Biogas from azolla biomass – the ultimate energy solution

For centuries, rice farmers in China & Vietnam have been using azolla as a green manure in their wetland fields. The aquatic fern fixes nitrogen directly from the atmosphere (with the help of blue-green algae called Anabaena azollae which lives symbiotically in the leaf cavities of the floating plant) and nourishes the fields. The protein content of azolla is about 20-30% of dry weight making it a good feed supplement for cattle, poultry & fish. The tiny plants are used to purify and recover nutrients from waste water. Azolla requires zero agricultural land and less water compared to terrestrial crops.

Recent studies show that azolla can generate biomass upto165 ton/hectare/year dry matter which is many times higher that can be achieved in the case of popular energy crops and azolla biomass yields high amounts of methane (480 l/kg) - which is equivalent to natural gas,  besides giving us speciality chemicals, jet fuel and bioplastic. 

Azolla World Record Biomass Producer

Biogas – not just cow power or poo power

Moved to Biogas – not just cow power - it is renewable natural gas

Biogas – not just cow power - it is renewable natural gas

Many of us consider biogas as just gobar gas or poo power. We can extract many times more energy from other biodegradable wastes than that from cow dung. For example, 1 kg of food waste when decomposed in an anaerobic environment yields 160 litres of biogas whereas non-edible oil seed cake produces 242 litres and bagasse gives 330 litres in the place of 40 litres of cooking gas with same weight of cow dung under similar conditions.

Biogas has vast potential as a sustainable renewable energy source.  Biogas is poised to lead the biofuel race owing to its advantages over the others.  When other biofuels require specific energy crops which may seize food crops or agricultural land, biogas can be generated from different biomass available – municipal waste being the most attractive option. After producing biogas, the anaerobic bacteria provide us a very good fertilizer whereas some other biofuel generation processes discharge toxic wastes. Utilisation of agricultural & other wastes as a resource and the value of the bio-fertiliser are significant for a country whose economy is depended on agriculture. Moreover, the energy content of biogas is higher than that of other biofuels extracted from biomass grown on a unit area. Some studies show that the average ethanol production from cereals and sugar cane crops is 2,400 litre of oil equivalent per hectare. Under the same conditions biogas delivers 4,500 litre of oil equivalent.  

Biogas consists mainly of methane along with carbon-dioxide and hydrogen-sulphide.  Purified biogas or biomethane being very similar to natural gas, it can be mixed with or substituted for the latter (called bio Natural Gas) in vehicles or other applications. In other words, biomethane can directly utilize the natural gas infrastructure.  In countries like Germany, biomethane is already being injected into their natural gas grids.

Biomethane is the cleanest fuel after hydrogen produced from water using solar or wind power.  Hydrogen to be used in fuel cells can be produced from methane also. But the recent technological developments allow the direct use natural gas or biomethane in the fuel cells with reduced cost of operation. Fuel cells, being more energy efficient, reliable and less polluting than other electricity generation methods, can be used in distributed power generation or in vehicles.

The transmission loss, cost of energy storage and transmission are very less for biomethane even compared to electricity as a long distance energy carrier.  The cost of building up natural gas/biomethane pipelines is said to be half that required to build electric transmission lines for the same quantity of energy transmitted. Biogas production at source of biomass will be convenient rather than transporting the biomass elsewhere for generating electricity. Besides all these, if waste heat from decentralised power generators can also be used, we could utilise up to 85% energy of the source compared to 30% energy reaching the users in the case of coal based power plants.

It is projected that by 2050 global primary energy demand will be 1014 EJ (Exa Joules) whereas the total biomass alone has an energy potential of 1,135 EJ without affecting food production.  Sweden is already using biogas to meet 25% of its energy requirement with majority being used for heating and as vehicle fuel including that for trains.

Our tropical climate is favourable for the bacteria in anaerobic decomposition of biomass and for the growth of energy crops or other biomass. Governments should create a natural gas infrastructure and promote biogas on a big way.  Even if they are not interested in helping the common man, it can bring about reduction in imports of petroleum (for fuel and fertiliser) to save the ‘poor’ oil marketing companies from their ‘under recoveries burden’.

Give a man a LPG cylinder and you provide him gas for a month. Give a man a biogas plant and you provide him cooking gas for a lifetime.

Give a man a LPG cylinder (with subsidy) and you provide him gas for a month. Give a man a biogas plant and you provide him cooking gas for a lifetime.

We have been hearing for quite some time about the Government of India’s desire to cut down LPG subsidy. If they are sincere enough in reducing people’s burden, Government should promote extensively the use of biogas generated from degradable wastes. Attractive subsidy may be given (one time, rather than giving subsidy for each LPG cylinder) for installing domestic biogas plant. Households can save at least half of the LPG by using biogas from the respective household kitchen waste alone.

Families depending solely on LPG for cooking who may be using a cylinder (14.2kg) a month can extend the cylinder usage for another month if the biogas is also utilised, which means that the investment on biogas will be paid back in a few years.  If your biogas plant allows other feedstock also, you may put non-edible oil cakes, agricultural wastes and even aquatic plants to generate more cooking gas.

A domestic biogas system of 1cu.m capacity from BIOTECH, Trivandrum costed me about Rs.13,500 (after subsidy from MNRE) which is sufficient for a small family. If the Government can subsidise the biogas plants to such an extent that it is attractive for all households, it will be beneficial for the country in many ways. The main benefits are as follows.

• Can reduce the demand for LPG – saves fossil fuel, reduces dependence on imported petroleum thereby saving foreign exchange.

• Better solution for disposal of kitchen waste without stench – better environment, reduces the burden of Municipalities / Corporations in the waste movement and processing.

• The slurry produced by the biogas plants is known to be good fertiliser – better for agriculture also. Good medium for growing aquatic plants like azolla and duckweed.

• Utilisation of clean energy from methane which might otherwise be lost.

Awareness should be created among the public on the economical and other benefits of domestic biogas plants.

Super plants – a solution to food-water-energy shortage

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.

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.