Engineers from Bath University have shown that it is possible to capture and use the energy generated by natural reactions that occur in microorganisms in the soil. And, most importantly, it can be used on site for water purification. Details of the development are reported in Applied Energy magazine.

A team of chemical and electrical engineers has demonstrated the potential of cheap simple “soil microbial fuel cells” (SMFCs) buried in the ground to power an electrochemical reactor that purifies water.

The already proven concept was demonstrated during field trials in northeast Brazil. SMFCs were found to be able to purify about three liters of water per day, which is enough to meet human daily water needs.

Tests were conducted in Icapua, a fishing village located in a remote, semi-arid location where rainwater is the main source of drinking water and access to a reliable power grid is limited. Rainwater must be chlorinated in order to be able to drink it. However, uncontrolled chlorination not only causes unpleasant taste and smell, but also is dangerous for human health. Immunically, local scientists were looking for safe methods of water purification.

SMFC generate energy through the metabolic activity of certain microorganisms (electrogens) naturally present in the soil, which are able to carry electrons beyond their cells.

The system itself consists of two carbon electrodes located at a fixed distance from each other (4 cm) and connected to an external circuit. One electrode, the anode, is immersed in the soil and the other, the cathode, is exposed to air on its surface.

Electrogenous bacteria fill anode surface and by “absorbing” organic compounds present in soil they generate electrons. These electrons are transferred to the anode and moved to the cathode through an external circuit, generating electricity.

Scientists point out that an important element of their project on safe and economical water treatment is training of new technologies. The fieldwork was conducted with elementary school students and their teachers in the problem region of Icapui, Brazil. They were trained in how to operate, install and maintain the system.