Ozone oxidation, radiation treatment with gamma-ray and alkaline treatment were used to recover the carbon source using waste activated sludge for the biological denitrification process. Gamma ray irradiation of 50 kGy, alkaline treatment of 15.0 mM NaOH and ozone oxidation of 0.56 g O3/g SS were applied for this purpose. Three processes were optimized to maximize the solubilization efficiency and control the final pH. As combining each process. [alkaline treatment-gamma ray irradiation-ozone]. not only the solubilization and biodegradability efficiencies could be maximized but also the pH of supernatant was controlled to neutral pH without an additional acid or alkaline treatment.