465 research outputs found
Threats and opportunities for post-closure development in dolomitic gold-mining areas of the West Rand and Far West Rand (South Africa) – a hydraulic view Part 2: Opportunities
No full textLargely dependent on gold mines for their economic survival, many mining towns in the Far West Rand fear the effects of the inevitable impact of mine closure, not only on the economy but also on social stability. Large-scale environmental degradation in the form of sinkholes and widespread radioactive pollution exacerbate such fears. Based on an analysis of mining impacts and potential threats for post-mining developments provided in Part I, this 2nd paper in a 3-part series aims to stimulate thought, through the discussion of potential opportunities centred on the rich water resources of the area. This is in full recognition of a subsequent need to assess the economic and technical feasibility of identified opportunities in more detail. Many opportunities are based on the concept that perceived mining liabilities may have the potential to be turned into assets. Examples include the restoration of dewatered karst aquifers and their use for storing large volumes of water, protected from evaporation losses, combined with artificial groundwater recharge and harvesting as well as underground generation of hydropower. This could well be complemented by other water-based developments such as aquaculture, agriculture and different forms of tourism relating to water, karst and mining. Possibilities for using waste land such as sinkhole areas and slimes dams include the establishment of a large game reserve on donated land as well as using tailings for biofuel production and generating solar- and wind-based electricity. Lastly, the re-establishment of a uranium-related industry is explored; this could capitalise on existing infrastructure and former expertise and benefit from the envisaged development of uranium as a strategic resource in SA. In view of the current media attention given to negative environmental and healtheffects, it is, however, questionable whether such development would be acceptable to local residents.Keywords: post-mining development, karst, groundwater storage and harvesting, subterranean hydro-energy generation, tourism, wasteland transformation, uranium industry, research opportunitie
Threats and opportunities for post-closure development in dolomitic gold mining areas of the West Rand and Far West Rand (South Africa) – a hydraulic view Part 1: Mining legacy and future threats
No full texthttp://www.scielo.org.za/scielo.php?pid=S1816-79502010000100008&script=sci_arttex
Threats and opportunities for post-closure development in dolomitic gold mining areas of the West Rand and Far West Rand (South Africa) – a hydraulic view Part 3: Planning and uncertainty – lessons from history
No full textMining is exposed to geological uncertainty as well as to economic forces beyond its control, such as commodity prices and exchange rates that govern profitability. Predictions of future scenarios in mining areas are thus inherently difficult and unreliable. This uncertainty is exacerbated by the long time periods required for pro-active planning of post-mining developments often spanning several decades. This paper presents examples from a gold mining area in the Far West Rand (South Africa) illustrating the variance between predicted scenarios and reality. The facts are embedded in a historical recount of events crucial for the design and approval of mine-closure plans, as well as post-mining development. It is argued that historical arrangements and data need to be understood and preserved in order to avoid the repetition of (costly) mistakes made in the Far West Rand. Owing to the pivotal role of water in the semi-arid area and the fact that some of the most important groundwater resources of South Africa were impacted on by deep-level mining, this paper in 3 parts adopted a largely hydraulic perspective. The loss of ‘institutional memory’ and local expertise has been identified as the main threat to planning. Part 3 presents an attempt to counteract such loss by providing an account of the events of 5 decades, as witnessed by the first author.Keywords: gold mining, dolomitic compartments, dewatering, farming, post-mining development
Using impacts of deep-level mining to research karst hydrology—a Darcy-based approach to predict the future of dried-up dolomitic springs in the Far West Rand goldfield (SouthAfrica). Part 2: predicting inter-compartmental flow and final groundwater tables
No full textSome of the world’s deepest goldmines operate below dolomitic karst aquifers in the Far West Rand (FWR) goldfield, South Africa. Associated impacts include the continuous dewatering of karst aquifers for over six decades and irreversible changes of the hydrogeological setting. Affecting an area of approximately 400 km2 by drawing down the water table up to 700 m, these impacts, and the large amounts of data generated in the process, are used as unique research opportunities to better understand the complex karst hydrology. The focus of this study is on predicting final water table elevations in rewatered aquifers after mining ceases taking the fact that mines hydraulically linked previously disconnected aquifers into account. While part 1 of this series develops the conceptual model, this second part utilises large sets of pertinent data to calculate actual flow rates for predicting the fate of dried up springs after mine closure. Following a Darcy-based approach first applied by Swart et al. (Environ Geol 44:751–770, 2003a) it is not only predicted that the springs will flow again but also shown that linear relationships exist between flow rates through a combined system of karst-fractured aquifers overlying the mine void and the associated hydraulic head driving them. This suggests that—at this scale—porous media-based equations can be meaningfully used to predict flow in non-porous media.http://dx.doi.org/10.1007/s12665-014-3298-2http://link.springer.com/article/10.1007/s12665-014-3298-
Determining hydraulic parameters of a karst aquifer using unique historical data from large-scale dewatering by deep level mining – a case study from South Africa
No full textAlthough karst aquifers constitute some of the most important water resources worldwide, generally accepted methods for reliably characterising their hydraulic properties are still elusive. This paper aims at contributing to the discussion by a first-ever attempt to utilise various sets of unique historical data derived from draining a large dolomitic karst aquifer by deep-level gold mines in South Africa. In contrast to conventional pumping tests which only penetrate thick aquifers to a limited extent from surface, this draining took place at the very bottom of the aquifer offering the rare opportunity to capture its entire thickness of nearly a kilometre. The datasets have been treated as analogies to conventional pumping tests applying various types of analytical methods designed for porous media. In order to increase the robustness of the results and to account for specific local conditions a total of four different analytical methods were applied to calculate (horizontal) transmissivity and storage coefficients. The obtained values, in general, compare favourably to previous studies in the area and values reported in literature for similar aquifer types confirming earlier findings that Darcy-based methods can be successfully applied to karst aquifers if the scale of investigation is large enough. Apart from improving the understanding of local karst hydrology the present study also aimed at retrieving and preserving valuable and unique historical datasets that otherwise would have been lost for scientific evaluation and the proactive preparation for mine closure.http://dx.doi.org/10.4314/wsa.v40i3.20http://www.ajol.info/index.php/wsa/article/view/105861/9587
Pseudomonas and Beyond: Polyamine metabolism, lignin degradation and potential applications in industrial biotechnology
No full textRenewable resources such as lignocellulosic biomass are promising feedstocks for the production of bio-fuels and value-added products. Biocatalysts are considered important tools in such processes. Pseudomonas putida S12 has a broad metabolic potential and is exceptionally tolerant towards a range of toxic organic solvents and aromatic compounds, which makes this bacterium a very suitable host for the production of aromatic compounds. The work described in this thesis provides insights into the metabolism of the polyamine putrescine in P. putida S12, which presumably plays a role in the response to solvent stress. The utilisation of lignocellulosic biomass as a renewable feedstock for sustainable energy and chemicals production, is gaining increased attention. Still, intensive research is required to enable efficient utilisation of all components contained within lignocellulose, and to expand the range of value-added products to be obtained from this resource. In this study, novel bacterial isolates have been investigated that could potentially serve as a source of lignin degrading enzymes. Application of such enzymes combined with the solvent tolerance of P. putida S12 could open up a new avenue for the valorization of the ubiquitously available renewable resource lignin. It has also been made clear, however, that the recalcitrant nature and complex structure of lignin greatly complicates the research into biological lignin depolymerization. Much is to be learned and possibly gained from bacterial lignin degradation, which justifies more and intensified research.BiotechnologyApplied Science
C5-technology in Pseudomonas putida S12: Construction, analysis and implementation of D-xylose metabolic pathways
No full textThe rising price of oil and impending deficit of fossil resources stimulate the development of alternative processes for the production of chemicals. The production of biochemicals from lignocellulosic biomass is a promising alternative. Lignocellulosic biomass consists of a mixture of sugars that can be converted into valuable products or chemicals by means of bioconversion. It is essential that, in order to establish an economically sound process, the feedstock is utilised as completely as possible. However, due to its heterogeneous nature, lignocellulosic feedstock is often metabolised incompletely. The same problem is encountered with the production of aromatic compounds by the solvent-tolerant micro-organism Pseudomonas putida S12. In order to increase the efficiency of biochemicals production from lignocellulose, strategies were explored to engineer D-xylose metabolic pathways in P. putida S12, to enable the consumption D-xylose, the second most abundant sugar present in lignocellulosic biomass. Two approaches to achieve D-xylose utilization by P. putida S12 were investigated: constructing a phosphorylative pathway using genes from Escherichia coli and establishing an oxidative pathway with genes from Caulobacter crescentus. The resulting strains were both capable of growing on D-xylose as carbon source. Analyses performed on the two strains yielded more insight in the metabolic pathways employed to utilize D-xylose. Also, as a case study for the production of aromatic compounds from D-xylose and a mixture of sugars, a p-hydroxybenzoate producing P. putida S12 strain was engineered with the phosphorylative D-xylose pathway. Chemostat experiments with the resulting strain demonstrated that aromatics production can be significantly improved by feeding mixtures of D-xylose and D-glucose or glycerol. As lignocellulose consists of mixtures of D-xylose and D-glucose, and because glycerol is expected to be a cheap feedstock in the future, these results are promising for the development of a sustainable aromatics production process.BiotechnologyApplied Science
The greywater situation in informal settlements of the Ekurhuleni Metropolitan Municipality - Eastern Region (Gauteng, South Africa)
No full textThesis (M. Environmental Management)--North-West University, Potchefstroom Campus, 2009.In recent years growing attention of international and local water research was directed to grey water as a potential water source, as well as its significance as a possible health risk to humans and as a source of pollution. Owing to a general lack of waterborne sewage infrastructure, health risks and pollution associated with grey water generation in informal settlements are of particular concern to municipal managers. However, so far only limited information on the grey water generation, use and disposal in informal settlements is available. Using four different informal settlements in the highly urbanised eastern region of the Ekurhuleni Metropolitan Municipality in Gauteng (also known as East Rand) this study aims to characterise selected aspects of the grey water situation as a first step towards future improvements through appropriate
interventions and grey water management. Following consultations with representatives of the local municipality (colleagues of the author) the following four informal settlements with distinctly different grey water appearance were selected as study sites: • Benoni - Harry Gwala • Springs - Gugulethu • Brakpan - Mkhanca • Nigel- Soul City As part of the reconnaissance phase of the study, each site was visited and field observations on infrastructure, habits and other grey water related aspects were made and suitable households for subsequent
interviews were identified. In each settlement a total of 25 households were chosen and a representative interviewed using a pre-designed questionnaire comprising eight sections, four sections covering the following aspects: access to and sources of water, general sanitary situation, water use and associated generation as well as disposal of grey water. Interviews were conducted between November 2006 and August 2007 and varied in duration between 20 and 30 minutes per interviewee totaling close to 48 hours. They were either conducted in Zulu or South Sotho, the most widely spoken languages of the interviewed residents. Answers were recorded in English on site. Results were subsequently captured in EXCEL and statistically evaluated. The average volume of grey water generated by the four different water usages, Le. bathing, cleaning, laundry washing and dish washing varies from 35 to 60 /household/day. With each household comprising an average
of four people (two children and two adults) this equals a grey water generation rate of approx. 9 to 15 l/person/day and is somewhat lower than reported in comparable studies in South Africa. Owing to the fact that all volume data are estimates, a comparatively large margin of error is to be expected, explaining why in some cases more water was estimated to be used than was actually fetched. Water use volume was found to be influenced by the availability of stand pipes and in one case was supplemented by collected rain water.
Generally, however, water was not perceived to be a problematic issue compared to more pressing needs such as housing, unemployment etc. Washing of cloths in all settlements was found to be the single most important source of grey water generation accounting for a third to almost half of all grey water generated. The smallest contribution comes from water used for cleaning (approx. 10%) while bathing and washing dishes accounts for equal proportions of the reminder. Chemical and microbiological analyses of grey water, sampled at selected sites across the four study areas, revealed significant variations in quality between the different sites, without allowing for clear distinctions between the impacts of different brands of detergents such as soaps, washing powder and dish washing liquids. Contrary to literature E-coli contamination was found not be confined to bath and kitchen waste water only, but also appeared in laundry water, frequently exceeding values stipulated in the general standards of waste water or effluent in South Africa This is of particular concerns since some of the grey water is disposed of into storm water canals and in other non-formal ways, that allow for subsequent exposure of humans to the contaminated waste water. In order to facilitate rapid drainage in some instances respondents created their own grey water disposal infrastructure e.g. by digging open waste water trenches across backyard borders. Regarding potential health risks it is to be noted that at least one respondent reported the use of the water
resource (Blesbokspruit) as toilet facility.
Apart from the actual findings the study also revealed the importance of an appropriate research design and conduct that addresses the peculiarities of an informal setting. This includes overcoming logistic challenges such as limited accessibility of the study sites during wet seasons owing to flooded and muddy roads, safety and security issues as well as difficulties to conduct indoor interviews owing to a lack of light (no windows, no electricity) leading to low temperatures in winter limiting interview duration. In addition to this socio-cultural aspects and attitudes of respondents have to be taken into account in order to obtain true reflections of facts through interviewing. In this regard it was helpful that the author, as a black female, was familiar with certain customs and perceptions regarding sensitive issues such as use of toilets, connotations of muti (= a traditional medicine that may be included in bathwater as a constituent) etc. Being aware of these peculiarities allowed the author to detect and explain differences between statements obtained from the respondents and her own observations.Master
Biological production of hydroxylated aromatics: Optimization strategies for Pseudomonas putida S12
No full textTo replace environmentally unfriendly petrochemical production processes, the demand for bio-based production of organic chemicals is increasing. This thesis focuses on the biological production of hydroxylated aromatics from renewable substrates by engineered P. putida S12 including several cases of strain improvement. Chapter 2 describes the construction of a P. putida S12 strain that produces p-hydroxybenzoate via the aromatic amino acid tyrosine. Previous research on biosynthesis of aromatic compounds has culminated in the construction of P. putida S12_427. This strain, which has an optimized carbon flux towards tyrosine, was employed as platform host for aromatics production. By introducing the heterologous gene pal/tal (encoding phenylalanine/tyrosine ammonia lyase; Pal/Tal) the conversion of tyrosine into p-coumarate was established, which compound is further converted into p-hydroxybenzoate by endogenous enzymes. The degradation of p-hydroxybenzoate was prevented by inactivating the gene pobA, which encodes hydroxybenzoate hydroxylase. The resulting strain, P. putida S12palB1, accumulated p-hydroxybenzoate at a yield of 11 Cmol % on glucose or glycerol in shake flask cultivations. A glycerol-limited fed-batch cultivation was performed to increase the product titers, yielding a final p-hydroxybenzoate concentration of 12.9 mM (1.8 g l-1) with a product-to-substrate yield of 8.5 Cmol %. Tyrosine availability was identified as the main bottleneck for p-hydroxybenzoate production in glycerol-limited chemostat cultivations. Since the enhanced flux towards p-hydroxybenzoate in P. putida S12palB1 mainly originated from a random mutagenesis approach, multiple system-wide changes were expected. Therefore, a chemostat-based comparative transcriptomics and proteomics analysis was performed as described in Chapter 3, to gain insight into the genetic background of the enhanced strain performance. The overall expression differences between parent strain and P. putida S12palB1 confirmed the system-wide changes effectuated by the strain improvement procedure. The higher net metabolic flux towards p-hydroxybenzoate was reflected in the upregulation of genes involved in tyrosine biosynthesis and the conversion of p-coumarate into p-hydroxybenzoate. Notably, on glucose some of the p-hydroxybenzoate biosynthetic genes were upregulated to a higher extent than in the glycerol-grown chemostats, while the phydroxybenzoate accumulation was not affected by the carbon source applied. Furthermore, a multidrug efflux transporter (PP1271-PP1273) was identified that may have a major role in phydroxybenzoate export. The 2.8-fold upregulation of hpd (encoding 4-hydroxyphenylpyruvate dioxygenase; first enzyme of tyrosine degradation via the homogentisate pathway) on glucose suggested that part of the tyrosine was directed away from p-hydroxybenzoate biosynthesis. This was confirmed by a 22-% increase of the product-to-substrate yield upon eliminating hpd. Although the hpd gene was not significantly differentially expressed on glycerol (1.5-fold), hpd deletion resulted in a 21 % improved p-hydroxybenzoate yield also on glycerol. The key precursors for the production of aromatic compounds, phosphoenolpyruvate (PEP) and erythrose-4-phosphate (E4P), are withdrawn from the lower glycolysis, respectively, the pentose phosphate (PP) pathway. Since the flux through the PP pathway is typically low in P. putida S12, the availability of E4P may be a bottleneck for p-hydroxybenzoate production. In Chapter 4, it was attempted to increase the availability of E4P by co-feeding xylose directly into the PP pathway. To this end, the genes xylABFGH (encoding xylose isomerase, xylulokinase and a high affinity xylose transporter) were introduced in the phydroxybenzoate producing strain to establish growth on xylose via the PP pathway. Growth performance on xylose was improved by an evolutionary selection approach. Surprisingly, this also resulted in a 25-% improvement of p-hydroxybenzoate production on either glycerol or glucose, indicating that the resulting strain, P. putida S12pal_xylB7, had an intrinsically elevated PP pathway activity. Chemostat experiments demonstrated that co-feeding of xylose (replacing part of the glucose or glycerol in the feed) considerably increased the production efficiency. On glucose, co-feeding of xylose improved the product-to-substrate yield by a factor 1.5 to 7.9 Cmol %, while on glycerol the product-to-substrate yield doubled to 16.3 Cmol %. Interestingly, product formation was not further improved by replacing more than 25 % of the carbon feed with xylose. This suggested that the availability of E4P was no longer the limiting step in p-hydroxybenzoate biosynthesis. The ability of co-utilizing xylose and glucose and the resultant improved production parameters implicated that lignocellulosic feedstock, containing around 20 % xylose and 50 % glucose, is a very suitable substrate for the production of aromatic compounds by engineered P. putida S12. In Chapter 5 the utilization of the industrial grade renewable feedstock crude glycerol was evaluated. In high-cell density fed-batch fermentations, P. putida S12 strains performed consistently better on crude glycerol than on purified glycerol, as shown by the higher biomass-to-substrate yield, maximum biomass production rate and substrate uptake rate. Moreover, the production of p-hydroxybenzoate by an engineered P. putida S12 strain was more efficient on crude glycerol. On crude glycerol a maximum p-hydroxybenzoate concentration of 43.5 mM (6.0 g l-1) was obtained with a product-to-substrate yield of 6.6 Cmol %, compared to 38.4 mM (5.3 g l-1) and 5.9 Cmol % on purified glycerol. In contrast, E. coli DH5? showed a decreased biomass-to-substrate yield and growth rate on crude glycerol compared to purified glycerol, and increased acetate formation (11.5 and 16.2 g l-1 on purified and crude glycerol respectively). The majority of the optimization approaches described in this thesis for p-hydroxybenzoate production can be applied for efficient production of other tyrosine derived compounds. This is exemplified in Chapter 6, where the production of the value-added compound phydroxystyrene from glucose is described. Production of p-hydroxystyrene was established by introducing the genes pal/tal and pdc, encoding phenylalanine/tyrosine ammonia lyase and p-coumaric acid decarboxylase respectively, into the tyrosine overproducing strain P. putida S12_427. These enzymes allow the conversion of the central metabolite tyrosine into p-hydroxystyrene, via p-coumarate. Degradation of the p-coumarate intermediate was prevented by inactivating the fcs gene encoding feruloyl-CoA synthetase. In fed-batch cultivation on glucose a maximum p-hydroxystyrene concentration of 4.5 mM was obtained with a yield of 6.7 Cmol %. At this p-hydroxystyrene concentration, growth and production were completely halted due to the toxicity of p-hydroxystyrene. Product toxicity was overcome by the application of a second phase of 1-decanol to extract p-hydroxystyrene during fedbatch cultivation. This approach resulted in a final p-hydroxystyrene concentration of 147 mM (17.6 g l-1) in the decanol phase, with a twofold increase of the maximum volumetric productivity (0.75 mM h-1) and a fourfold higher total concentration (21 mM). The work described in this thesis illustrates how hydroxylated aromatics can be efficiently produced by engineered P. putida S12 strains. Several strategies for analysis and optimization were performed to improve the aromatics production and understand the background and impact of the improvements. The biological production of various hydroxylated aromatics was established and largely improved. Hence, this work presents an important contribution to our efforts to replace petrochemical production by bio-based processes.BiotechnologyApplied Science
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