Browsing by Subject "Acid mine drainage"
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- ItemRestrictedBiokinetic 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 LAcid 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.
- ItemRestrictedEffect of culture conditions on the competition between lactate oxidisers and fermenters in a biological sulfate reduction system(Elsevier, 2012) Oyekola, Oluwaseun O; Harrison, Susan T L; van Hille, Robert PKinetic constants (μmax and Ks) describing the predominance of lactate oxidation and fermentation were determined in chemostat cultures. The kinetics of sulfate reduction and lactate utilization were determined from 0.5 to 5 d residence times at feed sulfate concentrations of 1.0–10.0 g l−1. The kinetics of lactate fermentation in the absence of sulfate were investigated at residence times of 0.5–5 d. The lactate oxidizers (LO) were characterized by a μmax of 0.2 h−1 and Ks value of 0.6 g l−1 compared with a μmax of 0.3 h−1 and Ks of 3.3 g l−1 for the lactate fermenters (LF). Using mathematical models, it was shown that LO competed more effectively for lactate at low lactate concentrations (⩽5 g l−1) and high sulfide concentrations (0.5 g l−1). Lactate fermenters outcompeted the oxidizers under conditions of excess lactate (>5 g l−1) and low sulfide (0.014–0.088 g l−1).
- ItemRestrictedEffect of culture conditions on the competitive interaction between lactate oxidizers and fermenters in a biological sulfate reduction system(Elsevier, 2012) Oyekola, Oluwaseun O; Harrison, Susan T L; Van Hille, Robert PKinetic constants (lmax and Ks) describing the predominance of lactate oxidation and fermentation were determined in chemostat cultures. The kinetics of sulfate reduction and lactate utilization were determined from 0.5 to 5 d residence times at feed sulfate concentrations of 1.0–10.0 g l1 . The kinetics of lactate fermentation in the absence of sulfate were investigated at residence times of 0.5–5 d. The lactate oxidizers (LO) were characterized by a lmax of 0.2 h1 and Ks value of 0.6 g l1 compared with a lmax of 0.3 h1 and Ks of 3.3 g l1 for the lactate fermenters (LF). Using mathematical models, it was shown that LO competed more effectively for lactate at low lactate concentrations (65gl1 ) and high sulfide concentrations (0.5 g l1 ). Lactate fermenters outcompeted the oxidizers under conditions of excess lactate (>5 g l1 ) and low sulfide (0.014–0.088 g l1 ). 2011 E
- ItemRestrictedEffect of sulphate concentration on the community structure and activity of sulphate reducing bacteria(Trans Tech Publications, 2007) Oyekola, Oluwaseun O; van Hille, Rob; Harrison, Susan T LThis study investigated the effect of sulphate concentration and residence time on the performance of anaerobic sulphate reduction by a mixed sulphate reducing bacteria (SRB) culture using lactate as the sole carbon source and electron donor. The process perforrnance is related to the population structure of the microbial consortia and dominant metabolic reactions. Laboratory scale chemostat cultures at different residence times (1-4 d) and sulphate concentrations (1.0-10.0 glL) were employed. Lactate oxidation was prevalent at feed sulphate concentrations of 1.0 to 5.0 glL. A colresponding increase in the volumetric sulphate reduction rate with increasing volumetric loading rate was also observed at this range. However, at the higher feed sulphate concentration range (10.0-15.0 glL), sulphate inhibition, lactate fermentation and an increased microbial diversity were evident. At each feed concentration of sulphate in the range 5.0 to 15.0 glL, varying dilution rates resulted in significant shifts in dominant metabolic reactions. Sulphate concentration and residence time have significant effects on both the structure of the microbial population and kinetics of biological sulphate reduction.
- ItemRestrictedKinetic 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 LThis 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.
- ItemRestrictedKinetic analysis of biological sulphate reduction using lactate as carbon source and electron donor: Effect of sulphate concentration.(Elsevier, 2010) Oyekola, Oluwaseun O; van Hille, Robert P; Harrison, Susan T LThis 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 l1 ). Similar phenomena were observed at feed sulphate concentrations of 1.0 and 10.0 g l1 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 h1 g1 . Contrastingly, the reactors fed with sulphate concentrations of 2.5 and 5.0 g l1 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 h1 , 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 l1 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.
- ItemRestrictedA 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 LThe 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.
- ItemRestrictedMetal sulphides from wastewater: Assessing the impact of supersaturation control strategies(IWA Publishing, 2012) Mokone, T P; van Hille, R P; Lewis, A EMetal 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.
- ItemRestrictedMitigating the generation of acid mine drainage from copper sulphide tailings impoundments in perpetuity: A case study for an integrated management strategy(Elsevier, 2010) Hesketh, A H; Broadhurst, J L; Harrison, S T LAcid mine drainage (AMD) is one of the most serious and pervasive challenges facing the minerals industry. Current philosophy in sulfide tailings management takes an end-of-pipe approach which is yet to be shown to be sufficient to prevent post-closure impacts from AMD and guarantee “walk-away” status. An improved, integrated approach to tailings management and AMD mitigation is proposed, whereby conventional tailings are separated with the use of flotation into a largely benign tailings stream and a sulfide-rich product. The key features of this conceptual approach are outlined and partly demonstrated for the case of porphyry-type copper sulfide tailings. The significance of this approach is that it provides a basis for the identification of opportunities for the development of new process designs incorporating waste management systems for mitigating AMD in a manner consistent with the principles of cleaner production and sustainable development.
- ItemRestrictedStudy of anaerobic lactate metabolism under biosulphidogenic conditions(IWA Publishing, 2009) Oyekola, Oluwaseun A; van Hille, Robert P; Harrison, Susan T LBiological sulfate reduction (BSR) has been reported to have potential for the treatment of acid mine drainage (AMD). The provision of a suitable carbon source and electron donor for this process remains a challenge. Lactate offers potential advantages as carbon source and electron donor in the biological sulfate reduction process. As this substrate is utilized by both fermentative bacteria and oxidative sulfate-reducing bacteria (SRB), the effect of feed sulfate concentration on the lactate pathways utilized under biosulfidogenic conditions was investigated. Studies were carried out in chemostat bioreactors across a range of residence times, using an enriched culture of SRB. The stoichiometry of biological sulfate reduction was affected by feed sulfate concentration and dilution rate. Incomplete oxidation of lactate was dominant at low feed sulfate concentration (1.0 g/L), while the yield of propionate from lactate metabolism increased at feed sulfate concentrations of 2.5–10.0 g/L, indicating the occurrence of lactate fermentation. Furthermore, at each sulfate feed concentration, in the range 2.5–10.0 g/L, the ratio in which lactate was metabolized by the oxidative and fermentative pathways varied with varying dilution rates. Lactate oxidation was higher at a feed sulfate concentration of 10.0 g/L relative to 2.5 and 5.0 g/L. The volumetric lactate utilization rate was enhanced by increasing the feed sulfate concentration. However, the proportion of total lactate consumed that was channelled into providing electrons for other activities apart from sulfate reduction also increased over the range of increasing sulfate concentrations studied and appeared to be a function of residual lactate and sulfide concentrations.