Effect of Acetic Acid on Growth and Ethanol Fermentation of Filamentous Fungi Rhizopus oryzae, Mucor indicus, Neurospora intermedia and Aspergilus oryzae

Toxic compounds and inhibitors in lignocellulosic hydrolysates such as acetic acid and phenolic compounds are the major challenge for biochemical conversion of lignocellulosic materials into biofuels like bioethanol. In this study, the performance of four filamentous fungi Rhizopus oryzae, Mucor indicus, Neurospora intermedia and Aspergilus oryzae on the fungal biomass production, sugar and acetic acid consumption as well as ethanol production was investigated in synthetic mediums containing 0, 3, 5 and 7 g/L acetic acid. The fungal biomass obtained after 48 and 72 hours cultivation showed that the rate of the fungi growth and lag phase decreased and increased by acetic acid addition into the medium, respectively. The inhibitory effect of acetic acid on M. indicus growth was higher than those of other fungi, i.e., its biomass production decreased significantly at higher concentration of acetic acid (5 g/L), while A. oryzae showed pretty good tolerance to acetic acid. The results indicated that the effect of acetic acid on the fungal biomass and ethanol production was dependent on acetic acid concentration and the fungus type which can affect positively and/or negatively on the fermentation. The ethanol concentration from A. oryzae and R. oryzae cultivation in the medium containing acetic acid was decreased and increased, respectively. According to the fermentation results, the medium containing 7 g/L acetic acid was enough to stop the fungi growth and ethanol production.