Researchers at Aalto University have developed a simple method for reducing the amount of phosphorus in the wastewater of a pulp mill. The method is called simultaneous precipitation using iron sulphate. A separate treatment stage is not required, as the precipitation takes place simultaneously with the actual biological wastewater treatment.
Iron sulphate is added to the wastewater prior to the biological wastewater treatment process, and the phosphorus dissolved into the water is precipitated with the biomass at the treatment plant. Finally, the phosphorus is removed from the plant with the sludge. In Finland, sludge is generally burned, in which case the phosphorus would end up in the ashes and would thus be reusable in the form of fertilizers, for example.