c. Kaldnes® processThis technology was developed by the Norwegian firm of M/S Kaldnes Miljoteknologi. Theprocesses consist of adding small cylindrical shaped polyethylene carrier elements (specific gravityof 0.96 g/m3) in aerated or non-aerated tanks to support biofilm growth. The small cylinders are about10 mm in diameter and 7 mm in height with a cross inside the cylinder and longitudinal fins on theoutside. The biofilm carriers are maintained in the reactor by a perforated plate (5×25 mm slots) at thetank outlet. Air agitator or mixers are used to circulate the packing continuously. The packing may fill25% to 50% of the tank volume. The specific surface area of the packing is about 500 m2/m3 of bulkpacking volume. The typical reactors are shown in Figure 5.86. The biofilm carriers are shown inFigure 5.87. The schematic is shown in Figure 5-88 overleaf.