The cumulative biogas yield was employed to evaluate the AD
performances. The changes of cumulative biogas yield with FW/AS
and AD times were shown in Fig. 2. It was obvious that the cumulative biogas yield in all reactors first rapidly increased with the
extension of digestion time, and gradually leveled off after 7 days of
AD. For instance, at FW/AS of 50%, the cumulative biogas yield
increased from 0 to 226 mL/gVSS within 7 days, and then remained
steady. Additionally, the cumulative biogas yield was profoundly
affected by FW/AS. For example, on the 15th day, cumulative biogas
yield increased from 155.3 to 254.4 mL/gVSS as FW/AS increased
from 10% to 30%, and then decreased to 166.1 mL/gVSS when FW/AS
continued to increase to 50%. On the basis of cumulative biogas
yield analysis, the decrease of biogas yield at FW/AS of 40% and 50%
might be attributed to the high lipid concentration brought with TH
pretreated FW, which inhibited the activity of methanogens (Cirne
et al., 2007).