High-rate ethanol production at low pH using the anaerobic granular sludge process

Biotechnol Bioeng. 2021 May;118(5):1943-1950. doi: 10.1002/bit.27708. Epub 2021 Mar 3.

Abstract

In this study, we investigated the operational performance and product spectrum of glucose-fermenting anaerobic granular sludge reactor at pH 4. A selective environment for the growth of granules was implemented by the introduction of a 2 min settling phase, a hydraulic retention time of 6 h and a solid retention time of 12 ± 3 days. The fermentation products were ethanol, lactate, and volatile fatty acids (VFA) with yields of 0.55 ± 0.03, 0.15 ± 0.02, and 0.20 ± 0.04 gram chemical oxygen demand (gCOD)/gCOD glucose, respectively. The obtained product spectrum was remarkably different from the VFA-dominated product spectrum reported in a previous study when the same system was operated at higher pH (4.5-5.5). The shift in product spectrum coincided with a shift in the microbial community structure with the dominance of eukaryotic Candida tropicalis, Pichia jaroonii, and prokaryotic Lactobacillus species instead of the Clostridia species obtained at higher pH-values. The control of the microbiomes and the associated product spectra provides bioprocess engineers with the option to tailor a suitable precursor compound mixture for subsequent chain elongation fermentation or PHA biopolymer production.

Keywords: VFA; ethanol; granular sludge; open/mixed culture fermentation; resource recovery.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Anaerobiosis
  • Bioreactors / microbiology*
  • Ethanol* / analysis
  • Ethanol* / metabolism
  • Fatty Acids, Volatile / metabolism
  • Fermentation / physiology
  • Glucose / metabolism
  • Hydrogen-Ion Concentration
  • Sewage / microbiology*

Substances

  • Fatty Acids, Volatile
  • Sewage
  • Ethanol
  • Glucose