Continuous classification of moisture content in waste activated sludges

Bound water content is generally taken as an index for differentiating the moisture content in a sludge. However, some recent works have demonstrated that such an index is an operationally defined value differing markedly when different techniques are employed. In this study, the continuous moisture distribution in waste activated sludge is constructed on the basis of the combined thermal gravimetry analysis (TGA) and differential thermal analysis (DTA). The water-solid bond strength is considered here to be an adequate classification index. The bound water contents measured via filtration, drying, or expression are interpreted as the portion of moisture displaying a bond strength higher than the threshold energy that could be provided by filtration, drying, or expression tests. Employing one of these bound water measurement methods is thereby equivalent to setting a threshold bond strength to divide the continuous moisture distribution into bound water and free water. Moreover, the effects of a freeze/thaw treatment on the continuous moisture distribution are discussed.