AWWA JAW51286

Mechanical freeze-thaw conditioning of water treatment residuals (sludge) producesa product with extremely high solids content. Intuitively, the process appears too expensive to be feasible. This article presents a model that can be used to investigate the economics of mechanical freeze-thaw conditioning. Model results reveal two cost-optimum freezing conditions: typically an initial solids content of 10 percent w/w or higher, and curing times >6 h. Also, the model is used to compare the cost of the optimum freeze-thaw designs with the costs of traditional residuals management trains. Results show that freeze-thaw conditioning may be cost-effective for moderate to high disposal costs (>$25/t [$28/metric t]) and low electricity rates (<$0.075 x kW-1 x h-1). Includes 36 references, table, figures.