Controlling Ethanol Use in Chain Elongation by CO2 Loading Rate

M. Roghair, Tim Hoogstad, D.P.B.T.B. Strik*, C.M. Plugge, P.H.A. Timmers, R.A. Weusthuis, M.E. Bruins, C.J.N. Buisman

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

138 Citations (Scopus)


Chain elongation is an open-culture biotechnological
process which converts volatile fatty acids (VFAs) into
medium chain fatty acids (MCFAs) using ethanol and other
reduced substrates. The objective of this study was to
investigate the quantitative effect of CO2 loading rate on
ethanol usages in a chain elongation process. We supplied
different rates of CO2 to a continuously stirred anaerobic
reactor, fed with ethanol and propionate. Ethanol was used to
upgrade ethanol itself into caproate and to upgrade the
supplied VFA (propionate) into heptanoate. A high CO2
loading rate (2.5 LCO2·L−1·d−1) stimulated excessive ethanol
oxidation (EEO; up to 29%) which resulted in a high caproate production (10.8 g·L−1·d−1). A low CO2 loading rate (0.5 LCO2·
L−1·d−1) reduced EEO (16%) and caproate production (2.9 g·L−1·d−1). Heptanoate production by VFA upgrading remained
constant (∼1.8 g·L−1·d−1) at CO2 loading rates higher than or equal to 1 LCO2·L−1·d−1. CO2 was likely essential for growth of
chain elongating microorganisms while it also stimulated syntrophic ethanol oxidation. A high CO2 loading rate must be selected
to upgrade ethanol (e.g., from lignocellulosic bioethanol) into MCFAs whereas lower CO2 loading rates must be selected to
upgrade VFAs (e.g., from acidified organic residues) into MCFAs while minimizing use of costly ethanol.
Original languageEnglish
Pages (from-to)1496-1505
JournalEnvironmental Science and Technology
Issue number3
Publication statusPublished - 5 Jan 2018


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