Evaluation of thickening and dewatering of the digested sewage sludge preconditioned by sonication

This study aimed to determine whether, and to what extent, preconditioning of excess sludge subjected to digestion can improve the final thickening and dewatering of sewage sludge. The substrate used in the study was excess sewage sludge. Sonication was conducted under static conditions in five test cycles for selected values of vibration amplitude: 7.88 mu m (1.6 W/cm(2)), 15.77 mu m (2.2 W/cm(2)), 23.65 mu m (2.7 W/cm(2)), 31.54 mu m (3.2 W/cm(2)), and 39.42 mu m (3.8 W/cm(2)). Sonication time ranged from 0 to 600 s. After sonication, the sludge was subjected to digestion, and capillary suction time, final water content, specific resistance, thickening curves, and thickening velocities were determined. The application of ultrasonic field in sewage sludge conditioning led to an increase in capillary suction time in proportion to increases in wavelength and operating time. Stabilization of sewage sludge preconditioned by sonication improved the filtration capacity of the sludge by reducing the capillary suction time. The final water content on each day of the digestion process also decreased. Sonication had a very positive effect on sludge thickening. Single, fragmented flocs were better packed and released free water.