Bibliography: leaves 106-113.

Includes bibliographical references (leaves 161-169).

Surfactants are chemical compounds that are able to alter interfacial properties, particularly surface tension. When they are biologically produced, the term biosurfactant is used. One of the most important groups of biosurfactants is a family of chemical compounds known as glycolipids, whose structure consists of a sugar group and a lipid tail. Glycolipids are subdivided into three main groups: rhamnolipids, sophorolipids and trehalolipids, named following their sugar moieties, respectively rhamnose, trehalose and sophorose. Biosurfactants exhibit attractive advantages over chemical surfactants. Examples of these are biodegradability, low toxicity, and effectiveness at extreme temperature, pH and salinity. The objective of the present research project was, first, to investigate the potential of liquid aliphatic hydrocarbons to induce biosurfactant production by the bacterium Ps. aeruginosa 2Bf isolated based on its ability to metabolise alkanes. The second objective was to optimise biosurfactant production using alkanes as sole carbon and energy source, through optimising the mixing & aeration conditions, media conditions as well as provision of alkane, in a stirred tank batch reactor system. The final objective was to describe the biosurfactant formed. Experiments were organised in three major series: the exploratory shake flask based experiments, the bioreactor-based experiments to optimise biosurfactant production and characterise biokinetics and performance, and the biosurfactant characterisation experiments. Following review of a number of methods, microbial cell counts were selected as the most reproducible measure of biomass formation in the presence of alkanes. The presence of biosurfactant was quantified functionally in terms of the emulsification index and alteration of surface tension. Using a shake flask-based study, nitrogen source was investigated in terms of biomass and biosurfactant synthesis. Four pre-selected nitrogen sources were tested in order to select the best for bioreactor based study. These nitrogen sources consisted of specific combinations of three nitrogen compounds, NH4NO3, NaNO3 and (NH4)2SO4. During the study, long chain liquid n-alkanes were used as sole carbon source and the C/N ratio maintained at the value of 18.6 in mass terms. Results confirmed that both a combination of NO3 ' and NH4+ ions or a nitrogen source composed solely of NH4+ ions were suitable for biomass growth and biosurfactant production. (NH4)SO4 was used as the N-source of choice in the remainder of the study. While the C14-C17 alkanes cut was the carbon source of interest in the study, two pure alkanes, n-C12 and n-C16 were tested and compared to the C14-C17 blend. The C14-C17 fraction, sourced as an industrial byproduct, compared favourably as a carbon source with respect to hexadecane and dodecane. ii Biosurfactant production was not observed in Ps. aeruginosa 2Bf cultures where glucose was the sole carbon source and the bacteria were not previously exposed to linear alkanes. Using a mixed carbon source of glucose and alkane, or on pre-exposure of the bacteria to alkane, biosurfactant production was induced. Induction was optimised where alkane was the sole carbon source over a period of four sub-culture steps. In the quantitative optimisation of biosurfactant production through the bioreactor based study, mixing and aeration were optimised; agitation and aeration proved to be equally important, the first at intermediate rates, the second at lower rates. Their interaction, when maximum biomass was used as the variable for response, was found to be important for agitation rates up to 500 rpm. Beyond this range of agitation speed, the interaction between aeration and agitation became negligible. In the case of Eindex as the variable for response, similar results were obtained with regard to the impact of the interaction between aeration and agitation on the process. It was significant from lower to intermediate agitation rates, and negligible from intermediate to higher rates of agitation. Lower aeration rate was found to enhance the oxygen utilisation rate, while mass transfer was relatively favoured by high aeration rate. Regarding the emulsification power of the product, quantitative tests were carried out on culture suspension, supernatant prepared by centrifugation and supernatant prepared by centrifugation and filtration at 0.22μm pore size filters. Results showed that some emulsification effect was lost through centrifugation and filtration. This loss of emulsification effect was more pronounced in the filtration case, thus showing that some biosurfactant was removed along some other material or substance through sticking on filter paper. Foam control was required, and two mechanical foam breakers were compared to anti-foam reagent. It was experimentally established that mechanical foam breakers are preferable to chemical anti-foam reagents. On comparing the two different mechanical foam breakers, the modified two blade paddle with three slits, FB-2, performed better than the simple two blade paddle foam breaker, FB-1. Further investigations showed that the interaction between type of foam control and agitation rate was negligible throughout the process. The Biosurfactant was characterised at the structural level and the antibiotic potential of Ps. aeruginosa 2Bf's biosurfactant was analysed. In addition to the thin layer chromatography, three different spectroscopic methods (mass, infrared & nuclear magnetic resonance) were used to study the chemical structure of the biosurfactant produced. Up to six rhamnolipid structures were tentatively identified with spectrometric analysis whereas only four to five structures could be detected with thin layer chromatography. Possession of an anti-microbial activity by the rhamnolipids produced was confirmed with the B. subtilis inhibition test.

Includes bibliographical references. / Hydrodynamic cavitation is a novel method for microbial cell disruption, mediated by intense pressure fluctuations caused by cavity oscillation and collapse. Selective release of intracellular microbial products is desirable to reduce the cost involved in their downstream processing. A study of the process variables that affect microbial cell disruption by hydrodynamic cavitation is presented in order to ascertain the conditions required for a selective release. Two model systems were considered (yeast and E. coil). Enzymes from different locations of the cell were studied and the release compared with other methods of disruption.

Includes bibliographies. / Bioleaching is now an established technology for the leaching of whole-ore copper heaps and the pre-treatment of refractory arsenical gold ores and concentrates. For the case of refractory arsenical gold concentrates, it offers an economically feasible alternative to pressure oxidation and has environmental advantages over roasting with regard to the quality of the liquid and gaseous effluent (Van Aswegen, 1993). The major disadvantage of bioleaching is the low residence time required to achieve high oxidation levels. Other potential complications include the solubilisation of substances in the mineral, or the use of reagents, that are toxic to the micro-organisms.

Includes bibliographical references (p. [181]-203).

Includes abstract. / Includes bibliographical references. / The intimate contact achieved between the gas and liquid phases in bubble columns, coupled with the inherent efficient mixing these reactors offer, yield excellent heat and mass transfer characteristics. These attributes have been exploited commercially for decades, however, due to the complexity of the underlying hydrodynamics, the prediction of bubble columns based on empirical models can be unreliable outside of the operating ranges used to fit these models. Computational Fluid Dynamics (CFD) has emerged as an attractive tool for simulating these reactors and is based on numerically approximating the fundamentally based Navier-Stokes equations on a discretized domain. The application of CFD has become more practical as the cost of computational resources has declined and has lead to the establishment of three distinct modelling approaches which have been evaluated for the purpose of bubble column simulation in a number of research papers over the past two decades. Here the Euler-Euler approach has been recommended for the simulation of large scale columns, however, this approach is based on the most assumptions and yields the least amount of flow field information. The Euler-Lagrange approach treats bubbles as discrete particles which allows for the incorporation of a deterministic bubble size distribution and the direct consideration of heat and mass transfer effects. The most fundamental approach, Direct Numerical Simulation (DNS), predicts flow properties at the bubble scale, however, is extremely computationally expensive and is therefore only practically applicable to the investigation of a very small number of bubbles. The objective of this study is to contribute to the simulation of gasliquid flow interaction occurring in bubble columns by proposing a novel technique for simulating bubble scale flow information at a significantly reduced computational expense. For this purpose, it is proposed to predict the micro-flow fields around individual bubbles, within an Euler-Lagrange framework, with an algebraic model termed the Bubble Cell Model (BCM). The high gradient regions around individual bubbles are thereby accounted for with an algebraic flow model that can be rapidly evaluated as opposed to the two-phase partial differential Navier-Stokes equations, thereby reducing the numerical complexity of the problem. Since no such flow models currently exist and accuracy and fast evaluation are imperative, a statistical approach to the construction of the BCM is justified.

Includes bibliographical references. / This thesis aims to assess the avoided environmental burdens of waste water treatment by additional on-site anaerobic waste water treatment prior to municipal treatment and disposal to river. It investigates the opportunity for further burden reduction by way of energy capture from generated biogas and re-integration within a plant-wide environment. The Life Cycle Assessment (LCA) was the analytical tool used to quantify burdens attributable to additional on-site effluent treatment, and further quantify the burdens avoided due to energy capture and re-integration. This thesis was born from the opportunity for energy reclamation from biogas, generated by SABMiller Newlands Brewery anaerobic digester. Western Cape power failures prompted the search for alternate energy sources, focusing SABMiller attention to the currently flared biogas emitted from the SABMiller Newlands effluent treatment facility.

Includes bibliographical references.

Includes abstract. Includes bibliographical references (leaves 164-167).