Optimization of freeze-thaw conditioning

Mechanical freeze-thaw conditioning of water treatment residuals (sludge) p roduces a product with extremely high solids content. Intuitively, the proc ess appears too expensive to be feasible. This article presents a model tha t can be used to investigate the economics of mechanical freeze-thaw condit ioning. Model results reveal two cost-optimum freezing conditions: typicall y 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-tha w designs with the costs of traditional residuals management trains. Result s show that freeze-thaw conditioning may be cost-effective for moderate to high disposal costs (> $2S/t [$28/metric t]) and low electricity rates (< $ 0.075 . kW(-1) . h(-1)).