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Hydrilla (Hydrilla verticillata Royle) is an exotic aquatic angiosperm which has become a problematic weed throughout the southern United States. Infestation by aquatic weeds like hydrilla increase loss of valuable water through evapotranspiration, choke waterways used for transportation, depress real estate values, and may present health hazards. Control strategies including herbicide treatment and mechanical harvesting have proven costly and of short term benefit. One reason for this is the vegetative dormant buds which allow the plant to overwinter and reestablish rapidly after attempts at control. This research focuses on elucidation of the bud formation process in hydrilla to provide the basis for development of a control strategy which combines use of herbicides with disruption of bud formation and hence the capacity for regrowth. The environmental and hormonal control of vegetative dormant bud formation was studied in the laboratory using algal-free cultures of hydrilla. Bud formation is stimulated by a photoperiod of less than 12 hours. This environmental stimulus appears to be sensed by the phytochrome system and hormonally induced by abscisic acid. Field sampling at Lake Conroe, Texas, confirmed, where possible, laboratory results and indicated that artificially prolonged photoperiods prevent bud formation. Ethylene, both in laboratory and greenhouse cultures, significantly reduced bud formation at a dose rate of 0.1 mg/l every two days. Coumarin significantly reduced bud formation when applied at 10('-6) M but information in the literature indicates that the mode of action of coumarin may be induced ethylene formation in the plant (Morgan and Cowell, 1970). Growth characteristics of hydrilla make it suitable for use in a bioassay for the assessment of the relative phytotoxicity of aquatic pollutants. Algae-free cultures of hydrilla were grown in the laboratory in 10% Hoagland's medium. Evaluation of chemical toxicity was obtained starting from two different life stages of the plant: dormant buds and apical fragments. Dormant bud production was also monitored in order to evaluate the potential for life cycle and chronic studies. Hydrilla appeared more sensitive to ammonium carbamate than were duckweeds and more sensitive to phenol than was a unicellular green alga. Growth rate was not quantitatively related to toxicant concentration, but yield, dormant bud sprouting, and dormant bud production were related. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of school.) UMI

A series of soil column tests and field experiments were designed to evaluate microbial removal of trace organics during rapid infiltration recharge of ground water. Field experiments demonstrated that operation of rapid infiltration systems using either primary or secondary wastewater can contribute trace organics to associated ground waters although concentrations of individual compounds can be reduced by the treatment process. Most of the removal occurred in the upper meter of the soil. Soil column tests demonstrated that trace organic removal from either primary or secondary wastewater was minimal when non-acclimated soil was conditioned by continuous flooding to eliminate adsorption as a removal mechanism. Batch tests indicated that most of the removal occurred in the wastewater prior to infiltration. Conversely, column tests using acclimated soil from an operational system demonstrated good removal of trace organics. Increased concentrations of target compounds in the feed did not always result in corresponding increases in the column effluent. Microbial adaptation was evident for some compounds. Other compounds appeared to exhibit a minimum concentration below which biodegradation did not proceed. Microbial activity was confirmed as a fate mechanism for several target compounds using radiolabels. In direct correlation with field results, the induction of anaerobiosis in the soil columns resulted in increased fractional breakthrough of trace organics.

A ground water humic material has been isolated using XAD-8 adsorption chromatography (Thurman and Malcolm, 1981). Partitioning studies for DDT, hexachlorobenzene (HCB), and bis(2-ethylhexyl)phthalate (BEHP) and soil column studies for HCB and anthracene have been completed. Partition coefficients for DDT, HCB and BEHP are 10('5.99), 10('4.64) and 10('3.66), respectively. A linear relationship between log solubility (mole fraction) and log partition coefficient (Kp) exists where: log Kp = -0.91 log S (mole fraction) -3.34 (R = 0.9984). These values are in agreement with those determined for soil sediments for compounds whose water solubilities are in the range of 1 (mu)g-l('-1), but are lower by an order of magnitude for compounds whose water solubilities are on the order of 500 (mu)g-l('-1) (Karickhoff, 1979). The classical contaminant retardation equation was modified to account for mediated transport by dissolved organic carbon (DOC). Soil column experiments exhibited mediated transport of HCB and anthracene by the humic material and provided strong evidence that the compounds move as an irreversible humic/organic complex. The implications and magnitude of this mediation of organic transport by ground water humics is discussed. The existence of such a complex may account for the enhanced migration of certain trace level organics in ground water.

To prevent the deterioration of groundwater quality, mathematical simulation models have been formulated to predict the transport of contaminants in complex aquifer systems and to design remedial schemes for the problems. Existing analytical and numerical approaches have serious disadvantages for large-scale nonhomogeneous field problems where well-pumping or injection is involved. The major difficulties relate to numerical dispersion and oscillations in highly advective-dominated simulations, computational accuracy, excessive computer expense, grid orientation problems, and an inability for simulating with random conductivity fields. Recent work by Ewing, Russell, and Wheeler (1983) has produced a very efficient and accurate method for miscible displacement in oil reservoirs. Their concept was adapted and then applied to groundwater contaminant transport problems in this thesis. The highly efficient code combines a mixed finite element procedure for groundwater flow and a modified method of characteristics and finite element procedure (MMOC) for the parabolic transport equation. The preconditioned conjugate gradient method was used to solve the resulting matrices for both equations. The method has been compared with two analytical solutions on a homogeneous domain. Excellent agreements were demonstrated through relative concentration contours and breakthrough curves. The method has also been compared with the currently popular USGS Solute Transport model. More accurate resolutions were achieved for the MMOC method than for the USGS Solute Transport model. In addition, much larger time steps were allowed in the MMOC method than the USGS Solute Transport model obtaining similar resolutions. The method has been applied to highly advective-dominated problems on a CRAY-XMP supercomputer and the results showed there are no dispersion or oscillation problems common in many existing numerical codes. The method has also been used to simulate cases with random hydraulic conductivity fields that were simulated from Turning Bands Method. Fingering phenomena developed because the concentration front is transported more rapidly in the zones of higher hydraulic conductivity. The method has been shown to be superior in many respects to currently used models in groundwater transport, especially in the presence of strong pumping or injection centers or heterogeneities in the flow field.

The ability of the subsurface microbial population to degrade the major organic contaminants at three sites was assessed. The three sites included an abandoned wood creosoting facility in Conroe, Texas where the silty sand aquifer was contaminated primarily with polynuclear aromatic hydrocarbons; a sandy aquifer in Traverse City, Michigan where a spill of jet fuel polluted the ground water with benzene, toluene, and xylenes; and a site on the Texas Gulf Coast in which the fine sand aquifer was contaminated with benzene, toluene, naphthalene, and bis(2-chloroethyl) ether. Representative subsurface cores and ground water samples were collected for each site and used in the experiments to characterize the microbial population, to determine their ability to degrade the organic contaminants particular to the site, and to ascertain the factors limiting biodegradation of the contaminants at these sites. Laboratory experiments on the Conroe site revealed that the microbial population found in the contaminated zone could degrade the pollutants, but the microorganisms were not acclimated in the uncontaminated areas. The limiting factor at this site was the supply of dissolved oxygen. Field tests and modeling simulations confirmed these results. At the Traverse City site, few organisms were found that could degrade the test compounds in the uncontaminated zone. The microorganisms from the uncontaminated site could not respond as rapidly to a natural substrate as organisms in the contaminated zone which suggests their metabolic status was altered by the contamination. Oxygen, not inorganic nutrients, limited biodegradation at this site although anaerobic degradation of the contaminants may also occur. At the third site, the organisms in the uncontaminated zone were active against benzene, toluene, and to a lesser degree, naphthalene. In the contaminated zone, a toxicant may have reduced the amount of biodegradation occurring. This project demonstrated that microorganisms in the contaminated zones of two sites were active against the contaminants, but were limited in their ability to degrade these contaminants by the supply of dissolved oxygen. At the third site, a toxicant appeared to control biodegradation.

The prevention of scale is an important chemical process in many commercial applications, such as water purification, electricity generation, and chemical production. Scale prevention is especially important in the area of oil and gas production, where scale formation can restrict or completely block fluid flow in a well. One economical way to prevent scale buildup in oil and gas wells is through an inhibitor squeeze treatment, where scale inhibitor chemical is injected into the producing formation. The concentration of inhibitor returning with the brine inhibits scaling. This return concentration is currently unpredictable, because the interaction between the inhibitor and the rock forming minerals have not been quantified. Thus, treatment can neither be controlled, optimized, nor predicted. In the current research, surface complexation, solubility, and phase transformation theory are used to quantify the inhibitor-rock interactions. Solubility and adsorption equilibrium constants of the chemical components in commercial Nitrilotri (methylene phosphonic acid), NTMP, have been determined from laboratory experiments or obtained from the literature. The precipitation and solubility of calcium-NTMP salts were observed to vary with experimental conditions and with extent of aging. This observation was similar to observations made with calcium phosphate precipitation. The equilibrium constants obtained were used to evaluate the chemical conditions in the formation during an inhibitor squeeze at the Texaco N. R. Smith #4 well. Results suggested that $Ca\sb{2.5}HNTMP*2H\sb2O$ and $CaHPO\sb3*1.5H\sb2O$ were in equilibrium with the return brine. The results also suggested that the relative concentration of the chemical components in the commercial product differed in the return brine. The equilibrium constants were also incorporated in a simplified transport equation to simulate the squeeze process. The simulation results suggested that calcite availability may limit inhibitor component precipitation. The results also showed that the adsorption and calcium salt solubility of the inhibitor components could be used to estimate the shape of the return curve.

The effect of electrokinetic phenomena on the performance of ceramic membranes is studied. The results of experiments that evaluate the effects of the ionic strength, pH and the composition of the feed water on the performance of ceramic microfiltration membranes are reported. Theoretical calculations that estimate the electroviscous effect on membrane performance are presented and compared to experimental observations. Experiments were conducted on the membranes with cross-flow filtration mode and dead-end filtration mode. The electrokinetic properties of the membrane and pore surfaces were evaluated. The ionic strength and pH of the feed water are shown to affect membrane permeation behavior. This effect was shown to vary with average pore size, structure and composition of the membrane. Electroviscous considerations were shown to account partially to the observed effects of the feed water chemistry on the permeate flux. The composition of the electrolyte solution and the mobility of the ions in solution were also shown to influence membrane permeation rates. Theoretical considerations indicate that the effect of electrokinetic phenomena were shown to be significant for membranes with high pore surface potential ($\geq-$100 mV) and at intermediate electrokinetic radii, $\kappa$a $\sim$ 2. This condition corresponds to a membrane with a pore radius, a of 0.1 $\mu$m and ionic strength of $2.5\times10\sp{-5}$ M resulting in a Debye parameter, $\kappa$ around $2\times10\sp7 {\rm m}\sp{-1}.$

Column transport experiments were conducted under saturated conditions to examine the effects of cell concentration and media pre-coating. Two strains of E. coli were used in the study; the commonly studied laboratory organism E. coli K12 D21 and a mutant of the waterborne pathogen E. coli O157:H7. Column experiments were conducted with both clean sand and sand that was pre-coated with bacteria. The influent concentration of the E. coli strains was varied over several orders of magnitude to examine the effect of cell concentration. Concentration dependent removal rates were observed for both organisms in both the clean and media pre-coated sand columns. It was also found that the media pre-coating either does not influence the transport behavior or it decreases the attachment efficiency. Although differences in transport are observed, these differences are not large enough to have a significant influence on the predicted travel distances. / Des expériences de transport par colonne ont été menées afin d'examiner les effets de la concentration des cellules et du pré-revêtement de média. Deux souches de bactéries ont été utilisées: E. coli K12 D12 et une souche mutante E. coli O157:H7. Les expériences par colonne ont été menées avec du sable propre et du sable qui a été préalablement enduit de bactéries. La concentration de l'influent en bactérie a été variée sur plusieurs ordres de grandeur pour examiner l'effet de la concentration cellulaire. Une dépendance du taux d'élimination à la concentration a été observée pour les deux souches de bactéries dans les deux types de sable. De plus, le pré-revêtement de média n'influence d'aucune façon le comportement du transport ni en réduit l'efficacité d'adhésion. Bien que des différences dans le transport ont été observées, celles-ci n'ont eu aucun effet significatif sur la prédiction de la distance à parcourir.

The attachment efficiency of two strains of Escherichia coli O157:H7 – one pathogenic strain and another non-pathogenic strain – was measured over a range of solution ionic strengths and in two different granular systems: a simple system made of clean quartz sand and a real system made of natural subsurface soil. In this study, the relevance of the non-pathogenic strain of E. coli O157:H7 as a potential surrogate for its pathogenic counterpart was investigated. The results suggest that it is not straightforward to find an appropriate surrogate for the pathogenic strain. Different porous media begets different attachment efficiency of the potential surrogate strain relative to the attachment efficiency of the toxigenic strain. A modest attempt was also made to build an artificial system that mimics the natural soil, by coating the clean granular sand with humic acids and adding clay component. / Pour étudier la contamination d'eaux souterraines, l'efficacité d'adhésion de deux variétés d'E. coli O157:H7 – une pathogène et une autre non-pathogène – a été mesurée sur une gamme de force ionique dans deux systèmes granulaires : un système simple fait de sable de quartz propre et un système naturel de sol souterrain. Dans cette étude, la pertinence de la variété non-pathogène (E. coli O157:H7) comme substitut potentiel pour sa contrepartie fut étudiée. Les résultats suggèrent qu'il est très difficile de trouver un substitut approprié de la variété pathogène pour ce type d'études, car différents médias porreaux engendrent différentes efficacités d'adhésion de la variété substitut potentielle. Une tentative a aussi été faite de construire un système artificiel dans le labo qui imite le sol naturel, en enrobant le sable de quartz avec des acides humiques et par l'addition d'un composé d'argile.