Thermo-alkaline pretreatment of waste activated sludge at low-temperatures: Effects on sludge disintegration, methane production, and methanogen community structure

•Effects of low-temperature thermo-alkaline pretreatment of sludge were examined.•Changes in sludge degradability with respect to treatment conditions were assessed.•Effective disintegration of sludge and enhanced production of CH4 were achieved.•Models to approximate sludge disintegration degree and CH4 production were created.•NaOH treatment had a significant influence on the methanogen community structure. Low-temperature thermo-alkaline pretreatment of waste activated sludge (WAS) was studied, within the region of 0–0.2M NaOH and 60–90°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 (R2>0.9, p