A change in the mix reduces energy consumption by 50 per cent



The water sector accounts for 2.4 per cent of the total energy consumed in Denmark; 65 per cent of that is consumed in wastewater treatment alone. Not surprisingly energy efficiency has become a top priority for the Danish Water and Wastewater Association (DANVA). DANVA has committed itself to reducing the national water sector’s energy consumption by 25 per cent by the end of 2013.

One wastewater plant, Drøsbro, has risen to the challenge with an on-going and in-depth investigation into how it can save energy:

“We are always seeking new ways to lower our energy consumption. Energy is a big expense and as a public institution we are under constant pressure from local authorities to lower our operating costs and our impact on the environment,” says Kurt Poulsen, Production Manager at Drøsbro. Recently he headed a project in cooperation with Grundfos that significantly lowered energy consumption.

Good for the environment – and budget

Wastewater entering the plant at Drøsbro goes through a series of processes to extract the clean water. Mixers are used to move the water between the various tanks, using ten per cent of the plant’s total energy consumption in the process. Together with Grundfos, Drøsbro set out to investigate if it were possible to save energy by replacing the mixers in two of the tanks with Grundfos flowmakers.

The analysis and test demonstrated that the replacement had reduced the tanks’ energy consumption by 50 per cent, which is naturally reflected in the energy bill. It also showed that the overall replacement would equate to a reduction in C02 emissions by around 11,200 kg/year.

“With this project we once again proved that it pays to do a thorough analysis, because huge amounts can actually be saved once you look into optimising your processes. In this case we were using a lot of unnecessary energy keeping the water flowing in the tanks,” Kurt says.

Hopes for the future

DANVA is currently evaluating its 25 per cent energy reduction goal, with results like the ones achieved at Drøsbro furnishing high hope for the upcoming results.

“The results from Drøsbro prove that our goal of a 25 per cent energy reduction by 2013 is not only an ambitious but also a realistic one. As we have seen with other cases it really pays off to take a close look at the processes as the potential savings are often bigger than first anticipated,” says Helle Katrine Andersen, Head of Water at DANVA.

An experienced partner

With increasing demands from legislators, and general pressure to keep running costs as low as possible, Kurt says Drøsbro needs to stay on top of its game in the energy arena at all times. He adds that it’s a situation in which it is a real advantage to work with an experienced partner. He says:

“There is no sense in buying a car that can hit 200 kilometres an hour if all you are allowed to drive is 110. Likewise, there is no sense in buying a pump or a mixer that uses more energy than you need. Grundfos has the experts to find the optimal solution with the minimum energy consumption.”

As a direct result of the projects’ success, Drøsbro is beginning another project together with Grundfos to optimise the mixers in their sludge tanks.


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Danish wastewater plant Drøsbro has reduced its tanks’ energy costs by 50 per cent following some rethinking – and replacing.





The Drøsbro plant tested the AFG.22.130.77 flowmaker from Grundfos.

The payback time on implementing the new flowmakers will be around four years.


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