Browsing by Author "Nemati, M"

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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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    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 kinetic study on anaerobic reduction of sulphate, Part I: Effect of sulphate concentration
    (Elsevier, 2002) Moosa, S; Nemati, M; Harrison, S T L
    The kinetics of anaerobic reduction of sulphate was studied in continuous bioreactors. The effects of initial sulphate concentration and its volumetric loading on the kinetics of reaction and activity of sulphate-reducing bacteria were investigated. The increase in initial concentration of sulphate in the range 1.0–Full-size image (<1 K) enhanced the reaction rate from 0.007–Full-size image (<1 K). For a given initial sulphate concentration increasing the volumetric loading rate of sulphate led to a linear increase in volumetric reduction rate. The initial concentration of sulphate did not have a significant effect on maximum specific growth rate (μm), decay coefficient (kd) on bacterial yields (Yx/sulphate and Yx/acetate), with the values of these coefficients being Full-size image (<1 K) bacteria/g sulphate and Full-size image (<1 K) bacteria/g acetate, respectively. The saturation constant (Ks) was an increasing linear function of initial sulphate concentration, with the lowest and highest values being 0.027 and Full-size image (<1 K), respectively. Using the experimental data a kinetic model, incorporating terms for the effects of initial and residual concentrations of sulphate and biomass, was developed.
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    A kinetic study on anaerobic reduction of sulphate, part II: incorporation of temperature effects in the kinetic model
    (Elsevier, 2005) Moosa, S; Nemati, M; Harrison, S T L
    The effects of temperature on the kinetics of anaerobic sulphate reduction were studied in continuous bioreactors using acetate as an electron donor. Across the range of temperatures applied from 20 to View the MathML source, the increasing of volumetric loading rate up to 0.08 to View the MathML source resulted in a linear increase in reduction rate of sulphate. The increasing reaction rate showed a lower dependence on volumetric loading rate in the range 0.1–View the MathML source. Further increase in volumetric loading rate above View the MathML source was accompanied by wash out of bacterial cells and a sharp decrease in reaction rate. Despite a similar pattern for dependency of reaction rate on volumetric loading at all temperatures tested, the magnitude of reaction rate was influenced by temperature, with a maximum rate of View the MathML source observed at View the MathML source. The effect of temperature on maximum specific growth rate (μmax) and bacterial yield was insignificant. The values of maximum specific growth rate and yield were View the MathML source and 0.56–0.60 kg bacteria (View the MathML source), respectively. The decay coefficient (kd) and apparent saturation constant (View the MathML source) were both temperature dependent. The increase of temperature resulted in decreased values of View the MathML source, and higher values for kd. Using the experimental data effect of temperature was incorporated in a kinetic model previously developed for anaerobic reduction of sulphate.
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    Particle effects in bioleaching of pyrite by acidophilic thermophile Sulfolobus metallicus
    (Springer Verlag, 2000) Nemati, M; Lowenadler, J; Harrison, S T L
    The effect of mineral particle size on the bioleaching of pyrite by the acidophilic thermophileSulfolobus metallicus was investigated in a batch bioreactor. Decreasing the particle size from a mean diameter of 202 micron (size fraction: 150–180 micron) to a mean diameter of 42.5 micron (size fraction: 25–45 micron) enhanced the bioleaching rate from 0.05 kg m−3 h−1 to 0.098 kg m−3 h−1. The particle size distribution of the mineral in this range did not influence the morphology and growth kinetics of the cells. The values of specific growth rate (μ) and yield factor (Y) were 0.018–0.025 h−1 and 0.67 × 1011–1.45 × 1011 cells (g iron)−1, respectively. Decreasing the particle size of the mineral to a mean diameter of 6.40 micron (size fraction <25 micron) adversely influenced the activity of the cells. The presence of fine particles apparently damaged the structure of the cells, resulting in their inability to oxidise pyrite.