Methane fermentation of the stillage was performed in an upflow anaerobic filter reactor with a working volume of 800 mL at 53 ◦C, as previously described (Sun et al., 2013). An 800-mL portion of thermophilic sludge was acclimatized by feeding synthetic wastewater [glucose, 35 g/L; corn steep liquor, 17.5 g/L; (NH4)2CO3, 1.0 g/L; Na2CO3, 0.3 g/L; K2HPO4, 0.2 g/L; and FeCl3·6H2O, 0.1 g/L] at a TOC loading rate of 1 or 2 g/L/d. After the reactor ran stable for approximately two weeks, the stillage was fed continuously at the same TOC loading rate. In order to enhance the methane fermentation, the stillage was supplemented with Ni2+ and Co2+