Effects of hydrothermal pretreatment and bamboo hydrochar addition on anaerobic digestion of tofu residue for biogas production.

The effect of hydrothermal pretreatment (HTP) of tofu residue (TR) and co-digestion of TR with hydrochar (HC) and a liquid fraction (LF) of hydrothermal pretreatment on biogas production was studied. The highest biogas and methane yield observed with the pretreated TR at HTP temperature of 140 °C reached 288 and 207 L/Kg VS, 24 and 37% above than the raw TR (control), respectively, and the highest content of methane 72%. Adding 4 g/L of HC (produced at 200 °C) enhanced the methane and biogas yield by 18 and 19% compared to untreated TR, respectively. It was found that HTP at temperature 140 °C and additive HC-200 (4 g/L) was the most efficient for biogas production from tofu residue and significantly reduced the digestion time needed from 20 to 10-13 days to reach 95% of biogas yield, which may result in substantial economic benefits.