Márquez-Nogueras, Karla M.

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    Anaerobic degradation of marine algae, seagrass and tropical climbing vines to produce a renewable energy source and the analysis of their anaerobic microbial communities
    (2013) Márquez-Nogueras, Karla M.; Ríos-Hernández, Luis A.; College of Arts and Sciences - Sciences; Santos Flores, Carlos J.; Sastre de Jesús, Inés; Department of Biology; Ríos-Soto, Karen
    Energy demand by contemporary societies and the excessive consumption of fossil fuels have impulsed research and the employment of renewable energy systems. It has been proposed, in terms of renewable systems, the use of biofuels generated by the degradation of organic matter, like bioethanol, biodiesel and methane, being this last one the more efficient one based on its calorific value. For this reason we propose the implementation of anaerobic reactors which degrade biomass that has relatively high growth rates, require low quantity of nutrients and eliminate any competition by its use, thus creating a cost-effective system. Tropical climbing vines provide biomasses with the previous characteristics; however, they contain high concentrations of cellulose and lignin that are polymers difficult to degrade. In contrast, biomass like marine algae contains low concentrations of both lignin and cellulose, which should make them an easier material for degradation. Finally, in comparison to marine algae another source of marine biomass, which can serve as biomass for the creation of these systems, is seagrasses. Nonetheless, seagrasses are more related to terrestrial plants than marine algae for which they could present the same difficulties towards degradation as climbing vines. This study aims to compare the efficiency of three different vegetation biomasses (marine algae, seagrass and tropical climbing vines) as primary substrate for anaerobic reactors. Moreover, to achieve what could be a highly cost effective system, the isolation and identification of anaerobic alginate degraders was studied. Alginate is a complex polysaccharide present in marine algae’s cell wall, representing up to 40% of its dry weight. The study was completed creating anaerobic microcosms, which contained 0.016 g/mL (0.5 g total biomass) of each biomass. Methane and intermediaries produced were determined for each microcosm. After chemical determinations, the microbial community was analyzed using molecular techniques. The isolation of anaerobic alginate degraders was achieved performing serial dilutions for the purification of the microbial community present in the samples selected, which in turn were analyzed using molecular techniques, such as PCR and DGGE. After 108 days, results demonstrated that there were significant differences between marine and terrestrial biomasses; the latter was the most efficient. In terrestrial biomass microcosms, a maximum production of 50% of methane achieved an energetic rendition of 8.37 W/h; in comparison with marine biomass microcosms in which the highest energetic rendition was 3.60 W/h. Molecular analysis of the microbial community present in the marine biomass microcosms had a low diversity. In the different marine and terrestrial microcosms, the bacteria that dominated was Desulfovibrio vulgaris, but the dominant methanogen depended on the biomass being degraded. Moreover, in the samples analyzed, the anaerobic alginate degraders demonstrated a convergence of a gram-negative spore former, which seemed favored during the purification process. Nonetheless, even though the isolation of anaerobic alginate degraders was successful, it is important that the microbial community works together to achieve the conversion of alginate to methane. Although there was a positive isolation of bacteria that can degrade alginate, methanogenic bacteria were not isolated this in spite of methane formation, which indicated their presence in the experimental microcosms.