Revision as of 01:01, 18 October 2014

Imperial iGEM 2014

Implementation

Overview

By attaching functional proteins to cellulose we can expand it's properties and selectivity capture specific contaminants in water. We used five different cellulose binding domains and fused them to different metal binding proteins, and sfGFP. We performed assays to test the binding of the CBD fusions to our cellulose.

Key Achievements

Made cellulose binding domains

Introduction

Ultrafiltration (UF) membranes have a pore size of 0.1 to 0.01um (10 to 100nm) and are capable of removing particulates, bacteria and viruses. Microbial cellulose sheets naturally have pore sizes in this range (Gatenholm, P., & Klemm, D. (2010), Mautner et al 2014). Current ultrafiltration cannot remove small molecule contaminants such as pesticides and heavy metals however. Whilst nanofiltration and reverse osmosis membranes can exclude these small molecules they are expensive and energy intensive to use. Flow rates are low, they require very high pressures and the input water must be already purified by primary and secondary processes to avoid damaging the membranes.

https://static.igem.org/mediawiki/2014/4/47/IC-14_Water_Purification_Spectrum1.JPG Size exclusion for different grades of filter (from http://www.edstrom.com/) Depending on input water quality UF systems may replace or complement existing secondary (coagulation, flocculation, sedimentation) and tertiary filtration (sand filtration and chlorination) systems in water treatment plants. Pretreatment of feed water is usually required to prevent reduce damage to the membrane units though ultrafiltration may be used in standalone systems for isolated regions. UF processes have the following advantages over traditional treatment methods:

Chemical free (aside from cleaning)
Constant product quality regardless of feed quality (excluding small molecule contaminants, changes in input water quality affect only the life of the membrane, not the quality of the flow through)
Compact plant size, efficient for small scale, decentralised purification
High quality of output water particularly with regards to pathogen removal

UF processes are currently limited by the high cost of membranes, inevitable membrane fouling means they must be regularly replaced. There use is also restricted by limitations in removal of small molecule contaminants. They can only be employed where feed water is free of these contaminants or in tandem with other (often slow or energy intensive) treatment methods for removing them.

Ultrafiltration

Phytochelatin-dCBD metal binding assay

Nickel filtration assay

The nickel ions are an example of heavy metals, poisonous even in relatively small concentrations in water and notoriously difficult to filter with current filtration methods. Therefore our filtration concept was tested against a concentration of nickel in water that far exceeds the safe limits. We have attempted to filter high amount of nickel (250 μM) through the cellulose filters grown by the G. Xylinus ATCC53582 strain (K1321305). The phytochelatin-dCBD fusion (K1321110) was coated on the surface of the cellulose to make a nickel specific functionalised ultra filtration membrane. To test the two membranes we have used coffee press. As a control measure we have also attempted to the filter the nickel solution through the cellulose that was not further functionalised.

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                  <ul>
                      <li>
-                         Pore size - average or maximum size of pores in the material</li>
+                         Chemical free (aside from cleaning)</li>
                      <li>
-                         Porosity - volume of the filter not occupied by solid material</li>
+                         Constant product quality regardless of feed quality (excluding small molecule contaminants, changes in input water quality affect only the life of the membrane, not the quality of the flow through)</li>
                      <li>
-                         Tortuosity - length of paths through the filter compared with a straight line</li>
+                         Compact plant size, efficient for small scale, <a href="https://2014.igem.org/Team:Imperial/Water_Report#decentralisation"> decentralised</a> purification</li>
                      <li>
-                         Adhesion - the strength of hydrogen bond interactions between the fluid and filter</li>
+                         High quality of output water particularly with regards to pathogen removal</li>
-                    <li>
-                        Kinetic rate constants - parameters defining how the filter material affects chemical reactions in the fluid</li>
                  </ul>
              </p>
              <p>
-                 These properties contribute to the filter’s flow rate, measured in units of fluid filtered per unit surface area of the filter per unit time (e.g. Ga m<sup>-2</sup> h<sup>-1</sup>). Altering the filter’s flow rate generally affects the filter’s efficiency at removing its targets, as increasing the flow rate typically involves increasing the pore size or reducing the surface area of the filter in contact with the fluid. This trade-off is the main hurdle in industrial water filtration, where demands for high-quality filtration require very low flow rates. Industrial processes are further complicated by blockage of the pores, fouling of the filter by organisms and the lack of a complete set of materials that will exhaustively filter all contaminants - heavy metal ions, small organic molecules and non-polar compounds remain difficult to filter without prior chemical treatments that themselves need to be filtered out.</p>
+                 UF processes are currently limited by the high cost of membranes, inevitable membrane fouling means they must be regularly replaced. There use is also restricted by limitations in removal of small molecule contaminants. They can only be employed where feed water is free of these contaminants or in tandem with other (often slow or energy intensive) treatment methods for removing them. </p>
          </section>
          <section id="Ultrafiltration">

Team:Imperial/Implementation

From 2014.igem.org