Adhesion behavior of dewatered sewage sludge during indirect thermal drying

Abstract

We comprehensively investigated the factors influencing sludge adhesion during indirect thermal drying. We analyzed sludge properties and assessed adhesion during thermal drying using peel and shear tests at temperatures ranging from 100 to 180 °C. We conducted a comparative analysis of sludge properties and adhesion, exploring their correlations. Additionally, we examined the relationship between sludge adhesion and changes in extracellular polymeric substances (EPSs) throughout the drying process. The results indicate that factors leading to increased sludge adhesiveness include higher drying temperatures and the initial soluble EPS (S-EPS) concentration (R > 0.88). Only the S-EPS concentration showed an initial increase during thermal drying, followed by a decrease. Sludge with higher initial S-EPS concentrations released more S-EPS during the early stages of thermal drying. Sludge adhesion tended to increase after the S-EPS concentration began to decline. These observations suggest that the adhesive properties of sludge are not directly related to S-EPS but rather to the heat-induced release and transformation of organic content into substances that enhance adhesion. Potential technical solutions to mitigate sludge adhesion include lowering the drying temperature or reducing the S-EPS concentration through anaerobic digestion.