OpenUCT :: Browsing by Author "Harrison, STL"

Browsing by Author "Harrison, STL"

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Open Access
The accuracy of linear flux models in predicting reaction rate profiles in a model biochemical reaction system
(2014) Hughes, Alistair Paul; Möller, Klaus; Harrison, STL
Metabolic flux analysis is commonly used in the modelling of biochemical reactions. The use of MFA models has gained large amounts of interest due to the simplicity of the computational procedures required for the model, and the exclusion of difficult to measure intracellular reaction data. There are many examples of the use of MFA models in literature studies in a number of applications, ranging from the medical industry through to the development of novel biochemical processes. Little to no mention is provided in literature studies regarding the applicability of the MFA model to a specified set of reaction data. Furthermore, the techniques and routines used to compute the flux models are not well described in these studies. The objectives of this research were to determine the sensitivity of the MFA models to various operating and kinetic parameters and to highlight the considerations required when setting up the computational routine used to solve the flux balances. The study was conducted using a model pathway populated with a set of hypothetical elemental reactions and branch points. The model pathway was used in this study to negate the affects of complex regulatory biochemical architectures which are not well described in literature. The use of the model pathway ensured that the reaction system was thermodynamically feasible and there was consistency in the mass balances. The exclusion of the complex regulatory reactions did not affect the accuracy of the results generated in this study. A set of reaction mechanisms were used to describe each reaction step and were populated with parameters reference from literature. The cellular and reactor mass balances were generated using correlations presented in literature.
Open Access
Anaerobic digestion of algal biomass for bioenergy production- a feasibility study
(2011) Inglesby, Alister Edward; Van Hille, Rob; Harrison, STL
AD technology is well developed, cost efficient and can be easily implemented in developing countries. Biogas production has become a very topical subject, with many European nations introducing initiatives to increase biogas production. AD of algal biomass was studied in detail during the 1980’s, however, with the current drive toward cleaner technology processes, there has been a renewed interest in the technology. This study investigated the feasibility of using algal biomass as a feedstock for AD.
Open Access
Analysis of particle suspension and mixing in biological systems : an application of tomography
(2006) Stevenson, Ryan; Harrison, STL
Includes bibliographical references.
Open Access
Biological conversion of alkanes to dicarboxylic acids : an investigation into process challenges and optimisation in hydrocarbon-based bioprocesses
(2005) Williams, Peta Clair; Harrison, STL; Clarke, K G; Smit, MS
The focus of this project is bioconversion of alkanes to dicarboxylic acids. Dicarboxylic acids are versatile chemical intermediates that can be used in the manufacture of perfumes, polymers, adhesives and antibiotics. The use of a hydrocarbon in a biological process, however, introduces several process challenges related to the nature of the substrate. Many of these challenges are common to all hydrocarbon fermentations, regardless of the product formed, and include flammability, volatility and inhibition of cell growth (notably at low carbon chain lengths), insolubility (notably at high carbon chain lengths) and mass transfer limitations, with respect to both oxygen and alkane substrate. In particular, the provision of adequate oxygen transfer to the organism in hydrocarbon-based bioprocesses has been regarded as especially challenging because of the absence of oxygen in the hydrocarbon backbone. In contrast to carbohydrate-based bioprocesses in which the carbohydrate itself supplies about half of the oxygen, the metabolic requirement for oxygen in hydrocarbon-based bioprocesses has to be met entirely by the transfer of oxygen to the broth. This suggests a proportionately higher requirement for oxygen transfer under these conditions. Consequently, the oxygen transfer rate (OTR) has been mooted as a likely major process limitation, leading to a process which is transport, rather than kinetically controlled and correspondingly, a sub-optimal yield and productivity.
Open Access
Biooxidation kinetics of Leptospirillum Ferriphilum attached to a defined solid substrate
(2011) Duku, Porogo; Petersen, Jochen; Minnaar, Sanet; Harrison, STL
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.
Metadata only
Carbon dioxide mass transfer within algal raceway ponds and the potential for improvement using slopes to create wave
(2016) Burke, Matthew; Harrison, STL
The growth of microalgae has the potential to be extremely useful for the production of a wide range of products or for specific processes, such as capture and cycling of CO₂. The fast micro-algal growth rates and ability to grow on agriculturally poor land and in waste water means that bio-production using algae has many advantages over traditional agricultural processes for certain applications. The raceway pond is the most common reactor used for the growth of microalgae, due to low capital costs, low operating costs, higher energy efficiency, improved net energy recovery and ease of installation. Low carbon dioxide mass transfer, which limits algal growth and productivity, is currently one of the largest issues in photo bioreactors of all forms. The microalgae within these systems only obtain carbon from the dissolved inorganic carbon and hence sufficient carbon dioxide mass transfer is one of the most important design parameters for any photobioreactor. This is particularly evident in raceway ponds as they have a lower volumetric mass transfer rate than other photobioreactors and are typically mass transfer limited. [Please note: the full text of this thesis has been deferred until 30 September 2017]
Open Access
Characterising the acid mine drainage potential of fine coal wastes
(2013) Kotelo, Lerato Olga; Broadhurst, Jennifer Lee; Becker, Megan; Harrison, STL; Franzidis, Jean-Paul
Acid mine drainage (AMD) is one of the major environmental challenges facing the South African mining sector. Acid mine drainage has received significant public attention in recent years. South Africa's long mining history has led to a growing concern that coal-related AMD from these mines (both operational and defunct) will continue for centuries to come. Pyrite bearing fine waste, generated during coal preparation and beneficiation, is thought to carry a significant amount of AMD pollution risk. Coal-related AMD generation has not been afforded the same exposure as AMD generation from high sulphide minerals such as gold and copper ores. This is exacerbated by the growing concern over water quality degradation in the Mpumalanga region of South Africa. The development of integrated solutions to address the management of coal-related AMD requires an understanding of the principle causes behind coal-related AMD. To date, most of the prediction methods described in literature have been derived for the prediction of AMD in metal bearing ores. Furthermore, some of these methods are based on assumptions and do not take into consideration the various sulphur species present. Additionally, some of these methods have limited applicability to coal due to the high total organic carbon content (TOC) of the material. This research project attempts to address these short comings and uncertainties by developing a systematic and meaningful framework for the characterisation of South African coal and coal waste. The research project contributes to the knowledge of coal-related AMD with particular emphasis on the characterisation methods responsible for sulphur speciation and mineralogy for coal. The approach entails carrying out a case study assessment aimed at empirically assessing a coal tailings sample according to: particle size distribution, textural reference, mineralogical characteristics, and how the aforementioned factors influence the acid potential in coal. The approach intends to address key factors which include: identifying the sulphur bearing organic and inorganic constituents related AMD generation in coal, assessing how the mineralogy, texture and particle size distribution contribute to AMD potential in coal tailings, and then identifying suitable analytical techniques and test methods which can provide data. The combination of these key outcomes will seek to provide a systematic and meaningful framework for the characterisation of coal and coal waste streams. The characterisation methods used in this case study outlined a framework focusing on four main areas of acid mine drainage characterisation for coal wastes, these included: chemical characterisation, mineralogical characterisation, sulphur speciation and AMD prediction. This comprehensive approach employed a suite of techniques, including: petrography, quantitative x-ray diffraction (QXRD) and quantitative evaluation of minerals by scanning electron spectrometry (QEMSCAN).
Open Access
Combining froth flotation and reflux classification to mitigate ARD generating potential of the Waterberg and Witbank coal ultrafines via sulfide removal
(2014) Iroala, Onyinye Judith; Franzidis, Jean-Paul; Harrison, STL
In South Africa, over 10 million tons of ultrafine coal wastes are discarded every year, typically in the form of ultrafine slurries. These fines have a high calorific value, and contain sulfur minerals, particularly pyrite. The high calorific value of these discards leads to a waste of energy that could be harnessed and used, while the high sulfur content contributes to adverse environmental effects such as acid rock drainage (ARD). The University of Cape Town (UCT) has developed a two-stage flotation process, which involves coal flotation in the first stage and pyrite flotation of the tailings in the second stage, for mitigating the ARD potential of ultrafine wastes. Research has shown that this two stage froth flotation process was sufficient to render the tailings non-acid forming. At the same time, North West University (NWU) has been carrying out research on coal fines using the recently invented reflux classifier. The reflux classifier is claimed to be capable of separating particles down to 38 ìm in size; however, no work has been done using the reflux classifier to separate pyrite from coal. This dissertation investigates the effectiveness of combining flotation and reflux classification for removing sulfide minerals from two South African coal ultrafines, whilst recovering valuable coal, and compares the results to those obtained using the UCT two-stage flotation process. As no previous work has been done using reflux classification to remove sulfide minerals from coal, this is the first time that the reflux classifier will be investigated for this purpose. Two process routes were investigated: (i) froth flotation followed by reflux classification of the tailings (process route 1), and (ii) reflux classification followed by froth flotation of the overflow (process route 2). Coal flotation, sulfide flotation and reflux classification were conducted on samples of Waterberg and Witbank coals, using a 3 L Leeds-type flotation cell and a 10 L batch reflux classifier constructed at NWU. Acid base accounting (ABA) and net acid generating (NAG) static characterization tests were performed on the products and feeds from all three process routes.
Open Access
Control and optimization of a multiple-effect evaporator
(2000) Smith, Patrick D; Swartz, Chris; Harrison, STL
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.
Open Access
Conversion of hydrocarbons to biosurfactants : an insight into the bioprocess optimisation of biosurfactant production using alkanes as inducers
(2009) Bamara, Prosper; Harrison, STL
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 0.22Î¼m 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.
Open Access
Design of an optimised fed-batch process for insulin precursor production in Pichia pastoris
(2011) Bhardwaj, Vinayak; Harrison, STL; Minnaar, Sanet
The increasing prevalence of diabetes worldwide has greatly increased the demand for insulin, a key type of treatment for many diabetics. For this purpose, the methylotrophic yeast Pichia pastoris has emerged as an additional microbial host for recombinant insulin production. A genetically modified Pichia pastoris MutS strain, engineered to produce the insulin precursor, was used as the experimental system in this study in order to optimise the insulin production process. The experimental system developed in this study employed a two-stage fed-batch feeding strategy in which growth was optimised by feeding glycerol to boost biomass followed by induction of the gene encoding insulin precursor by feeding methanol.
Open Access
A detailed investigation of microbial cell disruption by hydrodynamic cavitation for selective product release
(2004) Bangaru, Balasundaram; Harrison, STL
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.
Open Access
Development of an eicosapentaenoic acid production bioprocess using an indigenous microalgal isolate
(2015) Dickson, Darin; Harrison, STL
Eicosapentaenoic acid (EPA; 20:5) is an omega-3 polyunsaturated fatty acid of increasing interest as a nutraceutical. An indigenous microalgal isolate suitable for an EPA bioprocess was selected by screening monoalgal isolates from the Council for Scientific and Industrial Research (CSIR) micro-algal culture collection. A Cymbella diatom (A23.2) was selected for superior EPA production in both growth and stress conditions, using both fluorescent microscopy and flask studies. Studies investigated increasing biomass, improving EPA content, and optimising overall EPA productivity in a multi-stage bioprocess. Growth studies found self-regulatory systems in both phosphate and nitrate metabolism. These mechanisms were absent in silicate and bicarbonate consumption, prompting their optimisation in the bioprocess medium. Cultivation pH was found to have a statistically modelled optimal value of 7.2 and a light intensity at a low range of 60 – 70 ìmol.m-2.s-1 was found to be suitable. Nutrient and physicochemical parameters were assayed individually, and revealed cell productivities of between 2.0 x 108 to 3.0 x 108 cell.L-1.hr-1 in batch culture bioreactor studies. Further studies demonstrated the use of both nutrient stress and physicochemical stress to enhance EPA production. These results informed the choice of operating parameters for a proof of concept, multistage raceway-based EPA bioprocess, consisting of a single growth pond and three stress ponds linked in series. The growth phase EPA productivity data of 0.68 mg.L-1.day-1, was higher than that of the stress phase, supporting its classification as a growth-associated product. Further, the EPA productivity in the raceway was more than twice that of initial batch culture screening. Once experimental limitations are addressed, a re-design of the bioprocess can be undertaken by optimising growth phase residence time, medium flow-rate and partial/complete elimination of the stress phase. The EPA productivity of the diatom used in this work has the potential of reaching commercially viable values. The development of a commercial indigenous EPA producer has a dual impact, as it addresses various nutritional and medicinal market demands and improves the sustainability of the world’s fish stocks.
Open Access
Disruption of microorganisms due to agitation in slurries of fine particles
(1993) Pearce, Sarah Jane Amanda; Harrison, STL; Hansford, Geoffrey Spearing
This dissertation presents the results of an investigation into the disruption of microorganisms when agitated in slurries of fine particles in a stirred tank. The most widely used industrial process involving agitation of microorganisms in slurries of particles in stirred tanks is the biooxidation process. Mixed cultures of thiobacilli are used in stirred tank reactors for the biooxidation of sulphide minerals. In addition to operating conditions, the efficiency of biotechnological processes is dependent on the growth and metabolism of the microorganisms. The microorganisms are sensitive to the hydrodynamic conditions generated in the processes. In response to adverse hydrodynamic conditions there may be changes in the growth rate of the microorganisms, the nutrient uptake rate, the product formation rate and morphology of the microorganisms. Under extreme conditions cell damage and disruption may ensue. The presence of particulates in bioprocesses, in the form of solid substrates or support systems for attached growth, further complicate the hydrodynamic conditions. The knowledge of the effect of particulates on microorganisms is an important priority.
Restricted
An economic analysis of coal desulpharisation by froth flotation to prevent acid rock drainage (ARD) and an economic review of capping covers and ARD treatment processes
(2013) Jera, Melody Kudzai; Franzidis, Jean-Paul; Harrison, STL
Acidic drainage as a result of mining and mineral processing activities is a growing concern. The effects of Acid Rock Drainage (ARD) include environmental pollution in the affected areas and beyond. As South Africa has water challenges, the potential threat of continual depletion of useable water resources through their contamination by ARD and other mining activities may affect economic productivity, as well as quality of life. Currently used ARD remediation measures are variable and costly, not only in South Africa but worldwide. End of pipe approaches such as treatment by neutralisation fail to reduce the risk of ARD generation and provide long term solutions. Further it fails to address the limited resource utilisation of the byproduct materials, currently disposed of as ARD forming wastes. The Department of Chemical Engineering, at UCT, has focused research onto the prevention of ARD generation and minimisation of waste. One approach proposed is the two stage froth flotation process for separating sulphides, responsible for ARD formation, from the remaining tailings, leaving these benign with respect to ARD. Testwork results have proven its technical feasibility using porphyry copper tailings, fine coal and more recently gold tailings. Historically, ultrafine coal was not treated by most collieries in South Africa, but disposed as waste. Oxidation of the pyrite in the coal leads to generation of acidic water. In this project, an economic analysis of the coal two stage flotation process for the mitigation of ARD formation is considered. This project proposes ARD prevention by desulphurisation of sulphide rich waste coal material as an in-process approach which can be incorporated into mineral process flowsheets or as an add-on process for desulphurisation of old workings. The two stage flotation may yield a valuable mineral or coal product, as well as a low volume sulphide rich fraction which can be processed further to yield sulphuric acid or disposed of with containment and a benign tailings fraction which can be used as cover material or disposed conventionally.
Open Access
The effect of agitation on brewers' yeast (Saccharomyces cerevisiae) quality
(2004) Daramola, Mofoluwake M; Harrison, STL
Includes bibliographical references.
Open Access
The effect of carbon dioxide on the growth and activity of leptospirillum ferriphilum
(2010) Naik, Linus; Harrison, STL; Petersen, Jochen
Microbial oxidation rates catalysed by the acidophilic micro-organisms mediating mesophilic and thermophilic bioleaching of mineral sulphides have been well characterised under conditions typical of active tank leaching processes in the mineral industry. However, with the increasing need to beneficiate low grade ores, heap bioleaching processes are increasingly of interest. The physicochemical conditions within the heap bioleach differ considerably from the tank leaching system in terms of typical iron concentration, presence of dissolved salts and dissolved gases. This study focuses particularly on the kinetic description of the microbial ferrous oxidation rate and the microbial growth rate of the Leptospirillum species under conditions where the supply of carbon dioxide is limited.
Open Access
Effect of light supply in photobioreactors on the biomass productivity and energy efficiency of Scenedesmus sp
(2013) Gani, Aliya Habibti; Harrison, STL
Production of biofuel from microalgae is an attractive and sustainable option for meeting rising global energy demands and mitigating global warming. However, for commercial production of microalgae to be economically feasible, high biomass productivities and low auxiliary energy inputs must be achieved in large photobioreactors. According to literature, one of the main factors limiting growth is the inefficiency of light utilization (Posten, 2009; Janssen et al., 2003; Carvalho et al., 2006). In a photobioreactor, as biomass concentration and depth of culture increase, the amount of light that is able to penetrate the culture decreases exponentially. This occurs because of mutual shading of algal cells via adsorption of pigments or via scattering of cells. The purpose of this study was to optimize biomass productivity and biomass concentration by developing a thorough understanding of the microalgal response to light. In particular, the effects of light source, light intensity, configuration (internal and external), reactor design and the related variation in light/dark cycling were investigated.
Open Access
The effect of non-biological particulates on microbial cell disruption in a slurry bioreactor
(1998) Scholtz, Nicola Jeanne; Harrison, STL
Cell damage from hydrodynamic stress is an important consideration in biological systems since it can result in the growth and function of the cell becoming impaired (Toma et al. 1991, Lilly et al. 1992). In the extreme case of cell damage, cell disruption occurs. This dissertation presents the results of an investigation into the disruption of stationary-phase microbial cells in a stirred tank reactor when agitated in the presence of biologically inert solid particles in the absence of aeration. Applications of biological processes, where cells and solid particles are used, include bead mills, minerals bioprocessing, soil bioremediation and immobilised biocatalysts. An understanding of the rate, extent and mechanisms of cell disruption in these systems will facilitate the design of bioreactors to minimise or maximise microbial cell disruption, depending on the application. The primary objectives were to quantify and model the effect of incompletely and completely suspended solids on the kinetics of cell disruption, as a function of the solids concentration, agitation intensity and impeller ﬂow pattern. Saccharomyces cerevisiae was used as model micro-organism and silica as the solid particles. Modelling the cell disruption enabled its prediction as a function of the operating parameters and further allowed the cell disruption mechanisms to be elucidated. A final objective was to quantify the solids suspension as a function of the operating parameters.
Open Access
The effect of particulate-induced hydrodynamic stress on the bioleaching of chalcopyrite by a Sulfolobus sp.
(2005) Raja, Sashnee B; Harrison, STL
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.

Browsing by Author "Harrison, STL"

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