Warren Stiver

Biodegradation of Diesel Fuel in Soil Under Various Nitrogen Addition Regimes

Bioremediation is a growing technology for treating fuel-contaminated soils. Many biological, physical, and chemical parameters control the rate and efficiency of this process, including type and concentration of contaminants, temperature, oxygen content, and nutrient status. This study investigated the effect that nitrogen sources and concentrations had on the degradation rate of diesel fuel in nutrient limited soil at two carbon-to-nitrogen ratios. The different sources of nitrogen studied were ammonium nitrate, ammonium sulfate, potassium nitrate, urea, and urea oligomers (control release fertilizer). Laboratory experiments were conducted on field-contaminated soil using sealed bioreactors at a controlled temperature of 25°C. For both carbon-to-nitrogen ratios tested, hydrocarbon degradation rates were the highest for the ammonium sulfate (20:1 at 0.032 d−1; 40:1 at 0.019d−1) and urea treatments (20:1 at 0.025 d−1; 40:1 at0.011 d−1). A degradation rate correlation as a function of nitrate and ammonia concentrations was developed. The correlation suggests the occurrence of nitrate inhibition at elevated nitrate concentrations.

Measurement of solubilities in supercritical fluids using a piezoelectric quartz crystal

Abstract Solubility data is essential for any application of supercritical fluids. A new technique has been developed using a piezoelectric quartz crystal to measure solubilities. A small mass of solute is deposited on the crystal and solubility is measured by observing the crystal’s frequency change as this solute dissolves in the supercritical fluid. The technique is ideally suited to solutes which exhibit low solubilities. Solubility measurements of bis(acetylacetonato)copper(II) (Cu(acac) 2 ) in supercritical carbon dioxide were in good agreement with existing literature values. New solubility data were also measured for bis(thenoyltrifluoroacetonato)copper(II) (Cu(tta) 2 ).

Passive volatilization behaviour of gasoline in unsaturated soils

Abstract Gasoline behaviour in the unsaturated zone is difficult to predict as a number of soil factors, gasoline properties and environmental conditions will determine the eventual fate of a spill. These factors include the diffusive and convective processes that contribute to passive volatilization. To gain a better insight into passive volatilization and how it can impact the clean-up of a contaminated site, batch column experiments were completed. Three soils were tested at varying initial gasoline contents, water contents, and at room and sub-zero temperatures. The results indicate that immiscible phase movement to the surface is a significant contributor to passive volatilization. However, the immiscible phase movement ceases once the gasoline content has dropped below a threshold level. The driving force necessary for immiscible phase movement is maintained by gasoline precipitation at the soil surface. Higher soil water contents inhibited the volatilization of gasoline as water impacted both the diffusive and wicking movement of the gasoline. Sub-zero temperatures reduced volatilization and extended the time to cessation of wicking behaviour.

Retention capacities of immiscible chemicals in unsaturated soils

Retention capacities were measured in the laboratory for n-hexane and tetrachloroethylene (PCE) in three soils at varying soil water contents. Two experimental techniques were used; 1) saturation/drainage experiments where the soil columns were saturated with the chemical and allowed to drain freely for 24 h, and 2) spill simulations where a known amount of chemical was spilled on the surface of the soil column and allowed to infiltrate for one hour. Results show that the retention capacities on a volume basis were independent of chemical type. However, the retention capacities did decrease with decreasing porosity and increasing soil water content. The decrease of retention capacity with respect to soil water content was significant, with the decreases ranging from 38% to 94%. The implication of this decrease is rapid chemical penetration into the subsurface. Retention capacities obtained from spill simulations were consistently lower than those obtained by the saturation/drainage experiments due to hysteresis.

Supercritical carbon dioxide-soil partition coefficients

Abstract Supercritical carbon dioxide-soil partition coefficients have been measured for naphthalene, phenanthrene, 1,2,3-trichlorobenzene, 1,2,4,5-tetrachlorobenzene, and pentachlorobenzene in loamy sand and silt loam. The partition coefficients, which ranged from 1.7 to 3.9 gsoil/gCO2 at 35 °C and 10.7 MPa, appear to be dependent on soil and chemical properties.

Passive Volatilization of Gasoline from Soil

Abstract Gasoline spills were simulated in the laboratory with three air‐dried soils, using a synthetic gasoline and unsaturated soil to quantify passive volatilization over a period of up to 16 d. The total and individual gasoline components were monitored as a function of time and depth in the soil. The time required to deplete the overall gasoline concentration in the soil to 40% of the initial concentration ranged from 0.25 to 10 d for the three soils. Sand was the fastest, followed by loamy sand and silt loam. The volatilization rate of gasoline from soil was found to be dependent on soil, chemical type, and depth. Observation of individual components indicated that a wicking mechanism contributed to the gasoline flux toward the surface.

The Infiltration and Movement of Immiscible Chemicals in Unsaturated Soil

Organic chemical spills pose a threat to air, soil, surface water and groundwater quality. As such, prompt remedial action is required to minimize the environmental impact. While the principles behind the infiltration of a spilled chemical are understood, there is a paucity of data for parameter estimation for specific compounds and soil conditions. Laboratory simulations have been conducted with hexane and PCE in prepared soil columns to address this need. Both infiltration times and liquid front movement were measured as was the influence of soil type and soil water content on the spill behaviour. Infiltration times for both chemicals into a given soil were similar. The chemicals infiltrated fastest into the more permeable soil. The liquid front movement in air dry soils followed a log-log relationship with time that is similar to the Green and Ampt model. Increasing soil water content had a significant effect on both the infiltration times and liquid front movement: the infiltration times increased, wh...

A hydrodynamic model of a continuous supercritical fluid extraction system for the treatment of oil contaminated solids

ABSTRACT Supercritical fluid extraction (SFE) has the potential to recover compounds from a range of solid matrices if a fully continuous process can be commercialized. This paper presents the development of a hydrodynamic model for a continuous pilot scale SFE process, involving countercurrent flow of a slurry and a supercritical fluid. The model developed is based on first principles and focuses on predicting pressure and slurry level within the extraction vessel. The model was validated using pilot scale system data. Using adjusted parameters, the model accurately predicted steady state pressure and provided a good estimate of slurry level.