Ethanol Production from Waste Sweet Potato Using Recombinant Zymomonas mobilis
Sustainable process-product development & green chemistry
Sustainable & Clean Technologies - IIa: Energy Production (T1-5a)
Keywords: sweet potato, recombinant fermentation, process design
Abstract:
This research focuses on converting waste sweet potatoes that are left in the fields and cannot be marketed for various reasons. Sweet potato collected from a field in one of the family-owned farms in Texas is analyzed for its sugar content using HPLC. The sugars in these sweet potato samples include three major components, sucrose, fructose, and glucose. Based on the fresh biomass, the sucrose, glucose and fructose content is 4.35 ± 0.33%, 2.68 ± 0.64% and 2.21 ± 0.43%, respectively. However, since the dry mass content is only 19.4%, the average sugar content based on the dry biomass is close to 50%. Prior to the fermentation, the sweet potato was pretreated and the free sugar was extracted using DI water at different temperatures. The results show that the higher the extracting temperature, the higher the extracting efficiency. Two strains of recombinant Zymomonas mobilis, 8b and AX101 which were obtained from National Renewable Energy Laboratories, Golden, Colorado, are used to convert the prepared sweet potato to ethanol. Both, anaerobic fermentation and aerobic incubation have been evaluated and compared in terms of the ethanol production, at various bacteria loads. Further, in order to increase the ethanol production efficiency, an enzyme has been used to hydrolyze the starch to fermentable sugars prior to the ethanol conversion. The effects of the enzyme ratio, the enzymatic reaction time, and the incubation time have been investigated. The results show that recombinant Zymomonas is capable of converting all the sugars effectively. Additional studies are designed to optimize the fermentation conditions, and perform a feasibility study for a small industrial scale plant.
Presented Wednesday 19, 15:45 to 16:00, in session Sustainable & Clean Technologies - IIa: Energy Production (T1-5a).
