Markus Flury

Sorption of Brilliant Blue FCF in soils as affected by pH and ionic strength

Brilliant Blue FCF has been frequently used as a dye tracer to stain flow pathways in porous media. As an ionic organic molecule, the dye interacts in a complicated manner with the solid phase. For an adequate interpretation of stained flow pathways, the sorption characteristics of the dye need to be better understood. In this study, we investigate the suitability of Brilliant Blue FCF as a dye tracer in vadose zone hydrology. The objectives were to test the effect of aqueous solution chemistry on dye absorption spectra, and to evaluate the effect of ionic strength and type of cations on dye sorption to soils. Batch sorption studies were conducted with three different soils and different ionic strengths of the background solution. Ionic strength was adjusted with either CaCl or KCl. Sorption isotherms conformed to the Langmuir model, with the sorption capacity 2 ranging over one order of magnitude. Substantial sorption was found for the soil sample with the highest clay content and the lowest pH. Increasing ionic strength led to increased sorption of Brilliant Blue FCF. The type of background cation, Ca or K, did not influence sorption. In aqueous solution, the absorption spectrum of Brilliant Blue FCF is not sensitive to pH nor ionic strength. q 2000 Elsevier Science B.V. All rights reserved.

Comparison of different methods to measure contact angles of soil colloids

We compared five different methods, static sessile drop, dynamic sessile drop, Wilhelmy plate, thin-layer wicking, and column wicking, to determine the contact angle of colloids typical for soils and sediments. The colloids (smectite, kaolinite, illite, goethite, hematite) were chosen to represent 1:1 and 2:1 layered aluminosilicate clays and sesquioxides, and were either obtained in pure form or synthesized in our laboratory. Colloids were deposited as thin films on glass slides, and then used for contact angle measurements using three different test liquids (water, formamide, diiodomethane). The colloidal films could be categorized into three types: (1) films without pores and with polar-liquid interactions (smectite), (2) films with pores and with polar-liquid interactions (kaolinite, illite, goethite), and (3) films without pores and no polar-liquid interactions (hematite). The static and dynamic sessile drop methods yielded the most consistent contact angles. For porous films, the contact angles decreased with time, and we consider the initial contact angle to be the most accurate. The differences in contact angles among the different methods were large and varied considerably: the most consistent contact angles were obtained for kaolinite with water, and illite with diiodomethane (contact angles were within 3 degrees); but mostly the differences ranged from 10 degrees to 40 degrees among the different methods. The thin-layer and column wicking methods were the least consistent methods.

Fate and Transport of Viruses in Porous Media

Microbiological contaminants (e.g., bacteria, protozoa, and viruses) pose one of the greatest risks in water resources. About 70% of the waterborne microbial illness outbreaks in the United States has been associated with groundwater. Although viruses are not the only pathogens known to contaminate groundwater, they are much smaller in size than bacteria or protozoan cysts and are not filtered out to the same extent in the porous soil matrix. Knowledge of the factors that influence the fate and transport of viruses in soil and aquifers is critical to making accurate determinations of groundwater vulnerability and to developing regulations that are protective of public health. In this paper, we review the current state of knowledge on fate and transport of viruses in porous media which include (i) mechanisms and modeling of virus sorption, (ii) virus survival and factors affecting virus inactivation in the natural environment, and (iii) mechanisms of virus transport in porous media and available modeling approaches. Because viruses are surrounded by a protein capsid and are expected to behave similarly to proteins, an overview on the mechanisms of protein sorption and denaturation is also provided. Factors such as solution chemistry, virus properties, soil properties, temperature, association with solid particles, and water content have been found to influence virus sorption, survival, and transport in porous media. A review of protein literature provides some insights as to what mechanism might be involved in virus sorption that have so far not been studied. Some needs for future research are suggested.

Dependence of pesticide degradation on sorption: nonequilibrium model and application to soil reactors

Abstract The effect of sorption on degradation of the pesticide 2,4-dichlorophenoxyacetic acid (2,4-D) was studied in a soil amended with various amounts of activated carbon (AC). The relationship between sorption and decay of 2,4-D was analyzed using analytical solutions for equilibrium sorption and to a two-site nonequilibrium adsorption model coupled with two first-order degradation terms for the dissolved and sorbed pesticide, respectively. The sorption parameters in the latter model were determined based on data obtained from batch sorption experiments, while those for degradation were obtained from incubation experiments. The adsorption coefficients, ranging from 0.811 to >315 ml g −1 , increased at higher AC, and were negatively related to degradation as measured by the first-order rate constant, implying that degradation is faster from the liquid phase than from the sorbed phase. A nonlinear fit of the decay curves to the nonequilibrium model revealed that degradation rate constants were 0.157 and 0.00243 day −1 for the liquid and sorbed phases, respectively, differing by a factor of 65. Similar results were also obtained using the equilibrium model. A parameter sensitivity analysis of the nonequilibrium model indicates that nonequilibrium sorption will initially favor degradation; however, over the long term, will decrease degradation when desorption kinetics becomes the limiting factor in the degradation process. In the presence of a lag phase that allows appreciable amounts of chemical to diffuse into kinetic sorption sites, nonequilibrium sorption will only impede degradation.

Longitudinal and lateral dispersion in an unsaturated field soil

Lateral and longitudinal dispersion was quantified in a field soil under water-unsaturated conditions. The relatively mobile dye tracer Brilliant Blue FCF was applied as a line source and leached into the soil at two different rates of infiltration, 4 and 24 mm d−1, respectively. The resulting tracer plume was photographically recorded at vertical soil profiles excavated perpendicularly to the line source after ∼50, 100, and 200 mm of cumulative infiltration. An image analysis technique was used to determine two-dimensional concentration distributions from the photographs. Average horizontal and vertical concentration distributions were analyzed using the two-dimensional advection-dispersipn equation. Model parameters were fitted to optimize the agreement between measured and modeled averaged concentration profiles in both horizontal as well as vertical directions. Dispersivities showed a dependency on flow rates and amount of cumulative infiltration, but this dependency appeared to be related to the degree of irregularities of observed flow patterns. Large dispersivities were associated with higher degree of irregularities in the flow patterns and vice versa. Layer boundaries played a significant role for redirecting flow when flow rates were high and cumulative infiltration was large. This study demonstrates (1) that more than just the vertical concentration profiles are needed to define the transport regime under unsaturated conditions, and (2) that even subtle layer boundaries affect the lateral mixing regime and exert a marked influence on the transport in the main flow direction.

ALTERATION OF KAOLINITE TO CANCRINITE AND SODALITE BY SIMULATED HANFORD TANK WASTE AND ITS IMPACT ON CESIUM RETENTION

Caustic nuclear wastes have leaked from tanks at the US Department of Energy’s Hanford site in Washington State (USA) causing hundreds of thousands of gallons of waste fluids to migrate into the underlying sediments. In this study, four simulant tank waste (STW) solutions, which are high in NaOH (1.4 and 2.8 mol/kg), NaNO3 (3.7 mol/kg) and NaAlO2 (0.125 and 0.25 mol/kg), were prepared and reacted with reference kaolinite KGa-1 and KGa-2 at 50 and 80°C for up to 2 months. The structure and morphology of the resulting products were characterized using X-ray diffraction, scanning electron microscopy, and Fourier transform infrared spectroscopy. The products were also examined for cation exchange and Cs+ sorption as a function of ionic strength and types of cations in the background solutions. Cancrinite and sodalite were the only new minerals observed in all of the conditions tested in this experiment. Two major chemical processes were involved in the reactions: dissolution of kaolinite and precipitation of cancrinite and sodalite. Increasing NaOH concentration and temperature, and decreasing NaAlO2 concentration increased the transformation rate. Both cancrinite and sodalite appeared stable thermodynamically under the experimental conditions. The newly formed feldspathoids were vulnerable to acid attack and pronounced dissolution occurred at pH below 5.5. Cancrinite and sodalite can incorporate NaNO3 ion pairs in their cages or channels. Sodium in cancrinite and sodalite was readily exchangeable by K+, but less easily by Cs+ or Ca2+. The feldspathoid products sorb nearly an order of magnitude more Cs+ than the unaltered kaolinite. The Cs adsorption is reduced by competing cations in the background solutions. At low ionic strength (0.01 M NaNO3 or 0.005 M Ca(NO3)2), Ca2+ was more competitive than Na+. When the concentration of the background solution was increased 10 times, Na+ was more competitive than Ca2+.

Effects of pH, ionic strength, dissolved organic matter, and flow rate on the co-transport of MS2 bacteriophages with kaolinite in gravel aquifer media.

Viruses are often associated with colloids in wastewater and could be transported with colloids into groundwater from land disposal of human and animal effluent and sludge, causing contamination of groundwater. To investigate the role of colloids in the transport of viruses in groundwater, experiments were conducted using a 2m long column packed with heterogeneous gravel aquifer media. Bacteriophage MS2 was used as the model virus and kaolinite as the model colloid. Experimental data were analyzed using Temporal Moment Analysis and Filtration Theory. In the absence of kaolinite colloid, MS2 phage traveled slightly faster than the conservative tracer bromide (Br), with little differences observed between unfiltered and filtered MS2 phage (0.22 microm as the operational cut-off for colloid-free virus). In the presence of kaolinite colloids, MS2 phage breakthrough occurred concurrently with that of the colloidal particles and the time taken to reach the peak virus concentration was reduced, suggesting a colloid-facilitated virus transport in terms of peak-concentration time and velocity. Meanwhile mass recovery and magnitude of concentrations of the phages were significantly reduced, indicating colloid-assisted virus attenuation in terms of concentrations and mass. Decreasing the pH or increasing the ionic strength increased the level of virus attachment to the aquifer media and colloids, and virus transport became more retarded, resulting in lower peak-concentration, lower mass recovery, longer peak-concentration time, and greater apparent collision efficiency. Increasing the concentration of dissolved organic matter (DOM) or flow rate resulted in faster virus transport velocity, higher peak-concentrations and mass recoveries, and lower apparent collision efficiencies. The dual-role of colloids in transport viruses has important implications for risk analysis and remediation of virus-contaminated sites.

Impact of flow rate, water content, and capillary forces on in situ colloid mobilization during infiltration in unsaturated sediments

Received 12 September 2007; revised 17 January 2008; accepted 25 February 2008; published 17 June 2008. [1] We studied in situ colloid mobilization under transient flow conditions using columns repacked with Hanford sediments. Rainfall infiltration was experimentally simulated using different flow rates and initial moisture conditions. Five series of column experiments were performed with initial infiltration rates of 0.018, 0.036, 0.072, 0.144, and 0.288 cm/min, and the columns reached water saturations in the range of 53 to 81%. The infiltration of water into the columns provided unfavorable conditions for colloid attachment to the sediments. Colloids were eluted by the infiltrating water with the peak colloid concentrations in the outflow coinciding with the arrival of the infiltration front. A larger flow rate led to a greater amount of colloids released from the column. The cumulative amount of colloids released was proportional to the column water content established after steady state flow rates were achieved. We used the advection-dispersion equation with a first-order colloid release reaction to analyze the experimental data. The colloid release rate coefficient increased with the increase of water content. We calculated forces exerted on colloids, and found that electrostatic and van der Waals interactions, calculated based on the DLVO (Derjaguin-Landau-Verwey-Overbeek) theory, and hydrodynamic forces, were all less important than capillary forces in controlling colloid release. In one experiment, the ionic strength of the infiltration solution was increased, such that colloid attachment was favorable. Nonetheless, colloids were mobilized and eluted with the infiltration front, implying that non-DLVO forces, such as capillary forces, played a prominent role in colloid mobilization.

Reduction of transpiration through foliar application of chitosan

In this study, we investigate the potential of chitosan, a natural beta-1-4-linked glucosamine polymer, to reduce plant transpiration. Chitosan was applied foliarly to pepper plants and water use was monitored. Peppers were grown in pots in growth-chambers, where transpiration was measured by weighing pots. In an accompanying field study, water use was determined by monitoring soil moisture depletion with time domain reflectometry. An automated irrigation system replenished the water used each day. Plant biomass and yield were determined to calculate biomass-to-water ratios. Differences in canopy resistance between control and chitosan treated plants were analyzed with the aid of the Penman‐Monteith equation. Scanning electron microscopy (SEM) and histochemical analyses demonstrated that chitosan induced closure of the plant’s stomata, resulting in decreased transpiration. Foliar application of chitosan reduced water use of pepper plants by 26‐43% while maintaining biomass production and yield. We suggest that chitosan might be an effective antitranspirant to conserve water use in agriculture.

Detachment of colloids from a solid surface by a moving air-water interface.

Colloid attachment to liquid-gas interfaces is an important process used in industrial applications to separate suspended colloids from the fluid phase. Moving gas bubbles can also be used to remove colloidal dust from surfaces. Similarly, moving liquid-gas interfaces lead to colloid mobilization in the natural subsurface environment, such as in soils and sediments. The objective of this study was to quantify the effect of moving air-water interfaces on the detachment of colloids deposited on an air-dried glass surface, as a function of colloidal properties and interface velocity. We selected four types of polystyrene colloids (positive and negative surface charge, hydrophilic and hydrophobic). The colloids were deposited on clean microscope glass slides using a flow-through deposition chamber. Air-water interfaces were passed over the colloid-deposited glass slides, and we varied the number of passages and the interface velocity. The amounts of colloids deposited on the glass slides were visualized using confocal laser scanning microscopy and quantified by image analysis. Our results showed that colloids attached under unfavorable conditions were removed in significantly greater amounts than those attached under favorable conditions. Hydrophobic colloids were detached more than hydrophilic colloids. The effect of the air-water interface on colloid removal was most pronounced for the first two passages of the air-water interface. Subsequent passages of air-water interfaces over the colloid-deposited glass slides did not cause significant additional colloid removal. Increasing interface velocity led to decreased colloid removal. The force balances, calculated from theory, supported the experimental findings, and highlight the dominance of detachment forces (surface tension forces) over the attachment forces (DLVO forces).