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.