We’re cooking with Biogas

Its a Gas, gas, gas

If 2,500,000 Indians can do it, so can we. Biogas digesters can power a family of five from cow dung. Upma Arora finds out how:

Rangamma, 45, is one of just five users of the first functional community biogas plant in Kabbigere, a semi-arid village tucked deep inside the Tumkur district of Karnataka. Ever since she started using the bio-gas stove, she feels as if she has a new life. “I could never imagine I could ever be able to save any time for myself. For my entire life, making even a cup of coffee would mean a constant search for firewood.

Cooking meals would involve preparing the mud hearths every day. The worst was the black soot deposits on the vessels that took forever to scrape and clean. The clothes used to be completely soiled and one could feel the lungs weakening with constant exposure to smoke from the chullah (primitive cooking place, which uses wood). With the cooking gas now, all that seems like a distant memory.”

A biogas plant consists of two components: a digester (or fermentation tank) and a gasholder. The conventional (and cheapest) biogas plant create electricity from human or animal dung. Extracting chemical energy from organic materials in a sealed container called a digester produces biogas. That is simply used as gas to power a cooker or water heater or light, or it can be turned into electricity via a gas powered diesel generator.

A small 3 cubic meter plant needs 75 kg of waste material per day to produce 3 cubic meters of gas, which would be sufficient for the requirements of a family of five. To obtain 75kgs of waste the family would own 5 to 8 cattle depending on how they are fed — if they are left to graze they produce less excreta than farm fed cattle. 0.65 cubic meter of gas is required to produce one unit electricity/ one kilowatt. With technological development, feeding in Biomass like dead leaves can also produce electricity, wood and vegetable waste in the biogas plant, 1 to 1.5 kg of wood can generate one unit of power.

The digester is usually a squat, cement cylinder two to four meters in diameter, with a duct in the side that allows the dung or other organic wastes to be fed in, along with water. In ambient temperatures of 25 to 35 degrees centigrade, the material soon begins to ferment. The digester is attached to the gasholder, which is normally an airproof steel container that, by floating like a ball on the fermentation mix, cuts off air to the digester and collects the gas generated. The gasholder is equipped with a gas outlet, while the digester is provided with an overflow pipe to lead the sludge out into a drainage pit. This process produces a mixture of gases, primarily methane and carbon dioxide, and nutrient-rich slurry. The gas is drawn out through a valve at the top of the digester, and the slurry is drained off into settling troughs at its base.

The gas can drive a generator to make electricity. 100% biogas engines are now available which are than connected to alternators. To use these engines the plant size should be 15 or more cubic meter as the engine need 0.45 cubic meter of gas per hour to produce one horsepower of electricity. The cost of these engines varies on size, but on average, 100% biogas engines are available at around $800-1,000 while the dual-purpose engines are $300-400.

Advanced plants can also use household waste for producing biogas through a new compact technology which requires 1 kg of starch or sugar (in the form of vegetable waste, flour collected from the floor of a flour mill) and just 24 hours to produce 250 gms of methane gas. Application of just 2 kgs of feedstock is enough to daily provide a nuclear family with sufficient biogas to cook all meals. Since it requires less space and the raw material is a part of every kitchen, it has an advantage over the conventional biogas system. Methane is the combustible component of biogas and therefore, it is than piped into homes and attached to cooking stoves to be used as a cooking fuel, or used to fire a diesel engine to generate electricity. The slurry is such an excellent fertilizer that it’s often more highly valued than the gas – biogas plants are often called “Bio fertilizer plants.”

A biogas digester with a 3 cubic meter capacity is enough to meet the cooking needs of a family of five – costs approximately 188 sterling and requires . The smallest about 27 square metres of land. The costs of inputs are minimal assuming the household has a water supply and at least five cows – the minimum necessary to supply the digester.

To summarise, the required quantity of dung and water is mixed in the inlet tank and this mix in the form of slurry is digested inside the digester. The gas produced in the digester is collected in the dome, called the gasholder. The digested slurry flows to the outlet tank from the dig through the manhole. The slurry then flows through overflow opening to the compost pit where it is collected and composted. The gas is supplied to the point of application through the pipeline. This is attached to cooking stoves with a valve to control the flow of gas as a when required. The energy produced can also be used on the farm by piping it to lampposts or the energy can be sold, said the head of bio gas plant installation in the state of Madhya Pradesh in India, Mr Bamborriya.

He explained the nitty-gritty of bio gas and its requirement and touched on how the energy is used. Initially, the farmer uses the electricity produced on his own farm for his own requirements like pumping, lightning and etc. He saves money because he needs no or less electricity from outside sources. Surplus electricity can be sold to the nearest public utility company according to the Renewable Energy Law. Especially in such situations where there is no (or few) consumer on the farm that need electricity, the farmer earns money by selling the electricity from renewable energy biogas’. The heat produced can be used for the stables, the farmhouse, drying of grain and other useful purposes. 10 to 30% of the electricity and heat produced is used by the biogas plant itself. Surplus electricity and heat are sold on for the financing of the biogas plant. Normal times for writing-off are 4 to 8 years.

Of course, there are other ways to use biogas. For example, for heat production: steam or hot water. This is attractive if there is need for large amounts of steam. Or the heat can be used to power refrigeration, for cooling stored fresh milk in a dairy

Biogas in plants in countries like India and Sri Lanka have brought significant changes in the lives of farmers, Mr. Ratnayake is one of the beneficiaries of bio gas plant from a small village in north India. With nothing more than cow dung, he now has enough power to cook with, iron the laundry and provide heat and light for his home without using a single piece of wood. All he has to do is to collect the manure from his cows in a specially adapted cattle shed where they feed, mix it with water and leaves it to ferment in a large concrete tank or pit. The gas produced is collected in a simple storage tank, from where it is piped into his house to use. The dried manure left after biogas is generated is richer than ordinary manure and makes a fantastic organic fertilizer for Mr. Ratnayake’s crops, which he can sell at a higher price as organic produce.

A positive side-effect is that women and children are freed from firewood collection cleaning smoke-blackened utensils and the disposal of animal waste. They gain two hours a day for other activities. About 80% now use this time to earn extra income that currently accounts for approximately 24% of the family’s monthly income. Another advantage of using biogas is that there is very little waste from the process and it is environmentally friendly.

Biogas plants are not only a source of energy in third world countries, in countries likes Denmark, Germany, Scotland and Ireland also has widespread use of biogas. In these countries biogas plants are far more advanced and more integrated. For example, In Denmark you find three categories:

20 community biogas plants, each 540-7500 m3, delivering electricity to the grid and heat to the town. 50-70% manure and 30-50% industrial waste.

8 large, rather primitive farm biogas plants using the concrete manure storage tank as digester. With cogeneration.

18 “Smedemester” farm biogas with steel digesters, 45oC operation temperature. 150-800 m3 digesters. 2-5% fish waste oil co fermentation. Cogeneration units 100-500 kW.

Although, biogas in Denmark has not found a widespread use like in Germany. There is an important farm biogas sector in Germany, mainly using concrete digesters whereas almost all biogas plants in Denmark are from steel. In Germany many smaller farms have biogas and also on ecological and biodynamic farms you can find biogas. However, the widespread use of biogas in defiantly the next best and sensible thing to adopt to save energy and environment.

Biogas plants have being a source of energy for the third world countries for long, the use of biogas in rural areas have reduced human dependency on natural gas and firewood, saving forests and increasing soil fertility. The poor people can save money by using biogas rather than buying natural gas or firewood for their domestic needs, which have brought significant changes in their lifestyle. However, the waste material used to produce biogas is available everywhere and its time when we found ways to generate energy from renewable resources rather than using up the scare energy resources and save the environment. The experts believe that biogas is far more cost effective and environmental friendly than natural gas.

The developed countries like USA, pay cash to poor countries for not burning firewood, which leads to 25 percent of global greenhouse gas emissions due to human activities. Rather than paying poor countries, it would make much better sense for developed countries to cash in on the benefits of biogas themselves, as they have greater capacity for research and development to optimise the production and use of biogas.