The study investigated the effect of sludge composition on the limitations of aerobic stabilization. It was designed with the foresight that the stabilization mechanism could only be elucidated if the observed volatile suspended solids reduction were correlated with the fate of particulate components in sludge. Biomass sustained at sludge ages of 2 and 10 days were used in the stabilization reactors. Particulate components were determined by model evaluation of corresponding oxygen uptake rate profiles. Interpretation of the experimental data by modeling, based on death-regeneration mechanism without external substrate, could simulate the fate and evolution of major components in sludge during stabilization. It showed that both microbial decay and hydrolysis of non viable cellular material proceeded at much slower rates as compared with biological systems sustained with substrate feeding. Modeling also indicated that particulate metabolic products generated by sludge acclimated to high sludge age undergo slow biodegradation under prolonged stabilization. (C) 2014 Elsevier Ltd. All rights reserved.