In the past decades, energy demand and global warming effects due to the burning of fossil fuels have continued to increase. This negative environmental and economic impact of hydrocarbon use has led to a resurgence of interest in renewable energy sources such as ethanol and biodiesel. Currently, the United States produces fuel ethanol from corn using dry or wet milling process; biodiesel from soybean oil. While corn and soybean are the primary source of biofuels, many other sources are being researched.
Grewell’s biofuel group explores the use of ultrasound as pretreatment to release fermentable sugar, enhance transesterification rate for biodiesel production and improve anaerobic digestion for biogas production. Ultrasound is sound waves at frequency above the normal human hearing range (18-20kHz). The two main mechanism of ultrasound treatment in liquid media are cavitation and acoustic streaming. As ultrasound wave is applied to liquid media, it produces microbubbles, which upon collapse generates large amount of energy. On the other hand, acoustic streaming is the mechanism that promotes mixing and enhances the homogenous distribution of ultrasound into the liquid.