Bioethanol Production from Sweet Potato Residues

Sweet potato residues (SPR) left after extracting starch account for more than 10% of the total dry matter of sweet potatoes. In China, more than 2 million tons of SPRs cannot be utilized, and result in environmental pollution. Shandong University's Fangzhong Wang now aims to develop an environmentally friendly and highly efficient process for bioethanol production from SPRs.

Some SPRs were pretreated with cellulase alone while some were pretreated with a mixture of cellulase and pectinase. Cellulase plays a major role in viscosity reduction and glucose production while pectinase has a minor role in viscosity reduction but acts as a "helper protein" to assist cellulase in liberating glucose, especially at low cellulase activity levels.

In total, 153.46 and 168.13 g/L glucose were produced from SPRs with cellulase and a mixture of cellulase and pectinase, respectively. These hydrolysates were then fermented to form 73.37 and 79.00 g/L ethanol, respectively. Each kilogram of dry SPR was converted to form 209.62 and 225.71 g of ethanol, respectively.

The process developed has a potential for industrial production of bioethanol due to its low impact on the environment, high productivity and easy manipulation.