Green biorefinery represents an appropriate approach to utilize the fresh aquatic biomass, eliminating
the drying process of conventional bioenergy-converting system. In this study, fresh cattails were
homogenized and then filtered, whereby cattails were separated into a fiber-rich cake and a nutrient-rich
juice. The juice was used to cultivate microalgae Chlorella spp. in different media. In addition, the solid
cake was pretreated with the sonication, and used as the feedstock for ethanol production. The results
showed that the cattail juice could be a highly nutritious source for microalgae that are a promising feedstock
for biofuels. Sugars released from the cattail cake were efficiently fermented to ethanol using
Escherichia coli KO11, with 8.6–12.3% of the theoretical yield. The ultrasonic pretreatment was not suffi-
cient for pretreating cattails. If a dilute acid pretreatment was applied, the conversion ratio of sugars from
cattails has the potential to be over 85% of the theoretical value.