Abstract
Results of laboratory experiments on the behaviour of suspended solids (s), dissolved organic carbon (DOC) and dissolved solids (DS) during the freezing process of sewage sludge are presented. Several cylinders containing excess activated sludge were put in a freezer chamber maintained at a constant temperature -16.5°C. Each cylinder was taken out of the chamber one by one in sequence of freezing time. A cylinder taken out at the freezing halfway contained partially frozen part. The unfrozen part was separated from the frozen part by decantation, and the latter was thawed, and both parts were analyzed. Remarkable improvement of solid-liquid separation characteristics was observed after the sludge temperature fell under the freezing point of the sludge. This change was accompanied with the rapid increase of DOC and DS of frozen part due to the release of organic matter from the cell structure. The DOC concentration of the freeze-and-thawed sludge was about 250 mg·l-1, which was only one twentieth as compared to the DOC increase with heat treatment for sludge conditioning.
