Engineers at the University of Bath developed the system, showing it was possible to capture and use energy from the soil.
Working with a team of geographers from the Federal University of Ceará and a team of chemists from the Federal University of Rio Grande do Norte in Brazil, the engineers demonstrated the proof-of-concept soil microbial fuel cells (SMFCs) during field testing in North-East Brazil.
By powering an electrochemical reactor that purifies water, they were able to purify about 3l of water per day – enough to cover a person’s daily water needs.
SMFCs generate energy from the metabolic activity of specific microorganisms (electrigens) naturally present in soil, which are able to transfer electrons outside their cells.
The system, developed by staff from Bath's departments of chemical and electrical engineering, consists of two carbon-based electrodes positioned 4cm apart and connected to an external circuit. One electrode, the anode, is buried inside the soil, while the other, the cathode, is exposed to air on the soil surface.
Electrigens populate the surface of the anode, and as they consume organic compounds in the soil, they generate electrons. These electrons are transferred to the anode and travel to the cathode via the external circuit, generating electricity.
By building a stack of several SMFCs – and connecting this to a battery – it is possible to harvest and store the energy, and use it to power an electrochemical reactor for water treatment.
A research announcement said a single SMFC unit costs just a few pounds, which could be further reduced with mass production and with the use of local resources for the electrode fabrication.
The demonstrator technology, installed at a primary school, creates a small amount of power. The researchers said further work is needed to scale up its capacity.
The team aims to refine the design of the equipment and its efficiency to allow one piece of equipment to purify an entire family’s daily water supply.
Project leader Dr Mirella Di Lorenzo said: “Using soil microbial fuel cell technology to treat a family's daily water needs is already achievable in laboratory conditions, but doing so outdoors and with a system that requires minimal maintenance is much trickier, and this has previously proven a barrier to microbial fuel cells being considered effective. This project shows that SMFCs have true potential as a sustainable, low-energy energy source.”
She added: “We're addressing the issue of water scarcity and energy security in North-East Brazil, which is a semi-arid area. We sought a sustainable way to treat water effectively and make it drinkable. Rainwater is the main source of drinking water in the area, but this is not sterile – our approach in this work points to a way we could solve the issue.”
The research was published in Applied Energy.
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