Masters Degrees (Microbiology)

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Browsing Masters Degrees (Microbiology) by Subject "Acid mine drainage"

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    The biological sulphate removal process
    (Stellenbosch : Stellenbosch University, 2001-12) Greben, Harma; Wolfaardt, Gideon M.; Maree, J. P.; Stellenbosch University. Faculty of Science. Dept. of Microbiology.
    ENGLISH ABSTRACT: South Africa is one of the world's major coal producers, resulting in the second highest foreign exchange earner for South Africa. However, the mining industry contributes negatively to (ground) water pollution, due to the formation of acid mine drainage (AMD). AMD originates from the bacterial oxidation (Thiobacillus ferrooxidans) of pyrite (FeS) and contains high levels of sulphate and metals. Sulphate rich waters can be treated applying the biological sulphate removal technology. This study concentrated on biologically removing sulphate from synthetic feed- and mine water, using the single-stage completely-mixed reactor system. The advantage of using this reactor system is that except for removing sulphate from about 2000 to less than 200 mg/t', it can also partly biologically remove the formed sulphides. It was established that both ethanol and sugar can be used, as the carbon and energy source, however ethanol is more cost effective than sugar. Ethanol dosage and Hydraulic Retention Time (HRT) studies were undertaken to investigate at what concentration, the highest sulphate and sulphide removal rates were achieved. It was found that the highest sulphate reduction rates were obtained when using 1mf ethanol/f feed and that the removal rates were dependent on the HRT: the lower the HRT, the higher the sulphate reduction rate. The highest sulphide oxidation rate was achieved at the HRT of 6 h. It was, furthermore shown that the single stage completely-mixed reactor system could successfully be used to remove sulphate from Schoongezicht mine effluent, not only removing the sulphate, but also most of the metals, thereby increasing the mine effluent pH from 2.5 to 7. The conclusion of this study was that a completely-mixed reactor system, as described in this thesis, can successfully be applied to treating acid mine drainage using ethanol (1 m.e etanol/f feed water) as the carbon and energy source at a hydraulic retention time as low as 4 hours. This technology has great potential for pilot- and full-scale treatment of sulphate rich effluents such as acid mine drainage.
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    Determination of the bacterial diversity of a natural freshwater wetland impacted by acid mine drainage.
    (Stellenbosch : Stellenbosch University, 2015-12) Staebe, Karin; Cloete, T. E.; Oberholster, P. J.; Stellenbosch University. Faculty of Science. Dept. of Microbiology.
    ENGLISH ABSTRACT: Freshwater resources in semi-arid countries, such as South Africa, are under constant threat from pollution. One of the major pollutants is acid mine drainage, which not only lowers the pH of the water, but also increases sulphate and metal concentrations. Primary producers, such as bacteria and algae, are the first organisms to respond to stressors such as reduced pH and elevated sulphate and metal concentrations. A natural freshwater wetland, the Zaalklapspruit wetland in Mpumalanga, impacted by acid mine drainage and industrial effluent was studied to determine the change in algal and bacterial populations. Five study sites were identified including a reference site and four sites displaying various degrees of degradation. Physical and chemical parameters were measured at each site. Algae were identified microscopically and chlorophyll-a concentrations were measured. The algal species present at the five study sites were species previously associated with the conditions present at the various sites. Gyrosigma rautenbachiae proved to be an ideal bioindicator for industrial pollution. The diatom species Synedra ulna, Nitzschia spp. and Cymbella spp. were found at the acidic sites. The filamentous green algae Microspora quadrata and Klebsormidium acidophilum were abundant at the sites the most impacted by AMD. Metal tolerant K. rivulare were also identified in this study. The cyanobacteria Oscillatoria tenius and Glaucospira sp. were associated with enriched conditions. The bacterial populations were sampled from both the water column and sediment and subjected to next generation sequencing for identification. The phyla that were highly represented throughout all the samples were the alpha-, beta- and gamma-Proteobacteria, Bacteriodetes and unclassified species. The Bacteriodetes phylum was observed at significantly higher numbers at sites 1, 2, 3 & 5 in the March 2013 water samples and sites 1 & 4 in the March 2013 sediment samples. Firmicutes had significantly higher numbers at sites 2 (January 2013), 3 (March 2013) & 4 (January 2013) in the water samples. Both water and sediment samples of sites 2 (March 2013) & 4 (January 2013) had significantly higher numbers of Actinobacteria. The Chloroflexi phylum had significantly higher numbers in the site 4 & 5 (January 2013) water samples and site 5 (January 2013) of the sediment samples. Acidobacteria were only detected in significantly higher numbers in the January 2013 sediment samples of sites 1 & 5. This study was the first to assess the total bacterial diversity in a natural, acid mine drainage impacted wetland in South Africa and also the first to identify sequences from the genus Marinobacterium. The wetland ecosystem health was also determined using a rapid bioassessment tool and a proposed bacterial bioindicator. The bioassessment tool scored the reference site as mostly natural, two sites as severely modified and the last two as modified. The proposed bacterial bioindicator was simplistic in use and reflected the stability of the populations at the five sites accordingly. Lastly, the bacterial bioindicator was incorporated into the established bioassessment tool and was found to correspond with the latter’s results.
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    Synthetic domestic wastewater sludge as electron donor in the reduction of sulphate and treatment of acid mine drainage
    (Stellenbosch : Stellenbosch University, 2015-04) Van den Berg, Francis; Cloete, T. Eugene; Botes, Marelize; Stellenbosch University. Faculty of Science. Dept. of Microbiology.
    ENGLISH ABSTRACT: Acid mine drainage (AMD) is wastewater generated by mine and industrial activity with typically high heavy metal and sulphur content potentially resulting in toxic wastewater upon exposure to dissolved oxygen, water and micro-organisms. Due to the hazardous consequences of untreated AMD, treatment methods such as semi-passive biotic treatments, including constructive wetlands and microbial bioreactors were developed. Microbial bioreactors rely on suitable carbon sources such as ethanol, grasses and manure and the creation of anaerobic conditions for the reduction of sulphate, chemical oxidizable organic matter (COD) and to neutralise pH. Domestic wastewater sludge has also been identified as an economical and readily available carbon source that allows the treatment of both AMD and domestic wastewater. A synthetic medium simulating the COD and the biological degradable organic matter (BOD) of domestic wastewater sludge was formulated to exclude variations in the evaluation of domestic wastewater sludge as carbon source in the treatment of AMD. Firstly the BOD and COD of anaerobic domestic wastewater sludge was determined and used as parameters in the formulation of the synthetic medium. A ratio of 1:1 AMD: synthetic domestic wastewater sludge (SDWWS) was the optimum ratio in terms of sulphate and COD removal. Secondly, medical drip bags were used as anaerobic bioreactors to determine the microbial diversity in AMD treated with SDWWS using different variables. Data analyses from next generation sequencing showed that Chlorobium spp. dominated the 90 d pioneer trials at relative percentages of 68 % and 76 %. Transmission electron microscopy (TEM) images and the bright green colour of the liquid contents confirmed the data analyses. Sulphates and COD were removed at > 98 % and > 85 %, respectively. A shorter incubation time was investigated in the 30 d pioneer trial. Chlorobium spp. was dominant, followed by Magnetospirillum spp. and Ornithobacterium spp. The liquid content changed to a dark brown colour. COD and sulphate concentrations were reduced by 60.8 % and 96 %, respectively, within 26 d, after which a plateau was reached. The effect of an established biofilm in the bioreactors showed that Chlorobium spp. also dominated approximately 62 %, in comparison to the 36 % in the 30 d pioneer trial. A sulphate and COD reduction of 96 % and 58 %, respectively, was obtained within 26 d and the liquid content was the same colour as in the 30 d pioneer trial. It is possible that brown Green sulphur bacteria were present. Therefore, although Chlorobium spp. was present at a higher percentage as in the 30 d pioneer trial, the removal of COD and sulphate was similar. During the 30 d trials a white precipitant formed at the top of the bioreactors, consisting primarily of sulphate and carbon that was also indicative of the presence of Chlorobium spp. Incubation at reduced temperature reduced sulphates by only 10 % and COD by 12 % after 17 d, followed by a plateau. Ornithobacterium spp. dominated in the first trial and Magnetospirillum spp. in the second trial.