The total methane production of the maximal improvement obtained at 50g/L was 250.1L/kg VS after 7.0% NaOH dose treatment. With substrate concentration increasing from 50 to 80 g/L, the total methane production decreased. Com- pared to total methane production of 35 g/L, the decreases were 48.0%, 21.1%, 17.3%,