PHB Fermentation

Overview

The genetically engineered bacteria would be contained in the stirred tank bioreactor at 37 degrees Celsius and under anaerobic conditions. A continues flow of VFA rich stream is generated by the pump. The volume of the tank is 5L to account for the overflow and liquid recycling. The output stream, which contains some of the bacteria, secreted PHB and unused VFAs passes through a mechanical self-cleaning filter (0.2 micron filter scale) to remove and recycle the bacteria back into the bioreactor.

Other design options

The other designs that we have considered were:

• External membrane bioreactor (EMB)
• Immersed membrane bioreactor (IMB): specifically the hollow fibre and the flat sheet designs.
• Acoustic cell separation

The major problem associated with the membrane bioreactors is fouling. Fouling is a big counter-argument against a design on Mars, where crew-time is extremely precious and resources (new membranes) are limited. The literature search on acoustic cell separation have proven to not be applicable to the scale of our process. The stirred tank bioreactors comes with the advantages of continuous agitation and easy temperature control. The self-cleaning filter allows to eliminate the fouling issue and limited resources issue. The stirred tank bioreactor combined with the self-cleaning filter was chosen as the optimal design for the process.

	Self cleaning filter (smaller models are availible by ot ehr companies)	Stirred tank bioreactor
Power (kW)	2	0.38
Weight (kg)	16	15
Volume (m^3)	0.028	0.1153
Spares and consumables mass (kg)/day	0	0
Spares and consumables volume (m^3)	0	0
ESM Estimation	196.062	73.0