Low-temperature thermo-alkaline pretreatment of waste activated sludge (WAS) was studied, within the region of 0-0.2 M NaOH and 60-90 degrees C, for the effects of NaOH concentration and temperature on sludge degradability in anaerobic digestion (AD). Significant disintegration of sludge solids (up to 75.6%) and an increase in methane production (up to 70.6%) were observed in the pretreatment trials. Two quadratic models were successfully generated by response surface analysis (R-2 > 0.9, p < 0.05) to approximate how the degree of sludge disintegration (SD) and methane production (MP) respond to changes in the pretreatment conditions. The maximum responses of SD (77.8%) and MP (73.9% increase over the control) were shown at [0.16 M NaOH, 90 degrees C] and [0.10 M NaOH, 73.7 degrees C], respectively. NaOH addition showed a significant influence on the evolution of methanogen community structure during AD, whereas temperature did not. Aceticlastic Methanosaeta and Methanosarcina speceies were likely the major methanogens. (c) 2013 Elsevier Ltd. All rights reserved.