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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.

1. Membrane bound cytochromes
2. Conductive nanowires
3. Production of soluble electron mediators.

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 have formed 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, reduction of 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 make this viable. The initial costs of implementing such a bioreactor will be expensive. However, the idea is that once it is established the costs will cover themselves in the reduction of waste water cleanup, the costs of fossil fuel usage, and the quantity of water used. We are hoping that in time the bioreactor will pay for itself and its reduction to the potential damage to the environment making a positive impact on the environment as well as allowing profits to continue. Thus enabling this operation to be viable.

This is a potential application in developing and developed nations. This application is not just reversed 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 opens up the opportunity as an application for waste water treatment for sewage and water companies. Again this system could be used to not only to reduce the level of waste, but the energy produce by the bioreactor could be used to fuel the water plant by offsetting the costs and dependency of fossil fuels.

In 2007, Foster’s Brewery together with University of Queensland and University of Ghent, designed the first MFC using brewery waste water 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) in order to investigate the issues with scale up. There is little information regarding the performance of the study other than that the anode appeared to be comprised due to an excessive buildup of biofilm on the cathode (Logan, 2010). Despite setbacks experienced with scale up during this project, research must continue in order to investigate methods in order to overcome such issues in the future.

Further applications could also include the use of promoters that can eliminate heavy metals from waste water, such as lead and copper promoters. Adapting the promoter to the requirements of the waste water may improve the efficiency in which the MFC is able to decontaminate the water, but may also produce by-products such as caustic soda (Logan, 2010). In the case of paper and pulp mills caustic soda is used in the bleaching and pulping stage (Logan, 2010). Therefore, recycling the caustic soda produced by the MFC, may have a knock on effect in that it too reduces the costs of the plant but also reduce the amount of caustic soda leaching into the environment.

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