Interaction of ice-water interface with agglomerates of activated sludge during freezing

Abstract

Visual experiments were conducted to investigate freezing behavior of activated sludge. Experimental observations indicate that there existed strong interactions of advancing ice-liquid interface with sludge agglomerates during freezing treatment. Agglomerates would be pushed to move by advancing ice-liquid interface in the cases of lower advancing speeds while no needle-like ice-crystals forming at the interface. For faster freezing processes, the ice front interface line turned needle-like, while ice-crystals forming/generating at the interface, and crystals pierced into the sludge agglomerates rather than pushing them. The crystals served as roles holding the agglomerates. It seems that there was a critical speed below which repulsion occurred and above which the particles were entrapped without obviously pushing. The transition of these two cases is still needed to identify.