Effect of Preagitation on Freeze‐Thaw‐Conditioned Sludge Dewaterability

Abstract

Sludge dewatering processes are usually preceded by sludge conditioning, which improves the sludge dewaterability. Although sludge conditioning is most commonly achieved by the addition of chemicals, freeze‐thaw conditioning can also be beneficial. The most practical way of using freeze‐thaw conditioning is to dewater the sludge on a freezing bed. When sludge is pumped from its sources to the freezing bed, it is subjected to high shear force induced by the pump and turbulent pipe flow. This shear may affect the effectiveness of freeze‐thaw conditioning. The objectives of this study are to investigate the effects of preagitation on freeze‐thaw conditioning of anaerobically digested sludge. The results indicate that preagitation has positive effects on freeze‐thaw conditioning of anaerobically digested sludge. Agitation intensity was found to correlate with sludge dewaterability, with increased agitation leading to enhanced dewaterability of freeze‐thawed sludge.