Kalundborg Symbiosis is a circular economy collaboration project between the City of Kalundborg, Denmark, and a number of private companies in the area.
These companies benefit from the residuals from their collaboration partners. One partner’s waste becomes another partner’s resource. This model was developed more than 40 years ago and was founded with economic interests in mind, and it was not until later that the environmental benefits of the symbiosis were recognized. In Kalundborg, the wastewater from the industry is used for biogas production, heat pumps for district heating, and they are looking into phosphorus and nitrogen removal and production.