OpenUCT :: Browsing by Author "Harrison, S T L"

Browsing by Author "Harrison, S T L"

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Open Access
Advantages and challenges of microalgae as a source of oil for biodiesel
(InTechOpen, 2011) Griffiths, M J; Dicks, R G; Richardson, C; Harrison, S T L; Margarita Stoytcheva; Gisela Montero
Microalgal oil is currently being considered as a promising alternative feedstock for biodiesel. The present demand for oil for biofuel production greatly exceeds the supply, hence alternative sources of biomass are required. Microalgae have several advantages over land-based crops in terms of oil production. Their simple unicellular structure and high photosynthetic efficiency allow for a potentially higher oil yield per area than that of the best oilseed crops. Algae can be grown on marginal land using brackish or salt water and hence do not compete for resources with conventional agriculture. They do not require herbicides or pesticides and their cultivation could be coupled with the uptake of CO2 from industrial waste streams, and the removal of excess nutrients from wastewater (Hodaifa et al., 2008; An et al., 2003). In addition to oil production, potentially valuable co-products such as pigments, antioxidants, nutraceuticals, fertilizer or feeds could be produced (Mata et al., 2010; Rodolfi et al., 2009).
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Anaerobic digestion of Spirulina sp. and Scenedesmus sp.: a comparison and investigation of the impact of mechanical pre-treatment
(Springer, 2015) Inglesby, A E; Griffiths, M J; Harrison, S T L; van Hille, R P
Anaerobic digestion (AD) is a unit process that integrates beneficially and sustainably into many bioprocesses. This study assesses and compares the production of methane from the biomass of the microalga Scenedesmus sp. and the cyanobacterium Spirulina sp. in batch anaerobic digesters. Anaerobic digestion of whole cell Spirulina resulted in a substantially higher methane productivity (0.18 L CH4 Lreactor−1 day−1) and methane yield (0.113 L CH4 g−1 volatile solids (VS)) compared to the digestion of whole cell Scenedesmus (0.12 L CH4 Lreactor−1 day−1 and 0.054 L CH4 g VS−1). Spirulina, possibly due to a combination of osmotic shock, the filamentous nature of the cells and lower mechanical strength of the non-cellulosic cell wall, was more readily degraded by hydrolytic and acidogenic microorganisms, resulting in the generation of a greater amount of acetic acid. This in turn provided greater substrate for methanogens and hence higher methane yields. In addition, Spirulina cells could be disrupted mechanically more quickly (1 h) than Scenedesmus cells (4 h) in a bead mill. Mechanical pre-treatment improved the final methane yields (L CH4 g VS−1) obtained from digestion of both substrates; however, the improvement was greater for Scenedesmus. Mechanical pre-treatment resulted in a 47 % increase in methane production for Spirulina compared to 76 % increase for Scenedesmus fed digesters. The more substantial increase observed for Scenedesmus was due to the relatively inefficient digestion of the whole, unruptured cells.
Open Access
Anaerobic digestion of Spirulina sp. and Scenedesmus sp.: a comparison and investigation of the impact of mechanical pre-treatment
(Springer, 2015-05) Inglesby, A E; Griffiths, M J; Harrison, S T L; Van Hille, R P
AAnaerobic digestion (AD) is a unit process that integrates beneficially and sustainably into many bioprocesses. This study assesses and compares the production of methane from the biomass of the microalga Scenedesmus sp. and the cyanobacterium Spirulina sp. in batch anaerobic digesters. Anaerobic digestion of whole cell Spirulina resulted in a substantially higher methane productivity (0.18 L CH4 Lreactor −1 day−1) and methane yield (0.113 L CH4 g−1 volatile solids (VS)) compared to the digestion of whole cell Scenedesmus (0.12 L CH4 Lreactor −1 day−1 and 0.054 L CH4 g VS−1). Spirulina, possibly due to a combination of osmotic shock, the filamentous nature of the cells and lower mechanical strength of the non-cellulosic cell wall, was more readily degraded by hydrolytic and acidogenic microorganisms, resulting in the generation of a greater amount of acetic acid. This in turn provided greater substrate for methanogens and hence higher methane yields. In addition, Spirulina cells could be disrupted mechanically more quickly (1 h) than Scenedesmus cells (4 h) in a bead mill. Mechanical pre-treatment improved the final methane yields (L CH4 g VS−1) obtained from digestion of both substrates; however, the improvement was greater for Scenedesmus. Mechanical pre-treatment resulted in a 47 % increase in methane production for Spirulina compared to 76 % increase for Scenedesmus fed digesters. The more substantial increase observed for Scenedesmus was due to the relatively inefficient digestion of the whole, unruptured cells.
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Biological oxidation of ferrous sulphate by Thiobacillus ferroxidans: a review on the kinetic aspects
(Elsevier, 1998) Nemati, M; Harrison, S T L; Hansford, G S; Webb, C
Biological oxidation of ferrous sulphate by Thiobacillus ferrooxidans has proved to be a significant step in the bioleaching of sulphide minerals and treatment of acid mine drainage. The same bioreaction also has beneficial applications in the desulphurization of coal and removal of hydrogen sulphide from gaseous effluents. Owing to the numerous potential industrial applications, the process of biocatalytic oxidation of ferrous iron has been studied extensively over the years. In the present article different aspects of this biological reaction from both a microbiological and engineering point of view are discussed and an overview of the current knowledge with respect to T. ferrooxidans and the process it catalyses is provided.
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Biooxidation kinetics of Leptospirillum ferriphilum under heap bioleach conditions
(Metallurgy and Exploration Inc, 2008) Ojumu, T V; Harrison, S T L; Hansford, G S; Petersen, J
Although the kinetics of biological oxidation of ferrous to ferric iron–the key step in any bioleaching process–have been studied for a variety of organisms, the focus has always been on conditions typical of tank-bioleaching. In heaps, parameters such as pH and temperature vary widely across the heap and are usually far from optimal. Total iron concentrations are usually much lower than the tanks(except in gold heaps), and the presence of dissolved gangue mineral is usually much more significant.
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Bioreactor microbial ecosystems for thiocyanate and cyanide degradation unravelled with genome-resolved metagenomics
(Wley, 2015) Kantor, R S; van Zyl, A W; van Hille, R P; Thomas, B C; Harrison, S T L; Banfield, J F
Gold ore processing uses cyanide (CN−), which often results in large volumes of thiocyanate- (SCN−) contaminated wastewater requiring treatment. Microbial communities can degrade SCN− and CN−, but little is known about their membership and metabolic potential. Microbial-based remediation strategies will benefit from an ecological understanding of organisms involved in the breakdown of SCN− and CN− into sulfur, carbon and nitrogen compounds. We performed metagenomic analysis of samples from two laboratory-scale bioreactors used to study SCN− and CN− degradation. Community analysis revealed the dominance of Thiobacillus spp., whose genomes harbour a previously unreported operon for SCN− degradation. Genome-based metabolic predictions suggest that a large portion of each bioreactor community is autotrophic, relying not on molasses in reactor feed but using energy gained from oxidation of sulfur compounds produced during SCN− degradation. Heterotrophs, including a bacterium from a previously uncharacterized phylum, compose a smaller portion of the reactor community. Predation by phage and eukaryotes is predicted to affect community dynamics. Genes for ammonium oxidation and denitrification were detected, indicating the potential for nitrogen removal, as required for complete remediation of wastewater. These findings suggest optimization strategies for reactor design, such as improved aerobic/anaerobic partitioning and elimination of organic carbon from reactor feed.
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Characterisation of the complex microbial community associated with the ASTER™ thiocyanate biodegradation system
(Elsevier, 2014) Huddy, R J; van Zyl, A W; van Hille, R P; Harrison, S T L
The ASTER™ process is used to bioremediate cyanide- (CN−) and thiocyanate- (SCN−) containing waste water. This aerobic process is able to reduce the CN− and SCN− concentrations to below 1 mg/L efficiently in a continuous system, facilitating reuse of process water or safe discharge. Such remediation systems, which completely eliminate risk associated with the pollutants, are essential for sustainable mineral processing and the long term minimisation of environmental burden through both pollutant destruction and exploiting opportunities for nutrient recycle. Process robustness of these bioremediation options can be enhanced by good understanding of the microbial community involved in the process. To date, the microbial consortia associated with the ASTER™ bioprocess have been poorly characterised using isolation approaches only. As a result, the relative abundance and diversity of the community has been significantly under-represented. In this study, both planktonic and biofilm-associated biomass have been observed. Microscopy has revealed the diversity of these communities, including bacteria, motile eukaryotes, filamentous fungi and algae, with the biofilm densely packed with microorganisms. The results of the molecular characterisation study reported here, using a clone library approach, demonstrate that the microbial community associated with the ASTER™ bioprocess system is far more complex than previously suggested, with over 30 bacterial species identified thus far. On-going investigations focus on identification of key microbial community members associated with SCN− biodegradation and other critical metabolic functions, as well as the expected dynamic response of this complex microbial community to shifts in the operating window of the process.
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A comparative study on thermophilic and mesophilic biooxidation of ferrous iron
(Elsevier, 2000) Nemati, M; Harrison, S T L
High temperature biooxidation of ferrous iron was studied in a batch system, using the acidophilic thermophile Acidianus brierleyi. The effect of ferrous iron initial concentration on the growth and activity of the cells was investigated. A. brierleyi was able to grow on ferrous iron at concentrations below 7.5 kg m−3. The values of specific growth rate and yield were 0.043 h−1 and 2.2×1014 cells/kg iron respectively. At ferrous iron concentrations of 7.5 kg m−13 and higher the growth of the cells was prohibited, however the non-growing cells were able to oxidise iron. The maximum biooxidation rate of ferrous iron, 0.105 kg m −3 h−1, was achieved in a culture initially containing 7.5 kg m−3 Fe2+. The mesophilic iron oxidiser Thiobacillus ferrooxidans was capable of growing on ferrous iron at concentrations as high as 30 kg m−3. Moreover the rate of mesophilic biooxidation offerrous iron was significantly higher than that observed in the presence of A. brierleyi.
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A comparison of pyrrhotite rejection and passivation in two nickel ores
(Elsevier, 2013) Chimbganda, T; Becker, M; Broadhurst, J L; Harrison, S T L; Franzidis, J.-P
The non-stoichiometric sulfide mineral pyrrhotite (Fe1-xS) occurs almost ubiquitously inter-grown with the principal nickel mineral, pentlandite ((Fe,Ni)9S8). During Ni processing, pyrrhotite is generally rejected to the tailings stream by flotation to produce a low tonnage, high grade (Ni) smelter feed and reduce SO2 emissions. In this study, the effect of different pyrrhotite flotation rejection strategies (artificial oxidation and TETA: SMBS addition) are evaluated on a magnetic (Ore A) and non-magnetic (Ore B) pyrrhotite ore to determine if either may effectively depress and potentially passivate the pyrrhotite surface during flotation to produce benign tailings without compromising pentlandite recovery. For both ores, the best pyrrhotite rejection (pentlandite/pyrrhotite recovery) was obtained using TETA: SMBS. Differences in the flotation performance of the two ores are considered more a function of BMS content, liberation and ore handling rather than a difference in sulfide passivation from the inherent pyrrhotite mineralogy (magnetic vs non-magnetic pyrrhotite). Pyrrhotite passivation could possibly provide a means of rendering the tailings non-reactive and thus mitigate acid rock drainage (ARD) formation.
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A comparison of pyrrhotite rejection;passivation in two nickel ores
(Elsevier, 2013) Chimbganda, T; Becker, M; Broadhurst, J L; Harrison, S T L; Franzidis, J-P
The non-stoichiometric sulfide mineral pyrrhotite (Fe1-xS) occurs almost ubiquitously inter-grown with the principal nickel mineral, pentlandite ((Fe,Ni)9S8). During Ni processing, pyrrhotite is generally rejected to the tailings stream by flotation to produce a low tonnage, high grade (Ni) smelter feed and reduce SO2 emissions. In this study, the effect of different pyrrhotite flotation rejection strategies (artificial oxidation and TETA: SMBS addition) are evaluated on a magnetic (Ore A) and non-magnetic (Ore B) pyrrhotite ore to determine if either may effectively depress and potentially passivate the pyrrhotite surface during flotation to produce benign tailings without compromising pentlandite recovery. For both ores, the best pyrrhotite rejection (pentlandite/pyrrhotite recovery) was obtained using TETA: SMBS. Differences in the flotation performance of the two ores are considered more a function of BMS content, liberation and ore handling rather than a difference in sulfide passivation from the inherent pyrrhotite mineralogy (magnetic vs non-magnetic pyrrhotite). Pyrrhotite passivation could possibly provide a means of rendering the tailings non-reactive and thus mitigate acid rock drainage (ARD) formation.
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A critical evaluation of CO2 supplementation to algal systems by direct injection
(Elsevier, 2012) Langley, N M; Harrison, S T L; van Hille, R P
Microalgae are currently cultivated on a relatively small scale for nutritional products, supplements and aquaculture feed. In recent years there has been renewed interest in algal bioenergy, which would require cultivation at far greater scales. A key component of large-scale production systems is the delivery of CO2 to the algal cells, which is often a limiting factor in ponds and air sparged systems. Although many methods of CO2 supplementation to algal reactors have been investigated, the most commonly suggested method is still the direct injection of CO2 enriched gas into the growth medium. A sound understanding of CO2 gas–liquid mass transfer is critical to efficient operation of cultivation systems as mixing and gas compression may represent significant operational expenses. For carbon capture or sequestration through algal culture, CO2 recovery is equally important, particularly where carbon trading is involved. Chlorella vulgaris was grown in internal loop airlift reactors under varied CO2 partial pressures in the inlet gas. In these reactors, with an overall mass transfer coefficient of 0.0094 s−1, an inlet CO2 partial pressure of 0.0012 atm (1200 ppm CO2 by volume) was sufficient to overcome any mass transfer limitations. Under these operating conditions, a CO2 recovery of 26% resulted. Increasing the partial pressure of CO2 in the inlet gas above 0.0012 atm did not increase the algal productivity and caused significant decreases in CO2 recovery to 9.7% and 2.1% at inlet CO2 partial pressures of 0.00325 atm and 0.0145 atm respectively. Much research into algal growth is done without analysis of CO2 gas–liquid mass transfer, using influent CO2 partial pressures well in excess of the minimum value required to overcome CO2 gas–liquid mass transfer limitations, even in poorly mixed systems. This could result in algal growth being optimised under conditions that are not industrially practical or desirable.
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Demonstration of the Crabtree effect in Phaffia rhodozyma during continuous and fed-batch cultivation
(Springer, 1997) Reynders, M B; Rawlings, D E; Harrison, S T L
By monitoring cell yield and fermentation products during fed-batch and continuous growth, Pfaffia rhodozyma was shown to exhibit the Crabtree effect. In fed-batch culture at feed concentrations of 27 and 55 g glucose/l there was good agreement between the observed biomass formation and that predicted by a mass balance model. At 125 g glucose/l in the feed, biomass formation was less than predicted and fermentation products such as ethanol and acetic acid accumulated in the culture medium. In continuous culture with a feed concentration of 10 g glucose/l, the Crabtree effect became apparent at a dilution rate of 0.1 h -1 . Aerobic fermentation did not occur provided the sugar substrate was maintained at a concentration of less than 0.5 g/l. Although the cell yield coefficient was reduced from 0.5 g/g to 0.16 g/g during aerobic fermentation, the carotenoid content of the cells was unaffected.
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The effect of As(III) and As(V) on the batch bioleaching of a pyrite-arsenopyrite concentrate
(Elsevier, 1996) Breed, A W; Glatz, A; Hansford, G S; Harrison, S T L
The bioleaching of arsenical gold-bearing sulphide ores and concentrates solubilises iron, arsenic and sulphur. Previous work has shown that high concentrations of iron and arsenic in solution inhibit bacterial growth, with As(III) reported to inhibit bacteria to a greater degree than As(V). Batch bioleaching experiments were carried out over periods of one month. Varying quantities of either 0.020–0.040 M As(III) or 0.107–0.220 M As(V), were added to a slurry, consisting of a pyrite-arsenopyrite concentrate (20% solids (m.v−1)) in a nutrient solution. The slurry was inoculated with a culture, consisting primarily of Leptospirillum ferrooxidans and Thiobacillus thiooxidans. The culture was obtained from a continuous bioleaching mini-plant treating the same concentrate. The results obtained were compared with those of a culture to which no arsenic was added. The effect of the added arsenic was determined by monitoring three parameters: the oxygen utilisation rate, rO2, of the culture, the rate at which the arsenic in the concentrate was solubilised and the speciation of the dissolved arsenic. The results suggest that the nature of the As(III) and As(V) toxicity is different. The addition of the culture to a slurry containing As(III) resulted in a reduced rate of bacterial oxidation. However, the addition of the culture to a slurry containing As(V) resulted in both a lag phase and a reduced rate of bacterial oxidation. At sufficiently high dosages of As(III) and As(V) the maximum oxygen utilisation rate, rO2max, of the culture was also affected. The results indicate that As(V) toxicity, and the relative toxicity of As(III) and As(V) to a mixed culture, appear to be affected by the availability of an energy source. Hence the toxicity of As(III) is not necessarily in the region of three times that of As(V). Furthermore, the results suggest that the mechanism of arsenic resistance may be attributed to the Pst+ Pit− mutations and an energy dependent efflux pump.
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The Effect of CO2 Availability on the Growth, Iron Oxidation and CO2-Fixation Rates of Pure Cultures of Leptospirillum ferriphilum and Acidithiobacillus ferrooxidans
(Wiley, 2012) Bryan, C G; Davis-Belmar, C S; van Wyk, N; Fraser, M K; Dew, D; Rautenbach, G F; Harrison, S T L
Understanding how bioleaching systems respond to the availability of CO2 is essential to developing operating conditions that select for optimum microbial performance. Therefore, the effect of inlet gas and associated dissolved CO2 concentration on the growth, iron oxidation and CO2-fixation rates of pure cultures of Acidithiobacillus ferrooxidans and Leptospirillum ferriphilum was investigated in a batch stirred tank system. The minimum inlet CO2 concentrations required to promote the growth of At. ferrooxidans and L. ferriphilum were 25 and 70 ppm, respectively, and corresponded to dissolved CO2 concentrations of 0.71 and 1.57 mM (at 308C and 378C, respectively). An actively growing culture of L. ferriphilum was able to maintain growth at inlet CO2 concentrations less than 30 ppm (0.31–0.45 mM in solution). The highest total new cell production and maximum specific growth rates from the stationary phase inocula were observed with CO2 inlet concentrations less than that of air. In contrast, the amount of CO2 fixed per new cell produced increased with increasing inlet CO2 concentrations above 100 ppm. Where inlet gas CO2 concentrations were increased above that of air the additional CO2 was consumed by the organisms but did not lead to increased cell production or significantly increase performance in terms of iron oxidation. It is proposed that At. ferrooxidans has two CO2 uptake mechanisms, a high affinity system operating at low available CO2 concentrations, which is subject to substrate inhibition and a low affinity system operating at higher available CO2 concentrations. L. ferriphilum has a single uptake system characterised by a moderate CO2 affinity. At. ferrooxidans performed better than L. ferriphilum at lower CO2 availabilities, and was less affected by CO2 starvation. Finally, the results demonstrate the limitations of using CO2 uptake or ferrous iron oxidation data as indirect measures of cell growth and performance across varying physiological conditions. Biotechnol. Bioeng. 2012;109: 1693–1703
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Effect of inoculum size on the rates of whole ore colonisation of mesophilic, moderate thermophilic;thermophilic acidophiles
(Elsevier, 2014) Tupikina, O V; Minnaar, S H; Rautenbach, G F; Dew, D W; Harrison, S T L
Bioheap leaching of low grade copper sulphides has been applied successfully at the commercial scale for the extraction of copper from secondary sulphide minerals. It is important to optimise the inoculation of heaps in order to minimise the residence time required for the heap and to maximise extraction. Thermophilic bioleaching of the primary sulphide chalcopyrite poses an additional challenge of rising temperatures inside the heap demanding microbial succession. After heap start up, rising heap core temperatures make conditions less favourable for mesophilic microbial species, and the moderately thermophilic community succeeds them in the consortium. In turn, thermophilic microorganisms succeed the moderately thermophilic microbes as the higher temperatures are reached. A detailed understanding of the microbial colonisation of whole ore is necessary to optimise microbial succession during thermophilic bioleaching, as is that of microbial growth kinetics on whole ore. Most published research is focused on microbial growth rates of bioleaching organisms in liquid cultures; little work is reported on microbial colonisation of whole ore and subsequent microbial activity. To extend the information available on the microbial diversity and succession in a bioleaching habitat, a study of bioleaching microbes colonising the ore body is required. The aim of this work was to explore aspects of colonisation of low grade chalcopyrite ore at 23 °C, 50 °C and 65 °C by acidophilic micro-organisms. Laboratory column packed bed reactors were designed to simulate heap leach environments and to provide a systematic way of studying microbial dynamics on whole ore. The effect of inoculum size and inoculation strategies on microbial activity established and the subsequent leaching performance were investigated under conditions that support mesophilic, moderately thermophilic and thermophilic microorganisms. A relationship was shown between the inoculum size and the culture time required to achieve Eh values greater than 700 mV, especially at 23 °C and 65 °C. However, the culture time required to establish an active iron- (and sulphur-) oxidising culture was also influenced by ore type, irrigation rate and inoculum adaptation. The effect on effluent Eh, pH and dissolved iron levels is also discussed.
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The effect of temperature and culture history on the attachment of Metallosphaera hakonensis to mineral sulphides with application to heap bioleaching
(Elsevier, 2011) Bromfield, L; Africa, C-J; Harrison, S T L; van Hille, R P
Temperatures in excess of 60 °C are required for efficient bioleaching of chalcopyrite. Within heaps, colonisation of the mineral with thermophilic archaea is important in reaching and maintaining these high temperatures. The effect of temperature and culture history on the attachment of Metallosphaera hakonensis, an extreme thermophilic acidophile identified as a key player in heap bioleaching, to sulfide concentrates and low-grade ore was investigated in shake flasks and packed beds. Attachment studies were conducted at 25 °C, 45 °C and 65 °C. The results show a clear relationship between increasing temperature and attachment efficiency for both suspended and packed bed systems. Attachment at 25 °C was low. Increasing the temperature to 45 °C improved attachment efficiency by between 50% and 100% while a further increase to 65 °C improved attachment by an additional 20–50%. Cells cultured on elemental sulfur as energy source prior to contacting showed 1.3 times greater affinity for the mineral concentrate than those cultured on sulphide mineral concentrates or ferrous sulphate. In contrast to previous studies using mesophilic organisms the selective attachment ofMetallosphaera to sulfide minerals, relative to gangue, was less pronounced. Attachment efficiency was lower in the packed bed system which more closely mimicked flow through a heap. The cell surface properties surface charge and hydrophobicity as well as metabolic activity were investigated to provide insight into the observed phenomena. The data suggest that retention of thermophiles within the heap could be enhanced by a secondary inoculation following elevation of the temperature above 40 °C by the mesophilic pioneer species.
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Exposure to sulfide causes population shifts in sulfate-reducing consortia
(Elsevier, 2006) Icgen, B; Harrison, S T L
The shift in the community structure of a mixed culture of sulfate-reducing bacteria (SRB) at 0.5, 0.75, 1, and 1.5 kg m−3 sulfide loadings was investigated in an anaerobic continuous bioreactor used for treatment of sulfate-containing wastewater by fluorescence in situ hybridization (FISH), using SRB species-specific and group-specific 16S rRNA-targeting probes. Hybridization analysis using these 16S rRNA-targeted oligonucleotide probes revealed that sulfide was toxic for Desulfonema, Desulfobulbus spp. and the Desulfobacteriaceae group, although it was not toxic for Desulfobacter, Desulfotomaculum, Desulfobacterium spp. or the Desulfovibrionaceae group. On the other hand, only a high concentration of sulfide of 1.5 kg m−3 was found to be toxic for the Desulfococcus group in the bioreactor. When the sulfide in the feed was 1.00 kg m−3 the sulfate-reducing capacity of the system decreased, and this decrease was more pronounced when the inlet sulfide was further increased to 1.5 kg m−3
Open Access
Flotation of coal and sulphur from South African ultrafine colliery wastes
(Southern African Institute of Mining and Metallurgy, 2013) Mbamba, C K; Franzidis, J-P; Harrison, S T L; Broadhurst, J L
Flotation of coal and sulphur from a typical South African ultrafine colliery waste has been achieved in laboratory-scale batch flotation tests, using dodecane, kerosene, and oleic acid as coal collectors, and xanthates to float the sulphide minerals (with the aid of dextrin as a coal depressant). The use of oleic acid as collector, in conjunction with MIBC frother, produced a coal yield of 56 per cent (much more than was obtained with dodecane or kerosene) at an ash content of 18 per cent, from a feed ash of 34.4 per cent; and a low- sulphur tailings. Sulphide flotation using potassium xanthate (PAX) recovered 26.3 per cent of the total sulphur in the concentrate. Staged addition of xanthate increased the total sulphur recovery to 42.1 per cent and reduced the sulphur content of the tailing further.
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Identification of population dynamics in sulfate-reducing consortia on exposure to sulphate
(Elsevier, 2006) Icgen, B; Harrison, S T L
The microbial population structure and function of a mixed culture of sulfate-reducing bacteria (SRB) maintained in anaerobic continuous bioreactors were tracked before and after a major perturbation, which involved the addition of sulfate to the influent of a bioreactor when operated at steady state at 35 °C, pH 7.8 and a 2.5 day residence time with feed stream containing 10 and 15 kg m−3 sulfate as terminal electron acceptor and 19.6 and 29.4 kg m−3 ethanol as carbon source and electron donor, respectively. The population structure determined by fluorescence in situ hybridization (FISH), by using 16S rRNA-targeted oligonucleotide probes, was linked to the functional performance of the SRB in the reactor. Hybridization analysis using these 16S rRNA-targeted oligonucleotide probes revealed that a high concentration of sulfate was toxic for Desulfobacterium and Desulfobulbus. On the other hand, the Desulfococcus group was found to be the most dominant group of SRB in the feed stream containing 15 kg m−3 sulfate as terminal electron acceptor and 29.4 kg m−3 ethanol as carbon source and electron donor.
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Investigation and visualisation of microbial attachment trends to sulphide minerals in a bioleach environment
(Trans Tech Publications, 2009) Africa, C-J, van Hille, R P; Harrison, S T L
Two novel experimental approaches have been developed to investigate the attachment of microorganisms to sulphide minerals as a function of the mineral and microbial phase in a joint project with BHP Billiton, conceptualised in 2005 and initiated in 2006. In the first approach, selective attachment of pure cultures to minerals was studied in the “particle coated column reactor” using A. ferrooxidans and L. ferriphilum. The saturated reactor containing glass beads coated with fine mineral concentrates provided a quantifiable surface area of mineral concentrate and maintained good fluid flow. Results are reported for chalcopyrite and pyrite concentrates, a low grade chalcopyrite ore and quartzite. The latter, representing typical gangue material, is used as a control. A. ferrooxidans displayed greater attachment to pyrite, and selective attachment to sulfide minerals over quartz. Similar attachment behaviour trends resulted for Leptospirillum spp. In the second approach, a novel technique was developed to investigate microbial ecology of microbe-mineral attachment, site and mineral specific associations of microorganisms and spatial organisation of microbial communities present. Qualitative assessment and visualisation of microorganisms associated with the mineral surface and subsequent biofilm development was shown in the biofilm reactor, using microscopy techniques and fluorochromes. FISH analyses of A. ferrooxidans and L. ferriphilum on massive chalcopyrite sections are presented. The consequence of the observed attachment on heap bioleach performance is discussed.