Using a Novel Pervaporative Sequential-Co-immobilized Two-Sectional Bioreactor with an Ultralow Fouling–Biofouling Superhydrophobic Silicallite-1/PDMS Membrane to Enhance Bioethanol Production

Abstract

This study is on the efficient fermentation of high glucose (G) and xylose (X) levels (G/X ratio of 1.5:1), simulating the hydrolysate of lignocellulosic wastes, via an innovative integrated two-stage fermentation–pervaporation process. Immobilized Zymomonas mobilis (Z) and Pichia stipitis (P) were exploited in a sequential-co-immobilized culture (Z in the first stage and Z and P in second stage) to simultaneously increase bioethanol productivity and lessen the inhibitions. The threshold inhibition was evaluated in 100 mL shake flasks by raising the initial total sugar concentration from 50 to 200 g/L where complete inhibition was observed at 200 g/L. Subsequently, fermentation (G: 120 g/L, X: 80 g/L) was examined in a sequential-co-immobilized two-sectional bioreactor (ITB-2L) during 200 h. ITB resulted in 100% glucose and 16% xylose conversion, showing ethanol productivity of 0.26 g/L·h and yield of 0.4 ge/gs. To investigate the effect of reducing inhibitions, a tubular superhydrophobic silicalite-1/PDMS pervaporative (TSP) autoclavable membrane with antiswelling properties was fabricated. The pervaporative sequential-co-immobilized two-sectional bioreactor (PITB) using TSP enhanced xylose conversion (57%), ethanol productivity (0.39 g/L·h), and yield (0.47 ge/gs). The membrane surface was probed after 161 h of usage, and the limited presence of only negative ions on its surface proved its superior ultralow fouling–biofouling formation. PITB proved itself as a robust integrated process for the second-generation bioethanol production.