The board of BIOFOS, which treats wastewater for Copenhagen and 14 other municipalities, is due on 13 November 2026 to choose how to rebuild metropolitan treatment. Rebuilding all three plants in place is estimated at DKK 27.1 billion; closing Lynetten and building a new plant at Prøvestenen at DKK 26.5 billion, both at 2025 prices.
Land changes the arithmetic
Management recommends the Prøvestenen option. Net of the sale of the Lynetten site and an allocation of transmission costs, BIOFOS puts its own cost at DKK 21.2 billion, against DKK 25.7 billion for staying put. The site sale is estimated at DKK 3.7 billion gross, within a range of DKK 2.0 billion to DKK 8.5 billion, and would come 15 to 20 years after a decision.
Why capacity must grow
BIOFOS says it must raise treatment capacity by about 40% by 2045, as its load rises by about 620,000 person equivalents. It cites regional growth, tighter nutrient limits, a mandatory fourth treatment stage, climate change and security threats.
Estimates, not budgets
External reviewer EY raised contingency reserves to 75% for Lynetten and Damhusåen and 50% for other elements, against about 10% in the original estimate. The board is asked only for a principle decision and a planning budget of DKK 612 million for 2027 to 2031. A final investment decision is expected around 2031.
Bills would follow
BIOFOS projects its charge in the Lynettefællesskabet area rising from DKK 9.81 per cubic metre in 2027 to about DKK 23 in the early 2040s. Its share of HOFOR's Copenhagen water price would rise from 22% in 2026 to 36% by 2043.
What HOFOR is building in Copenhagen now, which tunnel contracts are in procurement, how the programme is financed and which decisions come next are set out in the report. The full report, Water Infrastructure Investment and Project Pipeline in Copenhagen, is available for USD 249. For a free overview, see Copenhagen City Snapshot.