Team:Westminster/Application

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Applications

Potential applications for our project could be used in both developed and developing countries for industry such as:

• Textiles
• Paper and pulp mills
• Cotton mill
• Brewery wastewater

The waste water from such factories could be used as the main carbon source for our synthetic Escherichia coli. In doing so will reduce the level of toxicity of the waste water and produce a green energy source which will offset the heavy reliance of fossil fuels.

The efficient transfer of electrons from an exoelectrogenic bacterium to an electrode is a challenging task faced by engineers and scientists. It has been shown that the efficiency of a microbial fuel cell power output is directly related to the composition and thickness of the biofilm grown. This conductive matrix that bacterial cells make around the anode enables higher kinetic rates of electron transfer using three possible exoelectrogenic routes.

The first example can be found in Shewanella oneidensis MR-1 species, and is understood to work as a chain of proteins (CymA-MtrCAB-OmcA) that transport electrons from inside the cell, past the inner and outer membrane of the bacteria to an electron acceptor. This pathway has been the focus of our research in trying to exhibit exoelectrogenic characteristics in a model organism such as E.coli.

How microbial fuel cell (MFC) works

In anaerobic conditions, when no oxygen is present the microorganisms produce carbon dioxide, protons and electrons when consuming a carbon source. The architecture of a MFC capitalises on this principal to create electricity. Once the bacteria form a biofilm around the anode, and start to break down organic matter, electrons are striped from the carbon source by an oxidation reaction and translocated out of the cell via an electron transport pathways found only in these specific exoelectrogenic bacteria. These donated electrons are transferred to a carbon electrode (anode) and moved along a wire to a cathode. As electrons pass through this wire an electrical current is generated. At the cathode the electrons reduce atmospheric oxygen to clean water with the addition of protons that are generated during the oxidation reaction. This enables the factory to become more self-sufficient in reduction of waste and power costs.

The size of the fuel cell will need to be upscaled in order to accommodate the high level of waste produced by the factory, but also to produce an adequate yield of electricity in order to offset the energy used from other power sources during the manufacturing process. The initial costs of implementing such a bioreactor will be expensive. However, once the system is in place, the reduction in costs related to wastewater clean-up and the offset of electrical energy used during the product manufacture, should cover all the debt incurred for the system set up. Not only can this new form of renewable energy save money for companies that are dealing with a high rate of wastewater disposal, but also most importantly, it can reduce the reliance on fossil fuels.

This application is not just reserved for industries listed above. It has been estimated that domestic waste water contains 9.3 times as much energy that is currently used to treat it (Logan, 2009). This adds another element to the viable uses of the system- wastewater treatment for sewage and water companies.

In 2007, Foster’s Brewery together with University of Queensland and University of Ghent, designed the first MFC using brewery wastewater as the organic carbon source for their microorganisms. Professor Keller and his team had positive results using a 10 litre prototype. This project was a small to medium sized scale (1000 litre) and was set up to better understand possible problems that could occur in relation to scaling up the system. There is little information regarding the performance of the MFC in the study other than that the anode appeared to become obsolete due to an excessive build up of biofilm on the cathode (Logan, 2010). Despite setbacks experienced with the scale up during this project, research must continue in order to develop solutions that can overcome such issues in the future.

Further applications could also include the use of promoters that can eliminate heavy metals from wastewater, such as lead and copper promoters. Adapting the promoter to the requirements of the wastewater may improve the efficiency of the MFC in decontaminating wastewater, and may also produce by-products such as caustic soda (Logan, 2010). This by-product can then be used in a variety of other product manufacturing processes. For instance, paper and pulp mills caustic soda is used in the bleaching and pulping stage (Logan, 2010).

Logan, B. E. (2009). Exoelectrogenic bacteria that power microbial fuel cells. Nature Reviews Microbiology, 7(5), 375-381. Logan, B, E. (2010). Scaling up microbial fuel cells and other bioelectrochemical systems. Appl Microbiol Biotechnol. 85: 1165-1671