UNIDIRECTIONAL FREEZING OF WASTE ACTIVATED SLUDGES - VERTICAL FREEZING VERSUS RADIAL FREEZING

Radial freezing and vertical freezing of waste activated sludge were c onducted in this work. In radial freezing, where the sludge sample is placed in a cylindrical chamber cooled at its outer wall surface, the ice front grows and migrates inwards from the rim region along a radia l direction. The corresponding freezing speed decreases gradually due to the increase in heat conduction resistance through the ice layer. I n vertical freezing, where the sludge was placed in sample tubes immer sed vertically into a freezing pool, the ice front grows upwards at a constant freezing speed. Comparisons between flee characteristics and the changes in chemical compositions resulting from both tests make cl ear the role of freezing speed. That is, if only the developing ice fr ont can reject foreign particles and thereby cause the gross migration of sludge flocs, the effects on sludge performance would be similar. The most influential factor that determines the freeze/thaw-conditione d sludge performance is discussed. (C) 1997 Elsevier Science Ltd.