Although the detention time for sludge on the freezing beds may be several months, the low temperatures involved will preserve the pathogens rather than destroy them. As a result, the process can be considered only as a conditioning and dewatering operation, with little additional stabilization provided; however, wastewater sludges treated in this way may be "cleaner" than sludges that are air dried on typical sand beds. This is due to the rapid drainage of sludge liquid after thawing, which carries away a significant portion of the dissolved contaminants. In contrast, air-dried sludges will still contain most of the metal salts and other evaporation residues.
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