stages at the aerobic bio-oxidation plant, and after purification the water is
discharged into the Gulf of Finland. The excess sludge treatment stage is at
present lacking, and the sludge is pumped as a suspension of the concentration
of about 9 g/L to the ash dump. With this sludge a quite considerable
amount of biologically treated water is dispersed as well about 0.4 m3/ton
of treated oil shale.