Everywhere cereal crops are grown, whether it being wheat for bread or barley for beer, whether it being in Denmark, Germany, or Switzerland, there will always be a side-stream of straw. Primary straw (dry and stock stable) is a wonderful product with such diverse derivatives as feed and bedding for animals, cellulose for packaging materials and even building materials, and as such should be used for industrial or agricultural value generating processes. Some of the primary quality straw is used in CHP plants converted from fossil coal to sustainable biomass. However, the shear amount of straw produced annually, and the logistics leaves large amounts un-utilized in the fields.
In 2020 in Denmark 41.5% of the straw was left in the fields, not being utilized for anything else than being plowed down. Plowing straw down comes with a price of increased unproductive GHG emissions as the straw is decomposed, and the benefits of improving soil fertility and structure by returning a carbon source to the soil. But there are ways to realize the energetic value tied to the above mentioned unproductive GHG emission, whilst not compromising the soil improvement properties of the straw. One of the answers are Biogas Plants.
The 41,.5% straw left in the fields of Denmark, corresponds to 2,276,300 tons. With standard biomethane potentials for straw this is equal to 446,698,151 Nm3 or 4,939 GWh. And this excluding the straw used as bedding material and without compromising any of the other utilization pathways of straw. By digesting straw in a biogas plant you exploit and contain the energetic value stored in the crop, effective converting the unproductive GHG emission to a productive GHG emission, through a manmade recycling carbon loop. The indigestible parts of the straw will be returned to the fields with the digestate in the increased fertilizer product where it will build up long-term soil carbon
Straw is the one of the keys to optimize and increase the biogas production from agricultural residues throughout Europe. As the market for good quality straw will ensure that the demand for these process pathways will be met, secondary quality and un-utilized straw should be freely used for biomethane production, realizing the energetic value tied within this golden resource.