Effect of the electric supply interruption on a microbial electrosynthesis system converting inorganic carbon into acetate.

Microbial electrosynthesis (MES) technology relies on the direct use of electrons to convert CO2 into long chain organic chemicals. Therefore, MES has been proposed to be coupled to the renewable electricity supply, mainly from solar and wind sources. However, those energies suffer fluctuations and interruptions of variable duration, which can have an adverse effect on MES performance. Such effects on MES has been evaluated for the first time under different interruptions time. H-cell-MES reactors were disconnected from power supply during 4, 6, 8, 16, 32 and 64 h. Interruptions affected the acetate production rate, causing a decrease of until 77% after 64 h off. However, after all the interruptions, the acetate production was restored, taking between 7 and 16 h for the reduction current to turn steady. Therefore, microbial community on MES proved to be resilient and able to recover the electro-autotrophic activity despite the duration of current supply interruptions.

Microbial communities from 20 different hydrogen-producing reactors studied by 454 pyrosequencing.

To provide new insight into the dark fermentation process, a multi-lateral study was performed to study the microbiology of 20 different lab-scale bioreactors operated in four different countries (Brazil, Chile, Mexico, and Uruguay). Samples (29) were collected from bioreactors with different configurations, operation conditions, and performances. The microbial communities were analyzed using 16S rRNA genes 454 pyrosequencing. The results showed notably uneven communities with a high predominance of a particular genus. The phylum Firmicutes predominated in most of the samples, but the phyla Thermotogae or Proteobacteria dominated in a few samples. Genera from three physiological groups were detected: high-yield hydrogen producers (Clostridium, Kosmotoga, Enterobacter), fermenters with low-hydrogen yield (mostly from Veillonelaceae), and competitors (Lactobacillus). Inocula, reactor configurations, and substrates influence the microbial communities. This is the first joint effort that evaluates hydrogen-producing reactors and operational conditions from different countries and contributes to understand the dark fermentation process.