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Production of mannooligosaccharides from pineapple pulp and pine sawdust using Aspergillus niger derived Man26A and determination of their prebiotic effect

  • Authors: Hlalukana, Nosipho Pretty
  • Date: 2022-10-14
  • Subjects: Oligosaccharides , Prebiotics , Lignocellulose , Mannans
  • Language: English
  • Type: Academic theses , Master's theses , text
  • Identifier: http://hdl.handle.net/10962/362853 , vital:65368
  • Description: Lignocellulosic biomass is the most abundant source of renewable biomass on earth. Lignocellulosic biomass consists of cellulose, hemicelluloses and lignin. These can be used as a source of renewable fuel as well as other value-added products . Mannans are part of the hemicellulose fraction of lignocellulosic biomass and are the major hemicellulosic polysaccharide fraction in softwoods, where they are found as galactoglucomannans and as glucomannans. Mannans are also found in hardwoods in the form of glucomannans. Mannans can be enzymatically hydrolysed using endo-mannanases to produce of short chain mannooligosaccharides (MOS). MOS have received significant attention for their prebiotic properties, as they promote the growth of probiotic bacteria, which have positively affects on gut health. This study focused on the production of prebiotic MOS from lignocellulosic biomass waste (LBW) and an evaluation of the prebiotic potential of the produced MOS. An Aspergillus niger derived endo-mannanase, Man26A, was fractionated and biochemically analysed. Purified Man26A had a fold purification of 1.25 and a yield of 41.1%. SDS-PAGE analysis of the enzyme revealed that it had a molecular weight of 46 kDa. The pH and temperature optima of Man26A were determined and the pH optimum was found to be pH 4.0 (but the enzyme displayed high activity over a broad acidic pH range, with up to 90% of the activity retained between pH 3.0 and 7.0). The temperature optimum was 50℃. The enzyme was shown to have the highest specific activity on locust bean gum (52.27 U/mg) and ivory nut mannan (57.25 U/mg), compared to guar gum (29.07 U/mg), which indicated that it was affected by the substitution pattern of the mannans. Man26A produced MOS of different diversity on model mannan substrates, where the MOS produced were mannobiose, mannotriose, and mannotetraose for ivory nut mannan, mannobiose, mannotriose, mannotetraose, and mannopentaose and MOS with a higher degree of polymerisation for locust bean gum, and mannobiose, mannotriose, mannotetraose, mannopentaose, and mannohexose and MOS with a higher degree of polymerisation for guar gum, as determined by thin layer chromatography (TLC) and high-performance liquid chromatography (HPLC). Pretreatment and characterisation of pineapple pulp (PP) and pine sawdust (PSD) was conducted, and the impact of the pretreatment procedures was analysed using Megazyme sugar kits, thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FTIR), and microscopic analysis using scanning electron microscopy (SEM) and light microscopy. Compositional analysis of the carbohydrates present in both substrates revealed that they had a glucan content of 36.41 and 50.47% for untreated PP and PSD, respectively. Their respective mannan content was 6.74 and 11.59% and was deemed sufficient for the production of MOS via enzymatic hydrolysis. TGA analysis revealed that untreated and sodium chlorite-acetic acid delignified samples decomposed at approximately the same time, and had a negligible ash content at 600℃, while delignified plus phosphoric acid swollen substrates decomposed at a faster rate, but had a residual ash content at 600℃. FTIR analysis of the substrates revealed slight changes in the structures of untreated and pretreated samples. SEM analysis of PP and PSD showed a change in the morphology of the substrates with subsequent pretreatment steps. Histochemical analysis for lignin for PP and PSD showed successful delignification upon pretreatment. Untreated and sodium chlorite delignified PP and PSD released low amounts of reducing sugars compared to delignified + phosphoric acid swollen substrates. The delignified + phosphoric acid swollen substrates were used for further experiments. MOS produced from delignified and phosphoric acid swollen (Del + PAS) PP and PSD at 0.1 mg/ml enzyme loading and 80 mg/ml (8% (w/v)) substrate concentration, ran between mannose and mannobiose and between mannobiose and manotriose on TLC, with low concentrations of MOS running between mannotetraose and mannopentaose. HPLC analysis of the MOS revealed that Del + PAS PP produced mannose to mannohexose, while Del + PAS PSD produced mannose, mannobiose, and mannotetraose. The MOS were analysed using FTIR, to determine whether the MOS produced contained any acetyl groups, which were present for Del + PAS PSD at 1706 cm-1. The MOS were stable at different pHs, and at temperatures below 200℃. The MOS were also found to be stable in a simulated gastrointestinal environment, in the presence of bile salts and digestive enzymes. The prebiotic effect of the MOS derived from Del + PAS PP and PSD was evaluated. MOS had a proliferative effect on probiotic bacteria (Lactobacillus bulgaricus, Bacillus subtilis and Streptococcus thermophilus). The production of short chain fatty acids (SCFAs) was evaluated on TLC, where no SCFAs were observed on the plate. The effect of MOS on the adhesion ability of bacteria revealed that they do not positively influence the adhesion of probiotic bacteria. The antioxidant activities of 1 mg/ml MOS produced from both substrates were determined to be approximately 15% using the ABTS radical scavenging assay, compared to a radical scavenging activity of 45% for the 0.02 mg/ml gallic acid standard. This study demonstrated that biomass waste could be used to produce prebiotic MOS, which play a positive role in gut ecology and provide health benefits. , Thesis (MSc) -- Faculty of Science, Biochemistry and Microbiology, 2022
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  • Date Issued: 2022-10-14

Evaluation of pre-treatment methods on production of bioethanol from bagasse and sugarcane trash

  • Authors: Dodo, Charlie Marembo
  • Date: 2019
  • Subjects: Lignocellulose
  • Language: English
  • Type: Thesis , Doctoral , PhD
  • Identifier: http://hdl.handle.net/10353/15387 , vital:40403
  • Description: A variety of methods have been researched on for bioethanol preparation from different feedstocks. Amongst the available feedstock, one such feedstock is the sugarcane plant. In most of the research on bioethanol preparation with sugarcane the sugary juice has been widely used, with the bagasse and trash having been discarded as waste. The “waste” bagasse and trash are usually removed and thrown away or burnt during harvesting or in sugar mills to supplement energy requirements. This research on lignocellulosic bagasse and trash was done so as not to discard them but to rather find ways in which to use this biomass constructively. Alternatives to burning that can potentially add value to this biomass need to be researched on by evaluating their hydrolysis content. The different lignocellulose pretreatment methods of concentrated and dilute acid pretreatment, with subsequent enzyme hydrolysis as well as alkali and oxidative alkali pretreatment with enzyme hydrolysis were experimented on the bagasse and trash for hydrolysis efficiency and effectiveness. There are two types of acid hydrolysis which were investigated on which are concentrated and dilute sulphuric acid pretreatments. Use of concentrated sulphuric acid yielded the highest amounts of reducing sugars but also resulted in the highest amounts of downstream process inhibitors formation. This resulted in the need for neutralisation steps which in turn increase the overall costs of using this method to obtain reducing sugars. It has however the advantage of occurring at a faster rate, within minutes or hours, than using biological enzymes which took days, up to 72 hours to obtain the highest reducing sugar amounts. Dilute sulphuric acid pretreatment offered the advantage of using fewer chemicals which are therefore less severe on equipment and result in fewer fermentation inhibitors being formed. Dilute sulphuric acid hydrolysis also takes a relatively shorter period than biological methods of pretreatment. A challenge of fermentation inhibitors formed during acid hydrolysis was countered by using the methods of overliming (calcium hydroxide) and comparing it to neutralization with sodium hydroxide. Alkali pretreatment with sodium hydroxide was researched on by applying different pretreatment concentrations during experiments on the lignocellulosic biomass. There was an increase in the available quantities of cellulose with a significant reduction in lignin with pretreatment. Alkali pretreatment proved effective in exposing the cellulose which made v more cellulose surface area available to cellulase enzymes for enzyme hydrolysis. The highest yield of reducing sugars was obtained from hydrolysates pretreated with 0.25 M sodium hydroxide for 60 min and a period of 72 h of enzyme hydrolysis. In general the longer the pretreatment time the more reducing sugars were produced from the enzyme hydrolysis. Alkali peroxide pretreatment also resulted in significant reductions in lignin quantities of lignocellulose material. In this method sodium hydroxide in combination with hydrogen peroxide were used in pretreating the biomass. Hydrolysates with even fewer fermentation inhibitors were produced as a result. The highest percentage concentration of cellulose of 63% (g/g) was achieved after pretreatment of bagasse with 5% alkali hydrogen peroxide and trash with 0,25M sodium hydroxide pretreatment. Pretreatment of biomass using alkali with subsequent enzymatic hydrolysis gave the highest yields of fermentable sugars of 38% (g/g) using 7% (v/v) alkali peroxide pre-treated trash than 36% (g/g) for 5% (v/v) with the least inhibitors. Reducing sugar yields of 25% (g/g) and 22% (g/g) were obtained after pretreatment with concentrated and dilute acid respectively. Neutralization of the acid hydrolysates was necessary to reduce inhibitors formed with neutralisation by sodium hydroxide resulting in low dilutions and loss of fermentable sugars as unlike in the case of overliming. Subsequent steps of fermenting the reducing sugars resulting from pretreatment into bioethanol were based on using the yeast Saccharomyces cerevisae. Pretreatment hydrolysates from alkali peroxide experiments produced higher bioethanol yields of 13.7 (g/l) after enzyme hydrolysates versus 6.9 (g/l) bioethanol from dilute acid hydrolyzates. A comparison of the effects of time showed there was more bioethanol yield of 13.7 (g/l) after 72 h of fermentation with the yeast versus 7.0 (g/l) bioethanol after pretreatment for 24 h. The only drawback is the longer fermentation period which thus reduces the process and so reduces the value of the increase in yield
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  • Date Issued: 2019

Evaluation of cellulase and xylanase production by two actinobacteria species belonging to the Micrococcus genus isolated from decaying lignocellulosic biomass

  • Authors: Mmango-Kaseke, Ziyanda https://orcid.org/0000-0002-8936-1149
  • Date: 2016-05
  • Subjects: Lignocellulose , Biomass energy
  • Language: English
  • Type: Master's theses , text
  • Identifier: http://hdl.handle.net/10353/24197 , vital:62442
  • Description: Bacteria were isolated from sawdust and screened for cellulase and xylanase production on carboxyl methyl cellulose (CMC) and birchwood xylan agar. The bacteria showing halo forms around the colony were selected for further analyses and those isolates with the highest cumulative halozone size (isolate PLY1 and MLY10) were chosen for detailed studies. Evaluation of cellulase and xylanase production by saw dust actinobacterial species whose 16S rDNA nucleotide sequences were deposited in GenBank as Micrococcus luteus strain SAMRC-UFH3 with accession number KU171371 and Micrococcus yunnanensis strain SAMRC-UFH4 with accession number KU171372. Optimum culture conditions for the production of cellulase for respective axenic culture include incubation period (96 h), incubation temperature (25oC), agitation speed (50 rpm), and pH 5. For xylanase production, the optimum culture conditions in the presence of 1percent (w/v) birchwood xylan include incubation period (84 h), incubation temperature (25oC), agitation speed (200 rpm), and pH 10. For Micrococcus yunnanensis strain SAMRC-UFH4 cellulase production was optimal under such conditions as, incubation temperature (30oC), agitation speed (0 rpm), and pH 5, while xylanase production was optimal at, incubation temperature (30oC), agitation speed (150 rpm), and pH 10. The high cellulase and xylanase activity obtained from these isolates suggest suitability of the organisms as important candidates for commercial application. , Thesis (MSc) -- Faculty of Science and Agriculture, 2016
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  • Date Issued: 2016-05

An investigation into the synergistic action of cellulose-degrading enzymes on complex substrates

The effect of GH family affiliations of mannanolytic enzymes on their synergistic associations during the hydrolysis of mannan-containing substrates

Ethanol production from lignocellulosic sugarcane leaves and tops

  • Authors: Dodo, Charlie Marembu
  • Date: 2014
  • Subjects: Biomass energy , Ethanol as fuel , Lignocellulose
  • Language: English
  • Type: Thesis , Masters , MSc (Chemistry)
  • Identifier: vital:11347 , http://hdl.handle.net/10353/d1019839 , Biomass energy , Ethanol as fuel , Lignocellulose
  • Description: Various methods for the production of bioethanol using different feedstocks have been researched on. In most work on bioethanol synthesis from sugar cane, tops and leaves have been regarded as waste and generally removed and thrown away. In this work, lignocellulosic sugarcane leaves and tops were not discarded but instead used as biomass to evaluate their hydrolyzate content. The leaves and tops were hydrolysed using different methods, namely concentrated acid, dilute acid pre-treatment with subsequent enzyme hydrolysis and compared with a combination of oxidative alkali pretreatment and enzyme hydrolysis. Subsequent fermentation of the hydrolyzates into bioethanol was done using the yeast saccharomyces cerevisae. Acid hydrolysis has the problem of producing inhibitors, which have to be removed and this was done using overliming with calcium hydroxide and compared to sodium hydroxide neutralization. Oxidative alkali pre-treatment with enzyme hydrolysis gave the highest yields of fermentable sugars of 38% (g/g) using 7% (v/v) peroxide pre-treated biomass than 36% (g/g) for 5% (v/v) with the least inhibitors. Concentrated and dilute acid hydrolysis each gave yields of25% (g/g) and 22% (g/g) yields respectively although for acid a neutralization step was necessary and resulted in dilution. Alkaline neutralization of acid hydrolyzates using sodium hydroxide resulted in less dilution and loss of fermentable sugars as compared to overliming. Higher yields of bioethanol, 13.7 (g/l) were obtained from enzyme hydrolyzates than 6.9 (g/l) bioethanol from dilute acid hydrolyzates. There was more bioethanol yield 13.7 (g/l) after 72h of fermentation with the yeast than 7.0 (g/l) bioethanol after 24h. However, the longer fermentation period diminishes the value of the increase in yield by lowering the efficiency of the process.
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  • Date Issued: 2014

Development & evaluation of modified lignocellulose-clinoptilolite composites for water treatment

  • Authors: Vala, Mavula Kikwe Remy
  • Date: 2012-12
  • Subjects: Lignocellulose , Lignocellulose -- Biotechnology
  • Language: English
  • Type: Doctoral theses , text
  • Identifier: http://hdl.handle.net/10353/24521 , vital:63051
  • Description: Municipalities, mining, textile and many other industries release wastewater into water bodies. Thus, the entire ecosystem (biota and abiota) including drinking water is affected by polluted effluents. The growing environmental concern over water pollution (due to inorganic and persistent organic compounds) attracts a significant amount of research in the removal of pollutants from water. In this study, lignocellulose and clinoptilolite were modified for the preparation of composites, with high adsorption properties, suitable for the removal of pollutants. Grass (Kikuyu grass) material was first treated with boiling water in order to remove soluble compounds and then with sulfuric acid in order to free functional groups within lignocellulose. The lignocellulose obtained was then chemically modified with three different siloxanes (3-aminopropyl-terminated poly (di)methylsiloxanes) of different molecular weights. For clinoptilolite, impurities were removed by reflux in hydrochloric acid before chemical modification with siloxanes. Grafting of siloxanes onto lignocellulose and clinoptilolite as well as the preparation of composites were successfully achieved by means of dibutyltin dilaurate (catalyst) after reflux under nitrogen. The modified materials were characterized by FT-IR, XRD, SEM and TGA and results confirmed successful modification of the materials. Solid state 29Si and 13C NMR were used to investigate the nature of the composite prepared with siloxane NH40D (CNH40D). The investigation revealed a possible bond between the modified lignocellulose and the modified clinoptilolite in the composite. The sorptive and/or ion exchange properties of the materials prepared for the removal of pollutants from water were then investigated. Phenol red, used motor (engine) oil and cyanide were used (with regard to textile, oil spill and gold mining effluents respectively) to simulate water pollution in the laboratory. It was found that adsorption properties of lignocellulose were significantly increased after sulfuric acid treatment, suggesting the availability of lignocellulose functional groups as adsorption sites. When further modified with siloxanes, lignocellulose showed less efficiency in adsorbing phenol red. The general mechanism of phenol red uptake onto lignocellulose and clinoptilolite modified with siloxane or composites was: rapid initial adsorption, slow uptake, small rate increase and then equilibrium. The mechanism of phenol red uptake could be well represented by the pseudo second-order kinetic model with equilibrium being reached after a period of time, ranging between 1-5 hours. The linear Langmuir model was the best model for describing adsorption of phenol red onto lignocellulose modified with siloxanes and composites while the Freundlich model appeared to be best for clinoptilolite modified with siloxanes. The general mechanism of used motor oil uptake onto lignocellulose and clinoptilolite modified with siloxane or composites was: rapid uptake, equilibrium and the process occurs over a short period (10 min). The pseudo second-order kinetic model appeared to be the best representation of this adsorption. The linear Langmuir isotherms are the best fitted model for used motor oil uptake onto the adsorbents prepared. Adsorption of cyanide occurred very quickly (10 to 30 min). For lignocellulose and clinoptilolite modified with siloxanes, desorption occurred soon after adsorption and thus no kinetic model nor isotherms of adsorption were deduced. However, adsorption of cyanide onto composites could be represented by the pseudo second-order kinetic model. Nanofibres were fabricated by electrospinning of the modified lignocellulose and composites by blending them with PAN in a solvent mixture of DMF-DMSO. Nanofiltration was achieved by packing the nanofibres prepared into a pipette and filtering polluted water. Nanofiltration was assessed by measurement of the turbidity of water which dropped from 63 NTU for polluted water to 3.06 NTU for filtered water. , Thesis (PhD) -- Faculty of Science and Agriculture, 2012
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  • Date Issued: 2012-12

Preparation and evaluation of Lignocellulose-Montmorillonite nanocomposites for the adsorption of some heavy metals and organic dyes from aqueous solution

  • Authors: Bunhu, Tavengwa
  • Date: 2011
  • Subjects: Lignocellulose , Lignocellulose -- Biodegradation , Water -- Purification , Adsorption , Separation (Technology) , Dyes and dyeing , Montmorillonite
  • Language: English
  • Type: Thesis , Doctoral , PhD (Chemistry)
  • Identifier: vital:11333 , http://hdl.handle.net/10353/535 , Lignocellulose , Lignocellulose -- Biodegradation , Water -- Purification , Adsorption , Separation (Technology) , Dyes and dyeing , Montmorillonite
  • Description: The need to reduce the cost of adsorption technology has led scientists to explore the use of many low cost adsorbents especially those from renewable resources. Lignocellulose and montmorillonite clay have been identified as potentially low cost and efficient adsorbent materials for the removal of toxic heavy metals and organic substances from contaminated water. Montmorillonite clay has good adsorption properties and the potential for ion exchange. Lignocellulose possesses many hydroxyl, carbonyl and phenyl groups and therefore, both montmorillonite and lignocellulose are good candidates for the development of effective and low cost adsorbents in water treatment and purification. The aim of this study was to prepare composite materials based on lignocellulose and montmorillonite clay and subsequently evaluate their efficacy as adsorbents for heavy metal species and organic pollutants in aqueous solution. It was also important to assess the adsorption properties of the modified individual (uncombined) lignocellulose and montmorillonite. Lignocellulose and sodium-exchanged montmorillonite (NaMMT) clay were each separately modified with methyl methacrylate (MMA), methacrylic acid (MAA) and methacryloxypropyl trimethoxysilane (MPS) and used as adsorbents for the removal of heavy metals and dyes from aqueous solution. The lignocellulose and NaMMT were modified with MMA, MAA and MPS through free radical graft polymerisation and/or condensation reactions. NaMMT was also modified through Al-pillaring to give AlpMMT. The materials were characterised by fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and small angle X-ray scattering (SAXS) and characterisation results showed that the modification of the montmorillonite with MAA, MMA and MPS was successful. The modified lignocellulose and montmorillonite materials were evaluated for the adsorption of heavy metal ions (Cd2+ and Pb2+) from aqueous solution by the batch method. The adsorption isotherms and kinetics of both Cd2+ and Pb2+ onto the NaMMT clay, AlpMMT and lignocellulose materials are presented. The Langmuir isotherm was found to be the best fit for the adsorption of both heavy metals onto all the adsorbents. AlpMMT showed very poor uptake for heavy metals (both Cd2+ and Pb2+). PMMAgMMT, PMAAgMMT, PMAAgLig and PMPSgLig showed improved adsorption for both heavy metals. The mechanism of heavy metal adsorption onto the adsorbents was best represented by the pseudo second-order kinetic model. PMPSgLig, NaMMT and AlpMMT showed relatively high adsorption capacities for methyl orange, while the adsorption of neutral red was comparable for almost all the adsorbents. Neither the Langmuir model nor the Freundlich model was found to v adequately describe the adsorption process of dyes onto all the adsorbents. The pseudo second-order model was found to be the best fit to describe the adsorption mechanism of both dyes onto all the adsorbents. The modification of lignocellulose and montmorillonite with suitable organic groups can potentially produce highly effective and efficient adsorbents for the removal of both heavy metals and dyes from contaminated water. Novel adsorbent composite materials based on lignocellulose and montmorillonite clay (NaMMT) were also prepared and evaluated for the removal of pollutants (dyes and heavy metals) from aqueous solution. The lignocellulose-montmorillonite composites were prepared by in situ intercalative polymerisation, using methyl methacrylate, methacrylic acid and methacryloxypropyl trimethoxysilane (MPS) as coupling agents. The composite materials were characterised by FTIR, TGA, TEM and SAXS. SAXS diffractograms showed intercalated nanocomposites of PMMAgLig-NaMMT and PMAAgLig-NaMMT, whereas PMPSgLig-NaMMT showed a phase-separated composite and the same results were confirmed by TEM. The lignocellulose-montmorillonite composites were assessed for their adsorption properties for heavy metal ions (Cd2+ and Pb2+) and dyes (methyl orange and neutral red) from aqueous solution. Among these composite materials, only PMAAgLig-NaMMT showed a marked increase in the uptake of both Cd2+ and Pb2+ relative to lignocellulose and montmorillonite when used independently. The adsorption data were fitted to the Langmuir and Freundlich isotherms, as well as to the pseudo first-order and pseudo second-order kinetic models. The data were best described by the Langmuir isotherm and the pseudo second-order kinetic model. On the adsorption of dyes, only PMPSgLig-NaMMT showed enhanced adsorption of methyl orange (MetO) compared with lignocellulose and montmorillonite separately. The enhanced adsorption was attributed to the synergistic adsorption due to the presence of MPS, lignocellulose and NaMMT. Competitive adsorption studies were carried out from binary mixtures of MetO and Cd2+ or Pb2+ in aqueous solution. The adsorption process of MetO onto the composite material was found to follow the Freundlich adsorption model, while the mechanism of adsorption followed both the pseudo first-order and pseudo second-order models. This particular composite can be used for the simultaneous adsorption of both heavy metals and organic dyes from contaminated water. The adsorption of neutral red to the composite materials was comparable and the pseudo second-order kinetic model best described the adsorption mechanism.
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  • Date Issued: 2011

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.
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  • Date Issued: 2007

Fungal and substrate-associated factors affecting lignocellulolytic mushroom cultivation on wood sources available in South African [i.e. Africa]

  • Authors: Da Serra, Maria Fatima
  • Date: 1997
  • Subjects: Lignocellulose , Mushroom culture , Cultivated mushroom , Fungi -- Cultures and culture media , Fungi -- Biotechnology , Mushroom culture -- South Africa
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:4020 , http://hdl.handle.net/10962/d1004080 , Lignocellulose , Mushroom culture , Cultivated mushroom , Fungi -- Cultures and culture media , Fungi -- Biotechnology , Mushroom culture -- South Africa
  • Description: Vast- quantities of lignocellulosic materials, representing potential substrates for the cultivation of speciality mushrooms, are produced annually in South Africa. A number of these materials are derived as waste products of the timber and agricultural industries, e.g. Maranti (Shorea spp.) and Port Jackson Willow (Acacia longifolia) respectively. The screening of various wood-degrading fungi, which are cultivated worldwide for their production of speciality mushrooms, indicated that under the environmental conditions considered, certain species were adapted to cultivation on these lignocellulosic wastes (Pleurotus species) whereas others were not (Lentinus edodes and Flammulina velutipes). Furthermore, intra- and interspecies specific differences in the growth and production potential of the various lignocellulolytic fungi investigated on synthetic and natural medium were discovered. Biochemical and genetical investigations of these strains indicated differences between and within species which were often significant. Species varied qualitatively and quantitatively in the lignocellulolytic enzymes produced, which was loosely correlated with productivity on the different media investigated. Genetical studies, using RAPD fingerprinting, indicated that the Pleurotus genus is highly variable which supports the observed differences in growth, yield and enzymatic activity between different strains and species.
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  • Date Issued: 1997
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