Homoacetogenesis during hydrogen production by mixed cultures dark fermentation: Unresolved challenge

This paper is a comprehensive review of H-2 consumption during anaerobic mixed culture H-2 dark fermentation with a focus on homoacetogenesis. Homoacetogenesis consumed from 11% to 43% of the H-2 yield in single and repeated batch fermentations, respectively. However, its quantification and extent during continuous fermentation are still not well understood. Models incorporating thermodynamic and kinetic controls are required to provide insight into the dynamic of homoacetogenesis during H-2 dark fermentation. Currently, no adequate method exists to eliminate homoacetogenesis because it does not depend on the culture's source, pre-treatment, substrate, type of reactor, or operation conditions. Controlling CO2 concentrations during dark fermentation needs further investigation as a potential strategy towards controlling homoacetogenesis. Incorporating radioactive labeling technique in H-2 fermentation research could provide information on simultaneous production and consumption of H-2 during dark fermentation. Genetic studies investigating blocking H-2 consuming pathways and enhancing H-2 evolving hydrogenases are suggested towards controlling homoacetogenesis during dark fermentation. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.