DETERMINING POROSITY PROFILES DURING FILTRATION AND EXPRESSION OF SEWAGE-SLUDGE BY NMR IMAGING

The formation of a filter cake during mechanical dewatering (filtratio n and expression) of sludge is studied using one-dimensional nuclear m agnetic resonance (NMR) imaging of porosity profiles. The experiments clearly showed the formation of a porosity gradient during filtration and the disappearing of this gradient during expression, forming a cak e with a uniform porosity. This technique makes it possible to investi gate the material behavior of the porous medium, which is needed befor e any model calculations can be performed. The results indicate that N MR imaging is useful in nondestructive monitoring of the filtration an d expression process of sludge.