British Researchers Stack Bacteria to Turn Urine into Electricity

10/05/2016 - 3 minutes

Researchers from Bristol in the UK developed a new design of microbial fuel cells (MFCs), a more efficient way to use wastewater to produce electricity. 

Want to power your smartphone with your pee? Biotechnology has been diligently working on the idea for decades now, with microbial fuel cells (MFCs).

A fuel cell is a technology that can transform chemical energy, in the form of reduced molecules (that have electrons available), into electrical energy – a specially useful form of energy.

In MFCs, microorganisms are used to bridge this conversion process. The microorganisms ‘breathe‘ the reduced molecules containing chemical energy, and then transfer the electrons to the anode (the ‘minus’ end of a battery) – thus producing electricity.

mfc_microbial_fuel_cell_urine_electricity
Fig: 1: a simple microbial fuel cell (MFC) using urine.

The idea has been around for more than a century, but scientists are still struggling with making the process efficient enough.

Now, researchers at Bristol BioEnergy Centre (B-BiC) have published a breakthrough in Biotechnology for Biofuels. The team developed a stack design of ceramic modules, that could allow the scale-up of this technology (always a tricky part).

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Biofilms of bacteria were developed on the surface of the module, which were partially submerged in urine.

Urine has a lot of energy-rich ammonia, making it a good substrate for MFCs – not to mention that it’s free. By using wastewater components in the process, MFCs do two jobs – electricity production and wastewater treatment.

urine_mfc_stack_bristol_b_bic
Fig. 2: Schematics of the novel stack design for MFC.

The novel stack design is meant to solve an old problem. The volumetric power density (W/m³) decreases if the cell is bigger and has a smaller surface-to-volume ratio. This is because the bacteria live on the surface of the cells.

In practical terms, this means that to produce relevant quantities of electricity (to power a house, for example) you have to build a bigger MFC – but the bigger you make it, the less efficient it is.

With their new design, the researchers managed to scale-up a MFC from 900 mL to 5 L, increasing the total power produced and maintaining the power density.

This simple design, made with inexpensive materials, could pave the way to a new, greener way of producing electricity.

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Even the US Navy is researching in microbial fuel cells…
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Figure 1 Credit: Ieropoulos et al. (2012) Urine utilization by microbial fuel cells; energy fuel for the future. Physical Chemistry Chemical Physics (doi: 10.1039/C1CP23213D)
Figure 2 Credit: Walter et al. (2016) Scaling-up of a novel, simplified MFC
stack based on a self-stratifying urine column. Biotechnology for Biofuels (doi: 10.1186/s13068-016-0504-3)

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