There’s no sense in having a car that can hit 200 kilometres an hour if all you’re allowed to drive is 110. Likewise, there is no sense in running a water treatment plant that uses more energy than it needs to.

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

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The Danish water sector accounts for 2.4 per cent of the country's total energy consumption and 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.

This has inspired the Drøsbro wastewater plant to pursue 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.

Good for the environment - and budget

Recently Kurt headed a project in cooperation with Grundfos that significantly lowered energy consumption. 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.

Grundfos investigated the energy-saving potential in replacing the mixers in two of the tanks with Grundfos flowmakers. The analysis and test demonstrated that replacement would reduce the tanks' energy consumption by 50 per cent with a payback time of four years. It also showed that an overall replacement would equate to a reduction in C02 emissions by around 11,200 kg/year.

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,"adds Helle Katrine Andersen, Head of Water at DANVA.