As shown in Table 1, the ethanol yield increased by 10.5% with the addition of a nitrogen source. Furthermore, ethanol yield increased by 6.3% with the addition of a phosphorus source, which was in accordance with the results obtained by Yu et al. (2009). Supplementing feedstock with the three kinds of salts resulted in the most significant improvement in ethanol yield. However, the addition of (NH4)2SO4 as nitrogen source led to the accumulation of SO42− in stillage, making it difficult to be treated in methane fer- mentation (Ikbal et al., 2003). In order to select a suitable substitute