Influence of Liquid-to-Gas Ratio on the Syngas Fermentation Efficiency: An Experimental Approach

Syngas fermentation by methanogens is a novel process to purify biogas. Methanogens are able to ferment non-desirable CO2, H2, and CO to methane. However, to use methanogens on an industrial scale, more research has to be done. There are studies that discuss the growth of methanogens on syngas in combination with acetate. In this research, growth of methanogens on syngas as sole carbon source is discussed. Effluent of an anaerobic fed-batch was selectively cultivated with syngas in 400 mL Eppendorf© bioreactors. After a period of 7 days, fifteen 120 mL flasks were filled with three different liquid-to-gas ratios (1:1, 1:3, 1:5). Results showed that different liquid-to-gas ratios change the metabolic preference of the anaerobic microbial community. Moreover, complete conversion in a four-to-eight-day period, via the carboxidotrophic pathway, was observed in all three liquid-to-gas ratios.

Molybdate to prevent the formation of sulfide during the process of biogas production

The process of anaerobic digestion producing biogas is an eco-friendly energy source that promotes recycling from waste biomass such as food chain residues, wet waste, wastewater. In this study, we focused on the problem of the sulfide (H2S) produced by the sulfate-reducing bacteria (SRB) in the presence of sulfate residues. This byproduct is dangerous for human health and an issue due to the highly corrosive effect on metallic components. To this purpose, the Molybdate, a sulfate analog, known in the literature to inhibit SRBs by blocking the first enzyme of the metabolic pathway of anaerobic respiration, was applied. The experiments carried out showed that a concentration of 0.3 mM of molybdate was enough to inhibit the SRB in a complex environment of the anaerobically digested sludge (ADS) took from a real biogas producing bioreactor. During the study, we observed the importance of the sulfate concentration sulfate in the system. Indeed, the production of sulfide was stopped only under the threshold ratio value of 1:10 (molybdate: sulfate). In the short term, the addition of molybdate did not alter the production and quality (% of methane) of the biogas, nor the anaerobic microbial community, including SRB population itself.

SEARCH OF THE POSSIBLE FACTORS OF TRANSMISSION OF THE LEUKOSIS VIRUS OF CATTLE BY ENDOBIOTIC WAYS

The gastrointestinal tract (GIT) of vertebrates is colonized by an extremely diverse anaerobic microbial community consisting of archaea, bacteria, fungi, and various protozoa. Trichostomic ciliates are among the most characteristic and largest protists of this complex enzymatic association, inhabiting both the anterior and posterior parts of the gastrointestinal tract. The transfer of ciliates – endobionts, occurs more often when animals come into contact with other animals of the herd. Regurgitation in cattle occurs reflexively, regularly and frequently, while a significant number of ciliates penetrate the oral cavity. In most ruminants, such social behavior as grooming involves licking the muzzle and sometimes the oral cavity of relatives, with some ciliates being transferred from the mouth of one animal to the mouth of another and soon swallowed. According to the results of PCR-studies of endobiotic ciliates from the rumen of cows for the presence of bovine leukemia virus (BLV) in them, a negative result was obtained in all samples. Thus, in a homogenized material consisting of different types of ciliates from 12 cows that were spontaneously infected, a PCR methods was obtained negative for the presence of the genetic material of bovine leukemia virus. In our opinion, the data obtained do not completely disprove the hypothesis of endobiotic transmission of BLV due to the relatively small sample of carrier animals and insufficient improvement of the PCR diagnostic method, and these studies should be continued using a larger number of infected with BLV animals and different diagnostic methods.

Aqueous film forming foam and associated perfluoroalkyl substances inhibit methane production and Co-contaminant degradation in an anaerobic microbial community

This work determines the components of aqueous film forming foam responsible for disrupting microbial community functions.

Preliminary assessment of methanogenic microbial communities in marine caves of Zakynthos Island (Ionian Sea, Greece)

Mediterranean marine caves remain largely unexplored, while particularly limited information is available about the microbial life existing in these unique environments. The present study is a preliminary assessment of the composition of the active anaerobic microbial community colonizing the walls of newly explored systems of underwater caves and small cavities in Zakynthos Island. The interior of these caves is densely coated with egg-shaped, foam-shaped and filamentous biological structures that are characterised by a strong odor of hydrogen sulfide gas. A total of twelve structures scrapped from cave rocks were subjected to anaerobic cultivation for up to 208 days. Strong to moderate methanogenesis was observed in two different types of egg-shaped structures and one foam-like structure. Interestingly, this was observed in experiments that were performed at room temperature (i.e. 25oC) which is substantially lower than those typically considered optimum for methane production (e.g. 35oC). Analysis of the 16S rRNA genes revealed a clear dominance of archaea and bacteria closely related to known methane producers and sulfate reducers, including members of the families Methanomicrobiaceae, Desulfobulbaceae, Desulfobacteraceae, Desulfuromonaceae, Campylobacteraceae, Marinifilaceae, Clostridiaceae, Incertae Sedis – Family I & II. These results show that Mediterranean marine caves can host members of archaea and bacteria with potential biotechnological interest that deserve further investigation.