Biogas from straw?
Straw is a high-energy raw material that is available in large amounts. It is being actively studied as straw is becoming more and more used as an additional type of raw material for biogas production. Like other energy-intensive raw materials, the efficient production of biogas from straw and the full use of the energy potential of raw materials requires appropriate preliminary preparation for fermentation.
Straw, as a raw material for biogas production, was drew attention in Germany as a result of a search for support raw materials, as an alternative to corn silage. Thus, according to theoretical calculations, the annual available amounts of straw in Germany can replace about 75% of the amounts of corn silage needed today. However, in practice, the use of the energy potential of straw is associated with the mandatory preliminary preparation of raw materials for fermentation due to the presence of lignin shell, which makes it impossible for methanogenic bacteria to access high-energy straw compounds and, accordingly, straw biogas is not produced.
Preliminary preparation of straw for fermentation is mandatory
Today, preliminary preparation of straw for fermentation is implemented in several ways, in particular:
- Grinding straw with a hammer crusher and the further process of its granulation. The process of а straw granulation destroys the density of the lignin shell of the raw material. The next step is the spraying of straw granules with sodium hydroxide, which contributes to the additional destruction of the raw fiber that is contained in the raw materials.
- Grinding, mastication, mixing straw with water and further fermentation process of the mixture. Recent practices confirm the effectiveness of this method of preliminary preparation of straw. From the straw prepared in this way, the biogas yield is increased by 35-50% compared with freshly grinded and ground straw. In addition, this method of pretreatment of straw allows biogas to be produced at a level of up to 80% of the biogas output rate from corn silage.
Straw corn – another promising type of raw materials
Straw is already widely used in biogas production. Corn straw is actively investigated, taking into account the energy potential and its reachability by anaerobic digestion.
On 1 hectare about 10,000 kilograms of corn straw is formed with a dry matter content in the range of 25-40%. Approximately half of this amount of straw can be collected and directed to fermentation to produce energy crops.
According to a number of laboratory studies, corn straw, as a raw material for biogas production, is characterized by a stable controlled course of fermentation.
1 hectare of corn straw can replace about 0.2-0.25 hectare of corn silage (Fleschhut, 2016).
In practice, corn straw biogas is not produced yet, but the dynamics of a comprehensive study of this type of raw material, which has considerable potential, suggests that corn straw is added to the list of raw materials that are effectively fermented in biogas complexes in the near future.
O. Sydorchuk, Ph.D in Technical Sciences.