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Hjørring Water


Although one of its main benefits is in significantly improving gas yields, Landia’s GasMix system is also playing a leading role in eliminating downtime, improving maintenance and reducing health and safety risks, as a wastewater treatment plant in northern Denmark has discovered.


Located just outside Hjorring, the Renseanlaeg plant, built in the 1970’s, is in a huge, sparsely populated region, with around 66,000 people living in an area of 926,000 square miles.  In addition to domestic waste, the site also takes in up to five tankers worth of herring, salmon and mackerel waste every week, depending on the season and EU quotas.  From two of 11 other plants in the region, surplus sludge is also brought to Hjorring for processing.


“Our main priority at the moment is to reduce solids”, explains Jacob Andersen, Head of Water & Wastewater for Hjorring Vandselskab A/S.  “That said, we do produce 800,000 kWh of gas pa.  This has increased since we brought in Landia’s GasMix, which only has to run for a very brief period each day.  In time we hope to retire our old generator, which is expensive to run, and introduce a new engine in order to optimise our gas production”. 


He added:  “Depending on the amount of fish waste we receive, our dry solids content varies from around two percent to six percent. We have two digesters and it only takes only a quick visible inspection of the one with GasMix to see that compared with the other tank, the whole digester is now being mixed properly. The sludge is far more alive.  Before, we had a settling problem with a floating layer.  We also no longer have any settlement problems with sand and gravel”. 


Installation of the externally-mounted GasMix was a simple retrofit (replacing a compressor) – requiring little more than holes to be drilled into the side of the existing tank.  The system comprises solids-reducing chopper pumps and a self-aspirating system.  By having everything on the outside, routine maintenance has been made much, much easier.  


“Previously we had gas lancers by compressor”, continued Jacob Andersen.  “It wasn’t a question of if they would break down, it was merely a matter of when!  Something always got stuck, so we were always running the risk of mixer failure.  But now, we have a mixing system with no moving parts in the tank.  This plant at Hjorring isn’t the largest, but recovering a broken-down mixer was a big operation.  Removing the lid at any AD plant is a big safety risk, but since we’ve had Landia’s GasMix, we‘ve not had any events to deal with.  It is extremely reliable, so our maintenance costs and downtime are nothing like what they used to be.  Together with additional gas, Landia’s GasMix brings a wide range of important benefits to our plant”.