Abstract
BackgroundLow-cost raw materials such as lignocellulosic materials have been utilized in second-generation ethanol production process. However, the sequential and slow conversion of xylose into target products remains one of the main challenges for realizing efficient industrial lignocellulosic biorefinery.ResultsBy applying different constant potentials to different microbial electrolysis cells with xylose as the sole carbon source, we analyzed the output of metabolites, microbial community structures, electron flow, and carbon flow in the process of xylose electro-fermentation by domesticated activated sludge. The bioreactors produced currents when applying positive potentials. The peak currents of the + 0.242 V, + 0.542 V and + 0.842 V reactors were 0.96 × 10–6 A, 3.36 × 10–6 A and 6.43 × 10–6 A, respectively. The application of potentials promoted the xylose consumption, and the maximum consumption rate in the + 0.542 V reactor was 95.5%, which was 34.8 times that of the reactor without applied potential. The potential application also promoted the production of ethanol and acetate. The maximum ethanol yield (0.652 mol mol−1 xylose) was obtained in the + 0.842 V reactor. The maximum acetate concentration (1,874 µmol L−1) was observed in the + 0.842 V reactor. The optimal potential for ethanol production was + 0.842 V with the maximum ethanol yield and energy saving. The application of positive potential caused the microorganisms to carry out ethanol fermentation, and the application of negative potential forced the microorganisms to carry out acetic fermentation. The potential application changed the diversity and community structure of microorganisms in the reactors, and the two most significantly changed families were Paenibacillaceae and Bacillaceae.ConclusionThe constructed microbial electrolysis cells with different potentials obtained better production yield and selectivity compared with the reactor without applied potential. Our work provides strategies for the subsequent fermentation processes with different needs.
Highlights
Low-cost raw materials such as lignocellulosic materials have been utilized in second-generation ethanol production process
The xylose in hemicellulose cannot be fermented by Saccharomyces cerevisiae, and its content sometimes accounts for 25% of the lignocellulosic material [5, 6]
Among all the reactors, the + 0.842 V reactor has the best performance based upon its high production of ethanol
Summary
Low-cost raw materials such as lignocellulosic materials have been utilized in second-generation ethanol production process. Ethanol is the most produced biofuel in the world. It is made from a large variety of carbohydrates (sugar cane, corn, sweet potato starch, etc.) [2, 3]. The second-generation ethanol production process utilizes low-cost raw materials such as lignocellulosic materials (sucrose, bagasse, corn stover, and straw). Cellulose contains glucose, which can be effectively fermented into ethanol by Saccharomyces cerevisiae. The xylose in hemicellulose cannot be fermented by Saccharomyces cerevisiae, and its content sometimes accounts for 25% of the lignocellulosic material [5, 6]. Efficient conversion of xylose presented in lignocellulosic biomass is essential for the production of second-generation ethanol
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