Effects of freezing rate, solids content, and curing time on freeze/thaw conditioning of water treatment residuals

The results presented herein are intended to aid in a fundamental understanding of conditioning water treatment residuals by the freeze/thaw process. Residuals were frozen such that the effects of freezing rate, solids content, and curing time were isolated. Residuals were frozen directionally on a copper surface maintained at subfreezing temperatures. In contrast to many of the results in the literature, freezing rate did not seem to affect the final de-waterability. However, the effects of initial solids content and curing time were noticeable. High solids content residuals yielded cake solids contents greater than 30% following freezing, thawing, and drainage under a vacuum. Samples cured at -10 degrees C for 1 h dewatered much more readily than uncured samples. The results will aid in the design of a mechanical freezing process; the cost optimum conditions for such a process appear to be fast freezing of a high solids content residual, followed by approximately 1 h of curing.