The new wastewater treatment plant at Metsä Group’s bioproduct mill in Äänekoski has been started up.
“Half of the wastewater from the existing mill was directed to the new treatment plant as part of its test use in May. Since mid-June, all of the wastewater from the existing mill has been directed to the new plant,” says project manager Johanna Harjula from Metsä Fibre.
The old wastewater treatment plant is being dismantled, and the old aeration basin will be replaced by a new safety basin.
Permit requirements have been met
The commissioning of the new treatment plant was successful.
“The biota needed for the treatment process was grown to the desirable level in about a week. Daily laboratory studies are showing that we have met the permit requirements with excellent results,” says Harjula.
Treated water has been directed to Lake Kuhnamo since late May. The sludge has been delivered to the EcoEnergy biogas plant next door for treatment.
We have met the permit requirements with excellent results.
According to process engineer Perttu Muhonen from Aquaflow, the company responsible for equipment delivery and process implementation for the treatment plant, the construction and commissioning were completed according to plan.
“As part of normal commissioning, we will still be making some adjustments to the equipment. We are currently focusing on finding the right balance of nutrients and optimising the sludge removal.”
“Policing” the treatment result
Similarly to the old wastewater treatment plant, wastewater runs through neutralisation, cooling and aeration stages to clarification in the new treatment plant.
“In the new treatment plant, it is also possible to direct the water into flotation basins and disc filters for tertiary treatment. In this phase, non-biodegradable matter and nutrients are removed from the water by means of chemical treatment,” Muhonen explains.
This is the first treatment plant in Finland with a tertiary phase of this exact type.
“The tertiary phase is something of a ‘police filter’. When needed, it is used to ensure that we meet the permit requirements under all circumstances. We will also be testing the tertiary treatment in July,” Harjula adds.
Full readiness to start up the bioproduct mill
The bioproduct mill will generate the same amount of wastewater as the existing mill – that is, around 50,000 cubic metres per day. The new treatment plant’s capacity is 70,000 cubic metres per day.
“The wastewater generated by the bioproduct mill is more concentrated than that from the existing mill. In terms of COD load, which indicates the chemical oxygen demand, the load from the bioproduct mill will be 110 tonnes per day, as opposed to 60 tonnes per day from the existing mill,” says Harjula.
The new treatment plant’s capacity is 70,000 cubic metres per day.
She is convinced that the treatment plant will be well-prepared for treating the wastewater from the bioproduct mill, which will be started up in mid-August.
“To a certain extent, the start-up of the bioproduct mill will also mean a new start for the treatment plant, as the plant will develop a new biota when the composition of the water to be treated changes.”