Åby treatment plant gets a boost with new filter sand from Dansand

Aarhus is growing, and this puts pressure on the city´s wastewater treatment plant. After 30 years of faithful service, the sand in Åby treatment plant has beenreplaced by new filter sand from Dansand and, despite using half the amount of filter sand in the cells, the filtration process is just as effective. The used filter sand has been recycled in a local construction project, resulting in big CO2 savings.

Åby treatment olant in Aarhus deals with wastewater from the equivalent of 84,000 people – that´s nearly a quarter of Aarhus municipality´s residents. The treatment plant is a so-called MBNDKF plant. The abbreviation stands for mechanical purification, biological purification, nitrification, denitrification, k(ch)emical purification and finally filtering through the sand filter – this is the process the wastewater goes through before being released into Aarhus harbour.
After 30 years´ service, it was time to update the plant. The old filter sand was removed from the plant´s 12 sand filters before they were re-filled with 210 tonnes of new filter sand from Dansand. During the renovations, it was decided to try using a smaller filter layer, and this has been a huge success.

Significant savings with new filter sand

After Aarhus Water replaced the sand in the sand filters and also renovated various worn parts at the plant, the back pressure in the air system halved, and the amount of filter sand could be reduced – without compromising the efficiency of the plant. Purification efficiency is vital as Aarhus is one of the fastest growing cities in Denmark. Since the plant was built in 1993, the municipality´s population has increased by more than 100,000 to just under 367,000 in the first quarter of 2024. Naturally, this puts pressure on the infrastructure, including the city´s wastewater treatment plant. With the new filter sand and other measures, the plant is well prepared for safe operation well into the future.

Reusing the filter sand locally

The 210 tonnes of sand thatserved as the last filter in the purification process at Åby treatment plant´s 12 sand filters haven´t just been dumped in landfill. Instead, Aarhus Water found a solution whereby the sand could be reused in a sewerage system project just a few kilometres away. This has led to an 86 % reduction in CO2 as compared with other methods of disposing of used filter sand.

Sources:

Recycling the sand from treatment plant saves resources, CO2, money (aarhusvand.dk)

AARHUS IN NUMBERS (aarhuskommune.dk)