Influence of back mixing and sawdust addition on convective drying of wastewater sludge: Temporal evolution of structural characteristics

Abstract

Adding dried matter to sludge is a method that can improve the drying effect of sludge. For the sawdust-sludge mixture, the object volume and total exchange surface decrease nearly linearly at first and then almost keep constant after 30 minutes with decreasing the water content of sludge.The order of magnitude of shrinkage is: orginal sludge > back-mixed sludge > sawdust-sludge mixture. The crack mainly happens in the center of the single extrudate for both the original sludge and back-mixed sludge during drying. However, for the sawdust-sludge mixture, the crack appears everywhere inside the single extrudate.