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Views The Renewable Outlook in Japan
Rice Paddy Power: Harnessing Microbial Energy
Could Tiny Organisms Provide Great Energy?

Energy harvesting transforms the latent energy of the natural world that flows through our everyday environment into power we can use. In the fields that produce Japan’s staple crop, rice, work to harvest this energy has already begun.

The Power of Rice and Microbes

As rice plants photosynthesize and grow, they release a portion of the organic material they create through their roots into the soil and water. Rice paddies are full of this material, which feeds a vast array of microorganisms. As they consume the food, their digestive process yields energy—a fact that is leading some researchers to explore ways of using rice paddies to produce electric power.

Watanabe Kazuya and his research team at the Tokyo University of Pharmacy and Life Sciences are leading research in power production using paddy microbes. In their experiments, the scientists place negative electrodes in the soil of rice paddies and positively charged electrodes in the water, generating an electric current as the energy emitted by the microbes in the soil is concentrated in the former. One recent experiment showed that a square meter of a paddy could produce tens of milliwatts of power—an extremely small amount, but still enough to power a watch or an LED bulb.

Professor Watanabe notes that the activity of the rice affects the amount of power generated. During the daytime, and especially on consecutive hot summer days with lots of sunlight, the photosynthesis is more active, boosting the amount of power generated.

The researchers carry out their experiments in community garden paddies in Noda, Chiba. When the rice is harvested in the fall, the tests have no effect on crop yield.

Fuel cells typically use a reaction of hydrogen and oxygen to produce power, but Watanabe’s team is attempting to capture the energy produced when the microbes consume organic material. In experimental settings, when microbes are grown and used as fuel cells, they require constant feeding by the laboratory staff. That is where the idea of using an entire rice paddy as a large fuel cell originated, says Watanabe.

In the paddies, the rice plants produce their own organic material through photosynthesis, and the microbes convert matter to energy. The symbiotic relationship between the organisms of the rice paddy produces power. While the energy capture technology is not yet commercially viable, Watanabe and his team are working to increase efficiency while they search for new energy-producing microbes. The aim is a fuel cell that makes use of microbes with particularly high production potential.

The Same Lifestyle on Half the Energy

Experimental Waste Water Microbial Fuel Cell

Professor Watanabe also has high hopes to convert the microbes present in sewer water into fuel cells. Using the organic matter present in sewage to produce power would also remove it, simultaneously filtering the sewage and producing power—a particularly attractive possibility.

Professor Watanabe says that the society of the future must make good use of biological systems.

Until now, humans have relied mainly on nonrenewable energy sources that must be extracted, such as oil. But going forward, we must shift to naturally renewable sources. To do so will require technology that gathers resources from nature, converts them to energy, and then allows for their reuse and renewal.

Using natural energy sources does not necessarily mean we need to live more frugally, though. Watanabe says that if more energy efficient technology is developed, we can continue to live a comfortable lifestyle while using half the energy we now do. This will also allow us to build a society that does not rely on resources like oil, he says.

(Originally written in Japanese by Satō Narumi.)

  • [2012.10.12]
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