BSc Hons Cape Town, PhD Cambridge
Department of Chemical Engineering
Faculty of Engineering and the Built Environment
Email: Sue Harrison
My research interests centre on the establishment of generic tools for use in the implementation of bioprocesses for economic, environmental and social benefit. These generic tools are developed at three levels of operation:
- the molecular and metabolic level at which understanding and manipulation is sought of molecular response to the process and subsequent metabolic flux of raw materials to product, - the process level at which the inter-relationship between individual units of the bioprocess is sought to inform process optimisation, and - at the sustainable process level at which the impact of process selection on environmental burden, resource utilisation and resource productivity is investigated.
It is centred on an integrated approach to the optimisation and modelling of bioprocess systems and sub-processes. While seeking generic tools, the research investigates specific microbial systems and products that are relevant to the SA context.
Research into microbial stress response in the process environment (operating at the molecular and metabolic level) is designed to address three requirements: assessment of performance, understanding of the fundamental response, and modelling and prediction of stress effects. The research field has received limited attention by the academic community, yet is a key requirement for optimisation of a bioprocess industry centred on large scale processes for commodity products or remediation. Such processes are common in SA and include ethanol production, biomineral processing, remediation of acid mine drainage, production of commodity amino acids, pigments and agricultural products.
In the bioreaction stage, knowledge of microbial stress response, microbial morphology and metabolic pathway analysis (metabolic level) is combined with the study of the inter-relationship of unit operations and the reactor modelling skills of colleagues to enable rigorous process optimisation and performance prediction (process level). Level of understanding sought at the biological level includes the population dynamics in mixed culture systems, their characterisation and the impact of population shifts on process performance. Similarly, at the physical level, contacting between the multiple phases of reaction is of key importance and studied through tomographic systems and mass transfer studies. In downstream processing, focus is placed on selective separations and the integration of production, liberation and purification operations to allow improved process yields. Holistically, assessment of process sustainability and its optimisation will inform all studies. Further tools are developed to facilitate the quantification of parameters of importance in analysis of the sustainability of specific bioprocesses, thereby allowing its wide-spread consideration (process sustainability level). An assessment framework for bioprocess sustainability has been developed and applied to biodiesel to compare enzymic and alkali catalytic production routes and to assess the bioplastic PHB vs polyolefins. A software tool is under development to enable rapid assessment of bioprocesses. In addition, review of the new wastewater treatment plant at a local brewery using LCA has highlighted targets for reduced environmental impact. Currently, energy capture and integration into the brewing process from the methane generated is analysed.
Specific microbial systems for study of the generic tools and approaches to be developed include the minerals bioleaching systems for metal recovery, acid mine drainage treatment and prevention, bioenergy from waste materials, use of the linear alkane byproduct of the gas-to-liquid-fuels processes as a resource for bio-conversion, and the production of enzyme biocatalysts. Systems where studies are initiated and under review for extension include alcohol fermentation (both in terms of bio-fuels and beverage production and largely driven by optimisation of stress response and optimising physiological response) and algal production both as a biomass resource for biofuels and as a source of carotenoids for feed, food and nutraceutical application.
Selected recent publications
Nemati, M, Lowenadler, J, Harrison S T L (2000). Particle effects in bioleaching of pyrite by acidophilic thermophile Sulfolobus metallicus. Appl. Microbiol. Biotechnol., 53, 173 Â- 179.
Nemati M and Harrison S T L (2000). Effect of solid loading on thermophilic bioleaching of sulphide minerals. J. Chem. Technol. Biotechnol., 75, 1-7.
Robinson A. and Harrison S T L (2001). Effect of aeration in propagation on surface properties of Brewers' yeast. In Applied Microbiology Volume 2 Focus on Biotechnology (ed. Durieux and J-P Simon. Dordrecht, Kluwer. Academic Publishers. 2,89-99).
Robinson A and Harrison STL (2001) Disk stack centrifugation for the Recovery of BrewersÂ' yeast: Its Effect on Yeast Cell Surface, Flocculation and Fermentation Performance. Proceedings of the Institute and Guild of Brewing Convention 8, 157-164.
Moosa S, Nemati M and Harrison STL (2002). A kinetic study on anaerobic reduction of sulphate, Part I: Effect of sulphate concentration. Chemical Engineering Science, 57, 2773-2780.
Harrison STL, Sissing A, Raja S, Pearce SJA, Lamaignere V and Nemati M (2003). Solids loading in the biotech slurry reactor: mechanisms through which particulate parameters influence slurry bioreactor performance. Biohydrometallurgy: a sustainable technology in evolution. Proceedings of the 15th International Biohydrometallurgy Symposium, pp359-375.
Harrison STL, Sissing A, Raja S and Nemati M (2003). Identifying and quantifying biological responses of Sulfolobus to high pulp densities in the slurry bioleach reactor. Proceedings of IMPC (ed. Lorenzen, Bradshaw and Thom).
Moosa S, Nemati M and Harrison S T L. (2005). A kinetic study on anaerobic reduction of sulphate. Part II: Incorporation of temperature effects in the kinetic model. Chemical Engineering Science, 60, 3517-3524.
Clarke K G, Johnstone-Robertson M and Harrison STL. (2006). Location of glucose oxidase during production by Aspergillus niger. Appl. Microbiol. Biotechnol. 70, 72-77.
Icgen B, Moosa S and Harrison STL (2006). A study of the relative dominance of selected anaerobic sulphate-reducing bacteria in a continuous bioreactor revealed by fluorescence in situ hybridisation. Microbial Ecology (In press).
Balasundaram B and Harrison STL (2006). Disruption of BakerÂ's yeast by hydrodynamic cavitation: process variables and their influence on selective release. Biotechnology and Bioengineering 94 (2), 303 - 311.
Clarke K.G., Williams P.C., Smit M. and Harrison S.T.L. (2006). Enhancement and repression of volumetric oxygen transfer coefficient through hydrocarbon addition and its influence on oxygen transfer rate in stirred tank bioreactors. Biochemical Engineering Journal 28, 237-242.
Stevenson R, Harrison STL, Miles N and Cilliers JJ (2006). Examination of swirling flow using electrical resistance tomography. Powder Technology 162, 157-165.
Balasundaram B and Harrison STL (2006). Study of physical and biological factors involved in the disruption of E.coli by hydrodynamic cavitation. Biotechnology Progress 22, 907-913.
Coram-Uliana N.J., van Hille R.P., Kohr W.J. and Harrison S.T.L. (2006). Development of a method to assay the microbial population in heap bioleaching operations. Hydrometallurgy 83, 237-244.