The microalgae Chaetoceros muelleri (Figure 1) is extensively used as feed for shellfish. It is believed to be very shear sensitive and is therefore typically cultivated in open tank systems or bubble columns.
Cultivation of microalgae in tubular photobioreactors (PBR’s) is far more cost effective. However, application of a tubular PBR could lead to shear stress that would be detrimental for Chaetoceros muelleri. In addition, oxygen accumulation in the tubes will inhibit cell growth. The combined effects of oxygen buildup and shear stress will eventually determine the optimal design of a tubular photobioreactor for shear sensitive microalgae.
Aim and research question
The objective is to find an optimal design for a tubular PBR (Figure 2) in which a shear sensitive species like Chaetoceros muelleri can be produced.
The effect of shear stress on the viability of Chaetoceros muelleri has been studied. Shear stress was applied to the algae in shear cylinders. The threshold value of shearstress at which the viability of algae was negatively influenced was between 1 and 1.3 Pa (Figure 3).
Our current research is focusing on the growth of Chaetoceros muelleri in a tubular PBR. The effect of the pumping rate on the productivity will be studied, to investigate if a higher pumping rate leads to a higher exposure to shear stress. The outcome of these experiments will confirm if Chaetoceros muelleri can be cultivated in a tubular PBR when shear stress is kept under a defined and limited level.
Furthermore, the effect of light availability during the different seasons on the productivity will be studied. The productivity can be enhanced by adjusting the biomassconcentration in such a way that the available light can be captured efficiently.
Then the effect of oxygen accumulation in a tubular PBR on the productivity will be studied. The oxygen accumulation is related to the productivity and the concentration ofoxygen will increase with the length of the tubes. This will evoke a change in productivity with the length of the tubes installed.
Within this project there are various possibilities for doing a BSc or MSc thesis. If you are interested in doing a BSc or MSc thesis, feel free to contact me.
The research is embedded in the Zeeland Sole (Zeeuwse Tong) project.
Michels, M.H.A., Goot, A.J. van der, Norsker, N.H. & Wijffels, R.H. (2010). Effects of shear stress on the microalgae Chaetoceros muelleri. Bioprocess and BiosystemsEngineering, 33(8), 921-927.