3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item An investigation into the Use of Fischer Tropsch wastewater as an organic source in the treatment of acid mine drainage (AMD) using dissimilatory sulfate reduction(2024) Magowo, WebsterAcid mine drainage (AMD) and Fischer Tropsch wastewater (FTWW) are two major pollutants associated with coal mining and usage, as such these pollutants are likely to be found in proximity to each other in coal mining regions. AMD is characterized by high sulfate and dissolved ion concentrations with little to negligible organic content, while FTWW has a very high organic content made mainly from alcohols and short chain fatty acids (SCFA). FTWW has very high COD of up to 30 000 mg/L. Sulfate reducing bacteria (SRB) can use organic substrates to reduce sulfate to sulfide in the process generating alkalinity. The hydrogen sulfide reacts with dissolved metals to form metal sulfide precipitates, while the alkalinity attenuates pH. This means SRB can be used to remove organic pollutants from FTWW and dissolved metals and sulfates from AMD. This study sought to use FTWW as the carbon source and electron donor for biological sulfate reduction in a fixed bed bench scale bioreactor treating AMD. Batch and continuous flow reactors including single stage and two stage continuous sulfate-reducing bioreactors were evaluated in this investigation. The reactors were assessed on their ability to remove COD from the FTWW, sulfate and dissolved iron from AMD. Considerable success was observed in batch reactors, with up to 99 % of iron removed from AMD, sulfate removals was at 95 %, while more than 99 % COD was removed from the effluent. Fed batch and continuous reactors were not as successful as the treatment efficiency dropped with time due possibly to the accumulation of inhibitory substances such as hydrogen sulfide and metal sulfide precipitates. The two-stage continuous bioreactor performed better compared to the single stage continuous reactor. All the reactors however maintained the pH above 7.0 against an influent pH of 2.0. Lower temperatures during winter reduced the performance of the bioreactors as the pH of the effluent dropped to below 6.0. There was a a large amount of residual sulfate, iron and COD in the reactors operated in winter than in those operated in summer. Another 2-stage bioreactor system consisting of a sulfate reducing bioreactor connected in series to a sulfate oxidising bioreactor was operated for converting the hydrogen sulfide produced in the sulfidogenic bioreactor to sulfur. Micro aerobic conditions were applied by pumping limiting amounts of oxygen into the sulfur oxidising reactor to allow for the oxidation of sulfide to elemental sulfur. Up to 92 % of sulfate was removed in the silfidogenic reactor with the subsequent production of an average 116mg/L/d of hydrogen sulfide during the operational period. The hydrogen sulfide was converted to sulfur in the oxidising reactor with 97 % sulfur recovery. An average102 mg/L/d sulfur was produced in the sulfur oxidising reactor. The results indicate the potential in using FTWW as a cost-effective electron and carbon source for biological sulfate reduction allowing for the co-treatment of AMD and FTWW.Item The influence of a chemical treatment plant and an existing wetland ecosystem on AMD pollution and water quality along the Blesbokspruit, South Africa(2019) Lourenco, MauroThe influence of the Eastern Basin Acid Mine Drainage (AMD) chemical treatment plant and the Blesbokspruit Wetland ecosystem in remediating AMD pollution has been determined. The research process involved making land use maps, using historical Rand Water quality data, and collecting water, sediment and soil samples along the Blesbokspruit. Being in operation since August 2016, the Eastern Basin chemical AMD treatment plant has had a major influence on water quality, and this influence is not entirely positive. The introduction of the treatment plant was completely necessary at the time due to the possible decant of AMD water from the abandoned Grootvlei mine into the Blesbokspruit wetland. However, phase one of treatment which makes use of chemical mechanisms to firstly neutralise the water with lime and thereafter remove the toxic metals that precipitate out of the solution has negatively influenced conductivity, magnesium, chloride and sulphate levels downstream. Over time, the concentrations of these parameters have increased to worse management level targets set out by the Blesbokspruit Forum. Conductivity and sulphate have reached unacceptable management target levels since the introduction of the chemical treatment plant. The reduction of iron, manganese, ammonium, nitrate and phosphate downstream of the AMD treatment plant is due dilution caused by increased discharge from the treatment plant and due to the wetland ecosystem removing these contaminants. The greater Blesbokspruit Wetland and the Marievale Wetland have a very low influence on improving water quality within the area. The wetlands do reduce nutrient levels according to Rand Water data, but the water quality in this study area is mainly influenced by what is occurring upstream of the wetlands at the AMD treatment plant. There are numerous environmental concerns within this study area which includes the Marievale Bird Sanctuary. Soil quality results suggest that the Blesbokspruit has a high influence on soil conductivity. River sediment heavy metal analysis results suggest that the river sediments collected from the eight sampling sites are highly polluted and have a low to moderate potential for ecotoxicity. Sediment trace metal concentrations are also highly concentrated near mine dumps and historical mine decant points. Increased soil conductivity and heavy metal contamination may have a negative impact on the waterfowl living at the Marievale Bird Sanctuary. Ground truth water sampling also identified that there is a seasonal signal of increased conductivity and sulphate during the dry winter months. The results of this research have highlighted the need for phase two of treatment (which would implement desalination infrastructure) to begin at the chemical AMD treatment plant as well as increased monitoring and protection of the wetland ecosystem within the study area.Item The spatial distribution of trace element contaminants, associated with gold mining, in lakes, dams, and pans across Benoni, Ekurhuleni(2019) Du Plessis, Devon MurphyThe City of Benoni, like many other cities in Gauteng, is synonymous with the extensive mining of gold in the Witwatersrand region. The city has several major tailings dams and mine dumps to the centre of the area, which can pose a possible risk of trace metal contamination in the several noticeable dams and pans that can be found within the area. Through extensive fieldwork and x-ray fluorescence (XRF) analysis of various sediment samples taken from several dams and pans across the region, a comprehensive understanding of the spatial distribution of trace metals (As, Cu, Fe, Mn, Ni, Pb, and Zn) associated with gold mining was identified. Further, from this, the distribution of trace metals within each site was also analyzed to identify and consider the varying nature of individual site dynamics. In order to identify the level of pollution at each site, a geoaccumulation index was undertaken, based on natural background levels for the areas. The sites that came across as being the most contaminated across the entire region were Amata Pan, Homestead Dam and Kleinfontein Dam. Amata Pan which is situated further south of the concentration of tailings dams, was the most polluted of all sites, with the main reason being the apparent dumping of oil at the site by a large springs manufacturing company. The most likely source of trace metals at Kleinfontein dam is the large mine dump situated right on the bank of the dam. The possible sources of contamination of Homestead Dam may come from the N12 freeway that is situated south of the site and the inflow of two rivers into the dam. Due to the predominance of wind in the area, there is some contribution of trace metals, across the entire region, from the main tailings’ dams and mine dumps towards the centre of the city area.Item The bioremediation of acid mine drainage utilising indigenous South African grass as the organic carbon source for dissimilatory sulfate reduction(2019) Greenway, NatalieAcid Mine Drainage (AMD) is an acidic sulfate-rich wastewater that contains a high concentration of heavy metals. Due to historic and ongoing mining activities around the Witwatersrand, large quantities of AMD is generated in this area which seeps into surface and ground water. AMD has negative environmental, health and economic impacts and requires treatment. Passive treatment is a cost-effective option for the remediation of AMD and involves the process of dissimilatory sulfate reduction (DSR) using sulfate reducing bacteria (SRB) and an organic carbon food source. Indigenous South African grass was identified as an inexpensive and suitable organic carbon source for the bioremediation of AMD. The research presented in this thesis identified a one-stage leach bed reactor (LBR), packed with indigenous South African grass, as a suitable and cost-effective reactor design and configuration for the treatment of AMD. A laboratory-scale LBR was constructed and an experimental analysis determined that an optimal ratio of indigenous South African grass to a synthetic AMD leachate was 6 g of grass / L of synthetic AMD. At higher solid/liquid ratios the system had higher sulfate removal efficiencies. The experiment was conducted using a synthetic AMD leachate and an AMD leachate in order to evaluate the performance of the designed process. The bioreactor containing a synthetic AMD leachate had an average sulfate removal efficiency of 59% and a dissolved iron removal efficiency of 65%. A black coating of iron (II) sulphide formed along the sides of the LBR and on the grass. The bioreactor containing an AMD leachate had an average removal efficiency of 28% and 31% of sulfates and dissolved irons respectively. The pH remained acidic throughout the course of the experiment. AMD has a complex chemistry, including a high concentration of various heavy metals, and has a high mineral and total acidity. A required pre-treatment step of alkaline dosing may be required. An investigation should be made into using a sequentially fed LBR coupled with an uplflow anaerobic sludge bed (UASB) in order to increase sulfate and dissolved iron removal efficiencies. A model of the one-stage LBR was developed and tested against the experimental results of synthetic AMD leachate and the AMD leachate. This research used the Anaerobic Digestion Model No.1 (ADM1) as the basis for the model and upgraded it to include the process of DSR and iron transformations. The model was able to qualitatively predict the behaviour of the system (10% < mean average percent error <30%) but there were discrepancies in predicting the dissolved iron concentrations. Further work should be conducted in upgrading the model to account for transformations and the weak acid-base chemistry of various heavy metals present in AMDItem Assessing how an adaptive management approach was incorporated in the mitigation strategies for acid mine drainage discharge in the Witwatersrand basin(2018) Rantsieng, Masekantsi RahabThe predicaments faced by humanity today differ from the past due to the increasing scale of human influence, complexities and uncertainties (Allen et al., 2010), which limit management options. Adaptive management is based on the philosophy that knowledge is incomplete i.e. there will always be uncertainty and unpredictability in the behaviour and dynamics of complex social-ecological systems. Given the complexity of the South African mining industry, this research aimed to explore the link between management and science by assessing the extent to which an adaptive management approach had been incorporated into short-term and long-term mitigation strategies for the discharge of acid mine water in the Witwatersrand Basin. The methodology included a review of the adopted mitigation strategy document, a literature review of adaptive management literature and an in-depth analysis of a case study using nine interviews, conducted with key informants and contributors from the government, an educational institution, industry (mines currently dealing with the issue), and civil society. An inductive and descriptive approach was followed to gather and analyse data to formulate answers to the research questions. The findings of the study indicated that the efforts that went into designing the short-term solutions were limited due to the lack of communicating amongst stakeholders and the failure to incorporate a value-based approach. Results also showed that complexities and uncertainties were not addressed to allow for adaptation to constant change. It was found that the short-term interventions had no managerial flexibility which limited learning. Insufficient monitoring and a lack of transparency regarding the dissemination of monitoring results were highlighted. Moreover, experimental efforts were limited due to lack of capacity and funding. In conclusion, although the long-term strategy incorporated some aspects of adaptive management, the short-term mitigation measures were reactive rather than proactive. It is recommended that on-going training and good communication are maintained amongst stakeholders. Recommendations for economic constraints include the sharing of costs through partnerships, evaluating trade-offs between costs and effectiveness and investigating cheaper measuring methods for monitoring. Risk-averse initiatives such as conducting risk assessments during pilot studies and accommodating for different project scales can be employed to mitigate against resources that are sensitive to change.Item Remediation of acid mine drainage using prawn shells(2018) Tshikovhi, Fhatuwani PreciousABSTRACT Acid mine drainage (AMD) is a serious global problem, particularly focusing on the Witwatersrand Basin, where most abandoned gold mines constituting mine waste containing pyritic rocks exist and leach sulfuric acid into surrounding waters as effluent containing trace elements like Fe, Co, Cu, Ni, Mg, Zn, Ca and U. Using currently available treatment technologies, it would be costly to remediate the approximately 3,000 miles of streams affected by AMD in Johannesburg hence probing a need for further research and new technology development. Therefore, this research explored the possibility of using prawn shells which contain a deacetylated form of chitin with a buffer capacity for use as a polluted mine water adsorbent. The effect of adsorption parameters such as contact time, absorbent dosage, initial pH, initial uranium ion concentration, competing anions and competing cations were investigated. An optimum adsorption of uranium(VI) of 92% was achieved using 1000 mg adsorbent dosage achieved optimum removal efficiency at pH 3, room temperature and 15 mg L-1 after 6 h equilibration time. The kinetics, isotherms followed pseudo second-order and the Freundlich models. The thermodynamic parameters for the adsorption of uranium onto prawn shells showed that the process proceeded in an exothermic nature, that is, adsorption capacity of uranium decreased with an increase in temperature. The desorption studies performed using HNO3 as an eluent gave efficiency of 19 ± 0.01% for 0.5 mg L-1, 37 ± 0.09% for 1 mg L-1 and NaHCO3 desorption capacity of 77.0 ± 0.01% for 0.5 mg L-1, 93.2 ± 0.05% for 1 mg L-1 and 99.7 ± 0.02% for 2 mg L-1, respectively. Consequently, NaHCO3 was found to be a good reagent for the desorption of uranium. The adsorption capacity was observed to be 0.17 mg g-1. At high concentrations the competing species showed an insignificant effect as uranium adsorption reached 97%. In all the experimental conditions, the speciation of uranium was determined using the PHREEQC geochemical modelling code. For instance, negatively charged U-carbonate complexes (e.g. UO2(CO3)22-) were predicted, explaining the potency of NaHCO3 as a desorbent for uranium. In the presence of competing ions, the speciation of uranium did not change significantly and hence the maintenance of elevated xv adsorption. Overall, the results of the study demonstrated that prawn shells are effective for the recovery of UO22+ ions, making them ideal for potential application for the remediation of uranium in liquid waste. Keywords: Uranium; Adsorption; Prawn shells; Acid mine drainage; ModellingItem Heavy metals removal from acid mine drainage using banana peels(2018) Mahlangu, Jan MbongeniThe sustainable removal of heavy metals from acid mine drainage (AMD) and wastewater has become a major challenge to scientists (Hossain et al., 2012), despite numerous treatment technologies. Most of the explored technologies cannot remove pollutants completely and others are too expensive and also have significant disposal challenges (Giwa et al., 2013). The need to develop a more effective and affordable technology for the removal of heavy metals from AMD is, therefore, inevitable. The banana fruit, the most abundant fruit that is almost consumed across the world its peels were explored to study their potential to remove heavy metals under AMD conditions. The banana peels were cut, washed, dried and ground into powder. Thereafter, the adsorption of zinc, copper and manganese metal ions were studied to investigate the effects of controlling parameters such as particle size, adsorbent dose, initial heavy metal ion concentration, contact time, pH and selectivity of the banana peel. Synthetic single- and ternary component solution, fortified AMD and actual AMD were used in a batch system. Langmuir and Freundlich isotherms were applied to describe adsorption equilibrium. The maximum amount of zinc, copper and manganese metal ions adsorbed, as evaluated by Langmuir isotherm were 9.017, 8.718 and 6.920 mg/g, respectively. The adsorption data fitted the pseudo second order very well and suggested that the adsorption is characterized by the valence forces through exchange of charges between banana peel powder and heavy metal ions. Continuous fixed bed column studies were conducted by using AMD at room temperature and the effects of various parameters such as flow rate (15, 30 and 45 mL/min) and bed depths (6, 12.4 and 17.8 cm) were investigated. The column bed capacity and saturation time increased with the increase of bed depth and decrease of flow rate. Furthermore, the results show that the column performed well at the lowest flow rate. The Thomas model and bed depth service time (BDST) model were applied to evaluate the breakthrough curves and to analyse the experimental data. Thomas model showed a consistent low level of regression coefficient, R2; 0.240 and 0.738 for Mn metal ion at bed depth of 6 cm and 17 cm and flowrate of 15 ml/min, respectively and 0.709 and 0.649 for Zn metal ion at bed depth of 6 cm and 17 cm and flowrate of 15 ml/min, respectively. It can be concluded that the experimental data did not fit well with this model. The BDST model showed adsorption of 150.759 and 27.722 mg/g for manganese and zinc, respectively. The results obtained in this study demonstrated that the banana peel powder can be used as an adsorbent for the removal of zinc, copper and manganese metal ions from AMD using batch and fixed bed adsorption system.Item Mapping acidic mine water using geophysics(2018) De Villiers, Daniel Petrus de WetThe oxidation of pyrite in water produces sulphuric acid that can decrease the pH of groundwater to the point where it is acidic itself. Furthermore, such an increase in acidity causes an increase in water conductivity. The water is referred to as acid mine drainage (AMD). It degrades the environment by enabling groundwater to carry high amounts of heavy metals. Efforts to remediate AMD effects in the Witwatersrand Basin include phytoremediation, specifically the use of Searsia lancea, Eucalyptus and Tamarix trees; these efforts are monitored by water periodically sampled from boreholes. This study investigates the potential of geophysical methods for identifying and monitoring the propagation of an AMD plume and the effects of phytoremediation associated with an old tailings dump in the Orkney area. The electrical resistivity method mapped the water table at a depth of 2-4 m and the maximum depth to bedrock at 18 m. Error analysis of the electrical resistivity data suggests that data can be interpreted down to a depth of only 10 m for profiles where the water is highly conductive due to its high level of contamination. The electrical resistivity results show a decrease in conductivity with distance from the contaminant source. In addition, a clear decrease in conductivity is observed downstream from a Tamarix woodland established for remediation. In the absence of metallic conductors in sediments the resistivity of the pore water governs the resistivity of the sediment medium. However, in this study the relationship determined between the conductivity of pore water and the geological unit is not linear and Archie's law is not applicable at this site, suggesting that either the resistivity of the surficial aquifer is poorly determined or the aquifer matrix is in itself conductive. The Induced Polarization (IP) method produces a chargeability response, which coincides with the Eucalyptus and Searsia lancea tree roots, suggesting that metallic contaminants are stored in and around the tree roots and are polarizable. Although ground penetrating radar has very little penetration in conductive media, GPR data were collected in an effort to image the plume geometry. However, the source waves did not penetrate through the topsoil due to the topsoil being conductive. This study demonstrates that the electrical resistivity method can effectively map the water table depth, can aid in groundwater conductivity mapping between boreholes and possibly tracking AMD. The data coverage of the electrical resistivity method was not sufficient to map the plume as a whole but does provide evidence for the effect of an established woodland in remediating groundwater. The IP method provides preliminary evidence for the removal of AMD pollutants from the groundwater by Searsia lancea and Eucalyptus tree roots.Item Influence of oxidation on leaf decomposition in acid mine water(2017) Mohasoa, Bongani PeterAcidification of freshwater systems by Acid Mine Drainage (AMD) is a persistent risk to aquatic ecosystems in South Africa, particularly in Gauteng and Mpumalanga. From several studies that have been conducted, it is clear that AMD has profound effects on aquatic life and functionality of the ecosystem. One of the ecosystem processes affected by AMD is the decomposition process. It has been established that AMD-affected streams inhibit the decompositon process. [Abbreviated Abstract. Open document to view full version]Item Assessment of changing urban dynamics in Johannesburg city regions as consequence of re-mining of the tailings dumps using Geographical Information System and remote sensing(2017) Mahao, Tseliso JohnThere is a growing interest in the reclamation of the old gold mines’ tailings dumps in Johannesburg city region driven by the economic value of the remaining gold resource. This reclamation activity is accompanied by various rehabilitation methods to reduce issues such as acid mine drainage and wind pollution. The impact of land use and land cover change (LULCC) can have an enormous impact on land development and planning. Monitoring of LULCC is very important in the planning and decision making processes. Remote sensing (RS) as the source of basic data for monitoring change is very highly recommended as tool to monitor changes occurring in the Johannesburg City Region as a result of rehabilitation and reclamation of the gold mines’ tailings deposits. The main aim of the study is to understand how the reclamation and rehabilitation of the historical tailings dumps in Johannesburg are changing land use patterns of the city and its precincts. The objectives are to quantify the changes in land use and land cover as the results of mining rehabilitation using Landsat earth observation data over a period of 30 years at five years intervals and; to recommend on how the land cleared of waste dumps could be used for looking at the surrounding environment spatially. Various Geographical Information Systems techniques are applied here for change detection analysis and monitoring of potential changes in urban dynamics patterns. The results show rate of rehabilitation and reclamation to be slow, taking several years to see a meaningful change. There is some form of bias towards transforming the reclaimed land into industrial zones as opposed to other activities. The success of tailings dumps rehabilitation through revegetation process is highlighted.
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