As a result of the growing number of wastewater treatment plants (WWTP), increasing quantities of sewage sludge are being produced. Biological treatments are usually the most frequent method used to treat this type of waste. However, due its poor biodegradability, a previous treatment is required to enhance this sludge. In this study, the application of a microwave pretreatment was evaluated at different power ratings (400 and 700 W) for a specific applied energy ranging from 0 to 30,000 J/g TS. The pretreatment was applied to floated sludge and centrifuged sludge from a WWTP. The effect of the variables power and specific energy differed depending on the type of sludge. Organic matter solubilization was evaluated in both sludges based on the CODs/TVS ratio (soluble chemical oxygen demand/total volatile solids). The results showed a 43% and 66% increase in solubility for the floated sludge at 400 and 700W, respectively, and a 162% and 187% increase for the centrifuged sludge at 700 and 400W, respectively. The increase in organic and nitrogenous matter during pretreatment had a positive effect on the aerobic biodegradability of the floated sludge and biodegradation kinetics, as the specific oxygen uptake rate (SOUR) increased up to 8.5 times for a specific energy of 15,000 J/g TS. Independently of the moisture content, the floated sludge showed the best results above 10,000 J/g TS. No significant differences were observed between the applied powers in terms of organic matter solubilization. (C) 2019 Published by Elsevier B.V. on behalf of Institution of Chemical Engineers.