Includes bibliographical references (leaves 137-150). / a,w-Dicarboxylic acids are reactive intermediates, widely used as raw materials to synthesise products such as perfumes, hot-melting adhesives, engineering plastics and high quality lubricants. These acids can be obtained via chemical or biological routes by using various feedstocks such as linear alkanes. Linear alkanes are chemically inert; hence, the production of reactive products requires complex and sophisticated reactions catalysed by either catalysts or enzymes. However, simultaneous by-product formation on chemical synthesis increases production cost and limits commercial availability, preventing their widespread application. Biological routes alternatively, selectively transform linear alkanes into fatty and a,w-dicarboxylic acids. Linear alkanes, due to their relative abundance and increased availability, following the expansion of gas-to-liquid fuels technology, are viewed as prospective feedstocks for the microbial production of a,w-dicarboxylic acids. The commercialisation of the biological conversion of linear alkanes is constrained by the low turnover frequency of the cytochrome P450 hydroxylase complex responsible for catalysing the first and rate limiting step of the monoterminal and diterminal pathways. Low product yields may be caused by the further catabolism of a,w-dicarboxylic acids, through the ~-oxidation pathway into energy, carbon dioxide and water. To prevent this, metabolic engineering techniques can be applied to prevent ~-oxidation by disrupting the genes encoding the enzyme catalysing the first step in the~-oxidation pathway. The specific productivity of bioconversion can then be increased further by over-expressing the genes encoding the cytochrome P450 hydroxylase complex. Recombinant Yarrowia lipolytica strains TVN 497, TVN 499, TVN 501 and TVN 502 were developed in such a manner by the collaborating research group at the University of the Free State and made available for this research.

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Includes abstract. / Includes bibliographical references. / Bioleaching can be categorized as being either stirred tank type (i.e. bio-oxidation) or irrigation type (i.e. heap/dump bioleaching) yet studies investigating the kinetics of bioleaching systems mostly use empirical data determined from stirred tank type and initial rate experiments in batch cultures or using iso-potential devices. Rate equations deduced from such empirical data is then used to model both the stirred tank type and irrigation type bioleaching systems overlooking the possibility that there may be significant differences in their environments and therefore the kinetics. Tank bioleaching systems are well mixed suspension systems dominated by planktonic microorganisms (freely suspended in the liquid medium). Heap bioleaching systems on the contrary, are heterogeneous in nature with chemical and physical conditions changing over time and are dominated by sessile microorganisms (attached microorganisms to the surface of a solid). The heap bioleaching system is therefore highly complex compared to the stirred tank-type systems. Microbial growth in bioleaching systems significantly influence the overall bioleaching kinetics yet biological kinetic effects in sessile/ attached environments are not well understood. Heap and dump leaching account for about 20% of the world’s copper production and are becoming popular methods of copper production from leaching low grade ores. It is therefore important that the kinetics of irrigation type bioleaching systems are well understood. A strategy to determine the microbial kinetics of a sessile microbial population is enforced in this study. From this, empirical data determined from irrigation type environments can then be used to derive equations which can be used to accurately model heap bioleaching systems. Three sets of experiments were conducted to try and achieve this: i. planktonic experiments - investigating the microbial kinetics of a planktonic microbial population ii. attachment experiments - investigating the nature of growth of the microbial population to the surface of a solid substrate during attachment to create a sessile microbial population iii. sessile experiments - investigating the microbial kinetics of the sessile microbial population A pure culture of Leptospirillum ferriphilum (a mesophilic, ferrous iron oxidizing bioleachingmicroorganism) was used in this study. Planktonic experiments were conducted in a completely mixed, well aerated continuous stirred tank reactor (CSTR) with a 1 litre working volume, operating at a pH of about 1.3 and temperature of 37oC. Attachment and sessile experiments were conducted using a CSTR with similar conditions to the planktonic experimental, however the system was modified by introducing a packed bed vessel (PBR) attached as a closed loop to the CSTR. Solution drawn from the CSTR was then continuously pumped through the PBR and back to the CSTR.

Includes abstract. / Includes bibliographical references (leaves 69-75). / Bioleaching has developed into a very important process for the recovery of valuable metals, particularly from low grade copper ores due to the ever increase in demand. A lag phase is present during the start-up phase of heap bioleach operations characterised by a low degree of microbial colonisation, a low ferrous iron oxidation rate and low microbial proliferation rates, ultimately resulting in a poor copper recovery rate.

Includes bibliographical references.

Bibliography: leaves 117-125. / Falling commodity prices have reduced the profit margins of Southern African sugar producers. Although these price falls have been severe, they reflect a long-term trend of reducing margins for basic commodity producers during the 20th Century. This trend has forced. producers to closely examine their processes and to look for areas in which improvements in productivity, yield and efficiency can be achieved. Evaporation is the most energy intensive unit operation in the sugar factory, and it is responsible for the removal of most of the water from sugar solution, or juice, which is extracted from the sugar cane. There is also a large potential to lose sucrose at the evaporators due to the high temperatures and long residence times employed there. The smooth control of the evaporators is thus vital to consistent factory operation, and the evaporators are commonly a sugar factory bottleneck. This study developed a control strategy for the particular evaporator configuration found at Triangle Sugar Mill in south eastern Zimbabwe. There are currently several evaporator control strategies being used in the sugar industry. Most of these are an assembly of single loop Proportional Integral Derivative (PID) controllers, which cannot optimally account for the interactions encountered in most evaporator stations. Ideally, any evaporator control system should be able to handle the multiple input multiple output problem while anticipating and handling constraints on inputs and outputs. Several multivariable approaches have been tried, but these usually require a great deal of expensive instrumentation.After a review of the multivariable control literature and testing of several alternative control systems, Dynamic Matrix Control (DMC) was chosen as the bestwsuited control algorithm for the Triangle control problem. A dynamic model of the Triangle evaporator station was, developed to formulate and test the DMC and other controllers. The model was based on a set of differential equations involving mass and energy balances through the evaporators. Real plant data were collected from the SCADA system and the model was tested against this data. After validation the model was. used to record step responses of the process to key input variables. The control system had nine (9) measurable inputs, and three (3) controlled outputs. The objective of the control system was to deliver the maximum amount of consistently high quality symp, within plant constraints. This was formulated in an objective function which seeks to minimize a weighted sum of the errors of syrup concentration from a setpoint, and the fluctuations in juice flowrates. Two alternative formulations were developed, and tested on the plant model.

The use of blackstrap cane molasses in industrial ethanol production is characterised by fluctuations in fermentation efficiency due to its compositional variation. Crucial to optimisation of ethanol production is thorough knowledge of the constituents and properties of molasses which affect fermentation, in order to implement measures to diminish negative and augment positive impacts. These include both major and minor constituents. According to literature, aspects of fermentation media which affect yeast fermentation include nutritional availability, the presence of trace elements and growth factors such as vitamins, without which yeast proliferation is inhibited. High osmotic pressures, found in VHG (very high gravity) fermentations, have a detrimental effect on the fermentation process. Additionally, elevated concentrations of inorganic salts and ionic strength in industrial fermentation media have been implicated in negatively affecting fermentation. Based on these limited literature findings, the study addressed the effect of three cation constituents of molasses (K+, Mg2+ and Na+), expressed in terms of overall concentration, osmotic pressure and ionic strength, on fermentation was investigated in molasses media and a sucrose-based media.

Includes bibliographical references (p. 121-135). / The potential of thermophilic micro-organisms to bioleach primary copper sulfides and other minerals has led to the need to develop a fundamental understanding of the mechanistic process involved. Ferrous iron oxidation has been established as a key step in bioleaching and is understood to be achieved largely by microbial action. The objective of this work was to determine an appropriate set of kinetic expressions that describe the rates of microbial growth and ferrous iron oxidation of a thermophilic archeal culture grown in continuous culture on ferrous iron between 60 and 80°C.

Includes abstract. / Includes bibliographic references (leaves 113-119). / While initially thought to be promising, crop based biofuels are an inadequate alternative to fossilenergy due to the unrealistic space requirement, competition with food crops for land use and greenhouse gas release on clearing for crop land several times greater than biofuels provide throughdisplacing fossil fuels, a factor inadequately accounted for in past studies. In contrast, biodiesel frommicroalgae is of interest due to the lower spatial requirements, much higher oil productivity, no requirement for arable land and rapid growth and harvesting cycles. To ensure the oversights of cropbased biofuels are not repeated, there is a need to explore the sustainability of an algal biorefinery in the context of biodiesel production in this early phase of process development. An integratedbiorefinery approach for the production of multiple products has been seen to improve the overallefficiency of biomass utilization in biofuel systems, contributing to both economic success and environmental sustainability and is of interest for microalgal biodiesel production

Includes bibliographical references. / In slurry reactors, hydrodynamic stress originates primarily from interactions between particles and cells in the reactor. This form of stress has been shown to negatively affect the process performance. The present study centres on slurry reactors utilised in the bioleaching industry. The micro-organisms employed in these processes include mesophilic micro-organisms and, more recently, thermophilic microbes which have shown much promise for improving the rate and extent of leaching particularly of recalcitrant minerals such as chalcopyrite. The drawback to using high temperature microbes is that these thermoacidophiles, unlike their mesophilic counterparts, are Gram-negative Archaea, not bacteria, hence they do not possess resilient cell walls and are more prone to hydrodynamic injury.