The microbial ecology of sulphidogenic lignocellulose degradation
- Authors: Clarke, Anna Maria
- Date: 2007
- Subjects: Microbial ecology , Lignocellulose , Sulfides , Lignin , Lignocellulose -- Biodegradation , Mines and mineral resources -- Waste disposal , Acid mine drainage
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4094 , http://hdl.handle.net/10962/d1008181
- Description: 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.
- Full Text:
- Date Issued: 2007
- Authors: Clarke, Anna Maria
- Date: 2007
- Subjects: Microbial ecology , Lignocellulose , Sulfides , Lignin , Lignocellulose -- Biodegradation , Mines and mineral resources -- Waste disposal , Acid mine drainage
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4094 , http://hdl.handle.net/10962/d1008181
- Description: 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.
- Full Text:
- Date Issued: 2007
The molecular microbial ecology of sulfate reduction in the Rhodes BioSURE process
- Authors: Chauke, Chesa Gift
- Date: 2002
- Subjects: Water -- Purification -- Biological treatment , Acid mine drainage , Water -- Microbiology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4082 , http://hdl.handle.net/10962/d1007475 , Water -- Purification -- Biological treatment , Acid mine drainage , Water -- Microbiology
- Description: The research reported here investigated the use of a Baffle Reactor in order to study aspects of the biological sulfur cycle, where a floating sulfur biofilm formation occurs and where complex organic compounds provide electron donor sources. The development of a laboratory-scale Baffle Reactor model system satisfied the requirements for sulfate reducing bacterial biomass growth and sulfur biofilm formation. Since relatively little is known about the microbial ecology of floating sulfur biofilm systems, this study was undertaken to describe the sulfate reducing sludge population of the system together with its performance. A combination of culture- and molecular-based techniques were applied in this study in order to investigate the microbial ecology of the sulfate-reducing bacteria component of the system. These techniques enabled the identification and the analysis of the distribution of different sulfate reducing bacterial strains found within the sludge bioreactors. Strains isolated from the sludge were characterised based on culture appearance, gram staining and scanning electron microscopy morphology. Molecular methods based on the PCR-amplified 16S rRNA including denaturing gradient gel electrophoresis were employed in order to characterise sulfate-reducing bacteria within the reactors. Three novel Gram negative sulfate-reducing bacteria strains were isolated from the sludge population. Strains isolated were tentatively named Desulfomonas rhodensis, Desulfomonas makanaiensis, and Clostridium sulforhodensis. Results obtained from the Baffle Reactor showed that three dominant species were isolated from the DNA extracted from the whole bacterial population by peR. Three of these were similar to those mentioned above. The presence of these three novel unidentified species suggest that there are a range of other novel organisms involved in sulfate reduction processes.
- Full Text:
- Date Issued: 2002
- Authors: Chauke, Chesa Gift
- Date: 2002
- Subjects: Water -- Purification -- Biological treatment , Acid mine drainage , Water -- Microbiology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4082 , http://hdl.handle.net/10962/d1007475 , Water -- Purification -- Biological treatment , Acid mine drainage , Water -- Microbiology
- Description: The research reported here investigated the use of a Baffle Reactor in order to study aspects of the biological sulfur cycle, where a floating sulfur biofilm formation occurs and where complex organic compounds provide electron donor sources. The development of a laboratory-scale Baffle Reactor model system satisfied the requirements for sulfate reducing bacterial biomass growth and sulfur biofilm formation. Since relatively little is known about the microbial ecology of floating sulfur biofilm systems, this study was undertaken to describe the sulfate reducing sludge population of the system together with its performance. A combination of culture- and molecular-based techniques were applied in this study in order to investigate the microbial ecology of the sulfate-reducing bacteria component of the system. These techniques enabled the identification and the analysis of the distribution of different sulfate reducing bacterial strains found within the sludge bioreactors. Strains isolated from the sludge were characterised based on culture appearance, gram staining and scanning electron microscopy morphology. Molecular methods based on the PCR-amplified 16S rRNA including denaturing gradient gel electrophoresis were employed in order to characterise sulfate-reducing bacteria within the reactors. Three novel Gram negative sulfate-reducing bacteria strains were isolated from the sludge population. Strains isolated were tentatively named Desulfomonas rhodensis, Desulfomonas makanaiensis, and Clostridium sulforhodensis. Results obtained from the Baffle Reactor showed that three dominant species were isolated from the DNA extracted from the whole bacterial population by peR. Three of these were similar to those mentioned above. The presence of these three novel unidentified species suggest that there are a range of other novel organisms involved in sulfate reduction processes.
- Full Text:
- Date Issued: 2002
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