However, a significant amount of removable ash formed in alfalfa stems subjected to sulfuric acid pretreatment. Thus, washing showed obvious effect on ethanol yield when expressed on a DM of substrate basis. When more sulfuric acid was added, more removable ash formed, resulting in greater improvement on ethanol yield after washing. The data indicated the removal of soluble ash was the primary mechanism for the improvements in ethanol yields by washing.
The removable ash could come from two portions. One portion was added ash, which contributed to the washing effect on ethanol yield. Another portion could come from original alfalfa stems, which should have no contribution to the washing effect, since this portion was the same between samples. Theoretical ash did not change much with sulfuric acid pretreatment (Fig. 5), as expected since the original ash contents of alfalfa stems across all the treatments were the same. The wash-removable ash was highly likely soluble salts, made of cations such as〖Na〗^+,K^+,〖Ca〗^(2+) and anions such as 〖Cl〗^-, 〖SO〗_4^(2-) which could pass the cell membrane (Klinke et al., 2004). Maiorella et al. (1984) found that NaCl and MgSO₄ can inhibit yeast cell growth. The inhibitory effect of the soluble ash including〖Na〗^+, 〖SO〗_4^(2-) and other ions was likely the mechanism for ash removal’s improvement of ethanol production.
However, a significant amount of removable ash formed in alfalfa stems subjected to sulfuric acid pretreatment. Thus, washing showed obvious effect on ethanol yield when expressed on a DM of substrate basis. When more sulfuric acid was added, more removable ash formed, resulting in greater improvement on ethanol yield after washing. The data indicated the removal of soluble ash was the primary mechanism for the improvements in ethanol yields by washing. The removable ash could come from two portions. One portion was added ash, which contributed to the washing effect on ethanol yield. Another portion could come from original alfalfa stems, which should have no contribution to the washing effect, since this portion was the same between samples. Theoretical ash did not change much with sulfuric acid pretreatment (Fig. 5), as expected since the original ash contents of alfalfa stems across all the treatments were the same. The wash-removable ash was highly likely soluble salts, made of cations such as〖Na〗^+,K^+,〖Ca〗^(2+) and anions such as 〖Cl〗^-, 〖SO〗_4^(2-) which could pass the cell membrane (Klinke et al., 2004). Maiorella et al. (1984) found that NaCl and MgSO₄ can inhibit yeast cell growth. The inhibitory effect of the soluble ash including〖Na〗^+, 〖SO〗_4^(2-) and other ions was likely the mechanism for ash removal’s improvement of ethanol production.
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