| Summary: | Thesis (M.Tech-Chemical Engineering)--Cape Technikon, Cape Town, 2001 === The white-rot fungus (WRF), Phanerochaete chrysosporium, is a well known microorganism
which produces ligninolytic enzymes. These enzymes can play a major role in
the bioremediation of a diverse range of environmental aromatic pollutants present in
industrial effluents. Bioremediation of aromatic pollutants using ligninolytic enzymes
has been extensively researched by academic, industrial and government institutions,
and has been shown to have considerable potential for industrial applications.
Previously the production of these enzymes was done using batch cultures. However,
this resulted in low yields of enzyme production and therefore an alternative method
had to be developed. Little success on scale-up and industrialisation of conventional
bioreactor systems has been attained due to problems associated with the continuous
production of the pollutant degrading enzymes. It was proposed to construct an
effective capillary membrane bioreactor, which would provide an ideal growing
environment to continuously culture an immobilised biofilm of P; chrysosporium
(Strain BKMF-1767) for the continuous production of the ligninolytic enzymes,
Lignin(LiP) and Manganese(MnP) Peroridase. A novel membrane gradostat reactor
(MGR) was shown to be superior to more conventional systems of laboratory scale
enzyme production (Leukes et.al., 1996 and Leukes, 1999). This concept was based on
simulating the native state ofthe WRF, which has evolved on a wood-air interface and
involved irnmobilisng the fungus onto an externally skinless ultrafiltration membrane.
The MGR however, was not subjected to optimisation on a laboratory scale.
The gradostat reactor and concept was used in this work and was operated in the deadend
filtration mode. The viability of the polysulphone membrane for cultivation of the
fungus was investigated. The suitability of the membrane bioreactor for enzyme
production was evaluated. The effect of microbial growth on membrane pressure and
permeability was monitored. A possible procedure for scaling up from a single fibre
membrane bioreactor to a multi-capillary system was evaluated.
Results indicated that the polysulphone membrane was ideal for the cultivation of P
chrysosporium, as the micro-organism was successfully immobi1ised in the macrovoids
of the membrane resulting in uniform biofilm growth along the outside of the
membrane. The production of Lignin and Manganese Peroxidase was demonstrated.
The enzyme was secreted and then transported into the permeate without a rapid decline
in activity. Growth within the relatively confined macrovoids of the membrane
contributed to the loss of membrane permeability. A modified Bruining Model was
successfully applied in the prediction of pressure and permeability along the membrane
The study also evaluated the effect of potential1y important parameters on the
production of the enzymes within the membrane bioreactor. These parameters include
air flow (Ch concentration), temperature, nutrient flow, relative redox potential and
nutrient concentrations
A sensitivity analyses was performed on temperature and Ch concentration. The
bioreactor was exposed to normal room temperature and a controlled temperature at
37°C. The reactors were then exposed to different O2 concentration between 21% and
99"10. It was found that the optimum temperature fur enzymes production is 3TJC.
When oxygen was used instead of air, there was an increase in enzyme activity. From
the results obtained, it was clear that unique culture conditions are required for the
production of LiP and MnP from Phanerochaete chrysosporium. These culture
conditions are essential fur the optimisation and stability of the bioreactor.
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