Browsing by Author "Van Hille, Rob"

Now showing 1 - 12 of 12
  • Thumbnail Image
    Item
    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.
  • Thumbnail Image
    Item
    Open Access
    Control of the desupersaturation reactor used in the SPARRO process
    (2003) Seewoo, Shilpa; Lewis, Alison Emslie; Van Hille, Rob
    The work described in this thesis focuses on the Slurry Precipitation And Recycle Reverse Osmosis (SPARRO) process. The process was designed to treat calcium sulphate (gypsum) scaling mine waters by encouraging preferentlal crystal growth onto introduced seeds, rather than on the reverse osmosis membranes. The major problem faced by the SPARRO process was the short membrane life span, possibly due to damage caused by contact with gypsum crystals. Gypsum exists in two extreme morphologies, plate and needle-like crystals, which are formed from high (0.2 M) and low (0.04 M) concentration of CaCl2 and Na2SO4 solutions respectively. This research reinvestigated the SPARRO process from a crystallisation perspective with the aims of: • Increasing the level of understanding of fundamental aspects of the SPARRO process. • Developing a technique to quantify the gypsum crystal morphology. • Developing design specifications for a 5 L lab scale desupersaturation reactor. • Developing and defining the critical parameters in controlling production of gypsum of a specified crystal size and morphology in the desupersaturation reactor.
  • Thumbnail Image
    Item
    Open Access
    Copper sulphide precipitation in a fluidised bed reactor
    (2002) Peterson, Karen Angeline; Lewis, Alison Emslie; Lacour, Stella; Van Hille, Rob
    The purpose of this thesis was an investigation into the feasibility of the removal of a single heavy metal (copper) by sulphide precipitation from a copper rich stream in a fluidised bed reactor, as well as developing an understanding of the behaviour of the copper sulphide system.
  • Thumbnail Image
    Item
    Open Access
    Evaluation of the competitive performance of an indigenous eicosapentaenoic acid producing microalgal isolate
    (2014) Smit, Monique; Van Hille, Rob; Maharajh, Dheepak
    Omega-3 fatty acids are known to have positive effects on brain function, as well as cardiovascular disease and inflammatory diseases. They currently sold as fish oil concentrates. The fish oil extraction processes are unsustainable due to the diminishing fish stocks in open waters. In addition to this is the fact that the omega-3 fatty acid content in fish are directly dependent on the fish's diet. If the fish does not have access to nutrients containing omega-3s, the fish will not have assimilated the relevant fatty acids. Currently, microalgae are a topic of interest regarding omega-3 fatty acid production because they are the ultimate de nova source of omega-3 fatty acids. In order to mitigate long-term fish resource depletion, it is imperative that the cultivation of edible fish becomes a priority. However, these aquaculture fish will not contain omega-3 fatty acids if this is not a part of their diet, either naturally or as a feed additive. Due to microalgae's de nova production of omega-3 fatty acids, this would be an ideal alternative to fish oil, as well as a source of omega-3 fatty acids for cultivated fish as a feed input. South Africa is an ideal location for the commercialisation of microalgal technology, due to its biodiversity and climate. There is thus a desire to exploit the biodiversity of South Africa and over 750 microalgal isolates have been collected from across South Africa and are housed at the CSIR Biosciences and the Centre for Bioprocess Engineering (CeBER) at the University of Cape Town. The main objective of this study was to investigate whether a locally selected isolate was a more suitable organism for omega-3 fatty acid production in an open raceway pond than a current species of choice. The objectives of the study were achieved by investigating the biomass, EPA production and response to reactor configuration and process conditions, with a view to assessing the potential to further scale up the bioprocess. A literature review was conducted to identify a list of possible omega-3 producing candidates. The published data were analysed to reduce the overall list of potential organisms to six species. Initial experimental analysis indicated that Phaeodactylum tricornutum was a suitable control species against which to compare the locally selected isolate in terms of biomass and EPA production. Average specific growth rate and overall average EPA productivity were 0.24 d-1 and 10.85 ìg.d- 1 respectively for P. tricornutum. The chosen CSIR species, WCA 23.2, had an average specific growth rate and overall average EPA productivity of 0.20 d-1 and 7.83 ìg.d- 1 respectively. Molecular identification confirmed the identity of Phaeodactylum tricornutum and indicated WCA 23.2 most likely to be an Amphora species. Selected environmental factors, such as pH and different nutrient regimes were chosen to study the effect on growth rate, biomass production and EPA production under laboratory conditions. A study was devised to test the effects of pH control under maintained nutrient conditions. All studies were subjected to a period of nutrient deficiency for the last 4-6 days of the experiment to assess the effect on EPA induction. The pH studies resulted in similar average specific growth rates for both species under pH controlled vs. uncontrolled conditions with WCA 23.2 and P. tricornutum demonstrating growth rates of 0.20-0.22 d-1 and 0.30-0.33 d-1 respectively. Specific EPA productivity was negatively affected for both species in the absence of pH control, where- the pH increased to above pH 9.4. For the pH studies, there was no observed increase in EPA content under nutrient (nitrate and silicon) deficient conditions. Subsequent experiments were performed with the pH controlled at pH 8.3 to ensure optimal biomass and specific EPA production. To evaluate the impact of different nutrient addition regimes at a chosen pH, a study was designed to supply cultures with the same amount of nutrients where (1) the batch culture had all the nutrients supplied at the start and (2) a fed-batch regime where smaller amounts of nutrients were supplied every second day. Average specific growth rates were similar for both species under batch and fed-batch conditions with values ranging from 0.23-0.25 d-1. Specific EPA productivities, however, were higher for both cultures when cultivated under the batch conditions with productivities of 0.412 mg.g-1d and 0.175 mg.g-1d for WCA-23.2 and P. tricornutum respectively. To assess the impact of scale-up, biomass and specific EPA production was assessed in an open raceway pond system (SO L volume) where species were cultivated, in duplicate, under batch conditions at a pH of 8.3, relying on the environmental temperatures and natural sunlight. Biomass productivities for both cultures were significantly lower when compared to the productivities from the laboratory scale studies. Biomass productivity was 2.5 times lower for WCA 23.2 and five-fold lower for P. tricornutum. In terms of specific EPA production, WCA 23.2 suffered a 4.5 fold loss while specific EPA production in P. tricornutum was 20% higher. While the locally selected isolate had a lower specific EPA production rate, it was quicker and easier to harvest. WCA 23.2 auto-flocculated and could be sieved within an hour, while P. tricornutum required an additional settling step to harvest the biomass, resulting in an overall harvesting phase that took two days. The experimental data indicated that EPA productivity was higher in P. tricornutum than WCA 23.2, under the conditions tested. However, the ease of biomass recovery and regulatory advantages associated with using an endemic species mean that a more thorough economic evaluation is required to draw a definitive conclusion.
  • Thumbnail Image
    Item
    Open Access
    Factors affecting the attachment of Metallosphaera hakonensis during the colonisation of low grade mineral sulphide heaps
    (2011) Bromfield, Lucinda; Van Hille, Rob
    This thesis pertains to the extraction of copper via heap bioleaching, focussing specifically on the bioleaching of the mineral sulphide, chalcopyrite (CuFeS2). Industrial heap bioleaching offers an attractive alternative to conventional extraction methods, such as smelting, for processing low grade ores. There remain a number of operational challenges associated with bioleaching heaps, such as the lag time before efficient extraction is achieved and ineffective heap inoculation, as well as the difficulty in controlling the conditions within the heap.
  • Thumbnail Image
    Item
    Open Access
    Interrelationship of hydrology, microbial colonisation and hydrometallurgy in a simulated chalcopyrite heap leach
    (2008) Spurr, Nicholas Robert Louis; Harrison, STL; Van Hille, Rob
    Chalcopyrite is the most abundant primary copper sulphide mineral found worldwide. As copper grades of ores available for extraction decrease, heap bioleaching is gaining interest as a potential operating alternative to traditional methods of roasting and smelting. The efficiency by which bacteria assist leaching chalcopyrite is governed by their interaction and association to the sulphide mineral in the ore. While both planktonic and mineral-associated micro-organisms contribute to the bioleaching of mineral sulphides through the oxidation of ferrous iron little information exists as to their ability to adhere and leach low grade chalcopyrite ore. This study was undertaken to determine the association of defined and mixed microbial species on a chalcopyrite concentrate and a chalcopyrite ore. At. ferrooxidans, At. caldus, At. thiooxidans and L. ferrooxidans were grown in pure culture and used to investigate the mineral-microbe association within defined experimental parameters of two experimental operations.
  • Thumbnail Image
    Item
    Open Access
    Investigation towards controlled precipitation of nickel using H2S(g) by harnessing pH dependent sulphide speciation
    (2007) Karbanee, Nazneen; Lewis, Alison Emslie; Van Hille, Rob
    Sulphide as a precipitating agent is effective as it facilitates the removal of heavy metals to very low residual concentrations (ppm - ppb levels) over a wide pH range, owing to the low solubilities (Ksp) of metal sulphides. However, previous work on metal sulphide precipitation has highlighted a number of challenges. The low solubilities of metal sulphides in combination with the rapid kinetics of sulphide precipitation leads to rapid, uncontrolled metal sulphide precipitate formation. The extremely high supersaturations result in high rates of nucleation, leading to the formation of particles with undesirable characteristics. In this thesis, to gain insight on the metal sulphide precipitation of nickel and cobalt from the RES, a simplified model system, consisting of a synthetic NiS04 solution with a concentration of 200ppm Ni2+, was utilised to determine the effect of H2S(g) as a precipitating agent.
  • Thumbnail Image
    Item
    Open Access
    An investigation towards passive treatment solutions for the oxidation of sulphide and subsequent removal of sulphur from acid mine water
    (2013) Mooruth, Neehal; Van Hille, Rob
    Mine wastewaters are presently generated at working and abandoned mining operations, both within South Africa and internationally. Currently, active treatment systems are being utilised to treat the voluminous quantities of acid rock drainage that are being generated within South Africa, largely as a result of groundwater rebound through abandoned workings. However these technologies are not economically viable for the treatment of smaller discharges from diffuse sources, such as coal spoil heaps, overburden and waste rock dumps, over a long period of time. In addition, they are questionable from a sustainability perspective. The Integrated managed passive (IMPI) treatment system is a semi-passive biological process, which was developed for the treatment of sulphate-laden mine water discharges. The system consists of modular sulphate reduction and sulphide oxidation units. A demonstration-scale plant was constructed at BHP Billiton’s Middelburg Colliery, however the sulphide oxidation unit, the linear flow channel reactor (LFCR) did not perform efficiently. This study was conducted to develop a greater understanding of the physical, chemical and biological processes occurring within the reactor. Data generated during previous studies were critically evaluated and a number of unsubstantiated assumptions and experimental deficiencies were identified.
  • Thumbnail Image
    Item
    Open Access
    The kinetics and mechanisms of the oxidation and precipitation of iron : the high density sludge (HDS) process
    (2008) Hove, Mfandaidza; Lewis, Alison Emslie; Van Hille, Rob
    The oxidation and precipitation of iron are key reactions in the treatment of hydrometallurgical waste water and acid mine drainage (AMD) by the high density sludge process (HDS). The removal of other pollutants by adsorption and coprecipitation using this technique depends on the nature and the process by which iron is removed. Although this technique is cheap and easy to operate and therefore the most common method by which hydrometallurgical waste water is treated, there are some problems inherent in this technique. Such problems include; the formation of gelatinous sludge which is difficult to dewater, the low solids density resulting in considerable water losses and a large land area for sludge disposal, the instability of the sludge thus requiring post neutralisation stabilisation and the formation of the solids as mixed sludge, thus diminishing chances for waste material recovery, reuse or recycle. In view of the above problems, the objectives of the present study were; to gain more understanding of the oxidation and precipitation reactions of iron through investigating the effect of pH on the oxidation rate and on the chemical and physical characteristics of the iron precipitates, to make an inference on the mechanisms by which iron precipitates are formed and finally to investigate the effect of seeding on the oxidation and precipitation of iron. To achieve the set objectives, experiments were carried out in a 4 L perspex batch reactor. The reactor was fitted with four equally spaced buffles and a draft tube to maximise mixing. Ferrous iron (Fe2+) was added as FeSO4.7H2O at initial concentrations of 200 mg/L and oxidised using air. pH control was achieved by titration with either 0.1 M NaOH or 0.1 M H2SO4 through a custom made Hitech Micro Systems controller. The reactions were carried out at pH levels 6.0, 8.0, 9.0 and 10.0. Three types of materials (recycled solids, natural haematite and natural goethite) at three concentration levels (Cs = 1.0, 0.5 and 0.1) were used as seed material in the seeded experiments.
  • Thumbnail Image
    Item
    Open Access
    Metal sulphide precipitation : effect of operational parameters on particle characteristics and process efficiency
    (2010) Mokone, Thebe Phillip; Lewis, Alison Emslie; Van Hille, Rob
    Acid mine drainage (AMD) is one of the major, long-term environmental challenges facing the minerals processing industry. Uncontrolled discharges have polluted thousands of kilometres of rivers, as well as surface and groundwater bodies with acidic effluents high in dissolved metals and sulphate. Conventional treatment technologies rely on oxidation, neutralisation and precipitation. While these may be effective they are expensive and not sustainable in the long term. Several biological treatment technologies, based on the activity of sulphate reducing bacteria (SRB), have been successfully developed and applied at both laboratory and industrial scale. The SRB uses sulphate as the terminal electron acceptor and with a suitable electron donor produce bicarbonate alkalinity and sulphide. These can be used to neutralise acidic effluents and effect precipitation of dissolved metal ions as metal sulphides. However, a number of challenges exist around the precipitation step, particularly where the recovery of valuable metals is desired. Metal sulphide precipitation reactions are inherently driven by extremely high levels of supersaturation. As a result, metal sulphide precipitation reactions are difficult to control and a large number of small particles are formed during the process. This leads to significant technical challenges with respect to solid-liquid separation and subsequent recovery of the precipitate. Despite the theoretically high metal removal, related to the low solubility of metal sulphides, practical efficiency is often significantly lower. Previous studies have shown that metal precipitation reactions require controlled physico-chemical conditions and the control of high levels of supersaturation to achieve optimum efficiency. The objective of this study was to extend this approach to metal suphide systems.Initial data indicated that conventional techniques to manage supersaturation were not effective and subsequent work focused on characterising the effect of reaction conditions on particle properties and investigating downstream processing options. The intention of this research was to bridge the gap between highly fundamental studies and practical application of sulphide precipitation technologies.
  • Thumbnail Image
    Item
    Open Access
    Microbial attachment to sulfide minerals in a bioleach environment
    (2009) Africa, Cindy-Jade; Harrison, STL; Van Hille, Rob
    This research pertains to bioleaching of copper containing ores with particular reference to the copper sulfide mineral chalcopyrite (CuFeS₂). While it is focused on heap bioleaching, it has applications to stirred tank bioleaching operations. Industrial heap bioleaching offers opportunities for processing of low grade ores but poses process operational challenges. These challenges include ineffective heap inoculation, a lag period before effective leaching commences and poor heap performance. These aspects are attributed to several contributing factors, such as heap construction, engineering and microbial activity. To date little attention has been paid to colonisation as a means of mitigating these challenges and effectively improving process operation. Current literature regarding microbial attachment to sulfide minerals is limited to pure culture studies using iron oxidising mesophiles, and the use of sulfide mineral concentrates. In a heap environment, mineral dissolution is accelerated through the presence of a mixed consortium of microbial species; with the contribution of each not yet fully understood. In addition, gangue minerals comprise the bulk of the minerals present and thus cannot be neglected when attempting to better understand microbial attachment and the role of micro-organisms in a heap environment. The predominant methodology employed to study microbial attachment in a bioleach context has used batch agitated systems (shake flasks). This may not adequately represent attachment under heap-like fluid dynamics. The idea of this project stemmed from a requirement to contribute to the mitigation of challenges faced by industry through addressing the aforementioned gaps prevailing in literature and improving understanding of the role of microbial attachment and colonisation under conditions simulating a heap. The aim of this study was to investigate attachment of three bioleach micro-organisms (A. ferrooxidans, L. ferriphilum and S. metallicus)to complex, sulfide-containing minerals ores in a bioleach environment using methodologies simulating heap-like conditions.
  • Thumbnail Image
    Item
    Open Access
    Optimising microalgal lipid productivity for biodiesel production
    (2011) Griffiths, Melinda Jane; Harrison, STL; Van Hille, Rob
    The purpose of this work was to identify promising microalgal species and strategies of nitrogen deprivation that optimise lipid productivity for biodiesel production. This was carried out by I) developing the tools necessary to measure lipid productivity accurately, II) identifying and quantifying the key characteristics of promising microalgal strains, initially through a literature survey and then experimentally, and III) investigating the effect of different degrees of N limitation, and different N culture regimes, on cell physiology and lipid productivity in Chlorella vulgaris.