Electricity from soil bacteria and reading lights from plants

Plant lucifer: The group used watercress and spinach as experimental plants.

We generate electric power through hydroelectric plants (in Bhakra, Nagarjunasagar or Hirakud dams), from coal and fossil fuels (Ramagundam, Bhilai and Neyveli), or nuclear plants (ones at Tarapur, Kudankulam or Kakrapar). Each method has its downside – be it water shortage or inter-state disputes, fouling the environment with pollution dust and greenhouse gases, or safety issues with radioactive damage. Can we at all have a pollution-free and nature-friendly power plant?

Biology appears to suggest a way. A group of researchers at the Wageningen University in the Netherlands, led by Dr. Marjolein Helder, has hit upon a method that generates electricity from living plants and the microbes that live beneath them in the soil, where the plants drop their roots. The plant of course does photosynthesis, using sunlight, water and atmospheric carbon dioxide, generating food in the form of carbohydrates and oxygen for our breathing. The microbes in the soil use some of this organic material coming out of the plants into the ground, metabolise them and, in the process, generate carbon dioxide and hydrogen ions and electrons.

While the plant above the ground does photochemistry, the bacteria beneath do electrochemistry, generating positive and negative ions. What Dr. Helder and colleagues have done is to place positive and negative electrodes in appropriate positions and obtain an electric current, just as we do with batteries. This method of producing electricity is through what is termed as plant microbial fuel cells (PMFC).

Look at the simplicity of it. The method is completely natural and environment-friendly, needs no externally added material and is part of a cyclic process in nature. But how much electricity is produced with such PMFC? It depends on the size. A small 50 cm x 50 cm plot of a garden is estimated to produce 5 volts of electricity, while a 100 square metre garden gives enough electric power to charge a cell phone or to light up several LED light bulbs. Indeed the Wageningen group has lit up their Atlas building with LED bulbs, using PMFCs, and a mobile phone charging station in a place at the nearby town Tilburg.

Theory suggests that one should be able to generate 3.2 watts of electric power per square meter (3.2W/m2), using PMFCs. The best level obtained so far in practice is but a sixteenth of it, namely, 220 mW/m2. Thus, improvement in efficiency needs to be done, both by adding such microbes in the soil which perform better, and by enhancing the area by miles and miles of grass lawns, farm lands and focus on paddy fields and similar acreages. These will also bring the cost–benefit ratio to acceptable proportions. It is with this in mind that Dr. Marjolein Helder came over to visit N. Chandrababu Naidu to consider taking up electricity generation across the state of Andhra Pradesh.

Plants that glow

Another dramatic advance, this one directly from the plants themselves rather than the microbes underneath, has come from Dr. Michael Strano of MIT, Cambridge, MA, USA. This is an audacious idea, namely, “how to make plants glow with light”! We know that a plant captures light, and using this, converts water molecules and atmospheric carbon dioxide into sugar. What Strano’s group aims to do is to make plants not just absorb but also emit light and, indeed, glow such that we may use such plants as a table lamp to help read a book in a dark room! In other words, make a plant glow as a firefly does.

A firefly glows because it has an enzyme that converts a molecule called luciferin into oxyluciferin, and the energy released in this reaction comes out in the form of visible light. The enzyme is called luciferase. (Incidentally, luciferin is named after the Latin word lucifer, meaning light-bringer or the morning star). Now, plants do not have luciferin or luciferase. If we can somehow inject into a plant luciferin and luciferase, perhaps the plant too will emit light — this was the idea that Strano had. Towards this, he used the technology of nanoparticles.

Taking watercress and spinach as experimental plants, his group first packaged luciferase in nanoparticles made of silica. Then, they packed luciferin in another set of nanoparticles made of the polymer PLGA. Each of these nanoparticles carried a tag that would allow it to go to one specific part of the plant cells. Then they also devised a third nanoparticle system, packed with molecules called co-enzyme A, which was to remove a product of the luciferin reaction, which inhibits or stops the reaction from proceeding.

They now immersed the plant in water, added the three sets of nanoparticles, and applied high pressure so that these will enter and position themselves in appropriate places inside the plants. Now, the reaction proceeded and the plant emitted feeble glow, a Eureka moment, which lasted for about 3 hours!

Clearly, more tinkering needs to be done in order to brighten the glow, increasing the time it lasts and other issues. Also how to turn off the light when you do not need it anymore (this has already been established by adding a switch-up the off molecule at will). Given the progress, these appear doable soon enough. Strano says: “our work seriously opens up the doorway to street lamps that are nothing but treated trees and to indirect lighting around homes”.

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Printable version | Apr 24, 2022 4:41:34 pm |