The freezing process consists of dissipating heat from the product until the final
temperature is lower than the temperature of crystallisation of that product. Freezing
can be used for numerous applications, including for disruption of waste-activated
sludge (WAS). The aim of this study was to calculate the estimated amount of heat
conveyed between the solidified carbon dioxide and the WAS, in the following ratios:
0.25:1; 0.5:1; 0.75:1 and 1:1. In heat of phase transformations, dry ice sublimation,
water solidification, the amount of heat transferred by other substances and heat
transferred from the sludge (dry sludge) were taken into account during the process
of WAS freezing. Heat changes on the surface of WAS were registered using a thermovision
camera. The effectiveness of WAS disintegration was confirmed by several biochemical
parameters such as soluble chemical oxygen demand (increase over 14 times), degree
of disintegration (48%), proteins (increase over 5 times), carbohydrates (increase
almost 7 times), RNA (increase by 2.23 mg L-1), ammonia nitrogen (increase over 23
times), phosphates (increase almost 27 times) and turbidity (increased over 7 times).
It was found that dry ice pretreatment of WAS can be an intriguing alternative for
the conventional methods used.