Kalundborg has shared its leftovers since 1972
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In the Danish port of Kalundborg, seventeen public and private companies have been exchanging water, energy and materials since 1972: what leaves one plant goes into the next. Every year Kalundborg Symbiosis saves 4 million m³ of groundwater and 586,000 tonnes of CO₂.
In the early 1970s the Kalundborg refinery flared off a gas it had no use for, its “eternal flame”. Gyproc, which made plasterboard in the town, began using it to dry its boards: the first exchange of what the town now calls the Symbiosis. Gyproc later replaced natural gypsum with industrial gypsum from the Asnæs power station. Both exchanges ended when the refinery and the power station changed how they operate, and Saint-Gobain Gyproc is moving its production to neighbouring countries, keeping only sales and logistics in Kalundborg.
The Symbiosis now has seventeen members: Novo Nordisk, Novonesis, Ørsted, the refinery, Unibio, Boehringer Ingelheim, the APM Terminals port terminal, the municipality and others. Novonesis employs about 750 people there and makes enzymes for detergents, animal feed and food. The water and heat utility, Kalundborg Forsyning, runs more than 30 kilometres of pipes laid between the partners, supplies surface water to the large plants and uses ozone at its treatment plant to remove pharmaceutical residues.
The Symbiosis publishes its figures. Every year surface water saves 4 million m³ of groundwater, 586,000 tonnes of CO₂ are avoided and 62,000 tonnes of residual materials are recycled. The Symbiosis has cut its CO₂ emissions by 80% since 2015, and the energy produced locally is carbon neutral. Its secretariat, based at Campus Kalundborg, looks for new exchanges plant by plant: in December 2025 it presented a process that recovers more than 99% of NMP, an industrial solvent, cutting 1.6 tonnes of CO₂ per tonne treated.
Heat is the open project. In October 2022 Novo Nordisk and Novozymes, now part of Novonesis, decided to connect their shared site to a district cooling system: the heat taken out of the plants can then warm homes through a heat pump. The Symbiosis estimates that Kalundborg’s industry gives off enough to heat more than 40,000 households, and it has invited the neighbouring municipality of Holbæk, where 17,500 households heat with natural gas. “Today, the excess heat from our production in Kalundborg is not used, as we have not had the opportunity to collect it,” said Jesper Haugaard, vice-president of the Symbiosis and head of production at Novozymes.
The model travels: in 2024 the secretariat screened possible exchanges in the Santa Cruz industrial district of Rio de Janeiro, and in 2026 it is working with the Western Cape province in South Africa. In Kalundborg it welcomes companies, universities and delegations on request through the form on its website. The presentation, tailored to the group, lasts up to two hours and includes a guided symbiosis tour of about thirty minutes if the group comes by coach. 2026 prices: 2,000 euros excluding tax for 5 to 30 people, 4,000 euros for 30 to 50.
Since 1972, seventeen public and private companies in Kalundborg have exchanged water, energy and materials through more than 30 kilometres of pipes. Every year the Symbiosis saves 4 million m³ of groundwater and 586,000 tonnes of CO₂, and recycles 62,000 tonnes of residual materials. Its CO₂ emissions have fallen by 80% since 2015. Heat from the plants could warm more than 40,000 households.
Photos: © Kalundborg Symbiose (1 2 3 4 5).
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