Dynamics of bacterial communities and substrate conversion during olive-mill waste dark fermentation: Prediction of the metabolic routes for hydrogen production

Abstract

The aim of this work was to study the biological catalysts and possible substrate conversion routes in mesophilic dark fermentation reactors aimed at producing H2 from olive mill wastewater. Bacillus and Clostridium were the most abundant phylotypes during the rapid stage of H2 production. Chemical analyses combined with predictive 2 functional profiling of the bacterial communities indicated that the lactate fermentation was the main H2-producing route. In fact, during the fermentation process, lactate and acetate were consumed, while H2 and butyrate were being produced. The fermentation process was rich in genes that encode enzymes for lactate generation from pyruvate.Lactate conversion to butyrate through the generation of pyruvate produced H2 through the recycling of electron carriers via the pyruvate ferredoxin oxydoreductase pathway.Overall, these findings showed the synergy among lactate-, acetate-and H2-producing bacteria, which complex interactions determine the H2 production routes in the bioreactors.

Thermophilic Dark Fermentation of Olive Mill Wastewater in Batch Reactors: Effect of pH and Organic Loading

“…During the second day (after 40 h) of the experimentation period, a constant increase in H 2 production was observed until t = 99 h, reaching a total H 2 volume of 376 mL. According to other published works [21,42], the maximum H 2 production observed under mesophilic biohydrogen potential tests or batch DF was 46 ± 15 mL H 2 /g vs. and 33.8 mL H 2 /g vs., respectively, whereas in our work, the corresponding yield was calculated to be significantly lower (18.6 mL H 2 /g VS). The decreased hydrogen yield could be attributed to the OMW phenols presence.…”

“…Due to the specific three produced metabolites, all the fermentation types that followed are characterized as H 2producing (acetate, ethanol and butyrate metabolic pathways) [47]. In Mugnai et al [21], during the third day of their experimentation period, where H 2 was detected, a completely different metabolites profile was observed. Even if acetate was still the dominant fermentation metabolite, lactate and formate were also produced, and butyrate was totally absent and appeared after the fifth day of their experiment.…”

“…Dark fermentation Production of H 2 and conversion of the substrate mainly to VFAs (and/or ethanol). [21] Aerobic process Good performance on organic compounds treatment and polyphenols degradation, however the organic load should be relatively low. [37] Compost production Production of a nutrient-rich fertilizer; however, reduction in moisture is mandatory.…”

“…According to Galliou et al [15], OMW solar drying and composting led to a final product of 3.5% N, 1% P, 6.5% K, and 0.29% phenolic compounds, which proved similar to commercial NPK fertilizers for pepper plants' cultivation. However, the case of dark fermentation (DF) has not yet been widely exploited, according to the literature, as only a few papers can currently been found [20][21][22].…”

Dark Fermentation Process Response to the Use of Undiluted Tequila Vinasse without Nutrient Supplementation

“…Indeed, the observed hydrogen production corroborated well with the consumption of lactate and acetate and the formation of butyrate. The lactate-driven hydrogen fermentation has been reported to take place using TV [7,18,25,28], but also with others such as cheese whey [33], sugarcane vinasse [42], olive mill waste [43], among others.…”