University of Bath engineers have demonstrated that it is feasible to trap and use the energy produced by the natural reactions taking place in microorganisms found in the soil.
A team of electrical and chemical engineers has shown the potential of economical, simple “soil microbial fuel cells” (SMFCs), buried in the earth, to drive an electrochemical reactor that decontaminates water.
The proof-of-principle design was exhibited during a field test in North-East Brazil in 2019 and revealed that SMFCs can clean about 3 L of water daily—sufficient for a person’s everyday water requirements.
The project is a partnership with a group of geographers from Universidade Federal do Ceará and a team of chemists from Universidade Federal do Rio Grande do Norte.
Testing was performed in Icapuí, a fishing village situated in a remote semi-dry location where the chief source of drinking water is rainwater and access to a dependable power network is limited.
Rainwater must be chlorinated to make it potable, and besides causing bad taste and odor, unregulated chlorination is hazardous to human health. Therefore, safe approaches to treat water are crucial.
Soil Microbial Fuel Cells Shown to Work in the Field
SMFCs produce energy by exploiting the metabolic activity of particular microorganisms (electrigens) naturally available in soil, which can emit electrons outside their cells.
Designed by staff from the Department of Chemical Engineering and Department of Electronic & Electrical Engineering at the University of Bath, the system comprises two carbon-based electrodes placed at a fixed distance (4 cm) from each other and linked to an external circuit. One electrode, i.e., the anode, is concealed within the soil, and the other one, the cathode, is open to the air on the soil surface.
Electrigens inhabit the surface of the anode and produce electrons as they “consume” the organic compounds available in soil. These electrons are transported to the anode and move to the cathode through the external circuit, thus producing electricity.
A pile of several SMFCs developed and linked to a battery helps produce and store this energy, as well as use it to run an electrochemical reactor for water treatment.
The cost of a single SMFC unit is just a few pounds, which could be brought down with large-scale production and by employing local resources for fabricating the electrode.
Cheap and Sustainable Solution for a Chlorination Problem
The demand for sustainable water purification in the region is because the chief water supply is from precipitation, which must be chlorinated to make it potable.
Set up at the EEF Professora Mizinha of Icapuí primary school, the new technology produces power in small amounts, which can be used to treat about 3 L of water per day. Additional research is required to upgrade its capacity.
The researchers are focused on improving the design of the system and its efficiency to enable one piece of equipment to clean the water required for a family per day. This poses three challenges: producing sufficient energy, gathering and storing that energy efficiently, and treating the water effectively to guarantee drinkability and quality.
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 source.
Dr Mirella Di Lorenzo, Project Lead, University of Bath
“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,” Dr Di Lorenzo added.
Another important element of our project is education around sustainable technologies. The field work was performed together with primary school pupils and their teachers. They were trained on the system’s working principles, installation and maintenance.
Dr Mirella Di Lorenzo, Project Lead, University of Bath
During the 2019 field test, the researchers set up a system at the primary school, where it was investigated to ensure it could reproduce results witnessed earlier in the lab.
The application of the technology, as well as the educational element of the project, provided a transformative experience to the pupils, that have broadened their world view. The pupils helped with the soil microbial fuel cells fabrication and have learned how to handle the technology. They also participated in a dedicated workshop to raise environmental awareness, based on the United Nations Sustainable Development Goals.
Dr Adryane Gorayeb, Brazilian Project Lead, Federal University of Ceará
The project is financially supported by Research England under the Global Challenges Research Fund (GCRF) frame and by The Brazilian National Council for Scientific and Technological Development. Additional funds for the study have now been awarded to continue the research to enhance the design and efficacy of the fuel cells.
Dziegielowski, J., et al. (2020) Development of a functional stack of soil microbial fuel cells to power a water treatment reactor: From the lab to field trials in North East Brazil. Applied Energy. doi.org/10.1016/j.apenergy.2020.115680.