New Insights into Calcite Dissolution Mechanisms under Water, Proton, or Carbonic Acid-Dominated Conditions.

Carbonate minerals are ubiquitous in nature, and their dissolution impacts many environmentally relevant processes including preferential flow during geological carbon sequestration, pH buffering with climate-change induced ocean acidification, and organic carbon bioavailability in melting permafrost. In this study, we advance the atomic level understanding of calcite dissolution mechanisms to improve our ability to predict this complex process. We performed high pressure and temperature (1300 psi and 50 °C) batch experiments to measure transient dissolution of freshly cleaved calcite under HO, H, and HCO-dominated conditions, without and with an inhibitory anionic surfactant present.

Tuning the Selectivity of Nitrate Reduction via Fine Composition Control of RuPdNP Catalysts.

Herein, aqueous nitrate (NO ) reduction is used to explore composition-selectivity relationships of randomly alloyed ruthenium-palladium nanoparticle catalysts to provide insights into the factors affecting selectivity during this and other industrially relevant catalytic reactions. NO reduction proceeds through nitrite (NO ) and then nitric oxide (NO), before diverging to form either dinitrogen (N) or ammonium (NH ) as final products, with N preferred in potable water treatment but NH preferred for nitrogen recovery. It is shown that the NO and NO starting feedstocks favor NH formation using Ru-rich catalysts, while Pd-rich catalysts favor N formation.

Impact of organic matter on transformation during thermal remediation of pyrene-contaminated substrates.

Thermal remediation (TR) is a broadly applicable technology that is effective at removing volatile and semi-volatile contaminants from soil. However, TR can be costly and inefficient in practice, with underlying removal and transformation mechanisms poorly understood. To better understand the role organic matter plays in removal, a series of experiments was performed with a humic substance, humic modified silica, and a natural soil in the presence of pyrene from 100 to 500 °C and compared to prior experiments using pure minerals.

Modeling EDTA-facilitated cadmium migration in high- and low-permeability systems using MODFLOW and RT3D.

Cadmium (Cd) has impacted groundwater resources and can pose a serious threat to human health and the environment. Its fate in groundwater is complex and challenging to predict, as it is affected by adsorption to sediments, complexation with aqueous phase ligands, and variations in hydraulic conductivity. In this study, a 2D reactive transport model based on MODFLOW and RT3D is used to simulate published experimental results of cadmium migration without and with EDTA present in a flow cell containing high- and low-permeability zones (i.

Kinetics of Hydroxyl Radical Production from Oxygenation of Reduced Iron Minerals and Their Reactivity with Trichloroethene: Effects of Iron Amounts, Iron Species, and Sulfate Reducing Bacteria.

Reactive oxygen species generated during the oxygenation of different ferrous species have been documented at groundwater field sites, but their effect on pollutant destruction remains an open question. To address this knowledge gap, a kinetic model was developed to probe mechanisms of •OH production and reactivity with trichloroethene (TCE) and competing species in the presence of reduced iron minerals (RIM) and oxygen in batch experiments. RIM slurries were formed by combining different amounts of Fe(II) and sulfide (with Fe(II):S ratios from 1:1 to 50:1) or Fe(II) and sulfate with sulfate reducing bacteria (SRB) added.

Fate of pyrene on mineral surfaces during thermal remediation as a function of temperature.

There is evidence that contaminants can transform at the elevated temperatures of thermal remediation; however, the contribution of redox active minerals to transformation has not been investigated. Three redox active minerals (, birnessite (MnO), magnetite (FeO), and hematite (FeO)) and one redox inactive mineral (Ottawa sand (SiO)) were spiked with pyrene and thermally treated. Under dry, anoxic conditions, 100%, 75% ± 3%, 70% ± 15%, and 14% ± 28% of the initial pyrene mass was removed with birnessite, magnetite, hematite, and Ottawa sand, respectively, after treatment at 250 °C for 30 min.

Contamination Assessment and Site-Management Tool (CAST): A Browser-Based Tool for Site Assessment.

Groundwater dependency is increasing globally, while millions of potentially contaminated sites are yet to be characterized for contamination levels. In particular, groundwater contamination due to light nonaqueous phase liquids (LNAPLs) continues to be a global challenge. Mathematical approaches (i.

Abiotic dechlorination in the presence of ferrous minerals.

Laboratory batch experiments were performed to assess the reduction of trichloroethene (TCE) and oxygen via natural ferrous minerals. TCE reduction under anoxic conditions was measured via the generation of reduced gases, while oxygen reduction via the generation of hydroxyl radicals was measured as a surrogate for potential TCE oxidation. Results showed that TCE reduction under anoxic conditions was observed for ankerite, siderite, and illite, but not for biotite; acetylene was the primary identified dechlorination product.

Impact of antibiotic concentration gradients on nitrate reduction and antibiotic resistance in a microfluidic gradient chamber.

In order to explore the impact of antibiotics on the bacterial metabolic cycling of nitrate within contaminated soil and groundwater environments, we compared the effects of polymyxin B (PMB) and ciprofloxacin (CIP) concentration gradients on the distribution and activity of a wild type (WT) and a flagella deficient mutant (Δflag) of Shewanella oneidensis MR-1 in a microfluidic gradient chamber (MGC). Complementary batch experiments were performed to measure bacteriostatic versus bactericidal concentrations of the two antibiotics, as well as their effect on nitrate reduction. Prior work demonstrated that PMB disrupts cell membranes while CIP inhibits DNA synthesis.

The role of chemotaxis and efflux pumps on nitrate reduction in the toxic regions of a ciprofloxacin concentration gradient.

Spatial concentration gradients of antibiotics are prevalent in the natural environment. Yet, the microbial response in these heterogeneous systems remains poorly understood. We used a microfluidic reactor to create an artificial microscopic ecosystem that generates diffusive gradients of solutes across interconnected microenvironments.

Using MODFLOW and RT3D to simulate diffusion and reaction without discretizing low permeability zones.

Low permeability zones (LPZs) are major sources of groundwater contamination after active remediation to remove pollutants in adjacent high permeability zones (HPZs). Slow back diffusion from LPZs to HPZs can extend management of polluted sites by decades. Numerical models are often used to simulate back diffusion, estimate cleanup times, and develop site management strategies.

Towards predicting DNAPL source zone formation to improve plume assessment: Using robust laboratory and numerical experiments to evaluate the relevance of retention curve characteristics.

We conducted multiple laboratory trials in a robust and repeatable experimental layout to study dense non-aqueous phase liquid (DNAPL) source zone formation. We extended an image processing and analysis framework to derive DNAPL saturation distributions from reflective optical imaging data, with volume balance deviations < 5.07%.

Adaptive Evolution of to Ciprofloxacin in Controlled Stress Environments: Contrasting Patterns of Resistance in Spatially Varying versus Uniformly Mixed Concentration Conditions.

A microfluidic gradient chamber (MGC) and a homogeneous batch culturing system were used to evaluate whether spatial concentration gradients of the antibiotic ciprofloxacin allow development of greater antibiotic resistance in strain 307 ( 307) compared to exclusively temporal concentration gradients, as indicated in an earlier study. A linear spatial gradient of ciprofloxacin and Luria-Bertani broth (LB) medium was established and maintained by diffusion over 5 days across a well array in the MGC, with relative concentrations along the gradient of 1.7-7.

Physiology, Metabolism, and Fossilization of Hot-Spring Filamentous Microbial Mats.

The evolutionarily ancient Aquificales bacterium spp. dominates filamentous microbial mat communities in shallow, fast-flowing, and dysoxic hot-spring drainage systems around the world. In the present study, field observations of these fettuccini-like microbial mats at Mammoth Hot Springs in Yellowstone National Park are integrated with geology, geochemistry, hydrology, microscopy, and multi-omic molecular biology analyses.

Contributions of biotic and abiotic pathways to anaerobic trichloroethene transformation in low permeability source zones.

Low permeability source zones sustain long-term trichloroethene (TCE) groundwater contamination. In anaerobic environments, TCE is transformed by both biological reductive dechlorination and abiotic reactions with reactive minerals. Little is known about the relative contribution of these two pathways as TCE diffuses from low permeability zones (LPZs) into high permeability zones (HPZs).

Diffusion-Based Recycling of Flavins Allows Shewanella oneidensis MR-1 To Yield Energy from Metal Reduction Across Physical Separations.

We fabricated a microfluidic reactor with a nanoporous barrier to characterize electron transport between Shewanella oneidensis MR-1 and the metal oxide birnessite across a physical separation. Real-time quantification of electron flux across this barrier by strains with different electron transfer capabilities revealed that this bacterium exports flavins to its surroundings when faced with no direct physical access to an electron acceptor, allowing it to reduce metals at distances exceeding 60 μm. An energy balance indicates that flavins must be recycled for S.

Motility of Shewanella oneidensis MR-1 Allows for Nitrate Reduction in the Toxic Region of a Ciprofloxacin Concentration Gradient in a Microfluidic Reactor.

Subsurface environments often contain mixtures of contaminants in which the microbial degradation of one pollutant may be inhibited by the toxicity of another. Agricultural settings exemplify these complex environments, where antimicrobial leachates may inhibit nitrate bioreduction, and are the motivation to address this fundamental ecological response. In this study, a microfluidic reactor was fabricated to create diffusion-controlled concentration gradients of nitrate and ciprofloxacin under anoxic conditions in order to evaluate the ability of Shewanella oneidenisis MR-1 to reduce the former in the presence of the latter.

Mechanisms for Abiotic Dechlorination of Trichloroethene by Ferrous Minerals under Oxic and Anoxic Conditions in Natural Sediments.

Bench-scale experiments were performed on natural sediments to assess abiotic dechlorination of trichloroethene (TCE) under both aerobic and anaerobic conditions. In the absence of oxygen (<26 μM), TCE dechlorination proceeded via a reductive pathway generating acetylene and/or ethene. Reductive dechlorination rate constants up to 3.

Geobiology reveals how human kidney stones dissolve in vivo.

More than 10% of the global human population is now afflicted with kidney stones, which are commonly associated with other significant health problems including diabetes, hypertension and obesity. Nearly 70% of these stones are primarily composed of calcium oxalate, a mineral previously assumed to be effectively insoluble within the kidney. This has limited currently available treatment options to painful passage and/or invasive surgical procedures.

Critical Review: DNA Aptasensors, Are They Ready for Monitoring Organic Pollutants in Natural and Treated Water Sources?

There is a growing need to monitor anthropogenic organic contaminants detected in water sources. DNA aptamers are synthetic single-stranded oligonucleotides, selected to bind to target contaminants with favorable selectivity and sensitivity. These aptamers can be functionalized and are used with a variety of sensing platforms to develop sensors, or aptasensors.

Intracellular versus extracellular accumulation of Hexavalent chromium reduction products by Geobacter sulfurreducens PCA.

Hexavalent chromium (Cr(VI)) reduction by Geobacter sulfurreducens PCA was evaluated in batch experiments, and the form and amounts of intracellular and extra-cellular Cr(VI) reduction products were determined over time. The first-order Cr(VI) reduction rate per unit mass of cells was consistent for different initial cell concentrations, and approximately equal to (2.065 ± 0.

Abiotic dechlorination of chlorinated ethenes in natural clayey soils: Impacts of mineralogy and temperature.

Laboratory batch experiments were performed to assess the impacts of temperature and mineralogy on the abiotic dechlorination of tetrachloroethene (PCE) or trichloroethene (TCE) due to the presence of ferrous minerals in natural aquifer clayey soils under anaerobic conditions. A combination of x-ray diffraction (XRD), magnetic susceptibility, and ferrous mineral content were used to characterize each of the 3 natural soils tested in this study, and dechlorination at temperatures ranging from 20 to 55°C were examined. Results showed that abiotic dechlorination occurred in all 3 soils examined, yielding reduced gas abiotic dechlorination products acetylene, butane, ethene, and/or propane.

Nanowires of Geobacter sulfurreducens Require Redox Cofactors to Reduce Metals in Pore Spaces Too Small for Cell Passage.

Members of the Geobacteraceae family are ubiquitous metal reducers that utilize conductive "nanowires" to reduce Mn(IV) and Fe(III) oxides in anaerobic sediments. However, it is not currently known if and to what extent the Mn(IV) and Fe(III) oxides in soil grains and low permeability sediments that are sequestered in pore spaces too small for cell passage can be reduced by long-range extracellular electron transport via Geobacter nanowires, and what mechanisms control this reduction. We developed a microfluidic reactor that physically separates Geobacter sulfurreducens from the Mn(IV) mineral birnessite by a 1.

Real rock-microfluidic flow cell: A test bed for real-time in situ analysis of flow, transport, and reaction in a subsurface reactive transport environment.

Physical, chemical, and biological interactions between groundwater and sedimentary rock directly control the fundamental subsurface properties such as porosity, permeability, and flow. This is true for a variety of subsurface scenarios, ranging from shallow groundwater aquifers to deeply buried hydrocarbon reservoirs. Microfluidic flow cells are now commonly being used to study these processes at the pore scale in simplified pore structures meant to mimic subsurface reservoirs.

Ligand Design for Isomer-Selective Oxorhenium(V) Complex Synthesis.

Recently, N,N-trans Re(O)(L)X (L = monoanionic N-O chelates; X = Cl or Br prior to being replaced by solvents or alkoxides) complexes have been found to be superior to the corresponding N,N-cis isomers in the catalytic reduction of perchlorate via oxygen atom transfer. However, reported methods for Re(O)(L)X synthesis often yield only the N,N-cis complex or a mixture of trans and cis isomers. This study reports a geometry-inspired ligand design rationale that selectively yields N,N-trans Re(O)(L)Cl complexes.