What is biogas?

Biogas is a combustible gas produced from the decomposition of organic matter. Biogas is a source of renewable energy because its generation requires the elimination of polluting waste, and its use considerably reduces greenhouse gases.

What raw material is used for biogas production?

Substrates for the production of biogas include agricultural waste, such as animal manure and harvest scraps; municipal organic waste, such as sewage sludge or food waste; and industrial organic waste. The essential thing is for this raw material to be separated from other types of waste properly.

How is biogas generated?

The production of biogas is carried out by a process of anaerobic digestion of the biomass. This means that, in an environment without oxygen, methanogenic bacteria that are capable of breaking down organic matter proliferate. In this process of digestion, these bacteria produce fertilizer and biogas, which is composed mainly of methane (CH₄) and carbon dioxide (CO2), along with small amounts of other gases such as nitrogen, oxygen, hydrogen sulfide, and water vapor.

The technology used to produce biogas can range from small biodigesters for family use to industrial-sized generation plants. Despite the differences between the more modest projects and the more developed ones, they usually have elements in common, such as: 

• A feeding tank, which the crushed biomass, then in an early state of decomposition, is poured into.
• A reactor where the organic matter is mixed, stirred, and fermented through the activity of bacteria. It must be closed tightly and completely filled with the fermentation mixture. The absence of oxygen creates an anaerobic environment conducive to the work of bacteria that will feed on the fats and carbohydrates of the biomass. Temperature plays a fundamental role in the productivity of the bacterial flora. Low temperatures slow down the process. The gas generated by the digestion of bacteria rises and separates from the liquid.
• Valves and capture systems that are located at the top of the biodigester. From there, it is channeled to be used directly as an energy source, stored in a tank, or taken to subsequent processes for greater purification.
• Storage tank.
• Discharge tank where the liquid processed matter arrives; that serves as an organic fertilizer that is stable and has no putrid odors.

Biogas also occurs spontaneously in an uncontrolled, unusable way in swamps and landfills where a large amount of decomposing organic matter is trapped. The livestock industry is being held responsible for some of the largest emissions of greenhouse gases precisely because manure generates a large amount of methane and carbon dioxide that is released directly into the atmosphere. An effective solution to reduce the impact of livestock farming on the environment is the incorporation of biodigesters into the sector’s typical production processes. 

In landfills, it is common to install torches that encourage methane combustion, as it produces a much greater greenhouse effect than carbon dioxide.

What is the difference between biogas and biomethane?

Biogas, as we have seen, is primarily composed of methane; however, it also contains some CO2, as well as other gases that interact negatively with metals. Biomethane is the methane gas that is purified in processes subsequent to the production of biogas, which enables its transportation, storage, bottling, and marketing as a quality fuel. 

What are the applications of biogas?

Fuel gas can be used for thermal power generation. With proper purification, it can be packaged and transported in the same way as natural gas.

The combustion of biogas can be used to generate electric power.

The very nature of the raw material of biogas production can support achieving models of circular economy, such as when waste from agricultural activity is used to generate energy that is used to meet domestic demand.

What are the advantages and disadvantages of biogas?

Advantages:

• During production, waste, environmental pollution, and bad odors are reduced.
• It is a source of renewable energy.
• Its production generates organic fertilizer as a by-product.
• The implementation of biodigesters entails financial savings and energy autonomy.
• The technology is applicable on a small scale, especially in rural populations.

Disadvantages:

• Biodigesters require space, which can be an obstacle in densely populated urban areas.
• The production of biogas requires regular maintenance of equipment to ensure efficient operation and prevent any technical problems.
• A constant supply of raw materials must be guaranteed.
• Accidents, such as uncontrolled biogas leaks, can contribute to global warming. On the other hand, poor management of digestate can contaminate water and soil.