Synergistic Effects of Combined Chemical and Physiochemical Pretreatment on Sugar Liberation for Bioethanol Production

This review paper explores the synergistic effects of a chemical and physiochemical combinative pretreatment, which includes microwave-assisted pretreatment, ultrasonic-assisted pretreatment and liquid-hot water (LHW) assisted pretreatment on the fermentable sugar and bioethanol yield from selected biomasses. Methods employed include assessing the delignification efficiency and the sugar yield of biomass from the different combinative methods. The analysis also encompasses the evaluation of the economic viability of using the combinative pretreatment methods for bioethanol production, along with an examination of its environmental impacts. Results demonstrate that the combinative pretreatment has considerable potential for sustainable energy practices due to its synergistic effects, leading to reduction in pretreatment time, low chemical consumption, reduced temperature and heating power. It was observed that with combinative pretreatment, a high fermentable sugar yield of up to 80% can be achieved on or before 240 min of exposure to the pretreatment conditions. The maximum exposure temperature and irradiation recorded was 200oC and 320W respectively. Despite challenges in cost competitiveness with the pretreatment equipment and the ecofriendly chemicals for the pretreatment, recycling of these green chemicals such as deep eutectic solvent, shows economic promise. Conclusively, chemo-physical combinative pretreatment presents a viable option for biomass energy, potentially playing a pivotal role in the biomass sector as the energy landscape shifts towards more sustainable solutions; although, the pretreatment conditions need further addressing through a robust process optimization design.