FÖRSÖK MED MIKROSAND SOM FLOCKHJÄLPMEDEL VID RINGSJÖVERKET / Tests with Microsand as a Coagulant Aid at the Ringsjö Plant
At the Ringsjö plant, laboratory and pilot scale tests has been carried out with a process for water treatment where the conventional process coagulation-flocculation-sedimentation is accelerated by dosing of microsand in the flocculation step. The microsand improves the sedimentation velocity of the flocs formed, while at the same time reducing the flocculation time needed. The microsand can be separated from the sludge by hydrocycloning and then recycled. Labscale tests showed that dosing of 300 mg/l microsand gave a lower content of aluminium in the water compared with normal flocculation-sedimentation, in spite of the fact that the flocculation time was only 20 min and the surface load on sedimentation was 2 m/h. Pilotscale tests showed that the flocculation time should be in the range of 20-25 minutes. The surface load on sedimentation can reach values of 2.7 m/h. Tests showed that hydrocyclones are really efficient in separating microsand from sludge. However one separation-step was not enough.