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.

There is an abundant availability of zinc sulphide (sphalerite) ore (160 million tons at 7.40 % Zn) at Gamsberg, Northern Cape in South Africa. The ore body is South Africa’s greatest unexploited base metal resource. Regardless of its size, the low zinc and high manganese content of the sphalerite combined with the low zinc price prohibits the development of the deposit. Sphalerite is the most common zinc mineral, hence 95 % of the world’s zinc production is from this mineral. Sphalerite is currently processed by crushing-milling-flotation, followed by the roast-leach-electrowinning (RLE) process. This route has major detrimental impacts on the environment, it produces SO2, and cannot treat ores of low grade or higher complexity. Therefore, alternative processes are being sought in order to circumvent the RLE process. This study compares three different process routes in the context of processing ore from the Gamsberg deposit for refining 3.4 million tpa ore in order to produce special high grade (SHG) zinc (>99.995% Zn). These routes include heap leaching and refining locally (route 1), preparing a flotation concentrate and refining it locally (route 2) and lastly, preparing a flotation concentrate and shipping it for toll refining in Europe (route 3). Zinc heap leaching has not yet been commercialised due to the absence of solvent extraction reagents which can selectively extract zinc from a low tenor acidic pregnant leach solution without incorporating the neutralization stage. Therefore, route 1 has higher risk as compared to the other routes. A desktop model which provides a comparison of capital cost, operating cost, NPV, IRR and PVR has been developed. Parameters such as average zinc grade, process recovery and zinc price are provided as inputs. The effects of fluctuations in important parameters such as working capital, and zinc price on NPV are assessed using Matlab.

Includes bibliography. / 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.

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.

Microalgae are recognised as a source of lipids for bioenergy, nutrients and pharmaceuticals. Photobioreactors, closed vessels for microalgal cultivation, are known to have high energy consumption due to mixing and aeration. Sparging is commonly used for mixing and gas-liquid mass transfer in photobioreactors, but is energy intensive. The aim of this work was to reduce these energy requirements by optimising conventional sparging and considering surface aeration coupled with mechanical agitation as an alternative. An airlift photobioreactor was used as a base for comparison with two novel, surface aerated reactors: oscillatory baffled and wave photobioreactors. The three bioreactors were compared in terms of power input, mixing, CO2 mass transfer, algal growth and lipid production. Prior to comparison, each photobioreactor was optimised based on these parameters. To calculate power input, isothermal gas expansion equations were used for sparged systems and calorimetry was used for mechanically agitation systems. Mixing was investigated using a salt tracer and phenolphthalein indicator and mass transfer was measured using the gassing-in method. Scenedesmus sp., a high lipid-producer, was cultivated in low nitrate media across a range of mixing rates in each photobioreactor.In the airlift photobioreactor a critical minimum CO2 supply rate (of 2.7×10-5 m s-1) was found, below which carbon was limiting and above which energy was spent on sparging without increased productivity (0.20 g L-1 d-1 biomass; 0.03 g L-1 d-1 lipid). In the oscillatory baffled reactor, insufficient mass transfer limited algal productivity (0.11 g L-1 d-1 biomass; 0.02 g L-1 d-1 lipid). The wave reactor had high CO2 mass transfer coefficients (10 – 140 h-1) in comparison to the airlift (2.7 – 40 h-1) and oscillatory baffled reactors (6.3 – 37 h-1). Sufficient biomass productivity (0.18 g L- -1 d-1) and higher lipid productivity (0.045 g L-1 d-1) at lower power input in the wave reactor resulted in higher energy efficiency compared to the airlift reactor. Life cycle analysis of simulated algal biodiesel production showed that bioreactor energy contributed 99% of total energy consumption. Therefore, the global warming potential was reduced by 73% when the airlift reactor was operated at the critical minimum CO2 supply (with gas compression to 2 bar) and a further 19% when the wave reactor was used. This work offers an energy efficient alternative to sparging, through the generation of a well-mixed wave in a surface aerated bioreactor. It also offers methods for optimisation of energy usage with respect to mixing and aeration. Reducing bioreactor energy consumption is key to feasibility, and was demonstrated here to reduce energy-related environmental burdens.

Amylases are hydrolytic enzymes that cause the breakdown of starch and related polysaccharides to simple sugars. Amylases are applied in brewing, food, detergent and textile industries. Most commercial amylases are derived from fungi or bacteria. Bacterial amylases are desired for commercial use, due to their thermo-stability and faster production rates. Bacteria of the genus, Bacillus, are considered to be a good source of extracellular proteins because they have high growth rates and have a naturally high capacity for secretion of extracellular proteins. Bacillus halodurans Alk36 is an alkaliphilic, thermotolerant isolate that can grow over a wide pH and temperature range. Preliminary studies have shown that B. halodurans Alk36 can grown in EnBase® medium (at pH 8.5) containing starch as the carbon source, without the addition of a commercial amylase. The ability to grow on starch, in the absence of an external amylase, indicated that this strain produces endogenous alkaliphilic amylases, which may be exploited for a number of industrial applications. In the present study, the physiological and biochemical characterisation of B. halodurans Alk36 and its endogenous amylases were investigated.

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]

Resistance to antibiotics by microbial pathogens continues to be a major global health problem. Treatment of bacterial infections is becoming increasingly complex and expensive. Tuberculosis (TB), caused by Mycobacterium tuberculosis infection, is affected by antibiotic resistance. In South Africa, the Western Province is the worst affected, with an increasing incidence of both multi-drug resistant (MDR) and extensively drug resistant (XDR) strains of M. tuberculosis. Both resistant forms of TB increase the length of treatment to almost 24 months and cost by as much as 1400 times that of regular anti-tubercular chemotherapy. A potential solution to this problem is the discovery of new drugs, which can be obtained from natural sources. Actinomycetes are good sources of these drugs, with over 45% of current medicines derived from these bacteria. The actinobacterium Streptomyces polyantibioticus SPRT (SPRT) was locally isolated and first described by Le Roes (2006). It has been shown to produce bioactive molecules active against a range of bacteria, including compounds (drugs) that have anti-tubercular properties. One of the anti-tubercular molecules was identified as 2,5-diphenyloxazole (DPO). DPO is currently used as a component of scintillation fluid for its luminescent properties and is synthesised chemically in industry. SPRT is the only reported biological source of DPO, it is however not yet produced commercially via a biological route. The present study was performed to inform future process development of DPO production from SPRT. An investigation into the growth and production of antimicrobial compounds from submerged cultures of SPRT in shake flasks, and scale-up of the process into a laboratory stirred tank bioreactor (STR) was done in the present study. The work focused on obtaining growth kinetics and suitable operating conditions for cultivation. Characterisation of the growth profile of SPRT and determination of the kinetic growth parameters was carried out. Additionally, the antimicrobial production phases, and factors influencing their production was investigated. It was determined that the most reliable method of measuring biomass concentration was by dry cell gravimetric measurement of whole shake flasks following vacuum filtration, as it best suited the non-homogenous filamentous nature of SPRT.

A transition is needed to shift the global economy to a more sustainable and clean economy to counteract the depletion of abiotic resources, generation of emissions and waste. Replacing petroleum plastics by bio-plastics is key to this move. This study identifies the bio-based and bio-degradable plastics, polyhydroyalkanoates (PHAs) as promising alternatives to petroleum plastics. PHAs are biologically synthesised polyesters which accumulate intracellularly in the presence of excess carbon from renewable resources and, limited nutrients in the form of nitrogen, phosphorus or sulphur. Different PHA polyesters can be synthesised by varying the growth conditions of the microbial culture. The flexible nature of PHA synthesis results in a large group of PHA polyesters with a variety of properties that span those of petroleum plastics in terms of strength, rigidity, durability and mechanical properties. Due to their versatility, PHAs have a wide range of applications in packaging and coating, health care and hygiene products, fibres, adhesives, components of toner and developer fluids and medical sutures and implant materials. Waste products of PHA production are mostly carbon dioxide and water. PHAs are biodegradable in all living systems including marine environment. PHAs are also bio-compatible and thus are not toxic to living organisms. In spite of the numerous advantages that PHAs offer, they have not yet achieved substantial commercial success due to poor market penetration arising from their high costs of production. The typical PHA sale price ranged from $ 4 to 9/kg in 2014. Factors that have been reported to affect the production costs of PHAs are the PHA content and concentration achieved by the microorganism, the purification and recovery process of PHAs together with the type of carbon substrate used. Additionally, the efficiency of the cell disruption and energy required for the washing steps can also influence the production system and are addressed in this study along with the other factors. The overall PHA production system must also be sustainable minimising its energy, water usage and carbon dioxide emissions. When faced with limited time and resources, insight is needed to identify which of the aforementioned factors or combination of factors are more crucial to optimise in order to lower production costs and environmental burden. Economic assessment is a powerful tool to identify promising economically viable process options and discard unfavourable ones. Since PHA production is not an established technology, process conditions and pilot scale data are not easily available. This study proposes a generic large scale PHA production system that can be simulated using minimum inputs to deliver material and energy inventories which can further be used to investigate the production costs of PHAs. The PHA monomer that was simulated is the most characterised PHA, polyhydroxybutyrate (PHB).

The South African coal mining industry generates large volumes of coal ultrafine waste (< 150 microns) each year, with a significant amount being dumped in tailing slurry dams. These slurry dams have been associated with prolonged pollution and loss of valuable resources. In the two stage flotation process developed at the University of Cape Town, froth flotation is used to both recover coal (stage 1) and remove pyritic sulfur (stage 2) from ultrafine coal waste, resulting in three outputs streams: a saleable coal product, a small volume sulfide-rich stream, and a reduced volume sulfide lean tailings stream. Pre-disposal removal of sulfide sulfur and coal recovery by means of froth flotation is aimed at effectively removing the acid rock drainage (ARD) risk associated with sulfide bearing waste s and at recovering valuable resources respectively. Previous studies have demonstrated the technical feasibility of this process for a number of coal waste types on a laboratory-scale, with results indicating that it is possible to recover large quantities of useable coal whilst generating a tailings waste stream with a reduced sulfur content and negligible ARD risk. An order of magnitude financial model for a fictitious plant has also been developed, and applied to demonstrate the economic viability for s elected case studies. To date, however, studies on the environmental viability of the process have only focused on the ARD mitigating potential of the two-stage flotation process and little attention has been given to the systemic environmental implication s of the process such as the energy and reagent usage. The research study therefore aims to evaluate the environmental burdens and benefits of the two-stage flotation process, particularly from a South African context, and to compare the environmental performance to the conventional disposal of untreated coal ultrafines. Furthermore, this project aims to establish which stages along the process contribute the most to the environmental burdens of the process and how the variations of the input parameters affect the overall environmental performance of the proposed process. To this end, a life cycle inventory of inputs and outputs was compiled on the basis of the empirical results derived from a previous laboratory-scale case study conducted on a sample of an acid generating ultrafine coal waste from the Waterberg region. Experimental results from the case study, which entailed two-stage flotation (using Naflote 9858 as a coal collector and xanthate (SIBX) as a sulfide collector in stages 1 and 2), and detailed characterisation of the feed and desulfurised tailings, was supplemented with literature information and data from mass and energy balance calculations for a fictitious plant. An environmental impact analysis was subsequently conducted using a combination of Life Cycle Impact Assessment and risk-based impact assessment techniques and criteria. The impact categories selected included climate change, terrestrial acidification, fossil fuel depletion, natural land transformation, aquatic water pollution risk, drinking water quality risk, aqueous acidification, salinity and consumptive water footprint. Aquatic water pollution risk, drinking water quality risk and aqueous acidification impact indicators were calculated by summing up risk potential factors for the constituents of the final disposed waste streams. The rest of the impact categories were calculated by multiplying the inventory result with a characterisation factor developed from impact assessment models The case study results indicated that the simple mentation of the two-stage flotation process results in a notable decrease in eco-toxicity, salinity, consumptive water footprint, metal toxicity, aqueous acidification, fossil fuel depletion and natural land transformation impacts. However, the results al so indicated an increase in atmospheric related impacts (climate change and terrestrial acidification impacts), which has been attributed to the additional energy consumption associated with the two-stage flotation process and the production processes associated with the flotation reagents. Analyses of the process contributions to the individual impact categories for the two-stage flotation process revealed the climate change and terrestrial acidification impact categories to be dominated by the electricity production process and the flotation reagents production process. The sensitivity analyses revealed a higher dependence of the fossil fuel depletion impact category on the percentage coal yield than the electricity consumption of the foreground process. Furthermore the sensitivity analyses indicated a strong dependence of the climate change and terrestrial acidification impacts on the electricity consumption and the SIBX dosage in the foreground process. In the South African context, implementation the two-stage flotation process would result in a significant recovery of coal (approximately 1.2 million tonnes for every 4 million tonnes dry coal ultrafines lost per annum) and a sulfide-rich product which can be utilised for electricity production and sulfuric acid production respectively, hence promoting resource efficiency. Although higher than in the case of conventional land disposal, the energy used in the two-stage flotation process is infinitesimal compared to the energy recovered in the process through the generation of additional coal, and results in only a 0.025 % increase in the annual greenhouse gas emissions. The implementation of the two-stage flotation would also result in reduced water losses in comparison to conventional land disposal, which is beneficial in the South African context as South Africa is a water scarce region. Lastly whilst the implementation of the two-stage flotation process would result in the reduction of water related impacts associated with acidification, salinization and metal pollution, it might pose a further threat to aquatic life if the xanthate salt reagents are emitted to local water sources. The limitations of the study were mainly associated with the quality of the input and output data, the impact categories and the system boundary and scenario development. The multiple sources of information and the variations in literature of the energy input estimates were noted as a source of uncertainty. The lack of characterisation factors for some of the substances in the system as well as the exclusion of the possibility of utilization of the sulfide-lean stream were also part of the limitations associated with the study. Recommendations for future work include improving the environmental assessment by incorporating various case studies and by incorporating downstream processing as well as optimizing the two-stage flotation process by using less energy and by using less toxic flotation reagents.