• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 288
  • 89
  • 41
  • 16
  • 15
  • 12
  • 9
  • 9
  • 9
  • 9
  • 9
  • 8
  • 8
  • 8
  • 6
  • Tagged with
  • 550
  • 550
  • 467
  • 142
  • 109
  • 98
  • 94
  • 58
  • 52
  • 50
  • 48
  • 46
  • 46
  • 43
  • 41
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
331

Obtenção de um ataque químico padrão, zona de annealing parcial e temperatura de fechamento para o epídoto através do método dos traços de fissão /

Nakasuga, Wagner Massayuki. January 2014 (has links)
Orientador: Carlos Alberto Tello Sáenz / Co-orientador: Eduardo Augusto Campos Curvo / Banca: Julio Cesar Hadler Neto / Banca: Silvio Rainho Teixeira / Banca: Sergio Roberto de Paulo / Banca: Neri Alves / O Programa de Pós Graduação em Ciência e Tecnologia dos Materiais, PosMat, tem caráter institucional e integra as atividades de pesquisa em materiais de diversos campi / Resumo: Durante os anos 1970 e 1980 pesquisadores da comunidade de traços de fissão discutiram os problemas relacionados à inclusão do mineral epídoto nesta metodologia, pois haviam discrepâncias significativas entre resultados apresentados pelos laboratórios/pesquisadores. Os debates não levaram a nenhuma definição clara sobre as condições de ataque químico para a revelação dos traços de fissão, bem como, da temperatura de apagamento total dos traços. Por fim, estes problemas culminaram no abandono dos estudos sobre este mineral dentro da metodologia por traços de fissão por um longo período de tempo. A fim de trazer à tona os estudos com este mineral, foram adquiridas 11 amostras de epídotos através de transações comerciais e/ou fornecidas por pesquisadores. Essas amostras formaram o grupo inicial para os estudos de ataque químico, datação e annealing deste trabalho. Após estudos sistemáticos, está sendo sugerido um ataque químico padrão de HF 40% a 15ºC por 80 minutos para epídotos com composição química Ca2Al2(A1, Fe3+)(SiO4)(Si2O7)O(OH). Ainda foram datadas 3 amostras das 11 do grupo inicial de epídoto. Essas amostras são da região do Rio Grande do Norte-Brasil, e as idades obtidas, como resultado, se mostraram compatíveis entre si. Também, foram obtidos 12 pontos de annealing (medidas de densidades superficiais e comprimentos reduzidos), 4 para o tempo de 1 hora (250, 300, 425 e 475ºC), 4 para 10 horas (250, 300, 430 e 510ºC) e mais 4 para 1000 horas (350, 500, 600 e 670ºC). Isto, tanto em densidade como em comprimento reduzidos. No caso da densidade, em cada ponto, foram analisados por volta de 100 campos e no caso do comprimento de traços confinados 100 traços medidos. Com o conjunto de dados de annealing apresentado no mestrado desde doutorando (Nakasuga 2010) mais os obtidos nesta tese pôde-se ajustar as curvas de annealing utilizando os modelos cinéticos de Guedes et. al. (2004) e... / Abstract: During the 70 and 80's researchers of fission tracks is discussed about issues related to inclusion of epidote mineral in this methodology because they had significant discrepancies between results reported by the laboratories/researches. The discussions did not lead to any clear definition of the conditions of etching for the development of fission tracks, as well as the temperature of the total fading of one. Finally, these problems resulted in the abandonment of the studies on this mineral in the method of fission tracks for a long period of time. In order to bring out studies with epidote, 11 samples epidotes were acquired through purchases or provided by researchers. These samples formed the initial group for studies of etching, dating and annealing of this work. After systematic studies, a standard etching has been suggested it is 40% HF at 15ºC for 80 minutes for epidotes with chemical composition Ca2Al2(Al,Fe3+)(SiO4)(Sl2O7)O(OH). Although 3 of the 11 samples of the inicial group of epidote were dated. These samples are from Rio Grande do Norte, Brazil region and the ages obtained, as a result, proved compatible among them. Moreover, 12 points annealing (measured surface densities and reduced length) 4 for 1 hour time (250, 300, 425 and 475ºC), 4 hours for 10 (250, 300, 430 and 510ºC) and another 4 for 1000 hours (350, 500, 600 and 670ºC) were made. This, in both reduced density and length of fission tracks. In case the density at each point, were analyzed around 100 fields and in the case the length of fission tracks 100 are confined measured. In the annealing data set shown in Nakasuga (2010) and the made in this thesis were adjusted annealing curves using the kinetic m odels Guedes et. al. (2004) and Lizandrão-Filho (2014). The result led to zones of Partial Annealing of 190-370ºC for data Nakasuga (2010) and 270-440ºC for the data made in this thesis, both for the period of 1 milion years. Through the Corsini et. al... / Doutor
332

Planning and development of mining towns in Ghana: an exploration of mining and urban development frameworks and practices

Gyogluu, Sarah January 2013 (has links)
Thesis submitted in fulfillment of the requirements for the degree Master of Technology: Town and Regional Planning in the Faculty of Informatics and Design at the Cape Peninsula University Of Technology 2013 / Ghana has had a long history of mining especially with respect to gold, dating back to the Trans-Saharan Trade where gold precipitated civilisations and was a main commodity of trade among Europeans, merchants and ancient kingdoms. In the 21st century, globalisation coupled with increasing urbanisation has been driving demand for mineral resources and thus the resurging commodity booms. This increases foreign direct investment (FDI) in mining countries like Ghana resulting in not only growth in gross domestic product (GDP) but impacts that transcend macro-level and have direct and indirect impacts on communities in mining regions. The result is often that livelihoods are altered, spin-offs on the local economy emerge and the attendant settlement functions impact on the efficacy of existing mining and development planning and regulatory frameworks. Tarkwa is one of Ghana’s traditional gold mining towns and is the substantive context of the research. The main objectives of the research were:  To identify the existing key mining and development planning regulations, gaps present and how these have impacted on the efficacy of governments management practices in responding to consequences of mining-led development.  To analyse the urban household’s perceptions of mining impacts on livelihoods, business enterprises and livelihood coping strategies and mechanisms.  To assess the implications of these emerging planning and development frameworks and trends for the effective planning and development of mining towns in Ghana The highlights of the findings of the research in relation to the above objectives included:  The research revealed that urban households’ perception of mining on their livelihoods was mixed. One of the perceived negative impacts of mining that stuck out from overall responses was scarcity of land for purposes of farming and building.  With respect to coping with mining impacts, respondents largely employed a combination of assets to survive the mining environment. However, respondents’ dependence on human capital-that is, their ability to work and generate income underpinned all livelihoods capitals.  Over 96 percent of business enterprises, perceived purchasing power of people and related available or potential market as the most positive spin-off from mining yet. The informal economy was dominant in terms of business enterprise ownership with informal trading as the most principal form of business enterprise in the informal economy. The research findings have significant meaning within the broad context of mining-led urban development and with implications for theory, the development and planning for resource-driven settlements (practice) and for further research. For example, with regard to development and planning practice, some glaring challenges include the lack of a proper land management system, “superiority” of some institutions (mine houses)in dealing with the Town and Planning Department and Municipal Assembly, lack of effective collaboration between related institutions, gaps in planning legislations make planning near impossible in Tarkwa. The effect being that Tarkwa is growing (spatially to accommodate businesses and people coming in) but without an effective and responsive development planning system to effectively channel and coordinate this growth so that long term development is sustained. The study concludes and recommends that, there is need for a rethink in the way mining towns are planned for and developed in Ghana and should include: a review of the Minerals and Mining law (Act 703) to engender more rights and protection to the communities, a constant review of concession and other agreements to reflect a constantly changing world order, institutional collaboration for planning and development, and long term planning which synchronises spatial and economic planning to capture advantages of agglomeration in and around the Tarkwa mining region.
333

Challenges and prospects for small-scale mining entrepreneurs in South Africa

Mkubukeli, Zandisile January 2016 (has links)
Thesis (MTech (Business Administration))--Cape Peninsula University of Technology, 2016. / Small-scale mining entrepreneurs are confronted with a variety of challenges during both the start-up and growth phase of their businesses not only in South Africa, but all over the world. Most small-scale mining entrepreneurs are not able to take advantage of the opportunities that are available to them. This retards the growth of their businesses. The aim of this study was to investigate the challenges and prospects for small-scale mining entrepreneurs in South Africa, the support structures available to them as well as the factors that could make them successful. The research problem in this study is that the mining sector is biased towards more established companies and against small-scale mining entrepreneurial operations, which marginalises small-scale mining entrepreneurs. Despite being a significant source of revenue for South Africa, the mining sector does not directly benefit the historically disadvantaged people. Notwithstanding government interventions, small-scale mining entrepreneurs face numerous challenges during both the business start-up and growth phase of their businesses with very few prospects of succeeding. This is a qualitative study that uses a series of face-to-face interviews with mining entrepreneurs in South Africa to generate data. Given that small-scale mining entrepreneurs are in most cases part of the informal sector and difficult to locate, a database of small-scale mining entrepreneurs was obtained from Mintek. Initially, 21 small-scale mining entrepreneurs were randomly selected to participate in this study. However, it soon became apparent that ten of them were no longer in business. This meant that the sample was reduced to eleven mining entrepreneurs, located in four provinces: Free State, KZN, Mpumalanga and Limpopo. The findings of this research reveal that small-scale mining entrepreneurs are handicapped by a lack of financial and technical resources, and therefore cannot purchase capital items. It seems that there are good prospects for small-scale mining, particularly in open markets. However, they are unable to exploit these prospects because they lack the necessary finance. Although there are support structures to assist them, they find it difficult to meet the criteria for loans or overdraft facilities from financial institutions. Although these mining entrepreneurs have benefited from the support they have received thus far, they need equipment and commitment to their businesses to remain successful. A series of recommendations are made to guide small-scale mining entrepreneurs already in business, prospective small-scale mining entrepreneurs and other stakeholder’s interested in transforming the industry. / Zandisile Holdings (Pty) Ltd National Research Foundation Mauerberger Foundation
334

Incorporação da variabilidade dos teores para análise de risco de recursos minerais e sequenciamento de lavra

Diedrich, Cássio January 2012 (has links)
A indústria de mineração investiga continuamente processos de reconciliação e técnicas adequadas para mapear possíveis riscos na recuperação do minério e no planejamento de lavra. Um estudo de caso em uma mina de cobre brasileira investiga a adequação do uso de teores simulados para a definição de áreas de risco que afetam o planejamento mineiro e as reservas minerais definidas. Simulações condicionais foram usadas para derivar múltiplos modelos de teores de cobre dentro de um típico corpo de minério do depósito e esses modelos foram comparados com os dados reais de produção (reconciliação). A comparação permitiu uma melhor compreensão sobre a variabilidade da qualidade e ajudou na definição de um plano de produção mais consistente. Com os intervalos de valores provenientes das simulações foi possível mapear importantes áreas de incerteza que afetam o plano de lavra. Análises de risco foram conduzidas para a definição da cava final através da comparação do limite previsto pela estimativa por krigagem ordinária e as cavas resultantes dos modelos simulados de teor de cobre, sendo possível avaliar os impactos operacionais nos principais fatores econômicos (valor presente líquido e fluxo de caixa descontado). Várias cavas finais foram geradas para vários modelos de blocos simulados, comparando-se com a cava anteriormente planejada através da utilização do modelo de blocos produzido pela krigagem ordinária. Além disso, foi definida uma escala de risco utilizando os modelos condicionalmente simulados e os valores estimados pela krigagem (comumente utilizados como referência para definição do orçamento e da alimentação de metal no moinho) a fim de minimizar as variações dos teores. Estas medidas se propõem a reduzir o risco no cumprimento das metas de produção de metal no planejamento de lavra. Esta abordagem, considerando o risco durante o sequenciamento de lavra, foi utilizada no plano de produção anual da mina e comparada com o realizado no período e com a abordagem tradicionalmente aplicada. Os resultados evidenciaram possíveis riscos associados com o limite da cava final operacional e demonstraram os benefícios do uso de análise de risco como uma ferramenta para visualizar e analisar os limites de cava final e planejamento de lavra, ajudando a tomar melhores decisões estratégicas no gerenciamento da mina referente aos fatores técnicos e indicadores econômicos. / Mining industry continuously investigates proper reconciliation procedures and techniques for mapping possible risks in ore recovery and mine planning. A case study at a Brazilian copper mine investigates the adequacy of using simulated grades for defining high risk areas affecting mine planning and the defined mineral reserves. Conditional simulations were used to derive multiple copper grade models within a typical ore-body of the deposit and compared these models against the real production data (reconciliation). The comparison allowed a better understanding of grade variability and helped in defining a more consistent mine plan. The range of values derived from the simulations mapped areas of significant uncertainty affecting the pushback’s plan. Risk analysis were conducted for the final pit definition by comparing the projected final pit limit and mining sequence against the simulated models of copper grade, assessing the operational impacts on key economical factors (mine net present value, discounted cash flow). Several final pit limits were generated for various simulated grade block models and compared to the previously pit planned using the ordinary kriging grade block model. Also, it was defined a risk scale using the conditional simulated models and the ordinary kriged values (commonly used for budget and mill feed reference) in order to minimize grade variations ensuring less risk on completion of the metal production goals on mine planning. This approach considering the risk for the mining sequencing was used on the annual mining plan and compared to the real production and to the traditional approach. The results highlighted possible risks associated with the operational pit limit and demonstrated the benefits of using risk analysis as a tool to preview and review the final pit limits and mine planning, helping to make better strategic decisions by the copper mine management related to the technical factors and economical indicators.
335

Problematika ochrany krajiny a nerostného bohatství na příkladu neregulovaného dobývání vltavínů / Issues of landscape conservation and mineral resources on the example of unregulated mining moldavites

HANUŠOVÁ, Judita January 2011 (has links)
This work investigates the impact of illegal logging moldavites on selected environmental components. The aim was to assess the significance of adverse effects according to established criteria and subsequent evaluation. The assessment process was conducted in the village Slavče in South Bohemia in the period from April 2008 to March 2011. Adverse effects were evaluated mostly as long-term, but with the possible return to its original state. The work is to propose measures to improve the situation.
336

Aplicação de autômatos celulares para modelagem de variáveis regionalizadas na mineração. / A novel application of cellular automata for the evaluation and modelling of mineral resources.

Antonio Carlos da Costa Martins 26 November 2012 (has links)
O trabalho proposto considerou o desenvolvimento de uma abordagem por autômatos celulares para modelagem de recursos minerais. De uma maneira geral, os autômatos celulares permitem a modelagem de sistemas e fenômenos levando em conta parâmetros de forma, dimensão, geometria, regras de evolução, regras de vizinhança e estado inicial. Para a aplicação dos autômatos celulares, foi desenvolvida uma ferramenta de software com apoio do Núcleo de Desenvolvimento de Software, do Departamento de Engenharia de Departamento de Sistemas Eletrônicos da Escola Politécnica da Universidade de São Paulo. A ferramenta de modelagem desenvolvida foi aplicada para modelar um banco de dados conhecido na mineração, que é o Walker Lake Dataset Isaaks e Srivastava (1989). Os resultados obtidos demonstraram que a abordagem por ACs tem potencial para a área de modelagem de recursos minerais, e indicaram a importância de definir uma metodologia específica para a seleção do método de interpolação mais adequado para cada conjunto de dados estudados. / This research project proposes a new approach for modeling geological resources using cellular automata. In general, cellular automata allow modeling systems taking into account parameters of shape, dimensions, evolution rules, neighboring rules and initial state of the cells. For the application of cellular automata in this project, a new tool has been developed in conjunction with the Software Development Group of the Department of Electronics of University of São Paulo. The modeling tool has been applied to model a popular dataset in mining which is the Waker Lake dataset (Isaaks e Srivastava,1989). The results showed that the approach has potential for ACs to the area of modeling of mineral resources and indicated the importance of defining an interpolation method most appropriate for evolutionary change of ACs for the dataset studied.
337

Incorporação da variabilidade dos teores para análise de risco de recursos minerais e sequenciamento de lavra

Diedrich, Cássio January 2012 (has links)
A indústria de mineração investiga continuamente processos de reconciliação e técnicas adequadas para mapear possíveis riscos na recuperação do minério e no planejamento de lavra. Um estudo de caso em uma mina de cobre brasileira investiga a adequação do uso de teores simulados para a definição de áreas de risco que afetam o planejamento mineiro e as reservas minerais definidas. Simulações condicionais foram usadas para derivar múltiplos modelos de teores de cobre dentro de um típico corpo de minério do depósito e esses modelos foram comparados com os dados reais de produção (reconciliação). A comparação permitiu uma melhor compreensão sobre a variabilidade da qualidade e ajudou na definição de um plano de produção mais consistente. Com os intervalos de valores provenientes das simulações foi possível mapear importantes áreas de incerteza que afetam o plano de lavra. Análises de risco foram conduzidas para a definição da cava final através da comparação do limite previsto pela estimativa por krigagem ordinária e as cavas resultantes dos modelos simulados de teor de cobre, sendo possível avaliar os impactos operacionais nos principais fatores econômicos (valor presente líquido e fluxo de caixa descontado). Várias cavas finais foram geradas para vários modelos de blocos simulados, comparando-se com a cava anteriormente planejada através da utilização do modelo de blocos produzido pela krigagem ordinária. Além disso, foi definida uma escala de risco utilizando os modelos condicionalmente simulados e os valores estimados pela krigagem (comumente utilizados como referência para definição do orçamento e da alimentação de metal no moinho) a fim de minimizar as variações dos teores. Estas medidas se propõem a reduzir o risco no cumprimento das metas de produção de metal no planejamento de lavra. Esta abordagem, considerando o risco durante o sequenciamento de lavra, foi utilizada no plano de produção anual da mina e comparada com o realizado no período e com a abordagem tradicionalmente aplicada. Os resultados evidenciaram possíveis riscos associados com o limite da cava final operacional e demonstraram os benefícios do uso de análise de risco como uma ferramenta para visualizar e analisar os limites de cava final e planejamento de lavra, ajudando a tomar melhores decisões estratégicas no gerenciamento da mina referente aos fatores técnicos e indicadores econômicos. / Mining industry continuously investigates proper reconciliation procedures and techniques for mapping possible risks in ore recovery and mine planning. A case study at a Brazilian copper mine investigates the adequacy of using simulated grades for defining high risk areas affecting mine planning and the defined mineral reserves. Conditional simulations were used to derive multiple copper grade models within a typical ore-body of the deposit and compared these models against the real production data (reconciliation). The comparison allowed a better understanding of grade variability and helped in defining a more consistent mine plan. The range of values derived from the simulations mapped areas of significant uncertainty affecting the pushback’s plan. Risk analysis were conducted for the final pit definition by comparing the projected final pit limit and mining sequence against the simulated models of copper grade, assessing the operational impacts on key economical factors (mine net present value, discounted cash flow). Several final pit limits were generated for various simulated grade block models and compared to the previously pit planned using the ordinary kriging grade block model. Also, it was defined a risk scale using the conditional simulated models and the ordinary kriged values (commonly used for budget and mill feed reference) in order to minimize grade variations ensuring less risk on completion of the metal production goals on mine planning. This approach considering the risk for the mining sequencing was used on the annual mining plan and compared to the real production and to the traditional approach. The results highlighted possible risks associated with the operational pit limit and demonstrated the benefits of using risk analysis as a tool to preview and review the final pit limits and mine planning, helping to make better strategic decisions by the copper mine management related to the technical factors and economical indicators.
338

Cost effective rehabilitation of an open cast chrome mine in the North West Province

Crous, Nadia Catharina 09 February 2009 (has links)
M.Sc.
339

Das Ruhrgebiet ist am Äquator entstanden - Gelungener Strukturwandel auf 51 Grad nördlicher Breite

Brüggemann, Jürgen, Melchers, Christian, Goerke-Mallet, Peter 29 July 2016 (has links) (PDF)
Der Beitrag beschreibt die Voraussetzungen des gelungenen Strukturwandels mit der Bündelung der Potentiale von Bodenschätzen, Geographie, Wirtschaft und Bevölkerung. Das Ruhrrevier in seiner heutigen Form ist im besonderen Maße Ausdruck der montanindustriellen Entwicklung. Diese wiederum hängt maßgeblich von der Ausbildung der Steinkohlenlagerstätte ab. So sind es die geologischen Schichten der Region, die diese nachhaltig gestaltet haben. Die Steinkohlenlagerstätte des Ruhrreviers entwickelte sich bereits vor über 300 Mio. Jahren unter subtropischen Bedingungen. Meeresnahe Ablagerungen sind Ursprung des „schwarzen Goldes“, der Steinkohle zwischen Ruhr und Lippe. Eine wechselvolle Geschichte führt über Gebirgsbildungen, Fort- und Rückschreitung der Küstenlinie sowie eiszeitlicher und fluviatiler Sedimentationen zur Gestaltung von Geologie und Morphologie im Ruhrrevier. Die heutige Raumstruktur des Ruhrgebiets entstand somit aus der Geomorphologie des Karbons mit den sich herausgebildeten Flüssen Ruhr, Emscher und Lippe und den sich daran orientierenden mittelalterlichen Städten und Siedlungen. Mit den Auswirkungen der industriellen Revolution auf Basis Kohle, Eisen und Stahl veränderte sich die Region von einem landwirtschaftlich geprägten Raum hin zum heutigen Ballungsraum mit über 5 Millionen Einwohnern. Von den ehemals über 400 Zechen im Ruhrrevier existierten im Jahr 2015 noch zwei fördernde Bergwerke. Das Bergwerk Auguste Victoria wurde Ende 2015 eingestellt, das Bergwerk Prosper Haniel wird Ende 2018 die Förderung einstellen. Damit endet der subventionierte Steinkohlebergbau in Deutschland aus ökonomischen Gründen. Die Lagerstätte im Ruhrrevier ist jedoch bei weitem noch nicht erschöpft. Die Beendigung des Bergbaues führte zu einem Strukturwandel, der in den 1960er Jahren begann und heute noch nicht sein Ende gefunden hat. Er hat eine industrielle, stabile Raumstruktur mit neuem Leben zu füllen. Zwischen Ruhr und Lippe sowie am Niederrhein haben 53 eigenständige Städte und Gemeinde das historische Erbe aufzunehmen und gemeinsam die regionalen Stärken zu fördern. Die großen Flächenstilllegungen wurdenin den prosperierenden Zonen zu modernen Stadtquartieren mit unterschiedlichsten Nutzungen entwickelt oder haben in den Zwischenräume die Landschaften und Freizeitgebiete vergrößert. / The article describes the prerequisites for a successful structural change in the Ruhr area during the last 60 years. Via the regional bundling of the potential in raw materials, geography, economy and population the region managed the termination of the coal and steel industry. More than 50 communities have to deal with the historic legacy and they have to promote the local features. The cessation of the intensive coal-mining phase requires creative ideas, intensive communication, coordination of a lot of stakeholders to ensure a development in the direction of new stable structures.
340

The microbial ecology of sulphidogenic lignocellulose degradation

Clarke, Anna Maria January 2007 (has links)
Acid mine drainage is a well known environmental pollutant, not only in South Africa, but throughout the world, and the use of microbial processes in the treatment of these wastes has been the subject of investigation over past decades. Lignocellulose packed-bed reactors have been used in passive treatment systems, and, although effective initially, they show early decline in performance while the packing material remains largely un-utilized. Little is known about this phenomenon which remains a severe constraint in the development of efficient passive mine water treatment systems. It has been proposed that the degradation pathways of the complex lignocellulose substrate may be limited in some way in these systems during the manifestation of this effect. This study has addressed the problem using a molecular microbial ecology methodology in an attempt to relate trophic functions of the microbial population to the physico-chemical data of the system. A field-scale lignocellulose packed-bed reactor located at Vryheid Coronation Colliery (Northern Kwa-Zulu Natal province, South Africa) was monitored for six years and the results showed the classic profile of performance decline related to a slowdown in sulphate reduction and alkalinity production. The reactor was decommissioned , comprehensive samples were collected along the depth profile and the microbial populations investigated by means of 16S rRNA gene methodology. The population was found to include cellulolytic Clostridia spp., CytophagaIFlavobacterlBacteroidetes, Sphingomonadaceae and as yet uncultured microorganisms related to microbiota identified in the rumen and termite gut. These are all known to be involved as primary fermenters of cellulose. Oesulphosporosinus was present as sulphate reducer. A comparison of substrata sampling and population distribution suggested that spatial and temporal gradients within the system may become established over the course of its operation. Based on these findings, a laboratory-scale reactor was constructed to simulate the performance of the packed-bed reactor under controlled experimental conditions. The laboratory-scale reactor was operated for 273 days and showed comparable performance to that in the field in both biomolecular and physicochemical data. Clearly defined trophic niches were observed. These results suggested that a sequence of events does occur in lignocellulose degradation over time. Based on the spatial and temporal column studies, a descriptive model was proposed to account for these events. It was found that fermentative organisms predominate in the inlet zone of the system using easily extractable compounds from the wood, thus providing feedstock for sulphate reduction occurring in the succeeding compartments. Production of sulphide and alkalinity appears to be involved in the enhancement of lignin degradation and this, in turn, appears to enhance access to the cellulose fraction. However, once the readily extractables are exhausted, the decline in sulphide and alkalinity production leads inexorably to a decline in the overall performance of the system as a sulphate reducing unit operation. These observations led to the proposal that with the addition of a limited amount of a readily available carbon source, such as molasses, in the initial zone of the the reactor, the ongoing generation of sulphide would be sustained and this in turn would sustain the microbial attack on the lignocellulose complex. This proposal was tested in scale-up studies and positive results indicate that the descriptive model may, to some extent, provide an account of events occurring in these systems. The work on sustaining lignocellulose degradation through the maintenance of sulphate reduction in the initial stages of the reactor flow path has led to the development of the Degrading Packed-bed Reactor concept and that, has subsequently been successfully evaluated in the field.

Page generated in 1.5699 seconds