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

Low-temperature thermo-alkaline pretreatment of waste activated sludge (WAS) was studied, within the region of 0–0.2 M 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 < 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 °C] and [0.10 M NaOH, 73.7 °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.