Excess activated sludge pretreatment in the wastewater treatment process aims at enhanced performance in sludge handling and in the stabilization of excess sludge. This study concentrated on the use of ultrasound as a pretreatment method and the aim was to characterize activated sludge before and after ultrasonic treatment of different ultrasonication duration times.The use of ultrasound in sludge treatment is based on cavitation. Imploding bubbles produce shear forces, and high local temperatures and pressures that break up flocs and cell structures. The use of ultrasound requires choosing operational parameters. In this study, the main variable was ultrasonication time. Sludge characterization techniques included temperature, particle size distribution, TTF, SVI, solids content, COD, biodegradability and carbohydrate content.Results showed that ultrasonic treatment increased sludge temperature, COD in supernatant and in filtrate, and carbohydrate content. The SVIs were also enhanced. Particle size distribution shifted towards smaller particles, causing the deterioration of filterability and supernatant turbidity during ultrasonication. Re-flocculation during ultrasonic treatment was observed. Ultrasonic treatment also caused partial inactivation of sludge during ultrasonication and the heating of sludge. Ultrasonic treatment had no effect on relative shares of total, volatile, and suspended solids.
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