Case

Cost-effective, eco-friendly centralisation project at Danish wastewater plant

With help from AVK, Mariagerfjord wastewater plant has been able to expand its capacity, cut costs and significantly reduce their environmental impact.

Looking at the population growth over the next 25 years, combined with a desire to greatly improve both the economic and environmental benefits of local wastewater treatment, Mariagerfjord Municipality has decided to build a new state-of-the-art wastewater treatment plant. With the supply of a wide variety of valves, AVK is proud to have been part of this newly established plant in the North of Jutland.

Today, the plant treats wastewater from approximately 75,000 population equivalents, but it is constructed to handle a wastewater amount equal to a population of 110,000, and to meet even stricter environmental legislation in future. The new plant is replacing 10 smaller plants, which in total have treated 5-6 million m3 of wastewater annually where only about 2 million m3 are from citizens and companies. The remaining wastewater is rainwater led into the wastewater sewers. An area that Mariagerfjord Water will optimise by making a 2-string pipeline where old 1-stringed network still exist and by replacing the combined sewers with separated sewers.

Significantly reducing sludge amounts
Centralising wastewater treatment in one large plant is a growing trend in Denmark. It makes it possible to treat the sludge and then stabilise it in an aerobe process in a digestion tank, where the organic material is transformed into methane and carbon dioxide. This, considerably, reduces sludge amounts making it a huge gain for the environment.

More specifically, a 2,000 m3 digestion tank reduces the amount of sludge, and makes it possible to produce bio gas that is transformed into energy used for heating and electricity. The digested sludge is dewatered in decanters and then transported in closed semitrailers, which is a cheap and “smell-safe” way to store the sludge. The cleaning process is so efficient that the discharge of organic materials, nitrogen, and phosphorus is significantly less than the total discharge of the 10 wastewater treatment plants it is replacing.

Eco-friendly discharge
Some of the old wastewater treatment plants discharged their cleaned wastewater into the fjord of Mariager. The maximum permitted amount of phosphorus is about a quarter of what it is for discharging into the ocean. The new wastewater treatment plant will be leading its cleaned wastewater 3.8 km out in the ocean of Kattegat, but will still comply with the stricter requirements for discharging into a fjord.

Cost effective centralisation
In addition to the environmental advantages of centralising, the cost of optimising the operations and maintaining the buildings is significantly reduced compared to that of many small plants distributed at various locations.

Also, by placing the plant 27 metres above sea level and discharging the wastewater through a pressure gravitational network, cleaned wastewater will most often run to Kattegat by gravity, and only if the pressure on the network increases, an installed pump will be used.

The construction of the new Mariagerfjord wastewater plant began in March 2012 and was finished in the fall of 2013.

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