Effect of ultrasonic waves on the rheological features of secondary sludge

The increasing production of sewage sludge is a problem for wastewater treatment plants today. Research has sought to improve sludge processing efficiency and minimization. This study examined the changes in the rheological features of secondary sludge as a function of ultrasonic specific energy. It has been analyzed the dependency of steady state viscosity on shear rate and the hysteresis area. Steady state viscosity and the hysteresis area decreased significantly with increased ultrasonic specific energy. This may be due to the disruption of sludge flocks leading to a less rigid internal structure. The centrifugation of ultrasonicated sludge increased the total solid content by approximately 21%, leading to dewatered sludge. This sludge showed less elasticity, viscosity and thixotropy than untreated sludge.