1Biotechnology Group, Department of Chemical Engineering, Tarbiat Modarres University, P.O. Box 14115-143 Tehran, I.R. IRAN
2Department of Biochemical Engineering and Biotechnology, Indian Institute of Technology (I.I.T), Hauz Khas, 110016, New Delhi, INDIA
Reaction constants and heat release during thermophilic aerobic digestion of typical secondary and mixed sludges were determined. Maximum reaction constant, determined by measuring the amounts of biodegradable volatile suspended solids (bVSS) removed, occurred in the temperature range of 55-60 ºC. Measurement of heat releases were carried out, at the same range, by the aid of a temperature programmable logic controller (PLC). An amount equal to 16.2 KJ/g-cell was measured for secondary sludge digestion. The maximum amount of kinetic constant for secondary sludge (0.45 d –1) was observed at temperature of 55 ºC. Addition of primary sludge to secondary sludges decreased kinetic constants due to stimulate of biomass growth. Cell growth in mixed sludges provided an extra heat equal to 6.7 KJ/g-cell generated. However, it decreased the overall rate of heat release compared to the rate in the secondary sludge digestion.