Carbon capture and utilization of fermentation CO₂: Integrated ethanol fermentation and succinic acid production as an efficient platform

Dark fermentative bioethanol production process yields carbon dioxide (CO₂) and organic acids as by-products. The so-yielded CO₂ is a nearly saturated gas of high CO₂ purity, which is commonly utilized in food industries as supplements. The potential utilization pathways for the CO₂ generated and released from the ethanol fermentation process (denoted as “fermentation CO₂”) include production of biofuels by CO₂ fixation of microalgae and succinic acid fermentation by non-photosynthetic microorganisms. This study compared the performances of these two CO₂ fixing pathways using Chlorella vulgaris or Actinobacillus succinogenes cultures. The highest carbon fixation rate achieved by Actinobacillus succinogenes was 388.8 g/L-d in 2-L reactor, which is about 188 times to that by Chlorella vulgaris (2.06 g/L-d) in the reactor at the same volume. This study ultimately demonstrated the advantages of adopting succinic acid production process compared to those frequently addressed in literature using microalgae-based biofuels.