Engineers at the University of Bath have shown that it’s possible to capture and use energy created by the natural reactions occurring in microorganisms within soil.
A team of chemical and electrical engineers has demonstrated the potential of cheap, simple ‘soil microbial fuel cells‘ (SMFCs), buried in the earth to power an electrochemical reactor that purifies water.
The proof-of-concept design was demonstrated during field testing in North-East Brazil that took place in 2019 and showed that SMFCs can purify about three litres of water per day- enough to cover a person’s daily water needs.
The project is a collaboration with a team of geographers from Universidade Federal do Ceará and a team of chemists from Universidade Federal do Rio Grande do Norte.
Testing took place in Icapuí, a fishing village located in a remote semi-arid location where the main source of drinking water is rainwater and access to a reliable power network is scarce.
Rainwater must be chlorinated to be drinkable, and in addition to causing bad taste and odour, uncontrolled chlorination is dangerous to human health—so safe methods to treat water are essential.
Soil microbial fuel cells shown to work in the field
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 Department of Chemical Engineering and Department of Electronic & Electrical Engineering, consists of two carbon-based electrodes positioned at a fixed distance apart (4cm) 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’ the organic compounds present in 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 by connecting this to a battery it is possible to harvest and store this energy, and use it to power an electrochemical reactor for water treatment.
A single SMFC unit costs just a few pounds, which could be further reduced with mass production and with…