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Abstract The environmental impacts and unsustainability of fossil fuel-based heating and cooling systems has encouraged a worldwide interest in developing sustainable sources of energy and complementary technologies for heating/cooling purposes. One of these technologies is ground source heat pump (GSHP) systems that use the ubiquitous low-enthalpy ground source heat found in the shallow subsurface and represents a sustainable way of heating and cooling homes and buildings. GSHPs can be used to extract or inject subsurface heat by installing boreholes that circulate an antifreeze-based carrier fluid which is cooled or heated through the subsurface. Although GSHPs have many advantages, they might develop subsurface thermal plumes, which can affect the efficiency and sustainability of the system and other subsurface infrastructures. In the present research, the effect of a multi-borehole vertical GSHP system designed to deliver annual heating and cooling to an office building located in three Canadian cities was examined. This was done using a three-dimensional model, developed in FEFLOW, that simulated a hypothetical GSHP system in all three cities. It was found that the city with the highest thermal load resulted in the biggest subsurface thermal plume showing a direct connection between building thermal load and thermal plumes. Cyclical simulations for 10 years showed that the plumes grew in both size and temperature disturbance after the 10-year operation. The developed model can be used to determine the thermal affected zone of a GSHP system to aid in planning of other subsurface infrastructures in that zone. Highlights • The thermal affected zone differs significantly with building heating/cooling load. • The thermal affected zone grow in both size and temperature disturbance after 10 years. • Imbalanced loads cause the plume to stay trapped inside the borefield. [ABSTRACT FROM AUTHOR]

Monoaromatic hydrocarbons such as benzene, toluene, ethylbenzene, and o, m, and p-xylenes (BTEX) are high-risk pollutants because of their mutagenic and carcinogenic nature. These pollutants are found with elevated levels in groundwater and soil in Canada at several contaminated sites. The intrinsic microbes present in the subsurface have the potential to degrade pollutants by their metabolic pathways and convert them to non-toxic products. However, the low subsurface temperature (5–10 °C) limits their growth and degradation ability. This study examined the feasibility of subsurface heat augmentation using geothermal heating for BTEX bioremediation. Novel potent BTEX-degrading bacterial strains were isolated from soil at 3.0, 42.6, and 73.2 m depths collected from a geothermal borehole during installation and screened using an enrichment technique. The selected strains were identified with Sanger sequencing and phylogenetic tree analysis, revealing that all the strains except Bacillus subtilis are novel with respective to BTEX degradation. The isolates, Microbacterium esteraromaticum and Bacillus infantis showed the highest degradation with 67.98 and 65.2% for benzene, 72.8 and 71.02% for toluene, 77.52 and 76.44% for ethylbenzene, and 74.58 and 74.04% for xylenes respectively. Further, temperature influence at 15 ± 1 °C, 28 ± 1 °C and 40 ± 1 °C was observed, which showed increased growth by two-fold and on average 35–49% more biodegradation at higher temperatures. Results showed that temperature is a positive stimulant for bioremediation, hence geothermal heating could also be a stimulant for in-situ bioremediation. [Display omitted] • Monoaromatic hydrocarbons such as BTEX are high-risk pollutants. • The isolates, M. esteraromaticum and B. infantis showed the highest degradation. • Bacterial growth and BTEX degradation increased with elevated temperature. • Heat generated from geothermal heating could be useful to enhance bioremediation. [ABSTRACT FROM AUTHOR]

Nano-scale zero valent iron (nZVI) has been used at a number of contaminated sites over the last decade. At most of these sites, significant decreases in contaminant concentrations have resulted from the application of nZVI. However, limited work has been completed investigating nZVI field-scale mobility. In this study, a field test was combined with numerical modeling to examine nZVI reactivity along with transport properties in variably saturated soils. The field test consisted of 142 L of carboxymethyle cellulose (CMC) stabilized monometallic nZVI synthesized onsite and injected into a variably saturated zone. Periodic groundwater samples were collected from the injection well, as well as, from two monitoring wells to analyze for chlorinated solvents and other geochemistry indicators. This study showed that CMC stabilized monometallic nZVI was able to decrease tricholorethene (TCE) concentrations in groundwater by more than 99% from the historical TCE concentrations. A three dimensional, three phase, finite difference numerical simulator, (CompSim) was used to further investigate nZVI and polymer transport at the variably saturated site. The model was able to accurately predict the field observed head data without parameter fitting. In addition, the numerical simulator estimated the mass of nZVI delivered to the saturated and unsaturated zones and distinguished the nZVI phase (i.e. aqueous or attached). The simulation results showed that the injected slurry migrated radially outward from the injection well, and therefore nZVI transport was governed by injection velocity and viscosity of the injected solution. A suite of sensitivity analyses was performed to investigate the impact of different injection scenarios (e.g. different volume and injection rate) on nZVI migration. Simulation results showed that injection of a higher nZVI volume delivered more iron particles at a given distance; however, the travel distance was not proportional to the increase in volume. Moreover, simulation results showed that using a 1D transport equation to simulate nZVI migration in the subsurface may overestimate the travel distance. This is because the 1D transport equation assumes a constant velocity while pore water velocity radially decreases from the well during injection. This study suggests that on-site synthesized nZVI particles are mobile in the subsurface and that a numerical simulator can be a valuable tool for optimal design of nZVI field applications. [ABSTRACT FROM AUTHOR]

The occurrence of subsurface buoyant flow during thermal remediation was investigated using a two dimensional electro-thermal model (ETM). The model incorporated electrical current flow associated with electrical resistance heating, energy and mass transport, and density dependent water flow. The model was used to examine the effects of heating on sixteen subsurface scenarios with different applied groundwater fluxes and soil permeabilities. The results were analyzed in terms of the ratio of Rayleigh to thermal Peclet numbers (the buoyancy ratio). It was found that when the buoyancy number was greater than unity and the soil permeability greater than 10 − 12 m 2 , buoyant flow and contaminant transport were significant. The effects of low permeability layers and electrode placement on heat and mass transport were also investigated. Heating under a clay layer led to flow stagnation zones resulting in the accumulation of contaminant mass and transport into the low permeability layer. The results of this study can be used to develop dimensionless number-based guidelines for site management during subsurface thermal activities. [ABSTRACT FROM AUTHOR]

Abstract: During thermal remediation the increase in subsurface temperature can lead to bubble formation and mobilization. In order to investigate the effect of gas formation on resulting aqueous concentrations, a 2D finite difference flow and mass transport model was developed which incorporates a macroscopic invasion percolation (MIP) model to simulate bubble expansion and movement. The model was used to simulate three soil scenarios with different permeabilities and entry pressures at various operating temperatures and groundwater velocities. It was observed that discrete bubble formation occurred in all three soils, upward mobility being limited by lower temperatures and higher entry pressures. Bubble mobilization resulted in a different aqueous mass distribution than if no discrete gas formation was modeled, especially at higher temperatures. This was a result of bubbles moving upwards to cooler areas, then collapsing, and contaminating previously clean zones. The cooling effect also led to possible non-aqueous phase liquid (NAPL) formation which was not predicted using a model without discrete bubble formation. [Copyright &y& Elsevier]

• Combinations of selected selenoprotein and redox related genes are significantly associated with markers of lipid metabolism. • Multimarkers analysis shows no or minor single SNP effects on markers of lipid metabolism and oxidative stress. • Allele combination analysis is more informative in identifying functional relationships between genotype and phenotype. Selenium (Se) and selenoproteins have been shown to be involved in lipid metabolism mainly due to their ability to modulate redox homeostasis in adipose tissue. The underlying mechanisms are yet to be evaluated. In the light of few data related to the association between polymorphic variants of selenoprotein encoding genes and metabolic syndrome or obesity in humans, the role of selenoprotein polymorphisms in lipid metabolism remains unclear. The aim of this study was to investigate the impact of allelic combination within selenoprotein and redox related genes on the markers of lipid metabolism and oxidative stress. The study comprised 441 healthy individuals from Poland, in the 18−74 year age group. Allelic combinations were investigated within the polymorphic variants of four selenoprotein encoding genes (GPX1 rs1050450, GPX4 rs713041, SELENOP rs3877899 and SELENOF rs5859) and the redox related gene (SOD2 rs4880). The impact of the most common allelic GPX1-GPX4-SELENOP-SELENOF-SOD2 combinations was assessed on the following markers: triglycerides (TG), total cholesterol (TC), high density lipoprotein cholesterol (HDL-C), low density lipoprotein cholesterol (LDL-C), glutathione peroxidase activities (GPX1, GPX3), lipid peroxidation (as TBARS), ceruloplasmin (Cp) and superoxide dismutase 1 (SOD1). Multivariable analysis revealed significant associations between three allelic combinations and markers of lipid metabolism, including HDL-C and TC/HDL-C ratio (AAAAa), LDL-C (aaAaa), and triglycerides (aaaaA), whereas two allelic combinations (aAaAA, aaaAA) were associated with GPX3 activity. This study confirms the possible implication of selenoproteins in lipid metabolism and warrants further research on specific allele combinations within selenoprotein and redox related genes in order to identify functional genetic combinations linked to metabolic phenotype. [ABSTRACT FROM AUTHOR]

There has been a worldwide interest in renewable energy technologies, as a means of decreasing reliance on fossil fuels, minimizing climate change effects, and reducing greenhouse emissions. One such technology is geothermal heating where the constant subsurface temperature is used to cool or heat building interiors via heat pumps. In Canada, the use of geothermal heating has become a popular option for heating and cooling buildings, and it is anticipated that, in the near term, most large buildings will include geothermal heating as part of their climate control strategy. However, little is known about the environmental impacts of geothermal heating on the subsurface environment. The present review will examine the effect of geothermal heating on groundwater flow and remediation efforts, whereby the heat generated by geothermal systems may help with urban pollution. "Geothermal Remediation" could leverage the subsurface heating resulting from geothermal systems to accelerate biodegradation of certain petroleum-based pollutants at brown-field sites, while providing building(s) with sustainable heating and cooling. This idea coincides with the rising momentum towards sustainable and green remediation in Europe and the United States. To ensure that Geothermal Remediation is achievable, the effect of heat on bioremediation needs to be examined. This review provides an insight into what we know about heat effects on bioremediation activities and subsurface transport. [Display omitted] • Geothermal heat pumps (GHPs) are used for heating and cooling of building via heat pumps. • GHPs could be used as the heat source for bioremediation, called Geothermal Remediation. • Considered to be eco-friendly as it links bioremediation with a clean and renewable energy storage system. • Injected heat increases microbial activity and alters the properties of pollutants, increasing the degradation rates. • Advantages and disadvantages of Geothermal Remediation are outlined. GHPs could be used as the heat source for bioremediation, called Geothermal Remediation which can enhance microbial activity and alter the properties of pollutants making them more bioavailable for bioremediation in a sustainable way. [ABSTRACT FROM AUTHOR]

Abstract: Since the late 1990s, the use of nano zero valent iron (nZVI) for groundwater remediation has been investigated for its potential to reduce subsurface contaminants such as PCBs, chlorinated solvents, and heavy metals. nZVI shows tremendous promise in the environmental sector due to its high reactivity and as such, numerous laboratory and field studies have been performed to assess its effectiveness. This paper reviews the current knowledge of nZVI/bimetallic technology as it pertains to subsurface remediation of chlorinated solvents and heavy metals. The manuscript provides background on the technology, summarizing nZVI reactions with chlorinated solvents and metals, and examines the factors affecting nZVI reactivity. Studies on subsurface transport of bare and coated nZVI particles are also reviewed and challenges with field implementation are discussed. This manuscript offers a comprehensive review of nZVI technology and highlights the work still needed to optimize it for subsurface remediation. [Copyright &y& Elsevier]

The use of a deep geological repository (DGR) for the long-term disposal of used nuclear fuel is an approach currently being investigated by several agencies worldwide, including Canada's Nuclear Waste Management Organization (NWMO). Within the DGR, used nuclear fuel will be placed in copper-coated steel containers and surrounded by a bentonite clay buffer. While copper is generally thermodynamically stable, corrosion can occur due to the presence of sulphide under anaerobic conditions. As such, understanding transport of sulphide through the engineered barrier system to the used fuel container is an important consideration in DGR design. In this study, a three-dimensional (3D) model of sulphide transport in a DGR was developed. The numerical model is implemented using COMSOL Multiphysics, a commercial finite element software package. Previous sulphide transport models of the NWMO repository used a simplified one-dimensional system. This work illustrates the importance of 3D modelling to capture non-uniform effects, as results showed locations of maximum sulphide flux are 1.7 times higher than the average flux to the used fuel container. [ABSTRACT FROM AUTHOR]

Bentonite clay is a key part of the engineered barrier system of the deep geological repositories (DGRs), designed by many nuclear nations worldwide to safely house the used nuclear fuel. However, the copper coated used fuel containers (UFCs) may undergo corrosion due to bisulfide (HS−) transport through the bentonite towards the containers. Understanding the sorption behaviour of HS− is therefore critical in understanding the HS− transport dynamics and in assessing the long-term safety of the DGR. As such, this study investigated HS− sorption onto bentonite, through laboratory batch experiments and microscopic/spectroscopic analyses, under the influence of various experimental conditions, such as contact time (1–120 h), temperature (10–40 °C), liquid to solid mass ratios (L:S) (100–1000), initial HS− concentration (1–6 mg L−1). The study results indicated that HS− sorption onto bentonite occurred faster and the equilibrium sorption capacity increased (by 3%) with increasing temperature (from 10 °C to 40 °C). Several established kinetic and isotherm models were applied to the experimental data to provide insight into the key processes driving HS− sorption onto bentonite. The desorption test results indicated that HS− was irreversibly sorbed on bentonite. The surface analyses of the bentonite test samples were conducted using scanning electron microscopy along with energy dispersive spectroscopy. These results suggested that the sorption might have occurred due to chemical reactions of HS− with the iron present in bentonite and subsequent formation of iron monosulfide (FeS). The findings of this study provided critical information to better understand the underlying sorption mechanism of HS− on bentonite, which can reduce HS− transport in the DGR. [Display omitted] • HS− sorption onto bentonite was fast and increased with increasing temperature. • The pseudo second order model best described HS− sorption kinetics. • HS− sorbed irreversibly on bentonite under the conditions investigated. • SEM/EDS results show that HS− likely reacted with Fe in bentonite and formed FeS. [ABSTRACT FROM AUTHOR]