Developing a high-rate ABE fermentation system for rice straw: CSTR with immobilization on granular-activated carbon with ex situ pervaporation

Abstract

This study assessed the performance of two continuous stirred tank reactors (CSTRs) to immobilize Clostridium acetobutylicum DSM 792 and Clostridium beijerinckii DSM 6422 on granular activated carbon. Dilution rates (D) from 0.05 to 0.60 h−1 were tested using a sugar mixture to mimic rice straw hydrolysate. Immobilization was shown to be a highly effective technique for processing high flows without cell washout. Both CSTRs demonstrated significantly higher butanol productivity than their free-cell counterparts, achieving the remarkable value of 2.29 g L−1 h−1 with C. beijerinckii at D = 0.60 h−1. Rice straw hydrolysate was fed to the high-rate CSTR, reaching a butanol productivity of 2.07 g L−1 h−1 at D = 0.30 h−1. A novel downstream configuration of ex situ gas stripping followed by two pervaporation cycles operated under rough vacuum was explored in discontinuous mode, that reduced the energy demand by 63 % of conventional distillation methods. This configuration holds great promise for the advance of the lignocellulosic biorefinery process.