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.
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.
|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. 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 occupy thousands of hectares.
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.