Image analysis of X-ray microtomograms of soft materials during convective drying.

X-ray microtomography is used to explore the textural evolution that soft materials undergo during a drying treatment. An original image processing algorithm is applied to vertical projections and reconstructed cross-section images in order to quantify the texture at different stages of drying. Measurements are performed both on grey-level and on binary images. It is shown that X-ray microtomography is a very promising tool in the field of drying investigations. It can be used to determine internal moisture profiles, and to follow crack development and shrinkage in an accurate and non-destructive way. This information is crucial to validate drying models. Waste-water sludges are used as test materials to assess the validity of the proposed methodology. The management of these sludges, often including a drying stage, will become a challenge in the forthcoming years in accordance with environmental regulations. Samples collected in two waste-water treatment plants are investigated. Their analysis by X-ray microtomography brings to the fore two different drying behaviours, illustrating that sludge drying is a complex unit operation very sensitive to the way the material is produced.