Effect of sludge cell disruption on compactibility of biological sludges

Abstract

Biological sludge contains various fractions of water associated with sludge solids which are mostly microorganisms. These water fractions affect the liquid-solid separation of sludge. A considerable amount of sludge water is trapped either inside the sludge microorganisms or within the floc structure and this is labeled interstitial water. Release of interstitial water held inside the cell structure involves disruption of sludge cells and this does not occur during conventional dewatering. In this study, sludge cell disruption is introduced as a new method to improve the compactibility of sludge. Biological sludge cells are disrupted by different methods including alkali treatment, NaCl treatment, heat treatment, and sonication. The effect of cell disruption on compactibility of biological sludge is investigated. The results of the study indicate that the disruption of the sludge cells changes the water distribution in sludge and improves the compactibility of sludge. Disruption apparently releases from 60% to 80% of interstitial water, depending on the disruption method used. On the other hand, it causes creation of extra surfaces for water binding and leads to an increase in the unfreezable water content (vicinal water, water of hydration and a fraction of interstitial water) of sludge. The cell disruption increases the solid content of compacted sludge up to 87% depending on the cell disruption method used.