Impact of low-thermal pretreatment on physicochemical properties of saline waste activated sludge, hydrolysis of organics and methane yield in anaerobic digestion

[Display omitted] •Effect of low-thermal pretreatment on anaerobic digestion performance was studied.•Higher temperature and longer pretreatment time favor solubilization of organics.•Methane yield increased from 13.7 to 29.6% by temperature rise from 60 to 120 °C.•Anaerobic digestion using 80 °C pretreated sludge is more economically feasible.•PCA showed positive correlation among treatment temperature and sludge properties. This work studied the influence of low-thermal pretreatment (60–120 °C) on anaerobic digestion of saline waste activated sludge. The findings showed higher temperature and longer pretreatment time considerably improve organics hydrolysis (soluble chemical oxygen demand increased by 4.2–11.9 times) and volatile solid reduction (maximum 24.6%). Carbohydrate and proteins solubilization accelerated by 5.6–43.8 times and 8.9–35.9 times, respectively by temperature rose from 60 to 120 °C. Low temperature (60 °C) promotes faster release of ammonia and phosphate. Thermal treatment had positive effect on biogas production because methane yield was enhanced by 13.7, 27.0, 29.0 and 29.6% when pretreated at 60, 80, 100 and 120 °C, respectively. Significant positive relationships observed between pretreatment temperature/duration and sludge properties. Energy and economic assessment displayed anaerobic digestion of 80 °C pretreated sludge is more economically feasible. Thus, low-thermal pretreatment technology could be useful for improvement of methane yield in anaerobic digestion.