Sludge Conditioning by Sonication and Sonication-Chemical Methods

Abstract

Abstract This paper investigated the potential impacts of sonication on sludge dewaterability and the optimal conditions. Both sonication conditioning and sonication-chemical co-conditioning were tested. Final water content of dry sludge was used to represent the sludge dewaterability. The results showed that sonication significantly changed the sludge dewaterability and the changes were strongly influenced by the ultrasonic power density and time. The best sonication for sludge conditioning, alone or together with chemicals, was 7 s and 0.8 W/ml. The optimal energy dose was 960 kJ/kgDS while energy input higher than 1200 kJ/kgDS deteriorated the sludge dewatering. Sonication alone only reduced the sludge specific resistance to filtration (SRF) by 40% and the final water content to 90%; thus, chemical conditioning was necessary. Combination of FeCl3 and polyacrylamide (PAM) was very effective for sludge conditioning and the optimal PAM/FeCl3 was 0.01. When chemicals were used, sonication effectively reduced the necessary chemical dose by 40-50% but showed little improvement in SRF. The best sludge conditioning parameters were found to be: sonication for 7 s at 0.8 W/ml, 1.5 g/L FeCl3, and 15 mg/L PAM. With such conditioning, sludge SRF decreased by 91% and the final water content was 72.8%.