domingo, 15 de julho de 2012

Biomass to energy using super aquatic plants - azolla and duckweed (forget algae)


Tiny water plants like duckweed and azolla are characterised by their tremendous growth. Under favourable conditions, they can double their mass in 1-3 days absorbing carbon dioxide from air through photosynthesis. These little plants can fix the greenhouse gas far better than other plants besides offering solutions to many other burning issues. These aquatic plants can be harvested easily, unlike algae which require a lot of energy to extract the biomass from water. Some 49 million years ago, azolla is believed to have reversed the greenhouse effect which is known as the azolla event.

Growing them
Various species of duckweed and azolla can be grown in shallow ponds or even in trays with water height less than 10cm or 4inch. These free-floating plants do not require full sunlight, a 50% shade is necessary for their optimum growth. Places getting heavy sunlight allow growing them in between other crops or on multileveled trays/channels with top level for drying harvested plants. The diluted slurry from biogas digesters and wastewater from industries or houses can be a used for their growth.  Vivekananda Kendra-Natural Resources Development Project (VK- NARDEP) in Tamil Nadu promotes growing of azolla on silpauline lined pits in the backyards or terraces to reduce the production cost of the small plant to less than 30paise per kg harvested.

Duckweeds grow by taking up nutrients like nitrogen, phosphorus & potassium from water and some of their species can tolerate salinity to an extent.  Azolla can fix nitrogen directly from the atmosphere with the help of blue-green algae called Anabaena azollae, which lives symbiotically in the leaf cavities of the fern plant. These little plants can rejuvenate biologically dead water bodies.

Biomass to energy
Some of the edible crops such as soybean and corn were diverted for use in biofuel extraction, which resulted in the rise of food prices. Even larger aquatic plants like water hyacinth are now considered as a resource and not as a menace, owing to their biomass potential. According to VK- NARDEP, the biomass yield of Azolla is 1000 MT/ hectare/year. On controlled environments with extended day light (using artificial lighting), increased carbon dioxide presence and with optimal nutrient availability in water we could achieve more biomass yield.

Biogas, which consists mainly of methane, can be generated easily from biomass using simple household biogas plants or using sophisticated plants that can convert any organic waste to pure methane and that can release it into a pipelined grid or bottled similar to LPG. Diluted slurry from biogas plants may be used for growing these water plants which make a closed loop of growth and utilisation of these aquatic plants. Biogas will help the houses, restaurants & canteens to reduce the use of costly LPG when cooking. Some scientists foresee the future of renewable energy in bio-methane as it is equivalent to natural gas. Studies show that in the absence of nitrogen, azolla can directly produce hydrogen.

Pacific Domes, an US company, grows duckweed along with fish and vegetables in ponds covered with domes maintaining consistent natural sunlight. Duckweeds are hand harvested, dried and fed into generator. A 24 foot dome placed in the backyard is sufficient to generate optimally 5kW electricity (along with 4-7 kg of food daily) at the same price as coal which is significantly cheaper than renewable sources like wind or solar. Carbon dioxide generated in the process here is offset by the growth of duckweed. They also claim that a 60 foot commercial unit optimally generates about 200 kilowatts of electricity besides purifying about 20,000 litres of grey-water per day. With multiple commercial units, it could be possible to generate many Giga Watts of power from the area occupied by typical thermal, hydro or nuclear power stations as they require thousands of hectares.

Any takers for this biomass to energy route?



Link : http://bharatnamaskar.blogspot.in/2012/07/super-plants-solution-to-food-water.html

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