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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