Ultrasonic freezing for solubilisation of sludge organic matter and enhanced conditioning

Two new freezing treatment methods (partial ultrasonic freezing and combined ultrasonic freezing) were examined for their effectiveness on both solubilisation of organic matter and enhancement of sewage sludge conditioning. The treatment efficiency of the new freezing methods was compared with that of conventional freezing. The test results revealed that the capacity of the two new freezing methods on solubilisation of sludge organic matter was comparable to that of conventional freezing with three to five freezing and thawing cycles. About five to seven times increase in sample soluble chemical oxygen demand and soluble protein concentrations were observed after treatment using the three different freezing methods. Significant improvement in sludge conditioning was also achieved; more than 80% reduction in settled sludge volume was noted in the freezing-treated samples. Overall, all freezing techniques examined showed great potential as effective treatment methods that could not only enhance sludge conditioning but also solubilise organic matter.