The modern mill uses water in an optimised way, recirculates it efficiently and treats wastewater so that impacts on surrounding water bodies remain very low. Water consumption is significantly lower than at the former Kemi mill, even though the new mill’s production capacity is several times higher.
The right water in the right place
Water is an essential part of the pulp production process and is used with careful consideration. In pulp manufacturing, water is needed for washing, cooling and various process stages, but the process is designed so that the same water is circulated through as many uses as possible.
“In washing processes, we apply the counter-current principle, which reduces the need for fresh water. In addition, secondary condensates and treated water fractions are returned to the process whenever possible. Treated wastewater is also used instead of fresh water in sludge handling and at the wastewater treatment plant,” says Anssi Nykänen, Environmental Manager at the Kemi bioproduct mill.
This overall approach makes Kemi’s water management exceptionally efficient and supports Metsä Group’s target to reduce process water use by 35 per cent, compared to the 2018 level, by 2030.
Closed cooling water circulation safeguards the marine environment
At the Kemi bioproduct mill, cooling water circulates in a fully closed system. This solution significantly reduces water intake and prevents thermal load from being discharged into the sea. At the same time, the closed system ensures that the mill’s operations do not affect the natural ice conditions along the coast.
“The local marine area is in good condition. The closed cooling water circulation and efficient treatment ensure that the mill’s impact on ice conditions and water quality is very limited.”
Efficient wastewater treatment keeps the load low
All wastewater from the mill is treated in a multi-stage biological wastewater treatment plant that represents state-of-the-art technology in the field. The plant effectively reduces organic load and nutrients and clearly outperforms the limit values set in the EU BAT (Best Available Techniques) conclusions. The high treatment efficiency is reflected in the very limited impacts on water bodies.
“The nutrient load from the mill into the water bodies is extremely low. Compared to the former mill, for example, our phosphorus emissions have been reduced by around 90 %.”
Sludge from the treatment plant is processed into biopellets, reducing waste volumes and supporting the mill’s circular economy.
Sulphuric acid plant reduces sulphate load
Kemi’s own sulphuric acid plant utilises sulphur compounds contained in the process odorous gases. This reduces the need for purchased sulphuric acid and lowers sulphate loads to water bodies. It is a significant step towards a more closed chemical cycle and a more environmentally efficient process.
Why is this important for water bodies? Sulphate is a sulphur compound generated in the pulp process that dissolves easily in water. If not recovered, it ends up in water bodies via wastewater, increasing salinity. Higher concentrations can affect local species and the overall load on the aquatic environment.
The Kemi sulphuric acid plant significantly reduces the amount of sulphate in the process by recovering sulphuric acid and reusing it. At the same time, the need for purchased sulphuric acid decreases, which also reduces the sodium sulphate load of the process.
Development work towards a wastewater-free future
We are actively developing solutions to minimise wastewater discharges in the long term. The development work focuses, for example, on reducing salt loads, optimising water quality requirements at different process stages and finding new ways to reuse already treated water in internal circulation loops.
The Kemi bioproduct mill serves as one of the key references for this work. A modern process, closed loops and efficient water treatment provide a strong foundation for further development.
“We are continuously developing the process so that we can further close water loops and thus reduce both water consumption and the load on the surrounding water bodies.”
A shared goal: a vibrant marine area
The marine area around Kemi is important both for nature and for people. Continuous monitoring of water impacts, efficient wastewater treatment and a closed cooling water circulation form a comprehensive approach that ensures the mill’s environmental impacts remain very low.
“When the whole system works together – closed loops, efficient treatment and continuous monitoring – we can be confident that the marine area will remain vibrant for generations to come.”