Difference between revisions of "Team:Calgary/SolidLiquidSeparation"

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</div>
 
</div>
 
<h2>Overview </h2>
 
<h2>Overview </h2>
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<p>The second stage of the process is required to remove all the solids from the feces and produce a sterile VFA rich liquid stream. Sterility is essential, since the genetically engineered <i>E. coli</i> can’t compete with other bacteria types. Considering very limited availability of resources (including power) on Mars, the initial experiments focused on mechanical and gravity-driven separation process: </p>
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<p>In the second stage of the process, solid partices from human feces are separated to obtain a sterile, VFA-rich liquid stream that can be passed to the next stage of the process. Sterility is essential, since genetically engineered <i>E. coli</i> in the next stage of the process, where PHB is produced, might be outcompeted if other types of bacteria are present. The separation of solids is achieved using centrifugation, which removes large solid particles, followed by filtration, which removed remaining small particles. </p>
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 +
<h2>Design options considered</h2>
 +
 
 +
<p> Considering limited availability of resources on Mars including power, the initial experiments focused on mechanical and gravity-driven separation process: </p>
 
<ul>
 
<ul>
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<li>simple filtration</li>
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<li>Gravity-driven filtration</li>
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<li>settlement </li>
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<li>Settling </li>
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<li> pressure filtration</li>  
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<li>Pressure filtration</li>  
 
</ul>
 
</ul>
  
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<p>It was found that low power requirement process either do not provide sufficient sterility or could not recover more than 55% of initial water present. The design that performed the best was the sequential pressure filtration – giving sterile liquid, but only 10% of initial water recovery. </p>
+
<p>After laboratory experiments, these low power requirement processes were unable to remove all solid particles including bacteria or recovered less than 55% of the water present in the sample. Sequential pressure filtration performed the best during lab experiments resulting in a sterile liquid but recovering only 10% of water. </p>
  
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<p>More advanced solid liquid separation technologies were then considered: </p>
+
<p>More advanced solid-liquid separation techniques were then considered: </p>
 
<ul>
 
<ul>
−
<li>torrefaction (mild pyrolysis)</li>
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<li>Torrefaction (mild pyrolysis)</li>
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<li> centrifugal separation followed by filtration </li>
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<li>Centrifugation followed by filtration </li>
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<li>and the screw-press dewatering system followed by a multi-filtration</li>
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<li>Screw-press dewatering system followed by multi-filtration</li>
 
</ul>
 
</ul>
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<p>Originally torrefaction appeared to be the best solution, since it allowed the recovery of natural and pyrolytic water, produced the liquid stream which was sterile and contained the required VFAs and produced char as by product. Char can be used in building, radiation shielding, as a food subtract and hence was a desired by-product. However, the ESM analysis showed that the torrefaction ESM parameter is larger than that of centrifugal separator.</p>
 
  
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<h2> ESM Analysis of different Solid-liquid separation technologies </h2>
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<p> Estimated ESM parameters for these process designs are summarized in Table 1. </p>
  
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<table>
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<p>Initially, torrefaction appeared to be the best solution, since it can recover natural and pyrolytic water, results in a sterile VFA-rich liquid stream and turns solid matter into char, which can be a used as a building material, radiation shielding, and as a food subtract. However, the product stream in the torrefaction process contains only water and VFA resulting in low pH and lack of nutrients and, therefore, cannot sustain bacterial growth during PHB production stage. This was also confirmed by lab experiments. Additionally, torrefaction had higher ESM parameters than centrifugation.</p>
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<tr>
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−
<th> </th><th> Screw-press dewatering system</th><th>Mutlifiltration </th><th> Torrefaction </th><th> Centrifugal separator </th>
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−
</tr>
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−
<tr>
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−
<th>Power (kW)</th><th>0.298 </th><th>1.84</th><th>0.88</th><th>5</th>
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−
</tr>
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−
<tr><th>Weight (kg)</th><th>179</th><th>232</th><th>378</th><th>5</th>
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−
</tr>
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−
<tr>
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−
<th>Volume (m<sup>3</sup>)</th><th>2</th><th>1.83</th><th>3.21</th><th>0.0138</th>
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−
</tr>
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−
<tr>
+
−
<th>Spares and consumables mass (kg)/day</th><th>0.0084</th><th>0.3669</th><th>0</th><th>0</th>
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−
</tr>
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−
<tr>
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<th>Spares and consumables volume (m<sup>3</sup>)</th><th>0.0098</th><th>0.004778</th><th>0</th><th>0</th>
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−
</tr>
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−
<tr>
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−
<b><th>ESM Estimation</th><th>1 809.5</th><th>1559.01</th><th>1 149.525</th><th>442.9877</th></b>
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−
</tr>
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−
 
+
−
</table>
+
  
 
<div id="Caption"><b>Table 1: </b> ESM analysis for different process designs for the solid/liquid separation stage of the process.</div>
 
<div id="Caption"><b>Table 1: </b> ESM analysis for different process designs for the solid/liquid separation stage of the process.</div>
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</table>
 
</table>
  
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<p>It was chosen to proceed with centrifugal separator followed by a filter as a technology for the solid-liquid separation.</p>
+
<p> After evaluating advantages and disadvantages of the proposed designs and considering the ESM analysis, centrifugation followed by filtration was chosen as the preferred method for the solid-liquid separation step. In addition, the team proposes to adapt torrefaction to treat the solid by-products after solid-liquid separation and the sludge from wastewater treatment on Mars to recover additional water and produce char.</p>
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<p>The team however also proposes to adapt <i>torrefaction technology</i> for the treatment of the by-product stream - sludge and the general sludge formed during the wastewater treatment on Mars.</p>
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</html>
 
</html>

Revision as of 22:32, 30 October 2017

Header

Solid-Liquid separation

Overview

In the second stage of the process, solid partices from human feces are separated to obtain a sterile, VFA-rich liquid stream that can be passed to the next stage of the process. Sterility is essential, since genetically engineered E. coli in the next stage of the process, where PHB is produced, might be outcompeted if other types of bacteria are present. The separation of solids is achieved using centrifugation, which removes large solid particles, followed by filtration, which removed remaining small particles.

Design options considered

Considering limited availability of resources on Mars including power, the initial experiments focused on mechanical and gravity-driven separation process:

  • Gravity-driven filtration
  • Settling
  • Pressure filtration

After laboratory experiments, these low power requirement processes were unable to remove all solid particles including bacteria or recovered less than 55% of the water present in the sample. Sequential pressure filtration performed the best during lab experiments resulting in a sterile liquid but recovering only 10% of water.

More advanced solid-liquid separation techniques were then considered:

  • Torrefaction (mild pyrolysis)
  • Centrifugation followed by filtration
  • Screw-press dewatering system followed by multi-filtration

Estimated ESM parameters for these process designs are summarized in Table 1.

Initially, torrefaction appeared to be the best solution, since it can recover natural and pyrolytic water, results in a sterile VFA-rich liquid stream and turns solid matter into char, which can be a used as a building material, radiation shielding, and as a food subtract. However, the product stream in the torrefaction process contains only water and VFA resulting in low pH and lack of nutrients and, therefore, cannot sustain bacterial growth during PHB production stage. This was also confirmed by lab experiments. Additionally, torrefaction had higher ESM parameters than centrifugation.

Table 1: ESM analysis for different process designs for the solid/liquid separation stage of the process.
Screw-press dewatering system Multifiltration Torrefaction Centrifugation
Power (kW) 0.3 1.8 0.9 5
Weight (kg) 179 232 378 5
Volume (m^3) 2 1.8 3.2 0.014
Spares & Consumables (kg/day) 0.0084 0.4 0 0
Spares & Consumables (m^3) 0.01 0.005 0 0
ESM Estimation 1810 1560 1150 443

After evaluating advantages and disadvantages of the proposed designs and considering the ESM analysis, centrifugation followed by filtration was chosen as the preferred method for the solid-liquid separation step. In addition, the team proposes to adapt torrefaction to treat the solid by-products after solid-liquid separation and the sludge from wastewater treatment on Mars to recover additional water and produce char.