Characterization of flow transport within pore spaces of an open-work gravel bed

Analysis of the flow dynamics within the near-bed and sub-surface regions of river bed sediment is critical in understanding fluid exchange and related chemical transfer/reactions. The knowledge in above is limited as these regions are difficult to measure using traditional instrumentation methods. In this paper, we tried the use of Magnetic Resonance Imaging (MRI) technique to non-invasively image flow dynamics of simulated river bed. We developed a bespoke MRI-compatible open-channel flume in order to acquire real-time flow images from within the MRI bore and used contrast agent (Gd-DTPA) as a tracer through an immobile, porous gravel bed. Single MR Image slices along the flume length were obtained for analysis. The flow tracer images from within the sediment bed are calibrated from the output data in order to provide fully quantitative maps of tracer concentration at regular time intervals. These ‘white-box’ (i.e. data from within the porous bed) tracer profiles were evaluated with the CXTFIT computer package to estimate the transport parameters. The intention was both, to illustrate the appropriateness of MRI for flow-sediment research and to analyse the relationship between tracer dispersion and gravel framework structure

MODELIRANJE TRANSPORTA OTOPINE U NISKOPROPUSNOME, HOMOGENOME I ZASIĆENOME TLU

Fickian and non-Fickian behaviors were often detected for contaminant transport activity owed to the preferential flow and heterogeneity of soil media. Therefore, using diverse methods to measure such composite solute transport in soil media has become an important research topic for solute transport modeling in soil media. In this article, the continuous-time random walk (CTRW) model was applied to illustrate the relative concentration of transport in low-permeability homogeneous and saturated soil media. The solute transport development was also demonstrated with the convection-dispersion equation (CDE) and Two Region Model (TRM) for comparison. CXTFIT 2.1 software was used for CDE and TRM, and CTRW Matlab Toolbox v.3.1 for the CTRW simulation of the breakthrough curve. It was found that higher values of determination coefficient (R2) and lower values of root mean square error (RMSE) concerning the best fits of CDE, TRM, and CTRW. It was found that in the comparison of CDE, TRM, and CTRW, we tend to use CTRW to describe the transport behavior well because there are prevailing Fickian and non-Fickian transport. The CTRW gives better fitting results to the breakthrough curves (BTCs) when β has an increasing pattern towards 2.00. In this study, the variation of parameters in three methods was investigated and results showed that the CTRW modeling approach is more effective to determine non-reactive contaminants concentration in low-permeability soil media at small depths.Fickovo i nefickovo ponašanje često se opaža kod prijenosa gdje postoji preferencijski tok i heterogenost tla (medija) kroz koji se događa protok. Stoga je uporaba različitih metoda mjerenja prijenosa otopina u takvim medijima važno područje istraživanja. Ovdje je prikazan model kontinuiranoga i vremenski slučajnoga gibanja (engl. skr. CTRW) kako bi se opisala relativna koncentracija tijekom prijenosa kroz niskopropustan, homogen i zasićen medij. To je demonstrirano konvekcijsko-disperzijskom jednadžbom (engl. skr. CDE) te dvočlanim modelom (engl. skr. TRM) i njihovom usporedbom. Programskim paketom CXTFIT 2.1 opisani su CDE i TRM, a paketom CTRW Matlab Toolbox v.3.1 model CTRW. Uočeno je kako veće vrijednosti koeficijenta determinacije (R2) te manje srednje kvadratne pogrješke (engl. skr. RMSE) najbolje opisuju podudaranje između CDE-a, TRM-a i CTRW-a. Usporedbom tih triju vrijednosti odabran je CTRW za opis ponašanja prijenosa, kako Fickova, tako i nefickova. CTRW se bolje podudara s krivuljama protoka (engl. skr. BTC), gdje β raste prema vrijednosti 2. Istražena je i promjena parametara u svim trima metodama, što je ponovno istaknulo CTRW kao najprimjereniji model u određivanju koncentracije nereaktivnih čestica u slabopropusnome tlu na malim dubinama

Designing a Permeable Reactive Barrier for the Remediation of Copper Contaminated Groundwater.

This project details the design of a sorption based pilot-scale permeable reactive barrier (PRB) for the removal of copper from groundwater. The reactive material for the barrier is the residual of coagulants used in drinking water treatment operations. Physical and chemical properties of these water treatment residuals (WTR) have been studied to optimize PRB design. Batch reactor tests have shown that equilibrium sorption of copper can be fit to a Langmuir type isotherm. Kinetic and column experiments have been conducted to understand the significance of chemical and physical mass transfer limitations. A leaching test indicated the concentrations of hazardous elements leached from the residuals do not exceed specified limits. Permeameter tests were performed with various mixtures of the WTR and an inert support material (pea gravel) to determine the ideal mix for matching the hydraulic conductivity of the field site. Additional work has been conducted at the site to determine groundwater flow direction, pore water velocity, and contaminant concentration for designing the optimal dimensions and placement of the PRB

Carbon Quantum Dots with Tracer-like Breakthrough Ability for Reservoir Characterisation

Predictions have shown that our demand for oil and gas will continue to grow in the next decade, and future supply will become more reliant on tertiary recovery and from nonconventional resources. However, current reservoir characterization methodologies, such as well logs, cross-well electromagnetic imaging and seismic methods, have their individual limitations on detection range and resolution. Here we propose a pioneering way to use carbon quantum dots (CQDs) as nanoparticle tracers, which can be transported through a reservoir functioning as conventional tracers, while acting as sensors to obtain useful information. These hydrothermally produced CQDs from Xylose possess excellent stability in high ionic strength solutions, durable absorbance and fluorescence ability due to multi high-polarity functional group on their surfaces. Consistency between our on-line ultraviolet–visible (UV–Vis) spectroscopy and off-line Confocal laser scanning microscopy (CLSM) measurements confirms that CQDs have the tracer-like migration capability in glass beads-packed columns and sandstone cores, regardless of particle concentration and ionic strength. However, their migration ability is undermined in the column packed with crushed calcite grains with positive charge. We also demonstrate that quantitative oil saturation detection in unknown sandstone core samples can be achieved by such CQDs based on its breakthrough properties influenced by the presence of oil phase

Mercury Mobilization from Contaminated Creek Bank Soils and Stabilization using Engineered Sorbents

As a global environmental pollutant, mercury (Hg), threatens our water resources and presents a substantial risk to human health. The goal of this research project was to evaluate the immobilization of Hg on sorbents to reduce ambient Hg concentrations in water leaching from contaminated East Fork Poplar Creek (EFPC) (Oak Ridge, TN, USA) soils. Using flow-through columns, we determined the potential of different kinds of engineered sorbents (i.e., ThiolSAMMS®, biochar, SediMiteTM, OrganoclayTM PM199) to reduce mercury fluxes from contaminated EFPC soils. The effectiveness of the sorbents in this experiment was determined based on the rate of Hg sorbed and the percentage of Hg removed as compared with the amount of Hg applied; i.e., a mass balance. All the sorbents removed Hg to a certain extent, but none of the sorbents was able to remove 100% of the Hg to which they were exposed. From all the evaluated sorbents, ThiolSAMMS® showed the highest percentage of Hg removed (~87%). A non-reactive Br- [bromide] tracer experiment was conducted to determine the hydraulic properties of the sorbent columns and to ensure that no flow along the walls or preferential flow occurred. Br- was also applied to qualitatively determine how quickly Hg breaks through the sorbent columns, most of the sorbents had a Hg breakthrough within the first 3 pore volume (PV). ThiolSAMMS® was the only sorbent to have retardation on the Hg breakthrough (7 and 70 PV). To determine mechanisms for the Hg uptake by the sorbents, we conducted a set of analyses to identify changes in concentrations of chemical constituents entering and exiting the sorbent columns. We noticed no difference in pH, anions (Cl [chloride], SO4 [sulfate], NO3 [nitrate]) or metals (Al [aluminum], Fe [iron], Mn [manganese] and Si [silica]). We also observed that the concentrations of dissolved organic carbon (DOC) were statistically different for biochar and OrganoclayTM PM199. Specific UV absorbance (SUVA) showed statistically significant differences for biochar. The differences in DOC and SUVA were minimal, overall, suggesting that the mechanism for Hg uptake remains unknown

Biological Manganese Oxidation by Pseudomonas putida in Trickling Filters

Manganese (Mn) is considered a nuisance chemical in drinking water. Manganese causes problems with staining, foul odor, undesirable tastes, and can be corrosive to pipelines. The United States Environmental Protection Agency (US EPA) recommends a secondary maximum contaminant level for Mn below a concentration of 0.05 mg/L. Currently manganese contaminated water is typically treated using expensive and potentially harmful oxidizing agents. Biological treatment techniques have been researched as a viable alternative for removing undesired chemicals from drinking water. In this study, bench scale trickling filters were constructed to compare the Mn removal efficiency between biochemical and abiotic processes. Glass beads between three and five millimeters in diameter were used as the solid media in the trickling filters with and without inoculation of a Mn oxidizing bacterium, Pseudomonas putida. Manganese oxidation and removal was found to be significantly greater in trickling filters with Pseudomonas putida biofilms after startup times of only 48 hours. Mn oxidation in Pseudomonas putida inoculated trickling filters was up to 75% greater than non-inoculated filters. One dimensional advection dispersive models were formulated to describe the transport of Mn in trickling filter porous media. Using the data collected in the experiments, the model predicted that that an average of 10 mg/L of influent Mn (II) concentration can be decreased by 78.56% with a filter depth of only 10 cm. The rapid startup time and the high Mn removal capacity of trickling filters inoculated with Pseudomonas putida can potentially become a mainstream treatment system in conjunction with sand filters

Transport of explosive residue surrogates in saturated porous media

Contamination of soils by munitions constituents is pervasive on Department of Defense operational ranges. Low-order detonations result in the heterogeneous distribution of explosives residues (ER) at shallow depths. At a limited number of ranges ER contamination of groundwater has been observed. Previous studies have shown that the downward migration of colloid-sized contaminants can significantly impact groundwater quality. The goal of this study was to investigate if colloid transport plays a role in the migration of ER contaminants. Our primary objective was to determine the transport potential of fine (\u3c5\u3eum) ER particles under ideal conditions for colloid transport. A secondary objective was to develop a direct detection method for the identification and quantitative analysis of particulate ER. A series of saturated transport experiments were conducted in columns (2x20 cm) packed with clean sand. 2,6- Dinitrotoluene was used as a surrogate for explosives chemicals. Experiments were conducted with both particulate and dissolved-phase DNT. Bromide and microspheres tracers were also used to characterize nonreactive transport. Particulate tracers were applied to the columns, either suspended in the influent solution, or directly to the top layer of sand, in order to more realistically replicate field conditions. Experimental results indicate that DNT movement through the columns occurred as a combination of solid and dissolved phase transport. Concentration differences between unfiltered and filtered samples indicate that particulate DNT accounted up to 30% of the total mass recovered in the effluent

The role of biosolids-derived dissolved organic matter on the interaction of selected endocrine-disrupting chemicals with two alluvial soils

Overpopulation is one of the major causes of many environmental problems we experience today. With increasing population, the demand for quality food and clean water is becoming difficult to realize. Although with advancement in technology, we are still able to cope with the demand, but eventually we will exhaust the supply for quality food and clean water as well as the different methods of achieving them. Quality food and clean water are necessities to live. To help in delivering these needs, federal regulations and policies were developed and implemented to protect the public from environmental contaminants that might be hazardous to human health. Contaminants such as organic compounds are ubiquitous in the environment because they are component of most goods that the public use on a daily basis. When these organic compounds are released into the environment they could undergo different processes such volatilization, microbial degradation, photodegradation, movement by run-off, adsorbed and held strongly in the soil, or move with the soil-water. When a hazardous organic compound is strongly held in the soil, it is possible that it will be taken-up by crops for human consumption or as feedstock. Organic compounds that are mobile in the water may also be taken-up by aquatic species, will bioaccumulate, or leach to the groundwater contaminating the source of the drinking water. A group of compounds found to disrupt the endocrine systems that brought a great concern to the scientific community was observed three decades ago. These compounds are collectively referred to as endocrine disrupting chemicals (EDC) and sometimes endocrine active compounds (EAC). Since then, various research studies have been conducted to potentially cover all aspects of EDCs. To establish the presence, and the spatial and temporal distribution of EDCs, monitoring studies of surface and even groundwater were often conducted. The effect of EDCs to wildlife, such as the feminization of frogs and fishes, and the potential health problems to humans were also intense research areas that involves EDCs. To determine the overall environmental risk of EDCs, the fate and transport of these compounds need to be evaluated as well. The fate and transport studies will explore the movement of these compounds in soil, water, and air. Also, how the physical and chemical properties of these compounds changes as they interact with other chemicals, microorganisms, and other components of the soil-water systems, such as the native dissolved organic matter (soil) and the exogenous dissolved organic matter (biosolids-derived). EDCs maybe released from residential, industrial, and agricultural sources. In wastewater treatment plant, the EDCs and other contaminants may not be completely removed during the treatment process and ends up in the biosolids and effluents. To recycle the carbon and the plant nutrients such as nitrogen and phosphorus, the biosolids are applied in agricultural fields and the effluents are used as irrigation water in relatively dry regions. The fate and transport study of EDCs is not well-explored. Since there are a lot of chemicals that are manufactured and released daily, and a lot of variability in the systems condition (ex. temperature, moisture, and pH) that impact the fate and transport of the EDCs, generating more data will definitely help in establishing more reliable results. Adsorption and column transport experiments are some of the processes used to predict the fate and transport of EDCs. In this study, three endocrine disrupting chemicals (EDCs), bisphenol-A (BPA), 17α-ethinylestradiol (EE2), and 4-nonylphenol (4-NP), were chosen because of their varying physico-chemical properties. Among the three compounds, BPA is the least hydrophobic and 4-NP is the most hydrophobic. We are hoping that these compounds can be used as model compounds to study the potential environmental risk of other organic pollutants with similar physico-chemical properties that are released in soil-water system. The impact on the transport of EDCs were also investigated in systems where the native dissolved organic matter and exogenous biosolids-derived dissolved organic matter (BDOM) were present. The concentrations of BPA, EE2, and 4-NP were monitored for six months at two wastewater treatment plants in Iowa and at their corresponding upstream and downstream discharge locations. The monitoring was conducted to assess if the three EDCs of interest were actually present in the wastewater effluent and water system. Results showed that BPA, EE2, and 4-NP were detectable in the water samples, although the frequency of detection was variable throughout the six months. The result also showed that the concentrations detected were below the method detection limit (MDL), and suggested that the analytical method adopted for the monitoring studies of environmental concentrations of organic contaminants were an important consideration in conducting this type of analysis. Soil materials are complicated matrices by themselves and in combination with water and biosolids-derived dissolved organic matter, the system becomes even more complex. Also, studying the interactions and fates of the three EDCs simultaneously in soil-water-BDOM systems is challenging, and therefore simplified systems, i.e., working with individual EDCs and interaction with individual system component (BDOM-carbon to soil, EDCs to soil adsorption-desorption, EDC to BDOM adsorption) was employed in this study. The two soils used are Hanlon and Zook soil samples. The two soil samples have contrasting properties. Of the two soils, the Zook soil sample has higher total organic carbon, total organic nitrogen, and higher clay content. The biosolids-derived dissolved organic matter that was extracted from the anaerobically digested biosolids from the Ames Wastewater Pollution Control Facility was characterized and was dominated by N-acetylated carbohydrates and aromatic components. Adsorption of BDOM to the two soils revealed the predicted maximum adsorption capacity and intensity was 188 mg C kg-1 soil and 0.015 L kg-1 soil, respectively for Hanlon soil sample and 640 mg C kg-1 soil and 0.015 L kg-1 soil, respectively for the Zook soil sample. Although the Zook soil sample had a higher maximum adsorption capacity, the intensity of adsorption for both soils was low and of the same magnitude, which suggests that the BDOM-carbon is likely to be mobile in saturated conditions. Some components of the BDOM-carbon were adsorbed to the soil samples, and fractionation of the BDOM-carbon revealed that hydrophobic acid (HoA), hydrophobic neutral (HoN), and hydrophilic base (HiB) structural fractions dominated the adsorption. Some adsorption mechanisms proposed were cation bridging, hydrophobic partitioning, and electrostatic attraction. The parameters determined to predict the behavior of the EDCs adsorbed to the two soil samples were described by the Freundlich-Langmuir model. This model allowed us to calculate the n parameter or the index of heterogeneity of sorption energy. The difference between the n values limits our ability to compare sorption capacities of the two soils. For example, for EE2, the n values calculated were 0.73 and 1.93 for the Hanlon and Zook soils samples, respectively. Among the three EDCs, the 4-NP had the highest adsorption maximum capacity (Qmax) and adsorption affinity constant (KLF) predicted based on the combined Langmuir-Freundlich model for both soil samples. Between the two soil samples, the Zook soil sample had a maximum adsorption capacity about 50 times higher and an adsorption affinity about ten times higher than the Hanlon soil samples. The EE2 had a higher adsorption affinity than the BPA, but the BPA had a higher maximum adsorption capacity than EE2. The BPA exhibited about the same magnitude of adsorption capacity and adsorption affinity for both soil samples. 4-NP, the most hydrophobic EDC, had the highest adsorption capacity and affinity, while the least hydrophobic BPA had the lowest adsorption affinity. The extent of binding between the EDC and the BDOM is important because it predicts the EDC-BDOM complex formation. The formation of a complex between the EDC and BDOM helps in understanding the role of the BDOM in transport, e.g., enhancing or deterring the movement of EDCs in the soil-water system. The results showed that BPA is strongly associated with the BDOM fraction, while EE2 and 4-NP did not form a strong association with the BDOM. Considering the other adsorption results from the concurrent study, we hypothesized that the BDOM will carry with it the BPA as it moves in the soil water, while the EE2 and 4-NP will most likely interact with the soil materials. To test the hypothesis of the influence of BDOM on the transport of BPA, a packed soil column experiment was conducted using the Hanlon and Zook soil samples. There were two concentration levels of BDOM used: 10 mg C L-1 and 40 mg C L-1. The BDOM was mixed with the BPA first before passing it through the soil column. The results showed that, contrary to the hypothesis that the BDOM would enhance the transport of BPA, the presence of exogenous BDOM enhanced the retention of the BPA in both soil samples. The data generated from this research project will be a valuable source of information for future studies of organic pollutants with similar physico-chemical properties. The result could also serve as a basis to improve the federal and state policy and regulatory frameworks pertaining to the direct discharge of organic chemicals from residential and industrial areas, land application of biosolids, and the re-use of effluent as irrigation water. The monitoring study showed detection of the three EDCs but the frequency of detection varied at each month of sampling. The result of monitoring could be used as a baseline data when in the future, the focus of monitoring study is on the different seasons of sampling (temporal variability). Estrogens and BPA were detected at polluting levels in groundwater (Focazio et al., 2008; Adeel et al., 2017). One process to reclaim the groundwater is soil aquifer treatment (Mansell et al., 2003). The results generated from this study could be used to improve the efficiency of the treatment process because the removal mechanisms is most likely influenced by hydrophobic or hydrophilic characteristic of the carbon structural fraction of the adsorbent used (Mansell et al., 2003). Also, we can improve the technology in wastewater treatment processes to eliminate most of the EDCs before they are released. Part of the waste treatment process is the use of soil as component of the bedding material that adsorbs the organic contaminants. The adsorption intensity, adsorption capacity, and retardation parameter values could therefore be a used to improve the adsorptive capability of the bedding materials used

A land application treatment strategy for landfill leachate and water reclamation

The objective of this study is to evaluate the potential of removing organic carbon and inorganic nitrogen contaminants, and metals from the leachate prior to any land application. New guidelines are needed to ensure the environment and our health is not put at risk. The cost of installation, operation and maintenance are for many communities a critical factor. It is our goal to incorporate into the process a number of potential savings as well as revenue streams that could mitigate the overall cost. The municipal solid waste has changed dramatically since 1950 with the introduction of plastics and industrial chemicals into the mainstream consumable products. The issue with these plastics and organic chemicals is their resistance to biodegradation and their impact on the environment and potential risk to human health. An estimated 100,000 landfills both closed and in operation existed prior to 1970 without any barrier beneath the solid waste to restrict the flow of water from entering the soil structure. The United States Geological Survey (USGS) has determined the groundwater beneath landfills are contaminated with leachate organic carbon contaminants e.g., aromatic hydrocarbons, phthalates, polycyclic aromatic hydrocarbons, pesticides, benzene, phenol, and household chemicals. The average amount of leachate collected each year is 60 billion gallons. with 50% hauled by trucks to a sewage treatment plant (STP) and co-treated with the residential wastewater. The USGS has determined both the STP liquid discharge and biosolids contain a significant amount of the leachate organic carbon contaminants and metals. The United States Environmental Protection Agency continuously reviews possible inclusion of a number of contaminants of emerging concern (CECs) into the National Pollution Discharge Elimination System (NPDES) that regulates the discharges from any wastewater treatment plant that discharges into a surface water such as rivers and creeks. Persistent long-term droughts have impacted not just the western United States, but also many countries worldwide. The impact is so dramatic that the focus on wastewater has shifted from treatment to reclamation. In order to replenish the aquifers, the quality of the treated wastewater needs to be higher to ensure the aquifers are not adversely contaminated with these organic and metal contaminants. The current status of landfill leachate treatment has reduced some of the organic carbon contaminants and no reduction in metals. Without installing changes that address these issues, it is safe to say that the land application of landfill leachate would put the groundwater and health at a significant risk. A series of batch reactors were set up to study the impact of 3-different native soils, 3-different leachate organic carbon contaminant concentrations, and exposure time to investigate their effects on phenanthrene degradation rate constant, based on a 1st -order reaction. Using an initial phenanthrene concentration, 20 ug/L, in 3-leachate treatment conditions, 0-, 200-, 2000-mg COD/L, in 3-native soils, creek, forest, tilled farm, resulted in a mean phenanthrene degradation rate constant: 0.051 day-1 + 0.007, 0.036 day-1 + 0.004, 0.017 day-1 + 0.001, respectively. The degradation rate constant kcreek decreased by 22% and 75%, kforest decreased by 43% and 90%, and ktilled decreased by 32% and 62% with increase of organic carbon concentration from 200 mg COD/L to 2,000 mg COD/L, respectively. The analysis of bulk soil showed the mean water and low organic carbon contaminant leachate treatments in the 3-native soils removed 20.7% +4.2% and 15.2% +5.9% of the 50 ug phenanthrene after 120 hr., respectively. The analysis of the planted soil showed the mean water and low organic carbon contaminant leachate treatments in the 3-native soils removed 38.9% + 8.8% and 25.7% + 4.2% of the 50 ug phenanthrene after 120 hr., respectively. The mean water treatment in the 3-native planted soils, creek, forest, and tilled removed 46.6% +3.9%, 42.1% + 2.8%, 28.1% +5.8% of the 50 ug phenanthrene after 120 hr., respectively. Overall, the 3-native soils demonstrated differences in phenanthrene degradation rates, and the leachate organic carbon contaminant reduced the phenanthrene degradation between 22% and 90%. The outcome demonstrates the need to reduce the organic carbon contaminant concentration significantly prior to a land application to reduce the needed surface area and increase the application rate