As mentioned above, the pretreatment was performed to increase the internal surface area and decrease the crystallinity. For this study, the pretreatment was conducted 6 times and 50 kg EFB was treated in every batch. This pretreatment is similar to an ammonia fiber explosion (AFEX) pretreatment [24], which had an effect on the increase of the biomass surface area through an explosion. When the surface area of the biomass is increased, enzymes can easily access the biomass substrate, which is then converted to glucose and ultimately to fermented ethanol [25]. After pretreatment, the treated biomass was washed and collected in the biomass buffer tank. The biomass was washed two times using a belt presser and two washing tanks. Because of the enzyme activation, H2SO4 was used in the first washing tank to neutralize the pH. This washing process required more time than the pretreatment process. Therefore, the pretreatment process could not be continuously operated. In order to operate continuously, the development of a simple and efficient washing process is needed.