Every year, around 60,000 tonnes of bottom ash remain after Hafslund’s waste incineration plants have burned residual waste that cannot be recycled. Many people think this ash is merely a waste product, but the truth is that there is gold to be found here—or at least metal. Lots of metal. The ash contains iron, aluminium, copper, zinc, brass and other metals discarded with the waste.

Around 55,000 tonnes of bottom ash from Hafslund’s facilities are sent for sorting each year, and in 2025, 4,505 tonnes of metal were recovered from the ash.

“The fact that more than 4,500 tonnes of metals were recovered from the bottom ash produced by our facilities in 2025 shows that this ash is a valuable resource. The recovered metals reduce the need to extract new raw materials. We also know that there is even greater potential to utilise the resources in the bottom ash,” says Ingrid Dolva, Energy and Climate Adviser at Hafslund Celsio.

Recovering metals from bottom ash can reduce the need for new extraction while also cutting emissions associated with raw material production. This delivers both environmental and economic benefits. The climate savings are difficult to quantify precisely because emission factors vary by metal type, technology, region and data source. A rough estimate indicates that the total emissions avoided by recovering metals from bottom ash at Hafslund’s facilities amount to approximately 15,000 tonnes of CO₂ equivalents* per year.

Collaboration on sorting and recycling

We do not extract the metals on our own. Stena Recycling collects the bottom ash from our facilities and transports it to Oredalen in Asker municipality. There, the ash is piled into large heaps resembling grey mountains before being sent through a sorting facility that separates the various metal fractions from the ash. Step by step, the valuable metals are extracted.

And what comes out is no small amount. Everything from heavy pieces of iron to tiny fragments of aluminium and copper is recovered from the grey heaps, ready to be melted down and given a new life in anything from bicycle frames to building materials. Every now and then, completely recognisable objects turn up too, such as a one-krone coin that has been through the incineration process yet can still be picked straight out of the ash. So there is literally money to be found in the ash.

After the metals have been sorted out, the remaining bottom ash is sent to landfill.

Report shows that the potential is even greater

The report “Bottom Ash: From Waste to Resource”, prepared by Sirk Norge, confirms that Norwegian waste incineration plants already recover large quantities of metal from bottom ash. However, the findings also show that even more can be extracted through better processing and greater collaboration between stakeholders. Analyses in the report indicate that more advanced processing could increase metal recovery from around half of the available metals today to over 80 percent. The most advanced solutions offer even greater benefits, but also require larger investments and more extensive coordination. 

Global demand for metals and other raw materials is increasing, driven in part by electrification, the expansion of energy systems and the green transition. This makes it all the more important to make the most of the resources we already have.

The report also points out that waste incineration plants’ contribution to the circular economy is largely overlooked or unrecognized.

“Recovering large quantities of iron, aluminium and other metals extracted from bottom ash at Norwegian waste-to-energy plants is an important but, unfortunately, rarely discussed measure. This is the circular economy in practice,” says Jon Iver Bakken, Head of Regulatory Affairs and Climate at Hafslund Celsio.

Nationwide, Norwegian waste incineration plants produce a total of around 300,000 tonnes of bottom ash each year. According to the survey, just over half of the metal actually present in the ash is currently recovered – but there is clearly scope to increase this proportion. Some Norwegian plants already achieve recovery rates of up to 93 percent of the available metal fractions when the technology, material volumes and organisation are in place.

The bottom ash itself can also be reused

But it is not only the metals that are recycled. The mineral fraction, which accounts for 80–85 percent of the bottom ash’s total mass, is currently largely landfilled in Norway. In several European countries, however, the treated mineral fraction is already used for various purposes. In Denmark, the Netherlands and Germany, it is used as a substitute for natural aggregates, including in road construction and other building and civil engineering projects. In Norway, too, the mineral fraction could potentially be used as a raw material in road construction, construction materials and cement production. For now, these opportunities are limited by the need for better documentation and unclear requirements for approving treated mineral fractions for further use. The report points out that further efforts in Norway should address precisely this—by establishing a stronger knowledge base and clearer regulations—so that this part of the bottom ash can also be put to use.

Collaboration may be the key

One of the report’s main findings is that the technology needed to increase metal recovery already exists. The challenge lies more in developing solutions that make it profitable to process larger quantities of bottom ash.

To achieve this, it is important that bottom ash is increasingly viewed as a resource, not merely as a residual product. With the right technology, a supportive regulatory framework and collaboration between stakeholders, more of the materials can be returned to the circular economy. This keeps valuable raw materials in use for longer and makes waste an even more important part of the solution to future resource challenges.

The report “Bottom Ash: From Waste to Resource” was prepared by Ive Ekeberg and Torny Madelen Rabak Holstein, summer interns at Sirk Norge in 2026. The purpose of the report was to assess the environmental and economic potential for increased metal recovery and other uses of bottom ash from Norwegian waste incineration plants. Eleven Norwegian incineration plants responded to the survey on which the report was based. 

*Rough estimate based on emission factors from the REdu report (Sirk Norge) and the amount of metal recovered in 2025. The figure represents the difference between producing metals from virgin raw materials and from recycled material. Independent industry figures (CEWEP) provide estimates of a similar magnitude or higher.