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

 
(22 intermediate revisions by 6 users not shown)
Line 14: Line 14:
 
<a href="https://2017.igem.org/Team:Calgary/Extraction"><img src="https://static.igem.org/mediawiki/2017/9/97/Calgary2017_RightArrowButton.png"></a>
 
<a href="https://2017.igem.org/Team:Calgary/Extraction"><img src="https://static.igem.org/mediawiki/2017/9/97/Calgary2017_RightArrowButton.png"></a>
 
</div>
 
</div>
−
<h3> Overview </h3>
 
−
<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>
 
  
−
<h3>Other design options </h3>
+
 
−
<p> The other designs that we have considered were:
+
<h2> Overview </h2>
 +
<p>In this stage of the process, the VFA-rich stream from the previous step is fermented by engineered <i> E. coli</i> to produce PHB. This continuous fermentation process occurs in a 5-L stirred-tank bioreactor at 37°C under anaerobic conditions. A continuous flow of the VFA-rich stream is generated by a pump. To achieve continuous fermentation, a mechanical self-cleaning filter with 0.2-micron pores is used to separate and recycle bacteria back to the bioreactor. The resulting bacteria-free harvest stream containing PHB is then passed on to PHB extraction and water recovery stages. 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>
 +
<div id="Caption"><b>Figure 1: </b> Diagram of the proposed PHB fermentation process.</div>
 +
 
 +
<br>
 +
 
 +
<h2>Design options considered </h2>
 +
<p> Considered design options included:
 
<ul>
 
<ul>
−
<li> External membrane bioreactor (EMB)
+
<li> External membrane bioreactor (EMB) </li>
−
<li>Immersed membrane bioreactor (IMB): specifically the hollow fibre and the flat sheet designs.
+
<li> Immersed membrane bioreactor (IMB), specifically the hollow fiber and the flat sheet designs </li>
−
<li> Acoustic cell separation
+
<li> Stirred-tank bioreactor with self-cleaning filter separation </li>
 
</ul>
 
</ul>
−
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.  
+
 
 +
<p>The major disadvantage of membrane bioreactors is fouling. Because of fouling, frequent filter cleaning and filter replacement might be required, resulting in higher crew time requirements and transportation costs to supply replacement membranes.</p>
 +
 
 +
<p>The stirred-tank bioreactor, on the other hand, provides continuous agitation and easy temperature control, and the implementation of the self-cleaning filter reduces fouling. An example of a stirred tank bioreactor can be found <a href="https://www.gelifesciences.com/gehcls_images/GELS/Related%20Content/Files/1440509368472/litdoc29117039_20161016015647.pdf">here</a>. Certain specifications, such as power, mass, and volume of the following model, were used in the ESM parameters estimation. An example of a smaller-scale self-cleaning filter can be found on the Eaton <a href="http://www.eaton.com/Eaton/ProductsServices/Filtration/AutomaticSelfCleaning/MechanicallyCleanedFilters/DCF/DCF4008001600/index.htm#tabs-4">website</a>. This filter operates by passing liquid through a cylindrical drum and using a mechanical "arm" to continuously scrub the fouling particles from the filter surface. With this in mind, the stirred-tank bioreactor combined with the self-cleaning filter was chosen as the optimal design for the process. The ESM analysis for the final PHB fermentation stage is summarized in Table 1.</p>
 +
 
 +
<div id="Caption"><b>Table 1: </b> ESM analysis for the proposed PHB fermentation system.</div>
 
<table>
 
<table>
−
<tr>
+
  <tr>
−
  <td></td>
+
    <th></th>
−
  <td>Self cleaning filter (smaller models are availible by ot ehr companies)</td><td> Stirred tank bioreactor</td>
+
    <th>Self-cleaning filter</th>
−
</tr>
+
    <th>Stirred-tank bioreactor</th>
−
<tr>
+
  </tr>
−
  <td>Power (kW)</td><td> 2</td> <td>0.38</td
+
  <tr>
−
</tr>
+
    <td>Power (kW)</td>
−
<tr>
+
    <td>2</td>
−
  <td>Weight (kg) </td><td>16</td> <td>15</td>
+
    <td>0.38</td>
−
</tr>
+
  </tr>
−
<tr><td>Volume (m^3)</td><td> 0.028</td><td>0.1153<td></tr>
+
  <tr>
−
<tr><td>Spares and consumables mass (kg)/day</td><td> 0</td><td> 0</td>/tr>
+
    <td>Weight (kg)</td>
−
<tr><td>Spares and consumables volume (m^3) </td><td>0</td><td> 0</td>/tr>
+
    <td>16</td>
−
<tr><td>ESM Estimation </td><td>196.062</td><td>73.0</td></tr>
+
    <td>15</td>
 +
  </tr>
 +
  <tr>
 +
    <td>Volume (m^3)</td>
 +
    <td>0.028</td>
 +
    <td>0.1153</td>
 +
  </tr>
 +
  <tr>
 +
    <td>Spares & Consumables (kg/day)</td>
 +
    <td>0</td>
 +
    <td>0</td>
 +
  </tr>
 +
  <tr>
 +
    <td>Spares & Consumables (m^3)</td>
 +
    <td>0</td>
 +
    <td>0</td>
 +
  </tr>
 +
  <tr>
 +
    <td>ESM Estimation</td>
 +
    <td>196</td>
 +
    <td>73</td>
 +
  </tr>
 
</table>
 
</table>
−
<p><center><img src="https://static.igem.org/mediawiki/2017/c/cf/Calgary2017_PHBFermentation.png" alt="PHB Fermentation" style="width:80%"></center></p>
 
  
 
</html>
 
</html>

Latest revision as of 19:06, 1 November 2017

Header

PHB Fermentation

Overview

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

PHB Fermentation

Figure 1: Diagram of the proposed PHB fermentation process.

Design options considered

Considered design options included:

  • External membrane bioreactor (EMB)
  • Immersed membrane bioreactor (IMB), specifically the hollow fiber and the flat sheet designs
  • Stirred-tank bioreactor with self-cleaning filter separation

The major disadvantage of membrane bioreactors is fouling. Because of fouling, frequent filter cleaning and filter replacement might be required, resulting in higher crew time requirements and transportation costs to supply replacement membranes.

The stirred-tank bioreactor, on the other hand, provides continuous agitation and easy temperature control, and the implementation of the self-cleaning filter reduces fouling. An example of a stirred tank bioreactor can be found here. Certain specifications, such as power, mass, and volume of the following model, were used in the ESM parameters estimation. An example of a smaller-scale self-cleaning filter can be found on the Eaton website. This filter operates by passing liquid through a cylindrical drum and using a mechanical "arm" to continuously scrub the fouling particles from the filter surface. With this in mind, the stirred-tank bioreactor combined with the self-cleaning filter was chosen as the optimal design for the process. The ESM analysis for the final PHB fermentation stage is summarized in Table 1.

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