The design of a freeze dewatering system must be based on worst-case conditions to ensure successful performance at all times. If sludge freezing is to be a reliable expectation every year, the design must be based on the warmest winter during the period of concern (typically 20 years or longer). The second critical factor is the thickness of the sludge layer that will freeze within a reasonable period if freeze-thaw cycles are a normal occurrence during the winter. A common mistake with past attempts at sludge freezing has been to apply sludge in a single deep layer. In many locations, a large single layer may never freeze completely to the bottom, so only the upper portion goes through alternating freezing and thawing cycles. It is absolutely essential that the entire mass of sludge be frozen completely for the benefits to be realized; also, when the sludge has frozen and thawed, the change is irreversible.
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