Browsing by Author "Harrison, Sue"

Now showing 1 - 18 of 18
  • Thumbnail Image
    Item
    Open Access
    Assessing environmental risks associated with ultrafine coal wastes using laboratory-scale tests
    (Trans Tech Publications, 2015-11) Opitz, Alex; Broadhurst, Jenny; Harrison, Sue
    Characterisation of the risk of acid rock drainage is typically achieved through the quantification of acid-generating and acid-consuming components present within a sample using initial laboratory-scale, chemical static tests. These static tests, however, consider ARD generation under chemical conditions and do not account for the role of micro-organisms. Their focus is exclusively on the net potential for acid generation, with no account of metal deportment or the relative rate of acid generation and consumption. The present study investigates the ARD potential of two ultrafine coal wastes samples using the standard static tests as well as the UCT biokinetic test to account for microbial ARD generation. The deportment of metal species under each test condition was also considered. The UCT biokinetic test results supported the static test classification, providing preliminary kinetic data on the ARD generation. Sequential chemical extraction tests allowed for differentiation of the host minerals according to their leaching potentials, providing supporting evidence for the deportment of metal species under the characterisation tests, thereby improving the knowledge base on which to classify coal wastes as benign or otherwise.
  • Thumbnail Image
    Item
    Open Access
    Assessment of water pollution arising from copper mining in Zambia: a case study of Munkulungwe stream in Ndola, Copperbelt province
    (2018) Mudenda, Lee; Harrison, Sue; Syampungani, Stephen
    Water pollution is recognized as one of the major environmental problems in the mining industry. This has been compounded with an increase in agriculture activities. Water pollution is a major problem on copper and coal mines throughout the world and Zambia, the focus of this study, is no exception. Worldwide freshwater resources, which provide important ecosystem services to humans, are under threat from rapid population growth, urbanization, industrialization and abandonment of wastelands. There is an urgent need to monitor and assess these resources. In this context, the physical, chemical and ecological water quality of the Munkulungwe Stream located on the Copperbelt of Zambia, was assessed with possible contamination from Bwana Mkubwa TSF, agriculture activities and subsequent impact on the surrounding community. The chemical and physical parameters were assessed at four sampling locations. Sampling site S1 was located on the Munkulungwe stream upstream of Bwana Mkubwa TSF, S2, S3 and S4 were on the main stream downstream of Bwana Mkubwa TSF. In addition, a macroinvertebrate composition analysis was performed to estimate the quality of water using the biotic index score. Finally, the relationship between physiochemical parameters and biotic index score was analysed to interrogate their inter-relationship with respect to water quality. The results showed that the average values of dissolved oxygen (DO) of 4.52 mg/l, turbidity (40.96 NTU), Co (0.24 mg/l), Pb (0.25 mg/l), Fe (0.36 mg/l) and Mn (0.22 mg/l) downstream exceeded international standards for drinking water. Upstream, the values of Co, Pb, Fe and Mn were within acceptable standards for drinking water, DO and turbidity were above acceptable standards. The metal concentration and total dissolved solutes were impacted by closeness to the mine tailings deposit with the heavy metal concentration being highest at S2 and S3. Moreover, high turbidity levels revealed that land erosion induced by agriculture activities is a severe problem in the area. Physical parameters were high in the rainy season due erosion escalated by rains while chemical parameters were high post rainy season. During the rainy season, the chemical contaminants are diluted and thus they are not such a big impact, but they tend to concentrate up during the dry MDNLEE001 III season. The stream at sampling points S2 and S3 was dominated by species tolerant (leech, Isopod and Snail: Pouch) and semi tolerant (Blackfly larvae and Amphipod or Scud) to pollution. The change in season influenced the composition of macroinvertebrates, with the number of species increased post rainy season. The average biotic index score (2.5) showed that the stream condition is not good, it is slightly polluted. The results showed that water quality downstream was substantially affected by Bwana Mkubwa TSF, agriculture activities and is likely to affect human health and food security. It is recommended that groundwater surrounding tailings dams should be monitored in both active and abandoned mines. Curtain boreholes around a tailings dam can be drilled and the water extracted and treated so that it doesn't contaminate other water bodies. To improve the environmental management of mining related impacts in Zambia, mining areas should be completely rehabilitated. There is need for remediation strategies for abandoned mine sites. Constructed wetlands, roughing filtration and phytoremediation are highly promising techniques, as they are reliable, cheap, effective and sustainable.
  • Thumbnail Image
    Item
    Open Access
    Desulphurisation of fine coal waste tailings using algal lipids
    (2018) Chiodza, Kudzai Godknows; Harrison, Sue; Fagan-Endres, Marijke
    The South African economy is an energy-driven economy which relies on coal to meet most of its energy demands. Coal mining has resulted in the generation of coal waste over 60 million tonnes, annually. Apart from the huge footprint of this waste, the sulphide minerals contained in the waste have resulted in the generation of acid rock drainage (ARD). A lot of techniques have been developed to prevent and mitigate ARD, however most of these techniques have fallen short in terms of meeting their desired objectives due to the long-term nature of ARD generation which can persist for hundreds of years after mine closure. This has resulted in emphasis being put on long-term prevention techniques that remove ARD risk over treatment techniques. One prevention technique which has shown good technical potential is the two-stage flotation method developed for desulphurisation of hard rock tailings and coal fines, developed at the University of Cape Town. On desulphurising coal, the first stage produces an upgraded coal product that may be sold, with the second stage used to separate the tailings from the first stage into targeted high-sulphide and low-sulphide fractions which may then be appropriately used or disposed of. An economic assessment of the process showed across a wide range of coal wastes the high cost of oleic acid used in the first stage of the process as a collector was a major contributor to the operating costs. The investigation undertaken in this thesis looked at the potential of algal lipids and their derivatives as biocollectors to replace the oleic acid collector in the desulphurisation process at the laboratory scale. A review of cost was carried out for a process that used raw algal lipids (RALs) or fatty acid methyl esters (FAMEs), which are derived from RALs through transesterification. Batch flotation experiments were used to assess the performance of the two bioflotation reagents in comparison to oleic acid and dodecane, an alternative but less successful chemical collector. The algal lipids cost review was a desktop study which was done by adapting literature data from Davis et al. (2014) which focused on economic evaluation of algal lipid biofuels production pathways. Results from laboratory experiments for two different coal waste feed samples showed that the performance of RALs and FAMEs was similar to that of oleic acid for the sample that was high in ash and sulphur, and better than oleic acid for the sample that was low in ash and sulphur. For example, the product from Site 1 discards from Waterberg had 24.37% ash and 2.76% sulphur using FAMEs, 26.13% ash and 2.56% sulphur with RALs, and 23.48% ash and 2.41% using oleic acid, at a reagent dose of 2.8 kg/t for all reagents. For Site 2 waste tailings from the Witbank area, the product had 23.17% ash and 0.72% sulphur when FAMEs were used as collector, 22.75% ash and 0.75% sulphur with RALs, and 20.18% ash and 0.74% sulphur using oleic acid, at the same reagent dose. Discards from Site 1 had an initial ash and sulphur content of 47.61% and 5.71%, respectively. Site 2 waste tailings had 25.56% ash and 0.91% sulphur before flotation. Increasing biocollector dosage resulted in higher yields with a compromise on the upgraded coal quality. The pH tests showed that the performance of the two bioflotation reagents was best at pH 4 in terms of yield. However, increasing the pH of the process from the natural pH of the sample (pH 2.7) to 7 resulted in collection of more ash and sulphur, thus reducing the product quality. The algal lipids cost review showed that RALs and FAMEs were potentially 20 to 21% cheaper than oleic acid, with more room for improvement. Both the laboratory experiments and the technical evaluation showed that algal lipids and their derivatives have the potential to replace oleic acid in the two-stage desulphurisation process for coal waste to obtain a saleable quality coal product while simultaneously decreasing the impact of ARD from coal waste.
  • Thumbnail Image
    Item
    Open Access
    Development of microalgae as a biopharming platform
    (2019) Els, Johann Hendrik; Rybicki, Edward; Hitzeroth Inga; Harrison, Sue
    Microalgae may be a powerful biopharmaceutical production platform that is still in its infancy of development. The research done in this project tested the feasibility of creating algal cell packs, a novel immobilised microalgae transient production platform for the expression of recombinant protein. First it had to be established whether the available plant expression vectors could be used for the transfer of genetic material into packed microalgae. The method showed successful transfer of the neomycin phosphotransferase II resistance gene (nptII). Further experiments analysed the plant expression vectors pTRAc and pRIC3.0 for expression of enhanced green fluorescent protein (EGFP) in Scenedesmus spp. by western blotting. Possible replication of the plant geminivirus-derived pRIC3.0 was then confirmed by comparing to replication in Nicotiana benthamiana by quantitative polymerase chain reaction (qPCR). Western blot results indicated EGFP expression in N. benthamiana but not in Scenedesmus. By using PCR the presence of EGFP DNA in Scenedesmus was detected but qPCR showed no increase of the pRIC3.0 replicon. Despite no detection via antibodies of EGFP in Scenedesmus, green fluorescence was observed. These initial results showed promise and points to a system that requires optimisation for increased transfection rates and protein expression. Following on from the initial work, the project set out to determine the feasibility of expressing a recombinant anti-Ebola viral inhibitor protein in three different plant based platforms namely N. benthamiana, a microalgal genus, Desmodesmus and a BY2 tobacco plant-cell culture. Protein expression was compared between the Desmodesmus algal cellpack, N. benthamiana plant expression system and BY-2 plant cell packs by western blotting. Four designs of the viral inhibitor fused to the maize ƴ-zein protein body inducing protein, ZERA, were expressed in trace quantities. Transient expression was more prominent in the algal cell packs than in N. benthamiana and BY-2 cells. The algal cell pack system may potentially be a powerful tool to test recombinant protein expression in a range of microalgal hosts via Agrobacterium-mediated genetic transfection. The future development of recombinant protein expression platforms could be enhanced by rapid testing of protein production in different species. Refinement needs to be done on the algal cell pack to increase transfection efficiency and expression in microalgae to produce commercially viable quantities of heterologous protein.
  • No Thumbnail Available
    Item
    Restricted
    Effect of physico-chemical and operating conditions on the growth and activity of Acidithiobacillus ferrooxidans in a simulated heap bioleaching environment
    (Elsevier, 2015-05) Govender, Elaine; Bryan, Chris; Harrison, Sue
    Recent understanding of microbial retention within heap bioleaching systems has highlighted the importance of quantifying microbial growth and activity in both the bulk flowing solution and in the ore-associated phases. Typically, industrial heap bioleaching operations report variations in process conditions such as inoculum preparation and concentration and elevated copper concentrations in the recycled irrigation solution. In this paper, a mini-column reactor system containing pre-constructed and agglomerated, low-grade ore samples representing grab samples from a larger heap, were used to investigate the effect of a selection of physico-chemical and operating conditions on microbial growth, colonisation and substrate utilisation kinetics, considering both the planktonic and sessile populations of Acidithiobacillus ferrooxidans. The factors studied included inoculum size, inoculum cultivation conditions, availability of ferrous iron in the bulk flowing solution and copper concentration in the bulk flowing solution. The microbial population in the interstitial phase, i.e. associated with, but not bound to, the ore, remained the most abundant within the heap under all physico-chemical conditions considered. A comparison of the tests with different inoculum sizes found that a smaller inoculum size resulted in an increased delay in microbial growth and ferrous iron oxidation, but similar apparent maximum specific growth rates and iron oxidation rates. In contrast to the microbial culture grown on pyrite, a delay in microbial activity was observed for the culture grown on ferrous iron. However, greater microbial cell densities were reached, in the interstitial and attached phases compared with the pyrite grown culture. The introduction of 6 g L-1 cupric ions into the feed solution containing 0.2 g L-1 ferric iron resulted in decreased microbial growth rate in the interstitial phase but not in the attached phase. Where the pyrite culture was pre-exposed to cupric ion, the microbial growth rate in the interstitial and attached phases was significantly enhanced. Nevertheless, the presence of cupric ion in the irrigation solution resulted in a decrease in microbial ferrous iron oxidation rate, irrespective of pre-culture conditioning. This study emphasises the important role played by the stagnant interstitial phase during the colonisation of a low-grade heap, particularly under adverse conditions for microbial growth and activity. It also highlights the role of inoculum culture conditions on the potential trade-off between increased heap colonisation and increased lag periods in microbial activity during heap start-up.
  • Thumbnail Image
    Item
    Open Access
    Evaluation of three carbon sources for the biological treatment of acid mine drainage through process modelling
    (2004) Gopal, Hemant; Harrison, Sue; Moosa, Shehnaaz
    South Africa is considered to be a semi arid to arid country (Harrison, 2004), hence its water resources are of great importance. In South Africa, the principal contributors to extensive sulphate pollution of ground water are the industries mining coal and metalbearing sulphidic minerals, which gives rise to the production of acid mine drainage (AMO). AMO is generated from both active and abandoned mining areas. The metal sulphides in the metal tailings are oxidised to produce large amounts of dissolved metals, sulphates and acids. These metals and acids constitute acid mine drainage. This natural process results from the exposure of ores to atmospheric conditions coupled with bacterial activity (Tsukamoto and Miller, 1999). Pollution by AMO can have a devastating effect on terrestrial and aquatic ecosystems. It is a long-term environmental problem since the oxidation of the metal sulphides can continue indefinitely after the closure of the mine {Tsukamoto and Miller, 1999). The traditional method of treating AMO is by neutralisation of the acid through the addition of lime (Santos et al., 2004). More recently, biological treatment of AMO has become attractive. However, a concern with this method is the requirement and availability of cost effective and efficient sources of carbon and electron donors. This thesis aims to evaluate three different substrates as sources of carbon and electron donor capacity (ethanol, molasses and primary sewage sludge) in terms of their availability and their impact on both final water quality and process economics. It seeks to determine the extent to which the carbon substrate is the limiting factor in terms of process economics. Further to the economic analysis, analysis of substrate requirements as a function of availability as well as impact of substrate used on process complexity and water quality is reviewed. These goals are approached through use of a process model. Data for the development of the model and its calibration has been taken from the literature. After an extensive review of the literature, a model of the anaerobic digestion process has been compiled using Excel, with the reactor being simulated using MATLAB. The program for the reactor is based on the simulation developed by Knobel (1999) in OCTA VE. The reactor was simulated as a CSTR that was well mixed and had no biomass retention. The statistical method used to verify the fit of the model to the data was the Chisquare statistic. This is a good method of comparing the model data with literature data as it showed the degree of deviation of the model from the literature values. The values obtained from this calculation were then compared to the critical value of i' at the 90% confidence level. The model was verified against four sets of anaerobic digestion data from literature with the carbon source being of various complexities. The results of the mass balance showed that AMD site 3 required the highest concentration of carbon substrate owing to the highest concentration of sulphate entering the system. AMD site 3 also had the highest production of H2S gas from both the anaerobic reactor as well as the mixer. As AMD site 3 treated the highest concentration of sulphate, it also produced the highest amounts of by-products. In the same respect, AMD site 1 treated the lowest concentration of sulphates and produced the least amount of by-products. The simulation was set up such that the final effluent sulphate concentration met the EPA standard of250 mg r1 and a sulphide level ofless than 10 mg rt. The only water parameter that needed analysis was the COD levels. The recommended COD level in the final effluent was 75 mg rt (DW AF, 1996 and Finn, 2004). Using the proposed flowsheet, only systems using ethanol as a carbon substrate approached this criterion. Both the molasses and primary sewage sludge systems failed to achieve this using the well mixed reactor system described by the model. For molasses or primary sewage sludge to meet the required COD levels, a reactor that could uncouple the hydraulic residence time and solids residence time and have high solids retention, would be required. The capital costing of the treatment plants was based on pricing obtained by Ball and Schroeder (2001) who had previously costed similar units. A factorial method was used for the cost scaling of the units. Inflation was also taken into account. The operating cost of the system was based on the methods presented in Sinnott (2000) and Turton et al. (1998). The economic results showed that using stainless steel was 16 times more expensive than using reinforced concrete as the material of construction. Hence, all further work was done on the basis of using reinforced concrete as the material of construction. Ethanol was found to be the most economically viable choice when the cost saving on the disposal of primary sewage sludge was not taken into account. Using a complex particulate carbon source such as primary sewage sludge as the carbon substrate proved to be the most expensive option of the three where no benefit of reduced disposal costs of this complex particulate was found. However, when the savings resulting from reduced disposal requirements of primary sewage sludge from wastewater treatment were included, primary sewage sludge proved to be the most economically viable option. This was an important finding as it showed that there was a high burden reduction on the wastewater treatment works and hence should be strongly recommended for use in the treatment of acid mine drainage. As a corollary to this, the ongoing development of reactor systems exploiting the uncoupling of hydraulic and sludge residence times and maximising sludge retention is of prime importance.
  • Thumbnail Image
    Item
    Open Access
    Investigation into the start-up and operation of upflow anaerobic sludge bed reactors
    (2022) Stott, Rory; Harrison, Sue; Ikumi, David
    High-rate anaerobic biological wastewater treatment using the upflow anaerobic sludge bed (UASB) reactor technology offers the potential to reform wastewater treatment. However, the lack of clarity regarding the mechanisms responsible for self-immobilisation of the microbial consortia involved, known as granulation, presents an obstacle to the wide-spread use of this technology. In this study, two laboratory-scale UASB reactors were commissioned for the purpose of generating datasets for model development. A sucrose-based feed was used for the experiments, which were conducted at 37°C. Deterioration of the sludge granules used as inoculum into undesirable bulking-type sludge resulted in refocusing the study to investigate the granulation process. After consulting the literature on granulation, an experimental investigation into the effect of providing additional hydraulic mixing by recycling reactor effluent on granulation was conducted. It was hypothesised that the additional hydraulic mixing would result in the formation of more settleable granules. However, it was found that inclusion of the additional hydraulic mixing resulted in a less dense sludge bed which contained more visual signs (presence of both more loosely-bound exogenous polymeric substance and long filaments presumed to be Methanosaeta Spp.) of bulking-type sludge. In hindsight it was found that application of too low a sludge loading rate in the experimental investigations was the cause of the granulation issues, but that this was exacerbated by the additional hydraulic mixing. Apart from granulation issues, a low effluent pH of 6.5 was obtained from the reactors during the experimental investigations in spite of a high feed pH of 8.0. It was hypothesised that the production of VFA and consumption of NH3 were the primary causes of the acidity generation. A fixed-conversion model of the digester pH was developed to investigate the conversions of the relevant weak acid and base species present and the effects of these conversions on the digester pH. It was found that the dissolution of CO2 to satisfy the vapour-liquid equilibrium between the headspace CO2 partial pressure and dissolved carbonic acid concentration was predominantly responsible for the decrease in pH across the reactors. It is on the basis of these findings that both hypotheses were refuted.
  • No Thumbnail Available
    Item
    Open Access
    Magnetic resonance imaging characterisation of the influence of flowrate on liquid distribution in drip irrigated heap leaching
    (Elsevier, 2015-12) Fagan-Endres, Marijke; Harrison, Sue; Johns, Michael L; Sederman, Andrew J
    Liquid irrigation is one of the key process control parameters following the construction of an ore leaching heap. This study uses 3D magnetic resonance imaging (MRI) to examine non-invasively the effect of liquid flowrate changes on heap hydrology when drip irrigation is used. Experimental results from a vertical column show that the increase in flowrate causes an increase in the number of rivulets in the ore bed. The new rivulets were found to be thicker, and their development caused an increase in liquid-solid contacting area which is considered advantageous for metal ion recovery. Experiments performed on larger samples showed that the effects of flowrate changes were limited to the region directly below the drip emitter because the increase in flowrate caused an increase in macro-pore flow and not capillary retention of liquid. Therefore the increase in flowrate was not found to perturb liquid distribution patterns in a way that would be substantially advantageous to heap leaching recoveries.
  • Thumbnail Image
    Item
    Open Access
    Maximising energy recovery from the brewery wastewater treatment system: a study evaluating the anaerobic digestion wastewater treatment plant at SAB's newlands brewery
    (2015) Nkadimeng, Lefa Steven; Harrison, Sue
    This study has been encouraged by the successful recovery of useful energy from brewery wastewater using anaerobic digestion technology. It aims to evaluate the environmental benefits or burden of improving energy production by using organic brewery by-products as additional feedstock into the SABWTP. An environmental impact assessment on the SABWTP and its associated process was carried out using life cycle assessment (LCA) tools. Anaerobic digestibility of the two major organic brewery by-products, brewer’s spent grain and brewer’s spent yeast, was evaluated experimentally using laboratory bench scale reactors. The results were used to postulate the feasibility of adding these feedstocks into the SABWTP. Based on these findings, three viable processing scenarios were synthesised and assessed in terms of environmental impact analysis. In the environmental impact analysis, the three scenarios were compared using average process conditions and the main contributing factors to environmental burdens associated with each scenario were identified.
  • Thumbnail Image
    Item
    Open Access
    MRI and gravimetric studies of hydrology in drip irrigated heaps and its effect on the propagation of bioleaching microorganisms
    (Elsevier, 2014-12) Fagan, Marijke A; Ngoma, I. Emmanuel; Chiume, Rebecca Angela; Minnaar, Sanet; Sederman, Andrew J; Johns, Michael L; Harrison, Sue
    Heap bioleaching performance is dependent on the contacting of the leach solution with the ore bed, hence on the system hydrodynamics. In this study two experimental setups were used to examine hydrodynamics associated with irrigation from a single drip emitter, one of the most common methods of heap irrigation. A specialist magnetic resonance imaging (MRI) method which is insensitive to the metal content of the ore was used to examine the liquid flow into an ore bed in the immediate vicinity of an irrigation point. The distribution of liquid in, microbial colonisation of and mineral recovery from a bioleach of a large scale 132 kg “ore slice” were subsequently monitored using sample ports positioned along the breadth and height of the reactor. In both systems the lateral movement of the liquid increased with bed depth, though preferential flow was evident. The majority of the liquid flow was in the region directly below the irrigation point and almost no liquid exchange occurred in the areas of lowest liquid content at the upper corners of the bed in which fluid exchange was driven by capillary action. The MRI studies revealed that the liquid distribution was unchanging following an initial settling of the ore bed and that, at steady state, the majority (~60%) of the liquid flowed directly into established large channels. The limited lateral movement of the liquid had a significant impact on the local leaching efficiencies and microbial colonisation of the ore with cell concentrations in the regions of lowest liquid content lying below the detection limit. Hence poor lateral liquid distribution with drip irrigation, and the associated impact on colonisation was identified as a significant disadvantage of this irrigation approach. Further, the need to optimise fluid exchange throughout the ore bed was identified as key for optimisation of leaching performance.
  • No Thumbnail Available
    Item
    Restricted
    A novel experimental system for the study of microbial ecology and mineral leaching within a simulated agglomerate-scale heap bioleaching system
    (Elsevier, 2015-03) Govender, Elaine; Bryan, Chris; Harrison, Sue
    Heap bioleaching systems are complex, with multiple sub-processes interacting at various scales within the heterogeneous reaction environment. This provides a challenge to determining the growth characteristics of micro-organisms and reaction characteristics of the mineral ore in a representative environment. The experimental system presented in this paper was designed to simulate heap bioleaching conditions using multiple, identically constructed agglomerate-scale mini-column reactors. Ore samples were prepared representatively as grab samples of a larger heap. Particle size distributions and agglomerate masses of the prepared ore samples were shown to be similar within acceptable variance and provided comparable surface areas for microbial colonisation and chemical reaction. The microbial abundance within the whole ore system was determined from effluent sampling for the planktonic population and the systematic and sequential sacrifice of identically operated mini-column reactors to determine the change in the ore-associated microbial population with time. Microbial colonisation and growth rate kinetics were determined from analysis of these populations. The growth curves obtained for the bulk flowing solution and ore-associated populations at the base case operating conditions were reproducible, within a 95 % confidence interval.
  • Thumbnail Image
    Item
    Open Access
    Optimising the growth of Cryptococcus species SS1, a potential probiotic for farmed abalone
    (2004) Van Wyk, Jennifer Caroline; Coyne, Vernon; Harrison, Sue
    Farmed abalone is a reliable and good quality source of abalone. Cryptococcus species SS1 was isolated from the gut of the South African abalone, Haliotis midae, and has been identified as a potential probiotic for farmed abalone. The implementation of strain SS1 as a probiotic for aquacultured abalone required the design of a fermentation system to produce hjgh concentrations of the yeast strain in order to supply the probiotic to commercial abalone producers. The aim of this project was to assist in the recommendation of a commercial fermentation process that is economically feasible for the production of strain SS1. This involved evaluation of all the main factors that will contribute to the cost of the fermentation; i.e. cultivation medium, fermentation space and time, and productivity.
  • Thumbnail Image
    Item
    Open Access
    Optimising the growth of Cryptococcus species SS1, a potential probiotic for farmed abalone
    (2004) Van Wyk, Jennifer Caroline; Coyne, Vernon; Harrison, Sue
    Farmed abalone is a reliable and good quality source of abalone. Cryptococcus species SS1 was isolated from the gut of the South African abalone, Haliotis midae, and has been identified as a potential probiotic for farmed abalone. The implementation of strain SS1 as a probiotic for aquacultured abalone required the design of a fermentation system to produce high concentrations of the yeast strain in order to supply the probiotic to commercial abalone producers. The aim of this project was to assist in the recommendation of a commercial fermentation process that is economically feasible for the production of strain SS1. This involved evaluation of all the main factors that will contribute to the cost of the fermentation; i.e. cultivation medium, fermentation space and time, and productivity.
  • Thumbnail Image
    Item
    Open Access
    Phase distribution identification in the column leaching of low grade ores using MRI
    (Elsevier, 2013) Fagan, Marijke A; Sederman, Andrew J; Harrison, Sue; Johns, Michael L
    Heap bioleaching is gaining importance as an approach for the recovery of valuable metals (e.g. Cu2+) from low grade ores. In this process iron and/or sulfur oxidising microorganisms are used to aid the oxidation of base metal sulfides in the ore, thereby liberating the metal ions into solution. Leach performance is strongly influenced by the contacting of the leach solution and the ore particles. In order to better understand the distribution of the leaching solution on the pore scale in these heaps, Magnetic Resonance Imaging (MRI) was used to acquire images non-invasively of a section of an irrigated ore bed. This was made possible by the use of specialist MRI acquisition sequences suited to the magnetically heterogeneous environment as presented by the ore material. From the images we were able to determine the pore-occupancy of the liquid and gas phases and to provide novel measurement of the interfacial area between air, leach solution and ore.
  • Thumbnail Image
    Item
    Open Access
    Selection of bacterial species from wastewater for potential production of poly (γ-glutamic acid): isolation, characterisation and growth kinetics
    (2013) Madonsela, Ziningi; Harrison, Sue
    Wastewater treatment plants represent a source of nutrients for microbial growth and product formation. In an approach in which bioresource productivity is maximised, it is desirable to not only achieve water treatment to the desired standard, but at the same time to harness the value in these resources. Wastewaters are a source of nutrients such as carbon, nitrogen and phosphates. Macronutrients typically comprise the major share of the operating costs of commodity bioprocesses, such as the production of alcohols, organic acids and polymers. The nutrient loads in municipal wastewaters are dilute, but add up to significant daily loads because of the massive volumes generated in urban populations. The effluent of most wastewater treatment plants in South Africa is released back into either rivers, lakes or the ocean without reuse. For many, there is a concomitant failure to comply with the country's effluent requirements. This has resulted in the need to move towards more sustainable water treatment systems, including more efficient and innovative solutions to treat wastewater. Additionally, by recovering value from waste, there is potential to improve plant operation; releasing water which is better treated, more compliant and can be reused, while simultaneously improving resource productivity and minimising environmental burden; thereby changing the economics of the wastewater treatment plant. This includes the recovery or the production of valuable resources, whilst in turn recovering clean water. Bioprocessing to reduce these nutrient loads in wastewater while producing a range of byproducts have conventionally included biogas and compost, produced with minimal modification of existing plants. In extending the potential product range of these ‘wastewater biorefineries', key design factors include using waste resources in a non-sterile environment, thus requiring a positive selection pressure for the product of interest, and ideally producing a product readily separated from the wastewater through a phase change such as precipitation. Stress and storage polymers satisfy both these requirements. In this project, we explore such a wastewater biorefinery approach in which we aim to use the nutrient component of partially treated domestic wastewater for the production of poly (γ-glutamic acid) (γPGA). γ-PGA, a polymer of D- and L-glutamic acid monomers connected by amide linkages, is a naturally occurring biopolymer, synthesized by a variety of micro-organisms. Most commonly, γ-PGA production has been studied in Bacillus species, such as B. subtilis and B. licheniformis. Bacillus species are ubiquitous in the environment, including an association with domestic wastewater treatment. Its enrichment has been associated with improved treatment processes. The favourable properties of this very promising polymer include its water solubility, anionic nature, biodegradability and non-toxicity towards humans, animals and the environment. Potential applications of γ-PGA are reported in the medical, food, cosmetic, wastewater treatment, plastic,agricultural and textile industries. In this project, we consider the production of γ-PGA by Bacillus-enriched species for the Synopsis iii partial treatment of domestic wastewater and concomitant production of the polymer for soil improvement and water treatment. To design and optimise a process using wastewater for γ-PGA production, it is important to understand the growth kinetics of Bacillus-like microorganisms that can be found in a domestic wastewater treatment plant. The base case for growth, substrate utilisation and biomass production has been presented for a Bacillus licheniformis type culture strain in this dissertation. In presenting this base case, a complete experimental methodology using both shake flasks and deep well plates is developed and appropriate analytical protocols selected. The second objective of this project was to characterise the growth kinetics of the microorganisms isolated from the wastewater obtained from the Mitchell's Plain wastewater treatment plant. Following enrichment of wastewater samples collected, 18 isolates were obtained and characterised in terms of morphology. Further, using DNA sequence data for the enzymes involved in PGA synthesis, primers were designed to identify strains carrying γ-PGA synthesis potential through molecular biology studies. Two different media; namely Medium E, containing glutamic acid, citric acid and glycerol as carbon sources, as well as a modified Medium E, in which the glutamic acid was replaced with glucose, were used for these experiments. Isolates showing reproducible growth and evidence of polymer production were selected for detailed screening in terms of growth. Based on this, six isolates were chosen. These experiments were performed in both shake flasks as well as deep well plates with the growth kinetics and biomass production by the various strains carefully analysed. Biomass concentrations varied from 2 to 8 g.L-1 while specific growth rates varied from 0.11 to 0.26 h-1 in these cultures. The results of the growth studies showed that the growth rates and biomass production of the different isolates varied greatly under identical cultivation conditions. Cultivation of the isolates in deep well plates generally yielded higher biomass concentrations in comparison to shake flask cultivation. A quantitative analysis of the data on carbon substrate utilisation in the media showed that glucose was the preferred of these, most consumed by the isolates for cell growth. Preliminary media optimisation was undertaken to identify optimal C:N:P ratios in the modified growth Medium E and to assess the impact of these medium components by using two-level Plackett-Burman factorial design. The dependence of biomass accumulation on C levels and maximum specific growth rate on N is illustrated. Response surfaces revealed the insignificant effect on the microorganism growth of varying P concentrations. Influence of P was attributed when P acted in tandem with C and N. Identification of the isolates selected for detailed screening was confirmed using 16S rRNA sequencing. There were two major families present – Proteobacteriaceae and Enterobacteriaceae – which grouped accordingly when analysed phylogenetically. The Bacillus, and opportunistically pathogenic enteric bacteria Klebsiella and Enterobacter, were reflective of genuses which have a high Synopsis iv probability of being present in a treatment plant which predominantly treats domestic wastewater containing high sewage loads, such as Mitchell's Plain. A suitable reactor configuration, capable of treating wastewater and simultaneously producing γ-PGA, was proposed for integration into Mitchell's Plain wastewater treatment plant after studying the selected Bacillus isolate in a laboratory-scale bioreactor in optimal medium. The sustained biomass production and growth rate, even at lower medium carbon inputs, shows a great potential for application by enrichment, growth and product production of this Bacillus subtilis strain in a wastewater treatment plant. Although this work was able to make a substantial contribution to the current knowledge of microbial growth kinetics in various media and bioreactor systems, the study limitations related to growth profiling in more dilute and variable nutrient concentrations, non-sterile environments and mixed culture dynamics are acknowledged. These present a scope and opportunity for further research in this exciting field. Analysis of extracted and purified γ-PGA showed a polymer composed of a combination of polysaccharides and protein (in roughly equal proportions in three of four of the isolates) in which histidine, homoserine and glutamic acid were typically the most dominant amino acids. The impure nature of this γ-PGA remains suitable for wastewater applications, but not for areas which require a product composed of specific, high molecular weight stereoisomers such as the medical industry. This study illustrates the importance of developing new experimental techniques for more γ-PGA-specific purification and improved analysis. Further it demonstrates the shortcoming of the gravimetric analysis of the crude extract typically reported in the literature. The findings of this project are intended to be used in a system which applies wastewater as an economical and sustainable source of nutrients with the aim of producing valuable products through bioprocessing applications.
  • No Thumbnail Available
    Item
    Open Access
    A study of permeability and diffusion at the agglomerate-scale in heap (bio)leaching systems
    (Trans Tech Publications, 2015-11) Govender, Elaine; Kotsiopoulos, Thanos; Harrison, Sue
    Multiple mini-column reactors, loaded with identically constructed ore samples representing grab samples of a larger heap, were used to study the behaviour of solution tracers to elucidate solution diffusion, dispersion and transport. The tracers were either introduced to the ore bed as a pulse, included during agglomeration of the ore or introduced to the system by submerging the ore bed. These methods of tracer introduction allowed for the characterisation of flow interchange in unsteady state systems. The resulting concentration-time distribution curves were analysed to allow characterisation of flow dispersion and diffusion, which facilitates exchange between the fast flowing and largely stagnant liquid phases. Preliminary results support the presence of distinct stagnant and flowing regions within the agglomerated ore bed. Agglomeration with the tracer promotes increased retention on the ore; potentially enhancing microbial transport via increased solution exchange after the initial period of attachment.
  • Thumbnail Image
    Item
    Open Access
    Synthesis of monodisperse silver nanoparticles for antibacterial purposes
    (2018) Adam, Sarah; Kooyman, Patricia; Smart, Mariette; Harrison, Sue
    Safe drinking water is a scarcity for many in the developing world. Currently, 884 million people, 48% of whom live in sub-Saharan Africa, are without access to even basic drinking-water services (WHO/UNICEF Joint Monitoring Programme for Water Supply and Sanitation, 2017). This has a severe impact on the health of those living in such communities, which is why the universal access to safe and affordable drinking water has been made a priority by the United Nations. There is an undeniable need for change so that the lives of these many millions of people may be improved. Silver nanoparticles have great potential in being used in water disinfection applications because of their high antibacterial activity and broad antimicrobial spectrum (Qu, Alvarez, & Li, 2013). Development in this area is critical, particularly in advancing technology to allow greater accessibility to clean drinking water for people in poor, rural areas in developing countries. Incorporating nanotechnology into current water disinfection systems, as well as developing new water treatment nanotechnology, shows promise in addressing this issue. However, much research needs to be done first before this can become a reality (Q. Li et al., 2008). There is particular concern about the toxicity aspects of silver nanoparticles, both in humans and towards the environment. Whilst the current study does not investigate their toxicity, it is important to highlight the need to fully understand the human and environmental impacts nanoparticles may have in assessing their applicability in microbial control. Literature indicates that, although the role of silver nanoparticles themselves in the antibacterial mechanism cannot be excluded entirely, it is the silver ions that are mostly responsible for their antibacterial activity (Foldbjerg, Jiang, Miclăuş, et al., 2015; Le Ouay & Stellacci, 2015; Panacek et al., 2006; Xiu, Zhang, Puppala, Colvin, & Alvarez, 2012). Sotiriou & Pratsinis (2010) found that silver nanoparticles of smaller than 10 nm had a negligible antibacterial effect in comparison to the ions they released. Thus, to isolate just the effect of the released silver ions, it was desired to prepare uniformly sized particles of smaller than 10 nm. Controlling the size of the formed particles requires consideration of parameters that affect their nucleation and growth (Thanh et al., 2014). These can be thermodynamic, kinetic or stoichiometric parameters. It is on this basis that the work described herein was developed. This study aimed to synthesise silver nanoparticles suitable for use in water disinfection applications by exploring how preparation conditions affect the particle size and distribution. To do this, two different aqueous chemical reduction preparation methods were performed and reaction conditions such as surfactant concentration, agitation rate, synthesis temperature, and method of chemical addition were varied to produce monodisperse silver nanoparticles with an average size of smaller than 10 nm. This study also aimed to investigate the antibacterial efficacy of silver nanoparticles deposited on quartz fibre filters against E. coli. Two silver nanoparticle syntheses procedures were extensively investigated. Method One (AL-Thabaiti et al, 2008) uses ascorbic acid as the reducing agent and SDS (sodium dodecyl sulphate) as the surfactant whilst Method Two (Yang, Yin, Jia, & Wei, 2011) uses aniline as the reducing agent, DBSA (dodecylbenzenesulfonic acid) as the surfactant and NaOH (sodium hydroxide) as the ‘activating’ chemical. The surfactant concentrations, agitation rates, synthesis temperature, reducing agent concentrations and methods of chemical addition were varied for each of these synthesis procedures and the effect thereof on particle size was investigated. Both synthesis methods produced fcc metallic silver nanoparticles with (111) and (200) lattice planes, confirmed by studying nanoparticle d-spacings. For Method One, the unaltered synthesis procedure produced the smallest particles with a numberbased mean size of 3.6 ± 3.8 nm and a volume-based mean particle size of 15.4 ± 6.4 nm. For Method Two, which is performed at 90 °C, the ‘hot’ injection of NaOH into the system resulted in the production of the smallest nanoparticles with a number-based mean particle size of 6.7 ± 5.4 nm and a volumebased mean particle size of 22.3 ± 10.9. Removing excess surfactant and collecting these nanoparticles in powder form would facilitate antibacterial efficacy studies, however this proved to be difficult. Additionally, the presence of large nanoparticles in both samples, as evidenced from the volume-based size distributions, means that in assessing antibacterial activity of the nanoparticles, it will be difficult to interpret whether the bactericidal effect is due to silver ions or because of an interaction between the bacteria and the actual nanoparticles. Antibacterial efficacy studies were therefore not performed on these synthesised silver nanoparticles. Silver nanoparticles deposited on quartz fibre filters via spark ablation were prepared at Delft University of Technology. SEM revealed that the deposited nanoparticles on the filters had a mean particle size ranging from 25 to 70 nm. Studies using E. coli (ATCC® 25922™) did not conclusively demonstrate antibacterial activity of the filters. It is believed the large particle size, and thus slow dissolution into silver ions, may be the reason for the lack of evidence of bactericidal activity over the 24-hour experimental period. The results of this study indicate how small changes in synthesis parameters can have a significant effect on nanoparticle size and uniformity, morphology, and degree of agglomeration. This reveals the importance in specifying exact parameters used in nanoparticle preparation to allow for better reproducibility, including vessel size, mixing speed, and rate of chemical addition. This work also showed that it is important to quantify the release of silver ions from silver nanoparticles before performing antibacterial efficacy assessments. Since silver ions are the most important factor in the antibacterial action of silver nanoparticles, understanding their rate of release will allow for improved experimental design thus producing useful results. There is great potential for the use of silver nanoparticles for disinfection, as evidenced particularly by the antibacterial efficiency of Ag+ against E. coli (ATCC® 25922™). However, improvements in both the synthesis of silver nanoparticles and methods of assessing their bactericidal efficacy are clearly necessary. This study has highlighted the challenges that may be faced in the pursuit of efficiently and safely using silver nanoparticles for water treatment and disinfection. Numerous recommendations for future studies have been put forward. These include: further optimisation of the nanoparticle synthesis procedure so as to produce particles of the desired size and acquire them in powder form, performing a thermodynamic estimation of the equilibrium silver ion concentration as a function of silver nanoparticle size to quantify the effect nanoparticle size will have on bactericidal activity, and using more realistic water conditions for antibacterial efficacy experiments to simulate the environment in which silver nanoparticles will be applied.
  • Thumbnail Image
    Item
    Open Access
    The effect of cooling on brewer's yeast quality
    (2001) Nkosi, John C; Harrison, Sue
    The primary concern of a brewer is to produce beer of a desired flavour and quality, in an economic and efficient manner. In large scale brewing operations, process efficiency and beer quality rely on consistent fermentation. Stewart (1977) reports that improper handling of yeast in the brewing process may result in beer of sub-standard quality.