New invention to save energy at water purification plant

City of Aarhus

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Arhus is Denmark’s 2nd largest city and the  financial centre of the Central Denmark Region. The city has a catchment area of 1.2 million people within a one-hour travel range and is well connected to Copenhagen and Hamburg.

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By Hans Christian bugge, November 18, 2013

Aarhus Water has joined forces with DHI and DONG Energy to develop a new sensor able to produce substantial energy savings. The sensor is used to optimise the aeration process necessary to purify waste water from sewage plants

Experiments are being conducted at the Aarhus plant to optimise purification of waste water even more. The aeration process is the subject of particular focus, as it is part of the overall process used to purify water.

Aeration is the most energy-intensive process at the plant. That’s why there are substantial savings to be made from thinking out of the box and deploying new technology to reduce the energy budget.

Sensor measures oxygen content
Water purification is achieved using sedimentation, passing the water through sediment which contains a range of bacteria and micro-organisms that reduce particulate matter in the water. To enable the micro-organisms to live and convert the particulate matter, the oxygen content of the water has to be sufficient. And that’s where a lot of energy is used. To oxygenate water, a number of diffusers are installed in the bottom of the sedimentation tanks to blow air in. This is a mechanical process that uses a lot of energy.

Although Aarhus Water already achieved energy savings by replacing surface aerators with diffusers mounted on the bottom, the new sensor can make significant improvements. Aarhus Water is developing a new control system in consultation with DHI and DONG which can optimise aeration via signals from the new sensor,

The sensor measures oxygen uptake in the water, and uses it to control how and when aeration takes place. This enables optimisation of energy consumption, with expected savings of 10% on electricity bills in the process. That will be the equivalent of 150,000 kWh per annum.

Besides having a purely practical energy-saving function, the project is also used for demon-stration purposes, to identify other advantages and improvement potential derived from the sensor.

DONG Energy is  one of the partners in the project because the company is highly interested in developing new technology able to reduce energy consumption, and thus reduce CO2 emissions. The water sector is particularly interesting, as it uses over 2% of Denmark’s total electricity consumption.



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