Optimization of freeze‐thaw conditioning

Abstract

Mechanical freeze–thaw conditioning of treatment residuals may be cost‐effective.Mechanical freeze–thaw conditioning of water treatment residuals (sludge) produces a 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 · kW–1· h–1).