At an HRT of 24 h, the third most abundant genus that was
independent of the HRT was Veillonella. Species of this genus
produce propionate and acetate from lactate fermentation,
and it has been demonstrated that Veillonella parvula produces
hydrogen as a side product when using ethanol as a substrate
[38]. The other OTUs observed (392, 806 and 742) appear in the
phylogenetic tree (Fig. 5) and had a relative abundance of less
than 0.56% of the sequences obtained from the microbial
analysis. These OTUs were related to genus Olsenella, Bifidobacterium
and Pelosinus, which have been reported in communities
of fermentative reactors