AWWA JAW50942

Freeze-thaw conditioning is an effective way to process water treatment residuals. For many years the process has used natural out-of-doors freezing, but development of mechanical processes has been hindered by a lack of fundamental information about the process. This article presents the results of experiments performed to study the effects of initial solids content, curing time, and freezing rate on dewaterability of residuals from five water treatment facilities in the northeastern United States. Dewaterability of all residuals sharply increased following freeze-thaw conditioning. In the experimental procedure used, dewaterability following freezing and thawing was independent of rate. However, initial solids content and curing time strongly affected dewaterability, which was best for residuals frozen at high solids content and cured for long times. Cake solids contents >40 percent w/w were achieved. Generally, the process was most successful for residuals that exhibited the best dewaterability before freeze-thaw conditioning. Finally, cost-optimum freezing conditions were determined. Includes 33 references, tables, figures.