Navid Moheimani

The effect of applied shear stress on Botryococcus braunii, in the presence of solvent is important to further understanding the mechanisms behind in-situ solvent extraction and will be critical in the design and scale up of an effective extraction process. This paper looks at the effect of various mixing rates on colony structure and culture photosynthetic activity in the presence of heptane. Partial colony disruption was found to occur at shear rates of 335 s -1, with the main mechanism of disruption believed to be microeddies generated by turbulence around the impeller. Photosynthetic activity was seen to drop by 55 % during the extraction period requiring a short recovery time of 3 days, reaching 66.5 % of its original value. These results provide valuable insight and data on the shear limits of B. braunii required in the design of a repeated milking process and will assist in the design and scale up of a viable milking process.