Thesis submitted in fulfilment of the requirements for the degree
DOCTOR TECHNOLOGIAE: ENGINEERING: CHEMICAL
In the
FACULTY OF ENGINEERING
At the
CAPE PENINSULA UNIVERSITY OF TECHNOLOGY
2009 / The white rot fungus, Phanerochaete chrysosporium strain BKMF-1767 (ATCC 24725),
produces the extracellular enzymes, Lignin peroxidase (LiP) and Manganese peroxidase
(MnP), that constitute the major route for lignin degradation by this organism. LiP and MnP
have also been shown to play a major role in aromatic pollutant degradation. Due to the need
for continuous production of LiP and MnP, a fixed-film bioreactor, classified as a membrane
gradostat reactor (MGR), was developed. The implementation of batch-reactor operational
parameters to the MGR system was found to be ineffective, thus creating the need for further
research to improve the operational aspects of the MGR system to optimise its capabilities
for continuous and industrial-scale operations. The research undertaken in this study,
provides information that can be used to classify the dissolved oxygen (DO) transport
kinetics into immobilised fixed-films of P. chrysosporium. Operational limitations of the MGR
relating to environmental stresses in the bioreactor during operation and to biofilm
deterioration, including limitations of DO mass transport, oxidative stress, trace element
accumulation and polysaccharide storage in the fungal biomass, were evaluated in single
capillary MGR systems (SCMGRs). These conditions were identified as existing in the
continuous MGR systems.
From DO profiles, the oxygen consumption and flux into the biofilms, including the
distribution of DO, was determined to be dependent on the immobilised biofilm’s age.
Younger biofilms showed higher DO distribution than older biofilms even when aeration was
directed to the extracapillary space (ECS) of the reactor against the biofilm’s surface. An
increase in anaerobic zone thickness was observed to be increasing with an increase in
biofilm thickness. Although, DO kinetic parameters were comparable with those obtained in
submerged mycelia pellets, higher oxygen consumption values were observed in biofilms
grown in the SCMGRs. The limitations of MGR were identified as: 1) poor DO distribution in
immobilised biofilms because of b-glucan production and storage in the immobilised
biomass, resulting in ethanol production; 2) the peroxidation of lipids of the biofilms, which in
turn will affect the long-term performance of the biomass caused by oxygenation and 3) trace
element ion accumulation enhanced by b-glucan production. Furthermore, trace element ion
accumulation was higher in the MGRs than in batch cultures using the same nutrient
medium.
The development of a perfluorocarbon (PFC) emulsion for the MGRs to counteract these
limitations was investigated. The compatibility of the emulsion with oxygen-carrying capacity
was shown with an improvement in biomass generation, LiP/MnP production and overall
consumption of primary substrates, mainly glucose and ammonium tartrate, in batch cultures.
The emulsions investigated were based on the addition of oxygen carriers: Perfluorooctyl
bromide (PFOB), Bis-(Perfluorobutyl) ethene (PFBE) and Perfluoropropylamine (PFPA),
using Pluronic F 68 (PF 68) as the surfactant. Concentrations of 10 to 30% (w/v) PFC and
8.5% (w/v) PF 68 were tested successfully in batch cultures. The emulsions containing
10% (w/v) PFCs resulted in improved biomass performance as opposed to emulsions with
higher PFC oil concentrations. An emulsion containing 10% (w/v) PFOB was used to
evaluate its efficacy in the SCMGRs, as the biomass yield and overall enzyme production
were superior to PFPA and PFBE-based emulsions with similar oil concentrations. After
successfully applying PFOB and PF 68 to the SCMGRs, the following results were obtained:
1) reduced ethanol production; 2) reduced trace element accumulation; 3) lower b-glucan
production and 4) improved DO-penetration ratio in immobilised biofilms.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:cput/oai:localhost:20.500.11838/927 |
| Date | January 2009 |
| Creators | Ntwampe, Seteno Karabo Obed |
| Publisher | Cape Peninsula University of Technology |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Rights | http://creativecommons.org/licenses/by-nc-sa/3.0/za/ |
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