Danish Water Companies Aim to Turn Waste into a Resource

HOFOR, Greater Copenhagen’s utility company, is leading a new project to explore how iron oxide in ochre sludge, a by-product from drinking water production, can be reused—potentially in biogas production. The goal is to reduce CO₂ emissions, minimize environmental impact, and save costs.

“This is the first project of its kind in Denmark,” says Anne Holm, project manager at HOFOR. “HOFOR and other Danish water companies produce more than 6,400 tons of ochre sludge every year. Currently, two-thirds of it is sent to landfill, which harms the environment and incurs high costs. We want to investigate how these many tons of sludge can instead be utilized for beneficial purposes.”

Partners in the project include VandCenter Syd, Frederiksberg Forsyning, biogas experts Fremsyn, and water technology firm Krüger. Iron oxides from the sludge may be used to replace synthetic chemicals currently used in biogas plants to remove toxic sulfur gases. Unlike synthetic chemicals, which emit CO₂ during production, the iron oxides are already available as a waste product.

HOFOR supplies drinking water and handles wastewater for over a million people in the Copenhagen area. Anne Holm emphasizes that the company is continually working to reduce the use of new materials and increase recycling: “At HOFOR, we are constantly improving how we use our resources to support a circular economy, where we rely on what we already have instead of producing new materials.”

The project also aims to reduce costs for water companies by avoiding expensive landfill disposal. It will examine whether supplying sludge to biogas facilities is a cheaper alternative and assess potential environmental impacts and other possible uses for the sludge.

The project runs until December 2027 and is supported with DKK 1.5 million from VUDP, a funding program for innovation in the Danish water sector.