spatial distribution in a water scarce soil system, such as an aridic environment.

Root systems are dynamic and adaptable organs that play critical roles in plant development. However, how roots grow and accumulate biomass during plant life cycle and in relation to shoot growth phenology remains understudied. A comprehensive time-dependent root morphological analysis integrated with molecular signatures is then required to advance our understanding of root growth and development. Here we studied Brachypodium distachyon rooting process by monitoring root morphology, biomass production, and C/N ratios during developmental stages. To provide insight into gene regulation that accompanies root growth, we generated comprehensive transcript profiles of Brachypodium whole-root system at four developmental stages. Our data analysis revealed that multiple biological processes including trehalose metabolism and various families of transcription factors (TFs) were differentially expressed in root system during plant development. In particular, the AUX/IAA, ERFs, WRKY, NAC, and MADS TF family members were upregulated as plant entered the booting/heading stage, while ARFs and GRFs were downregulated suggesting these TF families as important factors involved in specific phases of rooting, and possibly in regulation of transition to plant reproductive stages. We identified several Brachypodium candidate root biomass-promoting genes and cis-regulatory elements for further functional validations and root growth improvements in grasses.

ABSTRACT Understanding the basic biology that underpins soil microbiome interactions is required to predict the metaphenomic response to environmental shifts. A significant knowledge gap remains in how such changes affect microbial community dynamics and their metabolic landscape at microbially relevant spatial scales. Using a custom-built SoilBox system, here we demonstrated changes in microbial community growth and composition in different soil environments (14%, 24%, and 34% soil moisture), contingent upon access to reservoirs of nutrient sources. The SoilBox emulates the probing depth of a common soil core and enables determination of both the spatial organization of the microbial communities and their metabolites, as shown by confocal microscopy in combination with mass spectrometry imaging (MSI). Using chitin as a nutrient source, we used the SoilBox system to observe increased adhesion of microbial biomass on chitin islands resulting in degradation of chitin into N-acetylglucosamine (NAG) and chitobiose. With matrix-assisted laser desorption/ionization (MALDI)-MSI, we also observed several phospholipid families that are functional biomarkers for microbial growth on the chitin islands. Fungal hyphal networks bridging different chitin islands over distances of 27 mm were observed only in the 14% soil moisture regime, indicating that such bridges may act as nutrient highways under drought conditions. In total, these results illustrate a system that can provide unprecedented spatial information about interactions within soil microbial communities as a function of changing environments. We anticipate that this platform will be invaluable in spatially probing specific intra- and interkingdom functional relationships of microbiomes within soil. IMPORTANCE Microbial communities are key components of the soil ecosystem. Recent advances in metagenomics and other omics capabilities have expanded our ability to characterize the composition and function of the soil microbiome. However, characterizing the spatial metabolic and morphological diversity of microbial communities remains a challenge due to the dynamic and complex nature of soil microenvironments. The SoilBox system, demonstrated in this work, simulates an ∼12-cm soil depth, similar to a typical soil core, and provides a platform that facilitates imaging the molecular and topographical landscape of soil microbial communities as a function of environmental gradients. Moreover, the nondestructive harvesting of soil microbial communities for the imaging experiments can enable simultaneous multiomics analysis throughout the depth of the SoilBox. Our results show that by correlating molecular and optical imaging data obtained using the SoilBox platform, deeper insights into the nature of specific soil microbial interactions can be achieved.

The metabolic underpinnings of plant survival under severe drought-induced senescence conditions are poorly understood. In this study, we assessed the morphological, physiological and metabolic responses to sustained water deficit in Brachypodium distachyon, a model organism for research on temperate grasses. Relative to control plants, fresh biomass, leaf water potential, and chlorophyll levels decreased rapidly in plants grown under drought conditions, demonstrating an early onset of senescence. The leaf C/N ratio and protein content showed an increase in plants subjected to drought stress. The concentrations of several small molecule carbohydrates and amino acid-derived metabolites previously implicated in osmotic protection increased rapidly in plants experiencing water deficit. Malic acid, a low molecular weight organic acid with demonstrated roles in stomatal closure, also increased rapidly as a response to drought treatment. The concentrations of prenyl lipids, such as phytol and α-tocopherol, increased early during the drought treatment but then dropped dramatically. Surprisingly, continued changes in the quantities of metabolites were observed, even in samples harvested from visibly senesced plants. The data presented here provide insights into the processes underlying persistent metabolic activity during sustained water deficit and can aid in identifying mechanisms of drought tolerance in plants.

Underground storage in geological aquifers is one of the most important options for large-scale mitigation of CO2. During the supercritical CO2 (scCO2) injection process, water dissolved in scCO2 may have significant impact on the displacement process. In this study, a series of wet scCO2 (WscCO2, 100% water saturation) and dry scCO2 (DscCO2, 0% water saturation) displacement experiments were conducted in micromodels for a large range of flow rates. The displacement was visualized using fluorescence microscopy. Results showed that DscCO2 saturations were up to 3.3 times larger than WscCO2 saturations when the capillary fingering dominated the displacement. The specific interfacial areas and mobile fractions for the DscCO2 displacements were also much larger than those for WscCO2. The capillary forces combined with drying effects are identified as the leading causes for the considerably higher DscCO2 sweep efficiency. Results from this study showed the important impact of mutual solubility of scCO2 and water on the displacement process and saturation of scCO2 (SscCO2), suggesting that the conventional model describing the relationship between capillary pressure and SscCO2 needs to be modified for the effect of the mutual dissolution of multiple phases to more adequately describe the scCO2 displacement process in saline aquifer formation.

Sealing of wellbores in geothermal and tight oil/gas reservoirs by filling the annulus with cement is a well established practice. Failure of the cement as a result of physical and/or chemical stress is a common problem with serious environmental and financial consequences. Numerous alternative cement blends have been proposed for the oil and gas industry. Most of these possess poor mechanical properties, or are not designed to work in high temperature environments. This work reports on a novel polymer-cement composite with remarkable self-healing ability that maintains the required properties of typical wellbore cements and may be stable at most geothermal temperatures. We combine for the first time experimental analysis of physical and chemical properties with density functional theory simulations to evaluate cement performance. The thermal stability and mechanical strength are attributed to the formation of a number of chemical interactions between the polymer and cement matrix including covalent bonds, hydrogen bonding, and van der Waals interactions. Self-healing was demonstrated by sealing fractures with 0.3-0.5 mm apertures, 2 orders of magnitude larger than typical wellbore fractures. This polymer-cement composite represents a major advance in wellbore cementing that could improve the environmental safety and economics of enhanced geothermal energy and tight oil/gas production.

The aim of this work was to study the separate effect of fission fragment damage on the dissolution of simulant UK advanced gas-cooled reactor nuclear fuel in water. Plain UO2 and UO2 samples, doped with inactive fission products to simulate 43 GWd/tU of burn-up, were fabricated. A set of these samples were then irradiated with 92 MeV Xe-129(23+) ions to a fluence of 4.8 x 10(15) ions/cm(2) to simulate the fission damage that occurs within nuclear fuels. The primary effect of the irradiation on the UO2 samples, observed by scanning electron microscopy, was to induce a smoothening of the surface features and formation of hollow blisters, which was attributed to multiple overlap of ion tracks. Dissolution experiments were conducted in single-pass flow-through (SPFT) mode under anoxic conditions (<0.1 O-2 ppm in Ar) to study the effect of the induced irradiation damage on the dissolution of the UO2 matrix with data collection capturing six minute intervals for several hours. These time-resolved data showed that the irradiated samples showed a higher initial release of uranium than unirradiated samples, but that the uranium concentrations converged towards similar to 10(-9) mol/l after a few hours. Apart from the initial spike in uranium concentration, attributed to irradiation induced surficial micro-structural changes, no noticeable difference in uranium chemistry as measured by X-ray electron spectroscopy or 'effective solubility' was observed between the irradiated, doped and undoped samples in this work. Some secondary phase formation was observed on the surface of UO2 samples after the dissolution experiment. (C) 2017 The Authors. Published by Elsevier B.V.

Hydrothermal liquefaction (HTL) is a viable thermochemical process for converting wet solid wastes into biocrude that can be hydroprocessed to liquid transportation fuel blendstocks and specialty chemicals. The aqueous byproduct from HTL contains significant amounts (20-50%) of the biogenic feed carbon, which must be valorized to enhance economic sustainability of the process on an industrial scale. In this study, aqueous fractions produced from HTL of food industry wastes, municipal wastes, and biomass cultivated on wastewater were characterized using a wide variety of analytical approaches. Organic species present in these aqueous fractions were identified using two-dimensional gas chromatography equipped with time-of-flight mass spectrometry. Identified compounds include organic acids, nitrogen compounds, alcohols, aldehydes, and ketones. Conventional gas chromatography coupled with flame ionization detection and liquid chromatography utilizing refractive index detection were employed to quantify the identified compounds. Inorganic species in the aqueous streams were also were quantified using ion chromatography and inductively coupled plasma optical emission spectroscopy. The concentrations of organic compounds and inorganic species are reported, and the significance of these results are discussed in detail.

The use of proppants, especially larger and more dense proppants, during reservoir stimulation in tight oil and gas plays requires the introduction of highly viscous fluids to transport the proppants (mm mm) with the fracturing fluid. The highly viscous fluids required result in increased pump loads and energy costs. Furthermore, although proppant deployment with fracturing fluids is a standard practice for unconventional oil and gas stimulation operations, there are only a few examples in the US of the applying proppant technology to geothermal energy production. This is due to proppant dissolution, proppant flowback, and loss of permeability that, although also occurs during unconventional oil/gas stimulation (hydraulic fracturing) operations, it is amplified under the extreme temperatures found in enhanced geothermal systems (EGS). This work demonstrates proof-of concept of a novel, CO2-responsive, lightweight sintered-bauxite/polymer core/shell proppant. The polymer shell has two main roles; (1) increase the stability of the proppant dispersion in water without the addition of rheology modifiers, and (2) once at the fracture network react with CO2 to promote particle aggregation and prop fractures open. In this work, both roles are demonstrated together with the thermal and chemical stability of the materials showing the potential of these CO2-responsive proppants as an alternative proppant technology for geothermal and unconventional oil/gas applications.

In modeling of geological carbon storage, dissolution of supercritical CO2 (scCO(2)) is often assumed to be instantaneous with equilibrium phase partitioning. In contrast, recent core-scale imbibition experiments have shown a prolonged depletion of residual scCO(2) by dissolution, implying a non-equilibrium mechanism. In this study, eight pore-scale scCO(2) dissolution experiments in a 2D heterogeneous, sandstone-analog micromodel were conducted at supercritical conditions (9 MPa and 40 degrees C). The micromodel was first saturated with deionized (DI) water and drained by injecting scCO(2) to establish a stable scCO(2) saturation. DI water was then injected at constant flow rates after scCO(2) drainage was completed. High resolution time-lapse images of scCO(2) and water distributions were obtained during imbibition and dissolution, aided by a scCO(2) -soluble fluorescent dye introduced with scCO(2) during drainage. These images were used to estimate scCO(2) saturations and scCO(2) depletion rates. Experimental results show that (1) a time-independent, varying number of water-flow channels are created during imbibition and later dominant dissolution by the random nature of water flow at the micromodel inlet, and (2) a time-dependent number of water-flow channels are created by coupled imbibition and dissolution following completion of dominant imbibition. The number of water-flow paths, constant or transient in nature, greatly affects the overall depletion rate of scCO(2) by dissolution. The average mass fraction of dissolved CO2 (dsCO(2)) in water effluent varies from 0.38% to 2.72% of CO2 solubility, indicating non-equilibrium scCO(2) dissolution in the millimeter-scale pore network. In general, the transient depletion rate decreases as trapped, discontinuous scCO(2) bubbles and clusters within water-flow paths dissolve, then remains low with dissolution of large bypassed scCO(2) clusters at their interfaces with longitudinal water flow, and finally increases with coupled transverse water flow and enhanced dissolution of large scCO(2) clusters. The three stages of scCO(2) depletion, common to experiments with time-independent water-flow paths, are revealed by zoom-in image analysis of individual scCO(2) bubbles and clusters. The measured relative permeability of water, affected by scCO(2) dissolution and bi-modal permeability, shows a non-monotonic dependence on saturation. The results for experiments with different injection rates imply that the non-equilibrium nature of scCO(2) dissolution becomes less important when water flow is relatively low and the time scale for dissolution is large, and more pronounced when heterogeneity is strong. (C) 2016 Elsevier Ltd. All rights reserved.

The aqueous fraction generated from hydrothermal liquefaction (HTL) of algae contains approximately 20–35% of the total carbon present in the algal feed. Hence, this aqueous fraction can be utilized to produce liquid fuels and/or specialty chemicals for economic sustainability of HTL on an industrial scale. In this study, aqueous fractions produced from HTL of freshwater and saline-water algal cultures were analyzed using a wide variety of analytical instruments to determine their compositional characteristics. Organic chemical compounds present in eight aqueous fractions were identified using two-dimensional gas chromatography equipped with time-of-flight mass spectrometry. Identified compounds include organic acids, nitrogen compounds and aldehydes/ketones. Conventional gas chromatography and liquid chromatography methods were utilized to quantify the identified compounds. Inorganic species in the aqueous stream from HTL of algae also were quantified using ion chromatography and inductively coupled plasma optical emission spectroscopy. The concentrations of organic chemical compounds and inorganic species are reported. The amount quantified carbon ranged from 45 to 72% of the total carbon in the aqueous fractions.

We recently demonstrated Solvent Immersion Imprint Lithography (SIIL), a rapid benchtop microsystem prototyping technique, including polymer functionalization, imprinting and bonding. Here, we focus on the realization of planar polymer sensors using SIIL through simple solvent immersion without imprinting. We describe SIIL’s impregnation characteristics, including an inherent mechanism that not only achieves practical doping concentrations, but their unexpected 2-fold enhancement compared to the immersion solution. Subsequently, we developed and characterized optical sensors for detecting molecular O2. To this end, a substantially high dynamic range is reported, including its control through the immersion duration, a manifestation of SIIL’s modularity. Overall, SIIL exhibits the potential of improving the operating characteristics of polymer sensors, while significantly accelerating their prototyping, as it requires a few seconds of processing and no need for substrates or dedicated instrumentation. These are critical for O2 sensing as probed by way of example here, as well as any polymer permeable reactant. VC 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54,

In this study the aqueous phases resulting from the hydrothermal liquefaction (HTL) of biomass and the hydrotreatment (HT) of fast pyrolysis bio-oils were analyzed via TC, COD, GC-MS, GC-FID, HPLC, and ICP-OES to determine the organic and inorganic species present and the quantitative amounts of each. This work is necessary to address a significant knowledge gap in the literature related to the aqueous phases from thermochemical processes. Results showed that water from the hydrotreatment of eight different bio-oils contained less than 1 wt% total carbon, in many cases less than 0.2%. Negligible organic carbon was observed. HTL samples contained between 1 and 2 wt% carbon. Due to the large volume of water added to the HTL feedstock and the dilute samples generated, this accounts for 34-45% of the total carbon sent to the reactor. The majority of this carbon was present as acids, with glycolic acid and acetic acid having the highest concentrations. Alcohols, specifically methanol and ethanol, were also present. Numerous ketones were observed, consisting of mainly acetone and cyclopenta-ones. The amount of the total carbon identified and quantified in the HTL samples ranged from 64 to 82%. Inorganic species present in the HT samples were sodium, silicon, and sulfur. The highest levels of sulfur were observed in the grasses and agricultural residue (corn stover). The HTL samples exhibited much higher inorganic content, with very high levels of sodium and potassium. Alkali and alkali earth metals, as well as sulfur, were also present at levels high enough to raise concerns for the use of catalysts in downstream upgrading or reforming processes. (C) 2015 Elsevier Ltd. All rights reserved.

Pore-scale models are useful for studying relationships between fundamental processes and phenomena at larger (i.e., Darcy) scales. However, the size of domains that can be simulated with explicit pore-scale resolution is limited by computational and observational constraints. Direct numerical simulation of pore-scale flow and transport is typically performed on millimeter-scale volumes at which X-ray computed tomography (XCT), often used to characterize pore geometry, can achieve micrometer resolution. In contrast, laboratory experiments that measure continuum properties are typically performed on decimeter-scale columns. At this scale, XCT resolution is coarse (tens to hundreds of micrometers) and prohibits characterization of small pores and grains. We performed simulations of pore-scale processes over a decimeter-scale volume of natural porous media with a wide range of grain sizes, and compared to results of column experiments using the same sample. Simulations were conducted using high-performance codes executed on a supercomputer. Two approaches to XCT image segmentation were evaluated, a binary (pores and solids) segmentation and a ternary segmentation that resolved a third category (porous solids with pores smaller than the imaged resolution). We used a multiscale Stokes-Darcy simulation method to simulate the combination of Stokes flow in large open pores and Darcy-like flow in porous solid regions. Flow and transport simulations based on the binary segmentation were inconsistent with experimental observations because of overestimation of large connected pores. Simulations based on the ternary segmentation provided results that were consistent with experimental observations, demonstrating our ability to successfully model pore-scale flow over a column-scale domain.