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Case story

Modernizing secondary clarifier tanks with LINAK actuators

The Danish water utility company, Aarhus Vand, wanted to make better use of their secondary clarifier tanks for wastewater treatment. This meant a switch from manual handling of the water in the tanks to automatic regulation with electric actuators from LINAK. For the sub-department Egå Wastewater Treatment Plant, one of the benefits has been a 10% higher tank capacity.

Secondary clarifier tanks at Egå Wastewater Treatment Plant

When wastewater is treated, active sludge is added. The sludge cleans the water and is then removed again. This process takes place in secondary clarifier tanks. Sludge is heavier than water and will, therefore, settle to the bottom when the water is still. The sludge is then discharged through the bottom of the tanks and reused to clean new wastewater.

Egå Wastewater Treatment Plant has eight rectangular secondary clarifier tanks. According to Jakob Kaltoft, Operations Manager at Aarhus Vand, it is important that the water is distributed equally in the tanks, regardless of the water amount: ”If too much water gets into one tank, there is a risk of sludge escape, which is disastrous for the environment. This must not happen.


Modernizing with electric actuators

Jakob Kaltoft wanted to modernize and optimize the secondary clarifier tanks. The tanks are in good condition, but when building the plant, it was decided to make rectangular tanks due to space. As Kaltoft says: ”If more space had been available, circular tanks would have been the optimal choice. Many other plants are built this way and it is, therefore, much easier to distribute the water evenly. But I had to work with what I had.

This is why he began looking at the inflow of water at the nearby Åby Wastewater Treatment Plant as early as 2008. Together with a partner, he then developed a solution using electric actuators, which automatically distribute water into the tanks. The project showed excellent results, and Kaltoft then implemented the concept at the larger Egå Wastewater Treatment Plant:

At Egå, we mounted 16 LINAK® actuators – two on each of the eight tanks. The actuators could communicate with the treatment plant systems via Profibus. It is no secret that in the beginning I struggled to get the system up and running, due to insufficient documentation, but I succeeded in the end”, says Kaltoft.

The documentation has since been updated so that new systems are easier to set up.

LINAK actuator

From manual to automatic adjustment

At Egå Wastewater Treatment Plant, the flow distribution of the water to the secondary clarifier tanks is now completely automatic. The system notifies the actuators of how much they need to adjust to ensure an equal amount of water in all eight tanks. As Kaltoft says: ”Previously, an employee would have to manually turn a handle to distribute the water. How much to turn the handle was a bit of a guessing game and it was therefore difficult for us to make full use of the tanks' capacity. I have kept the handle, but installed an actuator to tip the weir - so we can still manually adjust it in an emergency. But day-to-day operation is electric.

By automating the flow distribution, Jakob Kaltoft estimates that the plant capacity has increased by around 10%. Egå Wastewater Treatment Plant can now handle 10% more water than previously. This optimization is essential for plant performance, especially during periods of heavy rainfall, when large quantities of water suddenly must be processed.

Hole for processed waterThe water pours in and makes the heavy pump redundant.

The heavy pump is gone

While modernizing the secondary clarifier tanks, Jakob Kaltoft had another great idea involving electric actuators: ”I do not know why we did not think of it before! Previously, when we emptied our tanks, we cleaned them by hauling a large and heavy pump to the bridge. The pump would pump the cleaned water into the tanks to rinse them,” explains Kaltoft.

The new solution was to make a hole between the cleaned water and the secondary clarifier tanks and add an electrically-controlled valve. Kaltoft continues: ”Now when a tank is to be cleaned, a LINAK actuator opens a valve and the water pours in. It is so simple, but not having to use the heavy pump anymore makes a great difference to both working environment and power consumption.


Multiple applications

The secondary clarifier tanks are not the only place at Egå Wastewater Treatment Plant that uses LINAK actuators. In fact, Kaltoft estimates that they have more than 70 LINAK actuators at the plant: ”We use them in so many places – especially where we once used pneumatics. And it really pays off. Electrical installations have to be made anyway – with pneumatics you need an additional installation. It is also more costly to use air, as it uses more energy and can cause leaks,” says Kaltoft and adds: ”For us, it is also important to have simple installations, because it is expensive to hire electricians. A LINAK actuator is a simple component to install for a simple task. And it is, of course, a benefit that the actuators from LINAK do not need servicing.

LINAK actuators at Egå Sewage Treatment PlantMore than 70 actuators are installed around the Egå plant.

The future

Jakob Kaltoft estimates that Egå Wastewater Treatment Plant has experienced an increased energy efficiency of around 30%. The modernization costs, therefore, have a good payback time, while the environment is protected from unnecessary energy consumption, and capacity is increased. As Kaltoft says: "We have really benefited from the optimizations made, and I am certain that other treatment plants would benefit just as much from similar modernizations."

But it does not stop here: ”I am constantly thinking about how we can become even better. And I can imagine using LINAK actuators in even more places. For example, I am considering using them for our decanter gutters. Our current installation is far too complicated, with too many cables being stretched too far. A simple installation with LINAK actuators would be a better solution here,” concludes Kaltoft.

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