Technology for spreading the recycled fertilizers.
Photo: Ari-Matti Seppänen
Unprocessed biogas digestate is not a straightforward fertilizer from the farmers’ perspective. Nutrient balances are not optimal and the digestate is dilute. Particularly, in large biogas plants the digestate should be processed into more concentrated and transportable forms.
Biogas plants have faced challenges in finding suitable and cost-efficient downstream processing technologies. The digestate can be separated into solid and liquid forms, in which case the solids (dry matter content 20-30 %) can be transported in a more cost-effective manner. Nitrogen-rich liquid can be concentrated, but many of the tested technologies have not been successful due to the heterogeneity of the material. Therefore, digestate processing is not currently very common, even internationally. Some processing technologies are currently under development.