Ultrasonic enhancement of industrial sludge settling ability and dewatering ability

This paper investigates the treatment of chromium (Cr) contaminated industrial sludge from a tanning process with ultrasound to enhance the sludge settling ability and dewatering ability. Ultrasound at various frequencies, intensities, and time was tested to optimize the operation. The results show that treatment with 30 kHz, 12 W/L ultrasound for 120 s shortened the sludge settling time from 3 h to 1 h and reduced the supernatant Cr concentration. The ultrasonic treatment also reduced the sludge volume from 4.02 mL/g to 2.58 mL/g and increased the sludge Cr concentration by 213. The treated sludge could then be reused in the tanning operation. Proper ultrasonic treatment can significantly reduce the sludge volume and enhance the Cr reuse.