Difference between revisions of "Team:Calgary/PHB Fermentation"

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<h2> Overview </h2>
 
<h2> Overview </h2>
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<p>The genetically engineered bacteria would be contained in the <i>stirred tank bioreactor </i>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 <i>mechanical self-cleaning filter</i> (0.2 micron filter scale) to remove and recycle the bacteria back into the bioreactor. </p>
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<p>In this stage of the process, engineered <i> E. coli</i> is fermented in a VFA-rich stream obtained in the previous step to produce PHB. This continuous fermentation process occurs in a 5L <u>stirred-tank bioreactor </u> at 37 degrees Celsius and under anaerobic conditions. A continuous flow of the VFA-rich stream is generated by the pump. To achieve continuous fermentation, a <u>mechanical self-cleaning filter</u> with 0.2-micron filters is used to separate and recycle bacteria back to the bioreactor. The resulting bacteria-free harvest stream that contains PHB is then passed to PHB extraction and water recovery. The proposed process is shown in Figure 1.</p>
  
 
<p><center><img src="https://static.igem.org/mediawiki/2017/c/cf/Calgary2017_PHBFermentation.png" alt="PHB Fermentation" style="width:100%"></center></p>
 
<p><center><img src="https://static.igem.org/mediawiki/2017/c/cf/Calgary2017_PHBFermentation.png" alt="PHB Fermentation" style="width:100%"></center></p>
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<div id="Caption"><b>Figure 1: </b> Diagram of the proposed PHB fermentation process.</div>
  
 
<h2>Other design options </h2>
 
<h2>Other design options </h2>
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<ul>
 
<ul>
 
<li> External membrane bioreactor (EMB)
 
<li> External membrane bioreactor (EMB)
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<li>Immersed membrane bioreactor (IMB): specifically the hollow fibre and the flat sheet designs.  
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<li>Immersed membrane bioreactor (IMB): specifically the hollow fiber and the flat sheet designs.  
 
<li> Acoustic cell separation
 
<li> Acoustic cell separation
 
</ul>
 
</ul>

Revision as of 21:16, 30 October 2017

Header

PHB Fermentation

Overview

In this stage of the process, engineered E. coli is fermented in a VFA-rich stream obtained in the previous step to produce PHB. This continuous fermentation process occurs in a 5L stirred-tank bioreactor at 37 degrees Celsius and under anaerobic conditions. A continuous flow of the VFA-rich stream is generated by the pump. To achieve continuous fermentation, a mechanical self-cleaning filter with 0.2-micron filters is used to separate and recycle bacteria back to the bioreactor. The resulting bacteria-free harvest stream that contains PHB is then passed to PHB extraction and water recovery. The proposed process is shown in Figure 1.

PHB Fermentation

Figure 1: Diagram of the proposed PHB fermentation process.

Other design options

The other designs that we have considered were:

  • External membrane bioreactor (EMB)
  • Immersed membrane bioreactor (IMB): specifically the hollow fiber 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 because filter cleaning comes at a significant cost of crew-time input, which is extremely valuable. Fouling also comes at a cost of extra membrane material supply, which is expensive to ship to space.

The literature search on acoustic cell separation have proven to not be applicable to the scale of our process.

The stirred tank bioreactor, on the other side, 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.

Table 1: ESM analysis for the proposed PHB fermentation system.
Self-cleaning filter Stirred-tank bioreactor
Power (kW) 2 0.38
Weight (kg) 16 15
Volume (m^3) 0.028 0.1153
Spares & Consumables (kg/day) 0 0
Spares & Consumables (m^3) 0 0
ESM Estimation 196 73