Effect of thermally-induced protein solubilisation on rheology of activated sludge

Thermal pre-treatment of activated sludge was shown as an effective method to increase biodegradability of activated sludge for higher biogas production in digesters. The underlying reason for better digestion is solubilisation of organic matter in sludge. This study investigates sludge compositional and rheological changes due to thermal degradation of organic matter when the activated sludge is subjected to cyclic thermal treatment between 20 and 80°C. Protein was directly measured by a spectrophotometer as the major organic matter which is irreversibly solubilised with thermal treatment. The calorimetric method was also used to track the irreversible organic matter denaturation. The apparent viscosity and yield stress of thermally-treated activated sludge was less than untreated sludge. The calorimetric results confirmed the irreversible and gradual denaturation of organic matter. The protein solubilisation rate showed a similar trend to the denaturation kinetic calculated from calorimetric data.