Moreover, methane fermentation of stillage could also protect environment from second pollution. Thus, methane fermentation was carried out.After the acclimatization at TOC loading rates of 1 g/L/d and 2 g/L/d with synthetic wastewater, stillage was fed. Fig. 5a shows that although fermentation was stable at a TOC loading rate of 2 g/L/d, VFA quickly accumulated up to approxi- mately 6000 mg/L and the gas evolution sharply decreased to less than 500 mL/L/d when the TOC loading rate increased to 3 g/L/d.