Ethanol fermentation could be inhibited by sulfide,which is harmful to the process of ethanol methane coupled fermentations.Compared to the control,at pH 4.0 and with 24 mmol/L sulfide existed,ethanol fermentation time was prolonged from 48 to 318 h,ethanol concentration was decreased from 90.73 to 82.28 g/L,yeast cell number was declined from 3.78 × 108 to 2.20 × 108 cell/mL,and glycerol concentration was increased from 6.99 to 11.02 g/L.Increased glycerol production could contribute to the decreased ethanol production when sulfide existed.Inhibition of sulfide to ethanol fermentation was weakened as delay of addition,because sulfide could escape from the fermentation broth with CO2 as the form of H2S.At pH 4.0,critical inhibition concentration of sulfide to ethanol fermentation was 1.2 mmol/L.cassava,fuel ethanol,sulfate,sulfide,critical inhibition concentration