Adhesion and Cohesion Characteristics of Sewage Sludge During Drying

The stickiness of sludge during the drying process is an effect of its adhesion and cohesion. Furthermore, the adhesion and cohesion characteristics of sludge are comprehensive results of sludge components and their correlation with moisture. This work presents a simple method to test the adhesion and cohesion characteristics of sludge during the drying process based on the Jenike shear test. The results show that the most significant sludge adhesion and cohesion emerges at a moisture content of approximately 45 to 70% and 30 to 60%, respectively, and at a heating temperature of 120 degrees C. An increase of the heating temperature to 200 degrees C only brings a small movement to the sticky range location. The possible reasons for sludge adhesion and cohesion are discussed based on the results of sludge component analysis. The contributions of mineral materials with tiny particle sizes and metal salts to the adhesion and cohesion are discussed in this study because the contribution of organic matter has been widely demonstrated. The adhesion and cohesion nature of sludge exhibits a large effect on its drying characteristics. A remarkable fluctuation of both the drying rate and stirring power, located between the first and second falling rate period, is observed when the adhesion force of sludge reaches the maximum. When the sludge cohesion force decreases to approximately 3800 N/m(2), sludge bulks are broken with the stirring of paddles.