Bioethanol is one of the most important renewable fuels due to the economic and environmental benefits of its use. Lignocellulosic biomasses such as waste wood are the most promising feedstock for producing bioethanol in Iran. Conventional methods for bioethanol production from Lignocellulosic biomasses take two steps: pretreatment (commonly acid or enzyme hydrolyses) and fermentation. Dilute acid hydrolysis takes the time in the range of a few minutes but needs high temperature and pressure and has low efficiency. While the concentrated acid hydrolysis takes the time more than ten hours but needs moderate temperature and pressure and has high efficiency. In this paper, we introduce a new two-step pretreatment method for bioethanol production from waste wood, which has the advantages of dilute and concentrated acid hydrolyses. In the first step, the sawdust is soaked in sulfuric acid at room temperature and for more than 12 hours. In the second step, the temperature of the mixture was raised to boiling point and for duration less than 4 hours. Different acid concentrations such as 2, 5, 10 and 20 percent are used in pretreatment steps, and each experiment was repeated three times. The results after statistical analysis showed that the maximum amount of total sugar achieved after about 120 minutes in 5% acid concentration.

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