• Energy Research

Immobilised fermentation can be achieved using biofilm resistance, resulting in improved fermentation efficiency and yield. The link between the cell cycle and biofilms deserves further study since reports are lacking in this area.

Abstract This study evaluated the feasibility of ethanol production from expired rice by surface immobilization technology fermentation. The process was carried out using temperature tolerant active fresh yeast TH-AADY cells immobilized on cotton fiber placed in a reticular hollow sphere. A 320-ton pilot reactor with a multi-layer packed bed immobilized structure and multi-branch circulation path was used instead of the typical cylindrical immobilized reactor. The average values of the alcohol degree and fermentation efficiency of the immobilized yeast cells were 12.46% (v/v) and 83.72%, respectively, which were 0.45% (v/v) and 3.2% higher than those of a free-cell fermentation. The fermentation was repeated for 32 batches with good reusability and long-term stability. In addition, fermentation via cell immobilization created an extra benefit of 6.37% per ton of fuel alcohol based on the mean market price in China. The results obtained in this study indicate that ethanol production from expired rice using immobilized yeast in the new bioreactor is feasible and may meet the demands of industrial production based on the fermentation indexes and economic evaluation.

Biofilm-mediated continuous fermentation with cells immobilized has gained much attention in recent years. In this study, thermoresponsive poly(N-isopropylacrylamide)-grafted cotton fibers (PNIPAM-CF) were prepared via an improved surface-initiated atom transfer radical polymerization. The modification process imparted switchable wettability to the surface while maintaining the thermal stability and biocompatibility of the CF. During the ethanol transformation, the rapid, reversible cell adsorption and detachment of Saccharomyces cerevisiae were performed through the modulation of wettability, displaying the enhancement of immobilized biomass and immobilization efficiency from 2.20 g/L and 59.43% to 2.81 g/L and 93.32%, respectively. Moreover, the biofilm adsorption matched well with the Freundlich model, indicating that multilayer adhesion was the main mode of biofilm formation. Based on the accumulation of the biofilm, the fabrication and utilization of PNIPAM-CF improved the efficiency of continuous immobilized fermentation, making the ethanol production reach 26.34 g/L in the sixth batch of fermentation. Meanwhile, wettability regulation further enhanced the reusability of the carrier. Therefore, the findings of this study revealed that the application of smart materials in cell immobilization systems had broad prospects for achieving sustainable and continuous catalysis.