Conversion of syngas (CO and H2) to biochemicals by mixed culture fermentation in mesophilic and thermophilic hollow-fiber membrane biofilm reactors

Abstract

Syngas (CO/H2) fermentation provides an alternative method for organics utilization. The hollow-fiber membrane biofilm reactor (HfMBR) offers a potential way to use CO and H2 effectively. However, studies on syngas utilization by mixed culture fermentation (MCF) in HfMBR were seldom reported. This study is the first to demonstrate and compare the in-situ production of volatile fatty acids via syngas by mesophilic and thermophilic MCF, in which CO and H2 utilization exceeded 95% and even reached 100%. Acetate (4.22 g/L), butyrate (1.35 g/L), caproate (0.88 g/L), and caprylate (0.52 g/L) were detected at 35 °C, whereas acetate was the main metabolite at 55 °C. The proportion of acetate ranged from 47.5% to 62.7% at 35 °C and exceeded 90% at 55 °C in the batch mode. Notably, the acetate concentration and the production rate could reach 24.6 g/L and 16.4 g/(L.d), respectively, at pH 6.5 in the continuous mode at 55 °C. Thus, thermophilic conditions are preferable for high-purity and high-concentration acetate production from syngas. As revealed by Illumina high-throughput sequencing, Clostridium (41.6%) and Thermoanaerobacterium (92.8%) were the dominant bacteria under mesophilic and thermophilic conditions, respectively. This study demonstrates a potential technique for syngas (CO/H2) utilization and biochemicals production by MCF in HfMBR.