What is Biogas? A Beginners Guide
Biogas is a type of biofuel that is naturally produced from the decomposition of organic waste. When organic matter, such as food scraps and animal waste, break down in an anaerobic environment (an environment absent of oxygen) they release a blend of gases, primarily methane and carbon dioxide. Because this decomposition happens in an anaerobic environment, the process of producing biogas is also known as anaerobic digestion.
Anaerobic digestion is a natural form of waste-to-energy that uses the process of fermentation to breakdown organic matter. Animal manure, food scraps, wastewater, and sewage are all examples of organic matter that can produce biogas by anaerobic digestion. Due to the high content of biogas (typically 50-75%) biogas is combustible, and therefore produces a deep blue flame, and can be used as an energy source.
The Ecology of Biogas
Biogas is known as an environmentally-friendly energy source because it alleviates two major environmental problems simultaneously:
- The global waste epidemic that releases dangerous levels of methane gas every day
- The reliance on fossil fuel energy to meet global energy demand
By converting organic waste into energy, biogas is utilizing nature’s elegant tendency to recycle substances into productive resources. Biogas generation recovers waste materials that would otherwise pollute landfills; prevents the use of toxic chemicals in sewage treatment plants, and saves money, energy, and material by treating waste on-site. Moreover, biogas usage does not require fossil fuel extraction to produce energy.
Instead, biogas takes a problematic gas, and converts it into a much safer form. More specifically, the methane content present in decomposing waste is converted into carbon dioxide. Methane gas has approximately 20 to 30 times the heat-trapping capabilities of carbon dioxide. This means that when a rotting loaf of bread converts into biogas, the loaf’s environmental impact will be about 10 times less potent than if it was left to rot in a landfill.
As opposed to letting methane gas release to the atmosphere, biogas digesters are the systems that process waste into biogas, and then channel that biogas so that the energy can be productively used. There are several types of biogas systems and plants that have been designed to make efficient use of biogas. While each model differs depending on input, output, size, and type, the biological process that converts organic waste into biogas is uniform. Biogas digesters receive organic matter, which decompose in a digestion chamber. The digestion chamber is fully submerged in water, making it an anaerobic (oxygen-free) environment. The anaerobic environment allows for microorganisms to break down the organic material, and convert it into biogas.
Because the organic material decomposes in a liquid environment, nutrients present in the waste dissolve into the water, and create a nutrient-rich sludge, typically used as fertilizer for plants. This fertilizer output is generated on a daily basis, and therefore is a highly productive by-product of anaerobic digestion.
To produce biogas, organic matter ferments with the help of bacterial communities. Four stages of fermentation move the organic material from their initial composition into their biogas state.
- The first stage of the digestion process is the hydrolysis stage. In the hydrolysis stage insoluble organic polymers (such as carbohydrates) are broken down, making it accessible to the next stage of bacteria called acidogenic bacteria.
- The acideogenic bacteria convert sugars and amino acids into carbon dioxide, hydrogen, ammonia, and organic acids.
- At the third stage the acetogenic bacteria convert the organic acids into acetic acid, hydrogen, ammonia, and carbon dioxide, allowing for the final stage- the methanogens.
- The methanogens convert these final components into methane and carbon dioxide- which can then be used as a flammable, green energy.
History of biogas
This anaerobic process of decomposition (or fermentation) of organic matter happens all around us in nature, and has been happening for a very long time. In fact, the bacteria that break down organic material into biogas are some of the oldest multi-celled organisms on the planet. Human use of biogas, of course doesn’t go that far back, however, some anecdotal evidence traces the first uses of biogas to the Assyrians in the 10th century and the Persians in the 16th century. More recently, the 20th century has brought about a renaissance of both industrial and small-scale biogas systems.
In the 18th century it became clear to Flemish chemist Jan Baptise van Helmont that decomposing organic matter produced a combustible gas. Soon after, John Dalton and Humphrey Davy clarified that this flammable gas was methane. The first major anaerobic digestion plant dates back to 1859 in Bombay. Not long after, in 1898, the UK used anaerobic digestion to convert sewage into biogas, which was then used to light street lamps. For the next century, anaerobic digestion was primarily used as a means to treat municipal wastewater. When the price of fossil fuels rose in the 1970’s industrial anaerobic digestion plants increased in popularity and efficiency.
Both India and China began developing small-scale biogas digesters for farmers around the 1960’s. The goal was to decrease energy poverty in rural areas, and make cleaner cooking fuels more accessible in remote areas. Close to one third of the global population still uses firewood and other biomass for energy, causing devastating health and environmental problems. (Link to blog post on developing countries)
In India the popular model is known as the floating drum digester, and China’s preferred biogas model is called the fixed dome digester.
Since then, family-sized biogas units are gaining more attention and popularity as both a means of reducing household waste and as a means of providing clean renewable energy to families throughout the world. In the past 15 years, countries around the globe are adopting biogas programs to make both household biogas systems and larger anaerobic digestion plants accessible, efficient, and convenient. As landfills get illegally overloaded, and as the release of methane poses more worrying problems, the benefits of using biogas systems to convert waste into energy are increasingly more relevant and important.
Many Uses of Biogas:
Biogas can be produced with various types of organic matter, and therefore there are several types of models for biogas digesters. Some industrial systems are designed to treat: municipal wastewater, industrial wastewater, municipal solid waste, and agricultural waste.
Small-scale systems are typically used for digesting animal waste. And newer family-size systems are designed to digest food waste. The resulting biogas can be used in several ways including: gas, electricity, heat, and transportation fuels.
For example, in Sweden hundreds of cars and buses run on refined biogas. The biogas in Sweden is produced primarily from sewage treatment plants and landfills.
Another example of the diversified uses of biogas is the First Milk plant. One of the UK’s biggest cheese makers is building an anaerobic digestion plant that will process dairy residues and convert into bio-methane for the gas grid. New anaerobic digestion plants like these with fascinating stories keep popping up every day!
Small-scale biogas systems
Small-scale, or family-size biogas digesters are most frequently found in India and China. However, the demand for such units is growing rapidly throughout the world thanks to more advanced and convenient technologies, such as HomeBiogas. As the modern world is producing more and more waste, individuals are eager to find ecologic ways to treat their trash.
Traditional systems typically found in India and China focus on animal waste. Due to a lack of energy in rural areas combined with a surplus of animal manure, biogas digesters are very popular, useful, and even life-changing. In many developing countries, biogas digesters are even subsidized and advocated by the government and local ministries, who see the variety of benefits produced from using biogas. In addition to having a clean renewable energy provide gas in the kitchen, many families make extensive use of the fertilizer by-product that biogas digesters provide.
In African countries, some biogas users even turn a profit by selling the bio-slurry by-product produced by biogas systems. This bio-slurry is different from the liquid fertilizer that is produced daily. Bio-slurry refers to the most decomposed stage of the organic matter, after it has been broken down in the system. Bio-slurry sinks to the bottom of the biogas system, and with the help of modern units like HomeBiogas, is easily emptied out once accrued (usually an annual process). This bio-slurry is in fact a nutrient-dense sludge that provides lots of benefits to soil, and can increase productivity of vegetable gardens.
Biogas is a technology that mimics nature’s ability to give back. Both industrial-size and family-size biogas units are becoming incredibly popular and relevant in today’s world. As the application and efficiency grows, biogas can make a significant impact on reducing greenhouse gases. As a clean source of energy and a renewable means of treating organic waste, biogas is applicable both in under-developed and industrialized countries.
Hilla is a passionate foodie and environmentalist. She writes on energy efficiency, food, and reducing waste.