Biomethanation and dewaterability characteristics of primary sludge (PS), secondary sludge (SS) and mixed sludge (MS) fractions were assessed after anaerobic stabilization under parallel batch and continuous mixing conditions at 35℃ in order to investigate the performance of the separate digestion system. Similar methane conversion/yield values were obtained in PS, SS and MS digestion with continuous mixing’s positive effect only in PS digestion. Continuous mixing resulted in 50% increase in the methane yield (600(+/-100) mL/g VSadd.d. SS digestion produced a comparable methane yield at 650(+/-100) mL/g VSadd.d showing no effect due to mixing pattern. Settling and dewaterability characteristics of the stabilized PS were superior to stabilized SS samples. A reverse relationship was obtained between settling and dewaterability characteristics where intermittent mixing enhanced settling ability while continuous mixing resulted in higher dewaterability of the stabilized sludges. Polyelectrolyte (PE) addition showed a negative effect on the settleability of the sludges. Low degree mixing resulted in 50% sludge volume reduction and an SVI of 64 mL/g VS compared to 25% volume reduction and 82 mL/g SVI in the continuous mixing mode for the stabilized PS. A similar trend for the stabilized SS but weaker values with 25% volume reduction and an SVI 182 mL/g in the intermittent mixing mode compared to 15% volume reduction and 200 mL/g VS SVI indicated a much lower settleability in the continuous mixing mode and compared to stabilized PS.