A combined ultrasonic and chemical conditioning process for upgrading the sludge dewaterability

Abstract

ABSTRACT Dewatering is of paramount step in sludge management, and conditioning with coagulant is considered as the commonest way to improve the sludge dewaterability. Sludge disintegration process was examined through Ultrasound (US) to strip the water from the sludge flocs and accordingly four coagulants: aluminium sulphate (Alum), iron (III) chloride (FeCl3), cationic polyacrylamide (CPAM) and combined ferric chloride and lime (CC) with optimum dosages were employed to improve the sludge dewaterability in terms of capillary suction time (CST), specific resistance to filtration (SRF) and moisture content (MC). The ultrasonic sludge disintegration with 1 min exposure with an energy dosage of 700 kJ/kg TS realises the best sludge dewatering efficiency. In addition, the effects of CPAM and CC conditioning on sludge dewaterability were higher compared with two other conditioners. The combined US-CPAM and US-CC with optimum dosages 8 and 101 mg/kg DS significantly improved sludge dewaterability parameters (MC: 68.50%, SRF: 1.03 × 1010 m/kg and CST: 31.82 s) and (MC: 72%, SRF: 1.08 × 1010 m/kg and CST: 31.82 s) compared with when conditioning experiments were performed alone. Scanning electron microscopy (SEM) images showed that the combined US-CPAM and US-CC conditioning formed a more porous structure and low compressible sludge filter cake which are desired to sludge dewatering. Therefore, the ultrasonic-assisted conditioning with CPAM and combined coagulant (lime + Ferric chloride) could significantly improve the sludge dewaterability indices.