Conditioning of wastewater sludge using freezing and thawing: role of curing

Abstract

Freeze/thaw (F/T) treatment is an efficient pre-treatment process for biological sludges. When bulk sludge was frozen, tiny unfrozen regimes in the ice matrix were continuously dehydrated by surrounding ice fronts, termed as the "curing stage". This work demonstrated that the F/T treatment could not only enhance sludge dewaterability, but also solubilize organic matters from sludge matrix. Most enhancement of sludge dewaterability was achieved during bulk freezing stage, with the waste activated sludge more readily dewatered than the mixed sludges after treatment. Conversely, the freezing stage released only limited quantities of organic matters to liquid. Conversely, the curing contributed mostly on chemical oxygen demand (COD) solubilization and NH(3)-N release. The crystallization of intra-aggregate moisture was claimed to damage cell membranes so to release intracellular substances to surroundings. The F/T treatment with sufficient curing is advised to effectively condition biological sludge as the feedstock of the following anaerobic digestion process.