Biogas: renewable energy from residual materials

What is Biogas?

Biogas is a natural gaseous fuel.

It is obtained through anaerobic digestion, as a product of the fermentation of substances of organic origin, both animal and vegetable, by bacteria that live in the absence of oxygen, inside specific digesters.

The gas obtained from this fermentation can be transformed, through cogeneration plants, into electricity and thermal energy, or used directly to replace the methane from vehicles to power means of transport.

Biogas is a renewable energy source.

It is completely ecological. Obtained from residues from breeding farms (slurry, manure and feed scraps), food production (fruit and vegetable leftovers, remnants of meat, fish and milk processing, leftovers from beer manufacturing, food scraps, etc.) and waste-water from industrial and municipal purifiers, it is an excellent solution for the disposal of organic waste.

The digestates obtained as a by-product in the biogas production process can in turn be used as a high-quality fertilizer.

Moreover, it does not affect the amount of CO₂ emissions. The production process generates only the amount of CO₂ absorbed by plants through photosynthesis.

What is Biogas made of?

CH4

50-70%

CO2

30-45%

H2S

0,1%

+ Traces of
other gases

In general terms, more than half of biogas is methane (CH₄), while the rest is made of carbon dioxide (CO₂) and other trace gases: CH₄: 50-70% CO₂ + CO: 30-45% H₂S: 0.1% traces of other gases.

The percentages may vary depending on the type of original organic substrate, its biodegradability and the processing conditions.

It is precisely this type of composition that means it can be used as a gaseous fuel in a cogeneration plant for the production of electricity and thermal energy.

What is anaerobic digestion?

Anaerobic digestion (AD) is a biochemical process which, in the absence of oxygen, leads to the degradation of complex organic substances with the production of biogas and digestate.

The process is carried out by different bacterial strains, each of which has a well-defined role and works to create a product that acts as a substrate for the action of the next bacterial strain.

Anaerobic digestion is the key, totally sustainable phase for the production of clean energy from renewable sources.

From anaerobic digestion to Biogas

Biogas is therefore formed thanks to anaerobic digestion in a watertight fermenter in which the organic substances undergo the processes of:

hydrolysis (liquefaction)

decomposition into volatile fatty acids, acetic acid, butyric acid, propionic acid (similar to the preparation of ensiling)

transformation into methane (CH₄), carbon dioxide (CO₂) and water (H₂O).

The fermentation process is carried out by different bacterial strains that live in a mixed cultivation inside the fermenter at a temperature between 38 °C and 55 °C and with a pH of around 7-7.5.

There is a close correlation between the digestion temperature and the residence time in the fermenter. The optimal residence time is 40-60 days, but with temperatures above 45 °C it can be reduced to 25 days.

Fermentable substances

Fertilizers derived from bovine slurry used in agriculture

Solid bovine manure / Pig slurry / Solid pig manure / Sewage

Agricultural residues from mown grass

Beet leaves / Silage

Residues derived from the agri-food industry and the manufacture of beer

Fruit leftovers / Vegetable leftovers / Rapeseed expeller / Cereal residues / Borlanda (from potatoes, beer, etc.) / Molasses

Residues from municipal slaughterhouses (rumen leftovers, fat separated by flotation)

Fat separator / Food waste / Large kitchen waste / Domestic waste-water

In principle, during the approval process it is necessary to check for disinfection measures for certain areas belonging to this group.

RENEWABLE ENERGIES

Green in our DNA

In a world increasingly in search of sustainability and protecting the environment, we want to make our contribution with an energy that does not run out, does not pollute and that comes from nature.

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