Sunday 16 September 2012

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. 

Sunday 2 September 2012

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’.

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