Freeze/thaw treatment on zone settling of waste activated sludges

Zone settling characteristics of the original and frozen waste activated sludges had been investigated experimentally. Based on the Richardson-Zaki correlation, the apparent floc size and floc density for various sludge systems were estimated. Due to the global floc network existing in the original sludges, the apparent floc density for the settling sludge was much less than those of the constituting flocs, which was generally observed in the floc systems studied. After a freeze/thaw treatment, nevertheless, the densities for the flocs were increased whilst the apparent density of the sludge could be taken as an average over all the constituting flocs.