Case story

Unmanned treatment plant with actuator technology

For a treatment plant to be unmanned, it is essential that the daily processes are completely automatic. This is the case in Denmark at two smaller treatment plants in Holbæk Municipality, where a total of 19 actuators from LINAK automatically regulate the amount of sludge in the plants' sludge beds.

The two unmanned plants in Svinninge and Gisline are Kim Skov Hansen's responsibility. He is the Production Technician at FORS A/S, which is responsible for wastewater treatment in the municipalities of Holbæk, Lejre and Roskilde. On a daily basis, the facilities are unmanned, but Kim Skov Hansen checks in a couple of times a week to make sure that everything is as it should be. Using actuators from LINAK, there are never any problems:

Previously we had a pneumatic solution installed but there were problems all the time. Water would build up in the compressed air system if we didn’t inspect and remove moisture from the system from time to time. The electric actuators are a much better solution as they don't need to be maintained or inspected as often,” says Skov Hansen.

 

Automatic valve regulation

The actuators at the plants in Svinninge and Gislinge are of the LA36 variant and are used primarily to regulate the sludge quantities in the sludge beds. The sludge beds are supplied with excess sludge from the treatment plants once a day when the electric actuators open the knife gate valves. As Skov Hansen explains:

The opening follows a fixed cycle, which is set and takes place automatically. But sometimes the valves need to be open for shorter or longer periods of time than the fixed cycle dictates. In these instances, I make an assessment together with my laboratory assistant and, if needed, we can easily regulate the opening sequence from the computer via remote access.

The sludge beds work by the excess sludge running into the bed, after which the water slowly seeps away while the sludge is left behind. After 10-11 years, the beds are drained of sludge, and the process starts afresh. It is important to give the beds a break now and then to allow them to dry out. During these periods, Skov Hansen simply deactivates the actuators' fixed opening frequency.

Unmanned treatment plant with actuator technologyA sludge bed is supplied daily with excess sludge.
 
 

Benefit of electric actuators

Skov Hansen is delighted to have switched from air to electric actuators on the 19 knife gate valves:

I personally think it's nice to have electric ones. There's no maintenance. We have had the actuators for five years now, and nothing has ever gone wrong with them. In the beginning there was just a control box that needed adjusting - but since then everything has run impeccably”. 

In the three plants managed by Skov Hansen, there are still areas that would benefit from replacing the current solutions with electric actuators in the future: 

I can easily see Fors A/S using LINAK actuators in other areas. It would be easy to mount them in those areas where we currently use air - there are already flanges and everything else in place, so it's just a matter of making a control. Using the electric solution frees up resources because we avoid having to air the valves,” concludes Skov Hansen.

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