Browsing by Author "Van Hille, Robert P"

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    Analysis of the microbial community associated with a bioprocess system for bioremediation of thiocyanate- and cyanide-laden mine water effluents
    (Trans Tech Publications, 2015-11) Huddy, Rob; Kantor, Rose; Van Zyl, Wynand; Van Hille, Robert P; Banfield, Jill; Harrison, Susan T L
    Gold extraction by cyanidation from refractory gold ores results in the formation of thiocyanate- and cyanide-contaminated wastewater effluents that must be treated before recycle or discard. Activated sludge processes, such as ASTERâ„¢, can be used for biodegradation of these effluent streams. The destruction of these compounds is catalyzed by a mixed microbial culture, however, very little is known about the community composition and metabolic potential of the thiocyanate- and cyanide-degrading microorganisms within the community. Here we describe our on-going attempts to better understand the key microorganisms, within the ASTERâ„¢ bioprocess, that contribute to the destruction of thiocyanate and cyanide, and how this knowledge relates to further process optimisation.
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    Characterisation of the Complex Microbial Community Associated with the ASTERâ„¢ Thiocyanate Biodegradation System
    (Elsevier, 2015-05-15) Huddy, Robert J; Van Zyl, A Wynand; Van Hille, Robert P; Harrison, Susan TL
    The ASTERâ„¢ process is used to bioremediate cyanide- (CN-) and thiocyanate- (SCN-) 13 containing waste water. This aerobic process is able to reduce the CN- and SCN14 concentrations to below 1 mg/L efficiently in a continuous system, facilitating reuse of 15 process water or safe discharge. Such remediation systems, which completely eliminate risk 16 associated with the pollutants, are essential for sustainable mineral processing and the long 17 term minimisation of environmental burden through both pollutant destruction and exploiting 18 opportunities for nutrient recycle. Process robustness of these bioremediation options can be 19 enhanced by good understanding of the microbial community involved in the process. To 20 date, the microbial consortia associated with the ASTERâ„¢ bioprocess have been poorly 21 characterised using isolation approaches only. As a result, the relative abundance and 22 diversity of the community has been significantly under-represented. In this study, both planktonic and biofilm-associated biomass have been observed. 23 Microscopy has revealed the 24 diversity of these communities, including bacteria, motile eukaryotes, filamentous fungi and 25 algae, with the biofilm densely packed with microorganisms. The results of the molecular 26 characterisation study reported here, using a clone library approach, demonstrate that the 27 microbial community associated with the ASTERâ„¢ bioprocess system is far more complex 28 than previously suggested, with over 30 bacterial species identified thus far. On-going 29 investigations focus on identification of key microbial community members associated with 30 SCN- biodegradation and other critical metabolic functions, as well as the expected dynamic 31 response of this complex microbial community to shifts in the operating window of the 32 process.
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    Effect 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 P
    Kinetic 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
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    The effect of different types of seeds on the oxidation and precipitation of iron.
    (Elsevier, 2009) Hove, Mfandaidza; Lewis, Alison E; Van Hille, Robert P
    The use of different types of seeding material to cause the layer deposition of desired iron phases is an attractive technique for the treatment of industrial waste waters, synthesis of iron products and the study of adsorption and dissolution reactions involving iron oxides. In this study, artificial solids (consisting of mainly ferrihydrite and lepidocrocite), natural goethite and natural haematite seeds were used during batch oxidation and precipitation of iron from a ferrous sulphate suspension. A 4 L standard stirred tank reactor was used. Air was used as the oxidising agent. High ferrous ion concentrations typical of acid mine drainage associated with South African coal and gold mining were used. All the three oxides of iron catalysed the oxidation reaction rate to almost the same extent. The products formed were mainly lepidocrocite for systems seeded with artificial solids and goethite for systems seeded with either goethite or haematite. The less stable ferrihydrite was not formed in the systems seeded with either goethite or haematite. Seeding resulted in reduced BET surface areas, improved settling rates and the formation of particles of bigger sizes.
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    Investigation of microbial metal-sulfide interfacial environments under mineral bioleach simulated conditions
    (2017) Africa, Cindy-Jade; Harrison, Susan T L; Van Hille, Robert P
    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. In the context of bioleaching, microbial extra-cellular polymeric substance (EPS) components are thought to complex chemical oxidants and extend the chemical reaction space available for mineral dissolution reactions, making the microbial-mineral-EPS interface the dominant active zone in terms of microbial oxidation and mineral dissolution. There is a limited understanding of microbial biofilm formation within a bioleach heap. The implication of various microorganisms having a set of defined or optimal conditions under which they colonise and proliferate is quite substantial. Understanding what creates favourable interfacial microenvironments enabling a sessile population to flourish (and thereby decrease lag time) has great implications for minimising costs and maximising productivity. Furthermore, limited work has been conducted on thermophilic microorganisms relevant to bioleaching. These microorganisms are pertinent to successful bioleaching at high temperatures, with work incorporating low grade ores and gangue mineralogy also being scarce. The aim of this research is to provide a thorough investigation into microbial-metal sulfide interfacial environments in situ, using a thermophilic archaeon M. hakonensis, low-grade metal-sulfide ores, a series of temperature regimes, heap-simulating conditions and an in depth extraction and analysis of the EPS produced under varied culturing conditions.