As shown in Fig. 5b, as soon as sulfate was added, the concentration of propio- nate decreased to below 500 mg/L and fermentation appeared to be stable again, while the inhibition of H2S (200 ppm in gas production) was insignificant, although sulfate was supplemented. Finally, methane fermentation was performed at a high TOC loading rate of 10 g/L/d, with an accumulation of VFAs of less than 1000 mg/L in the reactor.