This is an article written two years before for publication in the science & technology column of ‘THE HINDU’ daily. I sent to the science editor but no responses.
Green Electricity: A Novel Eco-Economic Bioenergy Strategy
The Great Chinese leader Mao said, “Political power grows out of a barrel of a gun”, but today political powers are growing out from the barrels of petrol and uranium mines. Wars are made and postponed on the basis of energy scenario. New unexpected alignments and coalitions are happening to answer the energy threats. Rather than the pressure created by global climate change and pollution, the threat for energy security had pushed the political powers towards sustainable, renewable energy sources. The Solar and Bioenergy are the major drivers of the future world but both carry its own drawbacks. The solar panels are expensive and practically accounts for many problems. Similarly the bioenergy had created a new threat for food security. Today a direct competition is emerged between the rich for fuel and the poor for food. The fact is unless the eco-friendly movements are made economic-friendly, their promises won't be realised. One such Eco-Economic Bioenergy strategy is devised by the researchers individually at the Wageningen University, Netherlands and Ghent University, Belgium. This is based on plant-microbe interaction in which the bacteria utilize the carbohydrates in the rhizosphere for current generation. This Green Electricity production is made possible by the integration of two different well documented concepts i.e., Rhizodeposition and Microbial Fuel Cells.
Rhizodeposition:
The plants are the best known solar energy harvesters through their photosynthetic activity and store the energy as carbohydrates. All forms of bioenergy production like biodiesel, bioethanol are derived from this organic source. It is estimated that nearly 60% of the harvested energy is released into the rhizospheric soil as root exudates in the form of carbohydrates. This process is termed as rhizodeposition. Besides carbohydrates, it also possesses fatty acids, sterols, hormones, enzymes, organic acids, aminoacids, vitamins and other metabolites. The rhizodeposits act as a substrate for soil biota. The beneficial microbes including Plant Growth Promoting Rhizobacteria utilize these organic substrates for their metabolic activity. In turn by their multifarious biological activities they help the plants in mineral uptake, antimicrobial activity and enhanced growth.
Microbial Fuel Cells:
The Microbial Fuel Cells (MFCs) is defined as, “a bioreactor that converts chemical energy in the chemical bonds in organic compounds to electrical energy through catalytic reactions of microorganisms under anaerobic conditions”. The living cells produce carbon dioxide and water when they utilize an organic source under aerobic conditions. While during anaerobic condition, they produce carbon dioxide, protons and electrons. These electrochemically active bacteria termed electricigens are employed in MFCs that generate current by transferring electrons from anode to cathode. It is proven that these bacteria can utilize the carbon sources as the substrate for electricity production in a clean way. By engineering the MFCs can be used for waste water treatment, biohydrogen production, as biosensors for pollutants, in robotics, in spaceships and in implantable medical devices like pace maker.
Plant-MFC:
In the experimental set up, as in a typical MFC it contains anodic and cathodic chambers. The chambers were filled with respective electrodes. The electrigens are inoculated in the anodic chamber. Dr. Hamelers group of Netherlands used Reed Manna Grass as a test plant. This plant is known to grow on the anaerobic riverbank sediments of Europe. Initially the roots of the plants were placed on the anodic chamber and maintained for 118 days. The current ouput was measured using multimeter. The total energy produced over the period from days 50 to 118 was 62 J. They estimated that the achievable electricity production of a plant-MFC is 21 GJ ha -1 year -1 (5800 kWh ha -1 year -1). This estimation is based on a solar radiation of 150 W m -2 in Europe and other conditions for a growth season of 6 months. So in temperate countries like India we can expect much more current generation. While Dr. Verstraete group from Belgium used Rice plants and successfully achieved current generation with usual yield. Thus this technology can be implemented in a diverse range of plant species including weeds, different soil and varying climate conditions.
Thus, if this technology of Green electricity is made to application level, it possesses several advantages. Besides answering the current energy crisis, it eliminates the economic issues associated with bioenergy production. This process is non-destructive in situ energy production, doesn't need harvesting, transport of plants and most importantly doesn't compete with food. In addition, more importantly it is carbon neutral and combustion emission-free operation that results zero pollution. Just imagine that our street lights are powered with the current generated from the trees on the roadside itself.
G Velmurugan
14th October 2008
