Ultrasound pretreatment of cassava chip slurry to enhance sugar release for subsequent ethanol production

The use of ultrasound pretreatment to enhance liquefaction and saccharification of cassava chips was investigated. Cassava chip slurry samples were subjected to sonication for 10-40 s at three power levels of low (2 W/mL), medium (5 W/mL), and high (8 W/mL), medium (5 W/mL), and high (8 W/mL). The samples were simultaneously exposed to enzymes to convert starch into glucose. The cassava particle size declined nearly 40-fold following ultrasonic pretreatment at high power input. Scanning electron micrographs of both unsonicated (control) and sonicated samples showed disruption of fibrous material in cassava chips but did not affect the granular structure of starch. Reducing sugar release improved in direct proportion to the power input and sonication time. The reducing sugar increase was as much as 180% with respect to the control groups. The slurry samples with enzyme addition during sonication resulted in better reducing sugar release than the samples with enzyme addition after sonication. The heat generated during sonication below starch gelatinization temperature apparently had no effect on the reducing sugar release. The reducing sugar yield and energy efficiency of ultrasound pretreated samples increased with total solids (TS) contents. The highest reducing sugar yield of 22 g/100 g of sample and efficiency of 323% were obtained for cassava slurry with 25% TS at high power. The reducing sugar yield at the completion of reaction (R-infinity) were over twofold higher compared to the control groups. The integration of ultrasound into a cassava-based ethanol plant may significantly improve the overall ethanol yield.