Browsing by Author "van Hille, R P"

Now showing 1 - 17 of 17
  • Thumbnail Image
    Item
    Restricted
    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.
  • Thumbnail Image
    Item
    Restricted
    Biokinetic test for the characterisation of AMD generation potential of sulfide mineral wastes
    (Elsevier, 2010) Hesketh, A H; Broadhurst J L; Bryan, C G; van Hille, R P; Harrison, S T L  
    Acid mine drainage (AMD) is formed by the microbially catalysed oxidation of sulfide minerals on exposure to moisture and air. It results in the ongoing contamination of water streams with acidity, sulfate and metal ions in solution, limiting subsequent use of the water without its remediation. AMD prevention is a key requirement for meeting mine closure standards and AMD prediction plays an integral role in waste management and AMD prevention. However, both the static and kinetic tests used currently have shortfalls, including only providing a worst case scenario, providing limited kinetic data, particularly with respect to microbial catalysis or requiring an excessive time frame for the provision of useful data. In this study, we review biological tests reported to predict AMD generation potential and propose an extension to these tests in the form of a biokinetic test. The proposed test provides information on the potential and likelihood of acidification upon microbial colonisation as well as the relative kinetics of the acid-consuming and acid-producing reactions. This provides more meaningful data than static tests, within a reasonable timeframe. Experiments performed to evaluate the biokinetic test, using copper sulfide flotation tailings, show results consistent with those of traditional static tests. However, these also provide additional kinetic information that could help to inform management strategies.
  • Thumbnail Image
    Item
    Restricted
    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.
  • Thumbnail Image
    Item
    Restricted
    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.
  • Thumbnail Image
    Item
    Restricted
    A continuous process for the biological treatment of heavy metal contaminated acid mine water
    (Elsevier, 1999) van Hille, R P; Boshoff, G A; Rose, P D; Duncan J R
    Alkaline precipitation of heavy metals from acidic water streams is a popular and long standing treatment process. While this process is efficient it requires the continuous addition of an alkaline material, such as lime. In the long term or when treating large volumes of effluent this process becomes expensive, with costs in the mining sector routinely exceeding millions of rands annually. The process described below utilises alkalinity generated by the alga Spirulina sp., in a continuous system to precipitate heavy metals. The design of the system separates the algal component from the metal containing stream to overcome metal toxicity. The primary treatment process consistently removed over 99% of the iron (98.9 mg/l) and between 80 and 95% of the zinc (7.16 mg/l) and lead (2.35 mg/l) over a 14-day period (20 l effluent treated). In addition the pH of the raw effluent was increased from 1.8 to over 7 in the post-treatment stream. Secondary treatment and polishing steps depend on the nature of the effluent treated. In the case of the high sulphate effluent the treated stream was passed into an anaerobic digester at a rate of 4 l/day. The combination of the primary and secondary treatments effected a removal of over 95% of all metals tested for as well as a 90% reduction in the sulphate load. The running cost of such a process would be low as the salinity and nutrient requirements for the algal culture could be provided by using tannery effluent or a combination of saline water and sewage. This would have the additional benefit of treating either a tannery or sewage effluent as part of an integrated process.
  • Thumbnail Image
    Item
    Restricted
    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.
  • Thumbnail Image
    Item
    Restricted
    Determining the effect of acid stress on the persistence and growth of thermophilic microbial species after mesophilic colonisation of low grade ore in a heap leach environment
    (Elsevier, 2013) Tupikina, O V; Minnaar, S H; van Hille, R P; van Wyk, N; Dew, D; Harrison S T L; Rautenbach, G F
    The microorganisms involved in the bioleaching of sulphidic mineral ores are acidophilic. Generally, a pH in the range of pH 1–2.5 is applied for optimal growth in these systems. In operating heaps, perturbation of conditions could result in changes in the pH outside this “safe” window, so an understanding of the effect of changes in pH on growth and activity of bioleaching microbes is needed. Previous work has shown that some microorganisms e.g. Acidithiobacillus thiooxidans, Leptospirillum ferriphilum and Leptospirillum ferrooxidans are able to adapt to low pH environments (∼pH 0.9). However, most studies on the response of micro-organisms implicated in mineral bioleaching to pH have been conducted under submerged, aerated culture conditions, with limited performance-based studies conducted under conditions mimicking a heap environment. In this study, the effect of acid stress on the persistence of the thermophilic micro-organisms in the ore bed inoculated at mesophilic conditions and their subsequent growth on reaching thermophilic conditions is considered. Following inoculation, five columns loaded with a low grade chalcopyrite ore were irrigated at a feed pH of 1.7 at 25 °C. After a few days, the temperature was sequentially increased from 25 °C through 37 °C to 50 °C, resulting in an Eh above 850 mV across all columns. The irrigation feed pH was then varied across the range pH 1.0 to 1.7 at 50 °C. Eh values greater than 800 mV could be attained in the columns with feed pH values between pH 1.2 and pH 1.7 at 50 °C. The Eh of the column receiving feed solution at a pH of 1.0 at 50 °C dropped to below 700 mV and did not recover. The temperature was then increased gradually to 60 °C. All the columns with feed pH of 1.2 and higher achieved Eh values above 800 mV. Quantitative analyses of the microbial community on selected PLS and ore samples indicated that lower pH affected the persistence of the thermophilic micro-organisms in the ore bed and their subsequent growth on reaching thermophilic conditions. The microbial population detached from the ore sample after 120 days decreased by a factor of 5–15 and 25–100 fold on decreasing the operating pH from 1.5–1.7 to 1.4 and 1.2 respectively. Poor microbial activity was found at pH 1.0, suggesting ineffective growth or persistence of the archaea.
  • Thumbnail Image
    Item
    Restricted
    Effect of post-precipitation conditions on surface properties of colloidal metal sulphide precipitates
    (Elsevier, 2012) Mokone, T P; Lewis, A E; van Hille, R P
    Metal sulphide precipitation is important in several hydrometallurgical processes. However, challenges exist in solid–liquid separation and recovery of the colloidal precipitates produced in some systems. This study presents the effect of downstream processing options on the surface properties of colloidal particles produced during copper and zinc sulphide precipitation. XRD and EDAX characterisation indicated the copper precipitate was a mixture of covellite (63%) and copper hydroxysulphate (37%), while the zinc sulphide was more pure, but less crystalline. The effect on surface charge and aggregation tendency of different concentrations of background electrolyte (1–100 mM KCl), suspension pH, aqueous sulphide, a divalent (Ca2+) and trivalent (Al3+) cation were studied. The magnitude of the negative surface charge increased with increasing suspension pH (pH 6 to pH 11) for both copper and zinc precipitates. The addition of aqueous sulphide (0.84 mM) to the zinc precipitate resulted in a significant decrease in the zeta potential and suppressed aggregation, due to adsorption of the negatively charged sulphide ions. This effect was reduced at high ionic strength. A higher sulphide concentration was required to replicate the phenomenon with the copper precipitate due to sulphidisation of the copper hydroxysulphate initially. Addition of a divalent cation (Ca2+) to the suspension had little effect on the surface charge of the particles and did not promote aggregation. However, addition of a small amount (0.5 mM) of Al3+ ions resulted in a significant change in surface charge (−30 to −10 mV for copper and −23 mV to −5 mV for zinc) and subsequent aggregation. The results of this study show that downstream processing of colloidal metal sulphide precipitates, produced where supersaturation cannot be managed, can lead to effective solid–liquid separation, by changing the surface properties of the precipitate.
  • Thumbnail Image
    Item
    Restricted
    Effect of post-precipitation conditions on surface properties of colloidal metal sulphide precipitates.
    (Elsevier, 2012) Mokone, T P; Lewis, A E; van Hille, R P
    Metal sulphide precipitation is important in several hydrometallurgical processes. However, challenges exist in solid–liquid separation and recovery of the colloidal precipitates produced in some systems. This study presents the effect of downstream processing options on the surface properties of colloidal particles produced during copper and zinc sulphide precipitation. XRD and EDAX characterisation indicated the copper precipitate was a mixture of covellite (63%) and copper hydroxysulphate (37%), while the zinc sulphide was more pure, but less crystalline. The effect on surface charge and aggregation tendency of different concentrations of background electrolyte (1–100 mM KCl), suspension pH, aqueous sulphide, a divalent (Ca2+) and trivalent (Al3+) cation were studied. The magnitude of the negative surface charge increased with increasing suspension pH (pH 6 to pH 11) for both copper and zinc precipitates. The addition of aqueous sulphide (0.84 mM) to the zinc precipitate resulted in a significant decrease in the zeta potential and suppressed aggregation, due to adsorption of the negatively charged sulphide ions. This effect was reduced at high ionic strength. A higher sulphide concentration was required to replicate the phenomenon with the copper precipitate due to sulphidisation of the copper hydroxysulphate initially. Addition of a divalent cation (Ca2+) to the suspension had little effect on the surface charge of the particles and did not promote aggregation. However, addition of a small amount (0.5 mM) of Al3+ ions resulted in a significant change in surface charge (−30 to −10 mV for copper and −23 mV to −5 mV for zinc) and subsequent aggregation. The results of this study show that downstream processing of colloidal metal sulphide precipitates, produced where supersaturation cannot be managed, can lead to effective solid–liquid separation, by changing the surface properties of the precipitate.
  • Thumbnail Image
    Item
    Restricted
    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.
  • Thumbnail Image
    Item
    Restricted
    An integrated algal sulphate reducing high rate ponding process for the treatment of acid mine drainage wastewaters
    (Springer, 1998) Rose, P D; Boshoff, G A; van Hille, R P; Wallace, L C M; Dunn, K M; Duncan, J R
    Acid mine drainage pollution may be associated with large water volume flows and exceptionally long periods of time over which the drainage may require treatment. While the use and role of sulphate reducing bacteria has been demonstrated in active treatment systems for acid mine drainage remediation, reactor size requirement and the cost and availability of the carbon and electron donor source are factors which constrain process development. Little attention has focussed on the use of waste stabilisation ponding processes for acid mine drainage treatment. Wastewater ponding is a mature technology for the treatment of large water volumes and its use as a basis for appropriate reactor design for acid mine drainage treatment is described including high rates of sulphate reduction and the precipitation of metal sulphides. Together with the co-disposal of organic wastes, algal biomass is generated as an independent carbon source for SRB production. Treatment of tannery effluent in a custom-designed high rate algal ponding process, and its use as a carbon source in the generation and precipitation of metal sulphides, has been demonstrated through piloting to the implementation of a full-scale process.The treatment of both mine drainage and zinc refinery wastewaters are reported. A complementary role for microalgal production in the generation of alkalinity and bioadsorptive removal of metals has been utilised and an Integrated ‘Algal Sulphate Reducing Ponding Process for the Treatment of Acidic and Metal Wastewaters’ (ASPAM) has been described.
  • Thumbnail Image
    Item
    Restricted
    Kinetic analysis of biological sulphate reduction using lactate as carbon source and electron donor across a range of sulphate concentrations
    (Elsevier, 2010) Oyekola, O O; van Hille, R P; Harrison, S T L
    This study investigated the effect of feed sulphate concentration on the kinetics of anaerobic sulphate reduction by a mixed SRB culture, using lactate as the sole carbon source and electron donor. Chemostat cultures were operated across a range of residence times (0.5–5 d) and feed sulphate concentrations (1.0–10.0 g l−1). Similar phenomena were observed at feed sulphate concentrations of 1.0 and 10.0 g l−1 with the volumetric sulphate reduction rate increasing linearly with increasing volumetric sulphate loading rate. These reactors were characterised by higher specific volumetric sulphate reduction rates with maximum values of 0.24 and 0.20 g h−1 g−1. Contrastingly, the reactors fed with sulphate concentrations of 2.5 and 5.0 g l−1 showed distinctly different trends in which the volumetric sulphate reduction rate passed through a maximum at the dilution rates of 0.014 and 0.021 h−1, respectively, followed by a decline with further increase in sulphate loading rate. The maximum specific volumetric sulphate reduction rates observed were 2–6-fold lower than those observed at 1.0 and 10.0 g l−1 feed sulphate concentrations. Profiles of specific volumetric sulphate reduction rate and biomass concentration suggested a shift in lactate utilisation from oxidation to fermentation at high dilution rates, implying a change in the dominant components of the microbial consortium. The data suggest that population structure was influenced by lactate affinity and dissolved sulphide concentration. The trends observed were attributed to the greater ability of lactate oxidisers to scavenge lactate under limiting concentrations of the substrate and their greater resilience to dissolved sulphide species in comparison to lactate fermenters.
  • Thumbnail Image
    Item
    Restricted
    Metal sulphides from wastewater: Assessing the impact of supersaturation control strategies
    (IWA Publishing, 2012) Mokone, T P; van Hille, R P; Lewis, A E
    Metal sulphide precipitation forms an important component of acid mine drainage remediation systems based on bacterial sulphate reduction. However, the precipitation reaction is inherently driven by very high levels of supersaturation with the generation of small particles with poor solid–liquid separation characteristics. In this study, the effect of strategies used to manage supersaturation was investigated during copper and zinc sulphide precipitation reactions. Initial batch studies showed the origin of sulphide (biological or chemical) had no significant effect on the efficiency of zinc sulphide precipitation. For copper, low metal removal efficiency was obtained at metal to sulphide molar ratios below 1.6 in the synthetic sulphide system. This was improved in the biogenic sulphide system, due to the presence of residual volatile fatty acids, but the presence or absence of particulate organic matter had no effect on recovery. Subsequent studies, conducted using synthetic sulphide solutions in a seeded fluidised bed reactor with multiple reagent feed points (2FP and 6FP) and different recirculation flow rates (300 and 120 mL min−1) showed efficient zinc sulphide precipitation, but limited (<10%) deposition on the seeds. Increasing the number of sulphide feed points (2–6) reduced precipitate loss as fines by approximately 10%. Zinc sulphide fines could be effectively recovered from suspension by settling under quiescent conditions. In the copper system, metal recovery was low (ca 40%) due to the formation of very small copper sulphide particles (mean particle size of ca 0.01 μm). Increasing the number of reagent feed points did not affect supersaturation to the extent of altering particle characteristics. The copper sulphide fines could not be recovered by settling, remaining in a stable colloidal suspension due to their highly charged surfaces (zeta potential −50 mV). The change in recirculation flow rate had a limited effect (ca 5% improvement) on process efficiency. The results show that the extremely high supersaturation prevalent during metal sulphide precipitation is difficult to control using conventional approaches and suggest that the seeded fluidised bed reactor is not suitable for this application.
  • Thumbnail Image
    Item
    Restricted
    Reactive oxygen species generated in the presence of fine pyrite particles and its implication in thermophilic mineral bioleaching
    (Springer Verlag, 2012) Jones, G C; van Hille, R P; Harrison, S T L
    In the tank bioleaching process, maximising solid loading and mineral availability, the latter through decreasing particle size, are key to maximising metal extraction. In this study, the effect of particle size distribution on bioleaching performance and microbial growth was studied through applying knowledge based on medical geology research to understand the adverse effects of suspended fine pyrite particles. Small-scale leaching studies, using pyrite concentrate fractions (106–75, 75–25, −25 μm fines), were used to confirm decreasing performance with decreasing particle size (D50 <40 μm). Under equivalent experimental conditions, the generation of the reactive oxygen species (ROS), hydrogen peroxide and hydroxyl radicals from pyrite was illustrated. ROS generation measured from the different pyrite fractions was found to increase with increasing pyrite surface area loading (1.79–74.01 m2 L−1) and Fe2+ concentration (0.1–2.8 g L−1) in solution. The highest concentration of ROS was measured from the finest fraction of pyrite (0.85 mM) and from the largest concentration of Fe2+ (0.78 mM). No ROS was detected from solutions containing only Fe3+ under the same conditions tested. The potential of ROS to inhibit microbial performance under bioleaching conditions was demonstrated. Pyrite-free Sulfolobus metallicus cultures challenged with hydrogen peroxide (0.5–2.5 mM) showed significant decrease in both cell growth and Fe2+ oxidation rates within the concentration range 1.5–2.5 mM. In combination, the results from this study suggest that conditions of large pyrite surface area loading, coupled with high concentrations of dissolved Fe2+, can lead to the generation of ROS, resulting in oxidative stress of the microorganisms.
  • Thumbnail Image
    Item
    Restricted
    Reactive oxygen species generated in the presence of fine pyrite particles and its implication in thermophilic mineral bioleaching.
    (Springer Verlag, 2013) Jones, G C; van Hille, R P; Harrison, S T L
    In the tank bioleaching process, maximising solid loading and mineral availability, the latter through decreasing particle size, are key to maximising metal extraction. In this study, the effect of particle size distribution on bioleaching performance and microbial growth was studied through applying knowledge based on medical geology research to understand the adverse effects of suspended fine pyrite particles. Small-scale leaching studies, using pyrite concentrate fractions (106–75, 75–25, −25 μm fines), were used to confirm decreasing performance with decreasing particle size (D 50 <40 μm). Under equivalent experimental conditions, the generation of the reactive oxygen species (ROS), hydrogen peroxide and hydroxyl radicals from pyrite was illustrated. ROS generation measured from the different pyrite fractions was found to increase with increasing pyrite surface area loading (1.79–74.01 m2 L−1) and Fe2+ concentration (0.1–2.8 g L−1) in solution. The highest concentration of ROS was measured from the finest fraction of pyrite (0.85 mM) and from the largest concentration of Fe2+ (0.78 mM). No ROS was detected from solutions containing only Fe3+ under the same conditions tested. The potential of ROS to inhibit microbial performance under bioleaching conditions was demonstrated. Pyrite-free Sulfolobus metallicus cultures challenged with hydrogen peroxide (0.5–2.5 mM) showed significant decrease in both cell growth and Fe2+ oxidation rates within the concentration range 1.5–2.5 mM. In combination, the results from this study suggest that conditions of large pyrite surface area loading, coupled with high concentrations of dissolved Fe2+, can lead to the generation of ROS, resulting in oxidative stress of the microorganisms.
  • Thumbnail Image
    Item
    Restricted
    Removal and recovery of zinc from solution and electroplating effluent using Azolla filiculoides
    (IWA Publishing, 1999) Zhao, M; van Hille, R P; Duncan, J R
    The removal of zinc ions from aqueous solutions and electroplating rinse effluent by Azolla filiculoides on batch and column studies was investigated. The maximum zinc uptake by Azolla in batch systems at an optimum pH of 6.0 was found to be 45.2 mg/g. The dried Azolla filiculoides showed good mechanical stability and flow-permeability in repeated column operations. The zinc uptake in column operation at pH 6.2 and 60% breakthrough was between 25.8–30.4 mg/g with varying flow rates (from 32 to 160 ml/h.g). Complete desorption of bound zinc was accomplished with 120 ml of either 0.2 N H2S04 or HCl. The data from regeneration efficiencies for six cycles, evidenced that the reusability of Azolla in the treatment of Zn2+-laden wastewater is viable. An effluent-free, closed loops of zinc treatment system, with Azolla biomass as the sorbent, is proposed.
  • Thumbnail Image
    Item
    Restricted
    Selection of direct transesterification as the preferred method for assay of fatty acid content of microalgae
    (Springer Verlag, 2010) Griffiths, M J; van Hille, R P; Harrison, S T L
    Assays for total lipid content in microalgae are usually based on the Folch or the Bligh and Dyer methods of solvent extraction followed by quantification either gravimetrically or by chromatography. Direct transesteri- fication (DT) is a method of converting saponifiable lipids in situ directly to fatty acid methyl esters which can be quantified by gas chromatography (GC). This eliminates the extraction step and results in a rapid, one-step procedure applicable to small samples. This study compared the effectiveness of DT in quantifying the total fatty acid content in three species of microalgae to extraction using the Folch, the Bligh and Dyer and the Smedes and Askland methods, followed by transesterification and GC. The use of two catalysts in sequence, as well as the effect of reaction water content on the efficiency of DT were investigated. The Folch method was the most effective of the extraction methods tested, but comparison with DT illustrated that all extraction methods were incomplete. Higher levels of fatty acid in the cells were obtained with DT in comparison with the extraction-transesterification methods. A combination of acidic and basic transesterifi- cation catalysts was more effective than each individually when the sample contained water. The two-catalyst reaction was insensitive to water up to 10% of total reaction volume. DT proved a convenient and more accurate method than the extraction techniques for quantifying total fatty acid content in microalgae.