The foam layers (thickness of 0.10-0.20 m) formed on the surface of activated sludge were removed and dehydrated at ambient temp. to the required hydration degree 0.65% (350 g/kg dry mass) on roofed or unroofed beds. Foam dehydration times at 17 and 19 degrees C on the roofed bed were 52-58 and 35-46 days, resp. The 0.15 m thick foam dehydration time was 49-76 days at 19 degrees C on unroofed bed depending on the rainfall vol. The 0.20 m thick foam did not achieve any required dehydration degree even after 113 days.