Aerobic Sludge Stabilization-Factors Affecting Kinetics

The effects of temperature, pH, sludge age in the prior activated sludge process, initial sludge solids concentration, and sludge type on the rate of solids degradation during aerobic sludge stabilization are discussed. Primary sludge (PS), waste activated sludge (WAS), and mixed primary and waste activated sludges (PS WAS) are stabilized. The results indicate that: (1) First-order kinetics satisfactorily describe biodegradable volatile solids (BVS) degradation for WAS and mixed PS WAS, but not for PS; (2) the BVS decay coefficient b increases with increasing temperatures between 10 to 30 °C with a thermal coefficient of 1.097; (3) b values decrease as the sludge age in the prior activated sludge process increases; (4) b values are higher at reactor pH values ⩾6.5; and (5) b values tend to decrease as the initial VS concentration of the sludge increases. The WAS has an initial BVS and refractory volatile solids (RVS) content of 44-67% and 33-56%, respectively; the mixed PS WAS has a content of 33-40% and 60-67%, respectively; and the PS has a content of 74-91% and 9-26% respectively. The WAS has less biodegradable solids and a greater percent of residual refractory volatile solids requiring disposal than does the PS.