Homoacetogenesis and solventogenesis from H2/CO2 by granular sludge at 25, 37 and 55 °C

• Published in: Chemosphere (Oxford) 2021-02, Vol.265, p.128649-128649, Article 128649
• Main Authors: He, Yaxue, Cassarini, Chiara, Marciano, Flora, Lens, Piet N.L.
• Format: Article
• Language: English
• Subjects: Acetic acid; Bioconversion; Biofuel; Ethanol; H2/CO2
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/j.chemosphere.2020.128649

CO2 fermentation is a promising process to produce biofuels like ethanol. It can be integrated in third generation biofuel production processes to substitute traditional sugar fermentation when supplied with cheap electron donors, e.g. hydrogen derived from wind energy or as surplus gas in electrolysis. In this study, granular sludge from an industrial wastewater treatment plant was tested as inoculum for ethanol production from H2/CO2 via non-phototropic fermentation at submesophilic (25 °C), mesophilic (37 °C) and thermophilic (55 °C) conditions. The highest ethanol concentration (17.11 mM) was obtained at 25 °C and was 5-fold higher than at 37 °C (3.36 mM), which was attributed to the fact that the undissociated acid (non-ionized acetic acid) accumulation rate constant (0.145 h−1) was 1.39 fold higher than at 25 °C (0.104 h−1). Methane was mainly produced at 55 °C, while neither acetic acid nor ethanol were formed. Ethanol production was linked to acetic acid production with the highest ethanol to acetic acid ratio of 0.514 at 25 °C. The carbon recovery was 115.7%, 131.2% and 117.1%, while the electron balance was almost closed (97.1%, 110.1% and 109.1%) at 25 °C, 37 °C and 55 °C, respectively. The addition of bicarbonate inhibited ethanol production both at 25 °C and 37 °C. Clostridium sp. were the prevalent species at both 25 and 37 °C at the end of the incubation, which possibly contributed to the ethanol production. [Display omitted] •Highest ethanol concentration obtained at 25 °C was 5-fold higher than at 37 °C.•Ethanol starts to be produced when pH is decreased to 4.7 at both 25 and 37 °C.•Bicarbonate addition enhanced acetic acid, but inhibited ethanol production.•Clostridium sp. were enriched and contributed to acetic acid and ethanol production from H2/CO2 at 25 and 37 °C.