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Landia lands sludge digester retrofit with Scottish Water

Denmark-headed pump and mixer manufacturer Landia A/S has announced that it has won an important new order with Scottish Water to retrofit two sludge digesters with its GasMix mixing systems. Two partly underground cast in-situ digesters (17m by 20m) at Nigg near Aberdeen will now be served by the externally- mounted GasMix – designed for easy maintenance and greatly improved gas yields.

Landia can retrofit its GasMix digester mixing system for steel or concrete tank (photo courtesy Landia).

Landia can retrofit its GasMix digester mixing system for steel or concrete tank (photo courtesy Landia).

According to Landia, the previous mixing system was problematical and under-performing. Now each digester at Nigg will be fitted with two diametrically opposite Landia chopper pumps, which draw thick liquid from the bottom of the
tank, where solids are chopped to accelerate the digestion process and prevent clogging of pipes and nozzles. All parts of the system are removable from the outside of the tank.

In the first stage of the mixing process, the liquid will be injected into the upper half of the tank, while biogas is aspirated from the top of the tank and mixed into the liquid.

This not only has the benefit of reducing buoyancy at the surface of the liquid but also continues to mix after the pumps are switched off thanks to the rising gas bubbles.

With 2 x 30kW systems on each 4 000 m3 digester, the installed power equates to a very economical 15 watts per cubic meter. When factoring in reduced running times which can be as low as 20 minutes in the hour, energy savings can be substantial. In addition, reduced running times means that pump-wear components last significantly longer.

Apart from installations in Denmark, this latest order for Landia’s GasMix digester mixing system follows successful installations in the UK such as in Jersey, London, Shropshire, and Somerset as well as numerous other overseas projects, including Australia, China, Germany, Ireland, Malaysia and the United States (US).

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