Biogas

Biogas is a renewable alternative fuel. Rotting food waste, animal and human sewage is converted into gas by anerobic conversion in a digester. The process of anerobic conversion is what happens naturally at the bottom of ponds and results in the production of marsh gas (methane). Biogas is actually a mixture of gases, usually carbon dioxide and methane. It is produced by a few kinds of microorganisms, usually when air or oxygen is absent ("anaerobic").

Animals that eat a lot of plant material, particularly grazing animals such as cattle, produce large amounts of biogas. The biogas is produced not by the cows themselves, but by billions of microorganisms living in their digestive systems. Besides being able to live without oxygen, methane-producing microorganisms have another special feature: They are among the very few creatures that can digest cellulose, the main ingredient of plant fibres. Another special feature of these organisms is that they are very sensitive to conditions in their environment, such as temperature, acidity, the amount of water, etc. Biogas also develops in bogs and at the bottom of lakes, where decaying organic matter builds up under wet and anaerobic conditions.

Besides being able to live without oxygen, methane-producing microorganisms have another special feature: They are among the very few creatures that can digest cellulose, the main ingredient of plant fibres. Another special feature of these organisms is that they are very sensitive to conditions in their environment, such as temperature, acidity, the amount of water, etc.

The Anaerobic Digester

Biogas is the result of the controlled microbial breakdown of organic materials such as animal manures or food scraps in an anaerobic digester. An anerobic digester (AD) is an air tight, oxygen-free container that is fed an organic material, such as animal manure or food scraps. The anaerobic digester is operated at a controlled temperature, pH and loading rate to encourage the growth of microorganisms that eat the organic matter and produce biogas and a more biologically stable liquid effluent. Biogas is a mixture of about 60-70% methane (natural gas), 30-40% carbon dioxide and other trace gases, such as hydrogen sulfide. The heat content is based on the amount of methane and is about 600 BTUs per cubic foot..

The harvesting of biogas is an important role of waste management because methane is a greenhouse gas with a greater global warming potential than carbon dioxide. The carbon in biogas was generally recently extracted from the atmosphere by photosynthetic plants, so releasing it into the atmosphere adds less total atmospheric carbon than the burning of fossil fuels.

The technology is particularly valuable in agricultural, waste treatment or animal processing units where there is excess manure (e.g. pig, cattle, chicken, human) or farm waste. The waste (slurry) is stored in containers called digesters which vary in size from large scale units to smaller units suited to domestic applications.

Uses of Biogas

Biogas production by anaerobic digestion is popular for treating biodegradable waste because valuable fuel can be produced while destroying disease-causing pathogens and reducing the volume of disposed waste. The methane in biogas burns much more cleanly than coal, and produces more energy with fewer emissions of carbon dioxide.

As well as producing the gas, digesters also produce a high nutrient slurry fertilizer and supports better sanitation on farms.

Depending on the system design, biogas can be combusted to run a generator producing electricity and heat (called a co-generation system), burned as a fuel in a boiler or furnace, or cleaned and used as a natural gas replacement.

Some manure AD systems are designed exclusively to combust biogas for heat. In addition to heating the digester, buildings or hot water, it is sometimes used to heat, dry or process agricultural feeds. The heat may have excellent application in greenhouses. Finding a use for surplus heat can be a significant contributor to making AD systems economical.

Biogas from biomass has historically been used in Asia as a fuel for household uses such as cooking. Denmark and Germany have many modern digesters operating on farms and in central locations using materials such as manure, energy crops, and food-based products and byproducts. These systems typically use biogas to produce electricity and heat.

Biogas is a Form of Renewable Energy

Biogas is considered to be a source of renewable energy. This is because the production of biogas depends on the supply of grass, which usually grows back each year. By comparison, the natural gas used in most of our homes is not considered a form of renewable energy. Natural gas formed from the fossilized remains of plants and animals-a process that took millions of years. These resources do not "grow back" in a time scale that is meaningful for humans.
Recently, developed countries have been making increasing use of biogas that has been generated from both wastewater and landfill sites where the gas is produced by automated biological treatment system

The most appropriate use of this gas is for domestic purposes. The gas can be piped to homes to provide a source of gas for cooking and heating.

Biogas is also used in factory boilers and in engine generator sets to produce electricity and heat. If internal combustion engines are fuelled with biogas to produce electricity, the factory can use the electricity or export it to the power grid. The factory can also use the heat from the engine exhaust and the cooling system for low-temperature heating needs in the plant (such as space heating, drying and pre-heating process materials).