According
to some U.N. estimates, by 2030, a rapidly growing population in the world will
need at least 50 percent more food, 45 percent more energy and 30 percent more
water. Small aquatic plants are promising a way out in this context.
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. 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 is found to be a good medium for their growth. Vivekananda Kendra-Natural Resources
Development Project (VK- NARDEP) in Kanyakumari, 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.
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| Azolla & duckweed |
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.
Azolla in
agriculture
Rice
farmers in China and Vietnam have been using azolla for centuries in their
wetland fields. Azolla is allowed to grow on rice fields before the rice plants
are transplanted. Azolla forms a thick mat over the water surface making it
difficult for weeds and mosquitos to grow. Studies by Tamil Nadu Agricultural
University shows that azolla can contribute, besides other nutrients, 40-60 kg
N/ha per rice crop. Use of urea/nitrogen fertiliser and other fertilisers can
be reduced if azolla is used as bio-fertiliser. Azolla has been used as green manure
for other crops also. Because they are grown locally, it reduces the use of
petroleum products otherwise needed for the processing & transportation of
fertilisers giving savings to the nation.
As a feed
Duckweed
and azolla contains about 30% protein on dry weight basis. They can produce more
than 9 tonnes of protein per hectare per year. Farmers around the world use them
as a feed supplement for cattle, poultry and fish.
Trials
carried out by the VK- NARDEP, with azolla as a feed supplement for diary
animals, shows an increase of milk yield when azolla was combined with regular
feed and shows that azolla feeding improves the quality of milk and the health &
longevity of livestock.
Poultry
and fish supplemented with azolla or duckweed were also reported to have
reduced the cost of feeds and at the same time shown increased productivity for
the farmers. Besides providing healthy
food through its use in agriculture, they being rich in proteins, essential
amino acids, vitamins & minerals, the small plants themselves are healthy
and nutritious food for humans.
In water
purification
Various
aquatic plants, mainly duckweed, have been used for treating domestic and industrial
wastewaters. These plants grow by absorbing the impurities in the wastewater,
thereby enabling us to recover the nutrients from the wastewater and allow
reuse of the precious resource. Punjab State Council for Science &
Technology is one of the promoters for the duckweed based wastewater treatment
system in India.
Biomass to
energy
Dwindling
petroleum reserves have prompted us to search for alternative sources of energy
and biomass is one of the promising routes to the future energy utilisation.
Lot of money is being spent on the research to bring out biofuels from
biomass. 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),
with increased carbon dioxide presence and 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. Scientists foresee the
future of renewable energy in bio-methane because it is equivalent to natural gas.
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.
To
summarise, the tiny plants can be seen as a
* cheap substitute
for imported chemical fertilisers which also gives higher crop yields
* solution
to reduce cost of feed for cattle, poultry & fish along with increased
productivity
* healthy
food for humans
* key for decreasing
water pollution and recovery of nutrients from waste water
* carbon
neutral renewable energy source, an alternative to the petroleum products.
In other
words, the super plants can reduce the cost and increase the availability of
food, water & fuels. Governments shall promote the use of the ‘green gold’ by
providing kits and training to the farmers, housewives & the unemployed and
shall make sure that no land is left uncultivated. Decentralised units for
generating electricity or biogas may be setup for utilising excess biomass
grown by farmers or wastewater treatment systems.
