Impact of the microbial inoculum source on pre-treatment efficiency for fermentative H2 production from glycerol

International audienceHydrogen (H2) production by dark fermentation can be performed from a wide variety of microbial inoculum sources, which are generally pre-treated to eliminate the activity of H2-consuming species and/or enrich the microbial community with H2-producing bacteria. This paper aims to study the impact of the microbial inoculum source on pre-treatment behavior, with a special focus on microbial community changes. Two inocula (aerobic and anaerobic sludge) and two pre-treatments (aeration and heat shock) were investigated using glycerol as substrate during a continuous operation. Our results show that the inoculum source significantly affected the pre-treatment efficiency. In aerobic sludge no pre-treatment is necessary, while in anaerobic sludge the heat pre-treatment increased H2 production but aeration caused unstable H2 production. In addition, biokinetic control was key in Clostridium selection as dominant species in all microbial communities. Lower and unstable H2 production were associated with a higher relative abundance of Enterobacteriaceae family members. Our results allow a better understanding of H2 production in continuous systems and how the microbial community is affected. This provides key information for efficient selection of operating conditions for future applications

Testing the Capacity of Staphylococcus equorum for Calcium and Copper Removal through MICP Process

This research focused on the evaluation of the potential use of a soil-isolated bacteria, identified as Staphylococcus equorum, for microbial-induced calcite precipitation (MICP) and copper removal. Isolated bacteria were characterized considering growth rate, urease activity, calcium carbonate precipitation, copper tolerance as minimum inhibitory concentration (MIC) and copper precipitation. Results were compared with Sporosarcina pasteurii, which is considered a model bacteria strain for MICP processes. The results indicated that the S. equorum strain had lower urease activity, calcium removal capacity and copper tolerance than the S. pasteurii strain. However, the culture conditions tested in this study did not consider the halophilic feature of the S. equorum, which could make it a promising bacterial strain to be applied in process water from mining operations when seawater is used as process water. On the other hand, copper removal was insufficient when applying any of the bacteria strains evaluated, most likely due to the formation of a copper–ammonia complex. Thus, the implementation of S. equorum for copper removal needs to be further studied, considering the optimization of culture conditions, which may promote better performance when considering calcium, copper or other metals precipitation

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

International audienceTo 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