Biogas production in Norway is growing rapidly and plays an important role in the transition towards a circular bioeconomy. At the same time, increasing biogas production generates larger amounts of digestate – a nutrient-rich by-product that must be managed sustainably. As production continues to grow, developing solutions that ensure efficient utilisation of digestate becomes increasingly important.
Why do we need new applications for digestate?
Today, the utilisation of digestate in Norway is limited by several factors. Its primary application is as agricultural fertilizer, but agricultural demand is seasonal while digestate is produced continuously throughout the year.
As described in a report by the Norwegian Environment Agency (pdf) (Miljødirektoratet), digestate therefore often requires long-term storage before it can be applied to farmland, creating challenges related to storage, logistics, and transportation.
Long storage periods can increase greenhouse gas emissions and costs, while transporting large volumes of water-rich digestate over long distances is both expensive and associated with additional emissions. These challenges, amongst others, have been documented in the Skitgass project.
The challenges are further compounded because biogas plants are typically located close to where organic waste is generated, whereas agricultural land requiring the nutrients may be located elsewhere. In addition, parts of Norwegian agriculture have limited demand for phosphorus-rich fertilizers (pdf) when phosphorus-rich biogas feedstocks, such as fish sludge, are used. This further restricts the opportunities for direct agricultural use of digestate.
There is therefore a need to develop alternative, higher-value applications for digestate that improve nutrient utilisation and strengthen the circular bioeconomy.
Several technologies are already being investigated to improve digestate management, including hydrothermal processes that can reduce volume and simplify storage and transportation. Such approaches have been investigated in the BioSynGas project. At the same time, there is a need for solutions that recover nutrients from digestate and convert them into valuable new products.
How can BioInnova contribute?
BioInnova addresses these challenges through two complementary activities.
The first activity is a national mapping of digestate from Norwegian biogas plants. The survey includes digestate volumes, feedstock composition, nutrient content, treatment technologies, and the regulatory framework governing digestate management. The results will provide a knowledge base for identifying new utilisation pathways and prioritising future development.
The second activity investigates how liquid digestate can be used as a nutrient source in cultivation systems for nutrient recovery. In particular, the project evaluates the potential for cultivating microalgae, which can simultaneously recover nitrogen and phosphorus while producing valuable biomass. Such solutions may reduce nutrient losses, improve resource efficiency, and support the development of new bio-based value chains.
By combining nationwide mapping with practical cultivation experiments, BioInnova will generate new knowledge and develop solutions that support more sustainable management and utilisation of digestate in Norway.
Project results
- Mapping of Digestate Originating from Norwegian Biogas Plants Using Feedstocks from the Food System (in Norwegian)
- Mapping of Digestate Originating from Norwegian Biogas Plants using Feedstocks from the Food System
- Microalgae Cultivation as a Method for Nutrient Removal and Valorisation of Liquid Digestate from Biogas