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Please read the abstract in the section, 00front of this document / Dissertation (MSc (Metallurgy))--University of Pretoria, 2004. / Materials Science and Metallurgical Engineering / MSc / unrestricted

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The potential of increasing disease problems through the use of recycled irrigation water in horticultural operations is a serious concern, yet basic research on waterborne plant pathogens in Virginia is lacking. In this work seasonal fluctuations and locations of Pythiaceae in a recycled water irrigation system at a container nursery were determined. <i>Pythium</i> spp. were recovered more frequently and in greater numbers than <i>Phytophthora</i> spp. Species of <i>Phytophthora</i> recovered in filtering assays were identified as <i>P. capsici, P. citricola, P. citrophthora, P. cryptogea, P. drechsleri,</i> and <i>P. nicotianae. P. cryptogea</i> and <i>P. drechsleri</i> were the only <i>Phytophthora</i> spp. recovered from baits placed on the surface of the irrigation reservoir, whereas a greater diversity of species was recovered from baits placed at depths. Hymexazol-amended medium was found to have limitations in recovery of <i>Phytophthora</i> spp. In pathogenicity tests, <i>P. cactorum, P. capsici, P. citrophthora,</i> and <i>P. nicotianae</i> caused significant mortality of <i>Salvia officinalis</i> and <i>P. cactorum</i> showed limited pathogenicity on <i>Gerbera jamesonii</i>. Asymptomatic (aboveground) plants were found to harbor inoculum long after <i>Phytophthora</i>-inoculation. Fresh weight analyses of roots and shoots of asymptomatic plants demonstrated that <i>Phytophthora</i> inoculation may either reduce or stimulate plant shoot growth, but little effect is apparent on roots. Irrigation with naturally infested irrigation water reduced plant growth. This research provides data for prioritizing development of detection technology and management practices for plant pathogens in irrigation water. The results may also lead to improvements in conventional water assay protocols for plant pathogens. / Master of Science

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The presence of hydrogen sulfide in a ground water source is noted by its rather obnoxious odor, similar to a "rotten egg". Concentrations as low as 0.05 ppm are noticeable, therefore, almost its entire removal is demanded prior to potable consumption. Hydrogen sulfide is formed primarily by the decomposition of organic matter in anaerobic conditions. Removal of this gas has been accomplished by means of aeration, detention, and chlorination over the years. The mechanisms behind each of these processes are complex and discussed in this paper. During the course of this investigation, a literature survey concerning the mature and sources of hydrogen sulfide, its removal by aeration and detention, and the experimental methodology has been conducted. Samples were collected from two ground water locations in Central Florida, namely City of Apopka Terrace Plant, and the City of Maitland Thistle Plant. These samples were taken before and after aeration and detained in containers similar to the storage tank dimensions. These samples were tested for Hydrogen Sulfide and pH with respect to time. The aerators were determined to remove 13 to 15 percent H2S, respectively. The pH values ranged between 7 - 8 prior to detention and rose slowly during H2S ionization to 8-8.6. Both locations were evaluated to determine the most economic operating conditions. Ideally, Apopka should be removing between 30 - 40 percent by means of aeration, and Maitland, between 40 - 50 percent. Chlorination will remove the remaining H2S. Although the existing aerators were operating less than their optimum removal range, they should remain in service. This is based on deducting the aerator "sunk costs" from the economic evaluation. Efforts should be encouraged to improve aerator efficiencies by increased agitation, contact time, and weir overflow rates in the aerator trays. These measures should increase the H2S reaction rate and improve its removal. Detention only removes the odor problem, but the chlorine demand still remains, as exerted by the forms HS- and S=.

In anticipation of government mandates regulating the quantity of the toxic mutagen, 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone, which can be released into potable waters or from industrial facilities, technologies for monitoring the concentration, reducing the quantity, and inhibiting the formation of this compound were investigated. Adsorption of the chlorinated hydroxyfuranone from laboratory systems (pH 7.2, 22°) utilizing the non-polar, polymeric resin, Amberlite XAD-4, was successful. As these system conditions are comparable to those present in drinking water treatment facilities, application of this resin to such systems should be investigated. However, typical concentrations of the chlorinated mutagen released from such facilities are some 100 times less then those employed in laboratory experiments. As such, highly sensitive analytical technology, such as fluorescent spectroscopy, would be required for direct detection of the mutagen in these aqueous systems. Since development of a fluorescent adduct of the mutagen, through either Schiff's base or halogen replacement reactions, failed, application of the adsorption methodology was not investigated. Approaching the problem in a different manner lead to ° investigations aimed at reducing the formation of the mutagenic compound. Since the mutagen is formed upon chlorination of waters containing lignin derived materials, lignification in intact growing plants, and the effects of modified substrates on this process, were investigated. All modified substrates tested increased the uptake of a C¹⁴ labelled lignin precursor into the lignin containing fraction of a living poplar stem. Research continues in this area to determine through what mechanism these compounds are affecting lignification. / Master of Science / incomplete_metadata

Fecal coliforms suspended in a natural stream water were exposed to rhodamine WT dye, chlorine and both in combination. Samples were analyzed for coliforms by three enumeration techniques. Statistical analyses of data by the paired-t test showed that for non-chlorinated samples no significant difference (0.10 level) was found between the recoveries by the three enumeration techniques. For chlorinated samples the standard membrane filter technique (Std-MF) yielded significantly lower recoveries (0.05 level) than the standard MPN procedure. A modified membrane filter technique employing a two-layer agar and a five hour 35°C preincubation period (Mod-MF) was found to yield recoveries consistently greater (0.05 level) than the standard MF technique. The data showed that exposing fecal coliforms to 100 to 1,000 ppb of rhodamine WT dye for 30 minutes, did not inhibit the recovery or enumeration of the organisms by any of the three assay methods. The number of fecal coliforms that survived exposure to 0.2 to 0.3 ppm of chlorine and 10 to 100 ppb of dye was not significantly different from the number enduring contact with similar concentrations of chlorine alone. / Master of Science

Little information is available regarding the applicability of various disinfectants to the control of microbial growths within water distribution systems, especially in relation to "nuisance" organisms. With regards to microbially mediated iron precipitation, an isolated heterotrophic iron precipitating bacterium was identified. An investigation of free chlorine, chloramines, and chlorine dioxide was undertaken to examine their applicability in the control and/or elimination of this type of deterioration in water quality. Environmental conditions were then varied to determine their effects on the disinfectant's efficiencies. The isolated bacterium was identified as Pseudomonas cepacia. It was determined that chlorine dioxide offered a serious challenge to chlorine as a secondary disinfectant on the basis of its biocidal capabilities and stability. Solution pH affected free chlorine's efficiency the greatest, while chloramine's poor efficiency suggested that its use should be avoided in areas of microbial iron precipitation. Water temperature and turbidity showed a minimal effect on the rate of inactivation of P. cepacia for all the disinfectants under consideration. / Master of Science