Cleaning urban road runoff with new green technology

State of Green
By State of Green, November 09, 2018

A unique water treatment plant has seen the light of day. The innovative cleaning technology is the first large-scale attempt to solve the challenges cities face with road runoff that pollute the aquatic environment and groundwater or that has to be pumped all the way through cities to be cleaned at sewage treatment plants.

Denmark’s first water treatment plant of its kind cleans 110 litres of road runoff per second. The plant is established in Ørestaden, Copenhagen by greater Copenhagen’s supply company HOFOR and CPH City & Port Development. Professor Marina Bergen Jensen from the University of Copenhagen has invented the plant’s cleaning technology.

Clean enough to be led directly out in nature

After a series of trials at smaller plants, the method can now be used on a larger scale to make the road runoff from Ørestad South clean enough to be directed directly into a nearby park (Amager Nature Park).

“We have invented a green technology inspired by the way in which substances are transported through the soil in the Danish nature. The so-called double-porous filter, which we have developed, can clean the road runoff completely without the need for electricity or chemicals”, said the inventor of the filter, Professor Marina Bergen Jensen from the University of Copenhagen.

-Related solution: Treatment of road-runoff with dual porosity filtration (DPF)

Through pipes, the water from the roads is led to the purification plant, where the first step is to clean it for leaves, plastic capsules, bags and other coarse particles. From here, the water flows into a kind of sandwich filter, where the double-porous filtration occurs. By using gravity, the water flows through the treatment plant, which catches and cleans very small particles and other pollutants. Afterwards, the water is directed out into the Amager Nature Park.

New method can solve multiple urban challenges

The new water treatment plant is a major improvement for both nature and climate. Road runoff in urban areas may be contaminated with e.g. microplastic, heavy metals and nutrient salts. This can contaminate lakes, streams and groundwater if led directly into nature. An alternative is to pump the water into a sewage treatment plant together with wastewater. However, this method utilises a lot of energy.

To solve this problem, the Danish utility company Hofor has established its first local, large-scale facility for cleaning road water.

“We have chosen this method because it solves a number of challenges with road runoff. By cleaning it locally, we can use the water locally for recreational purposes instead of pumping it all the way through the city and out to a sewage treatment plant. It is better for the local area and better for the environment. At the same time, we reduce the amount of rainwater that ends up in the sewage system, and this helps to ease the pressure on our sewers when it rains heavily”, said Claus Mouritsen, Project Manager at HOFOR.

Paving the way for cities to protect the aquatic environment

In Denmark, road runoff has historically not been cleaned to the same extent as for instance wastewater. However, the rising rainfall makes the need to retain the water locally more urgent, and at the same time, it is important to clean the road water before directing it to the aquatic environment.

“Society has become more aware of protecting the aquatic environment, but environmental authorities have lacked methods of dealing with urban emissions. I hope that this solution can pave the way for climate-resilient cities with a greater focus on protecting our nature – both in Denmark and abroad”, said Marina Bergen Jensen.

-Related solution: Climate adaptation at Bryggervangenand Skt. Kjeld’s Square

Right now, Marina Bergen Jensen is focusing on the further use of the technology. After a trip through the double-porous filter, the water quality is so good that the road water could be used directly for toilet flushing, car wash or similar purposes.


  • The idea for the technology comes from the Danish nature. The water treatment mimics the processes, which takes place underneath the Danish mould.
  • The water treatment plant is Denmark’s first of its kind for road water. It can clean 110 litres per second – that is more than one person’s water consumption on a whole day.
  • The plant measures a total of 51 x 13.5 metre.
  • The plant does not use any power, chemicals and it is both silent and odourless.
  • The plant removes tire cover (micro plastic), dust, brake lining, soot particles, oil, heavy metals and phosphorus (nutrient), which is often the reason for unclear water.


Source: Ingeniøren (in Danish)
Photo credit: HOFOR

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