Estudo de diferentes tipos de fonte de carbono como substrato para produção de hidrogênio por meio de fermentação escura e fotofermentação

Abstract

The supply to the global energetic needs, mostly, is dependent of fossil fuels. The hydrogen is considered a viable energy source for being a not polluting fuel that may be obtained by renewable resources. Besides, it may be produced biologically by fermentation applying agroindustrial residue as substrates that contributes to minimize their accumulation at the industrial processes. Thus, H2 is a promising alternative due to reduced environmental impacts. In this present study, the objective was study different types of carbon sources for hydrogen production by dark fermentation using a microbial consortium and photofermentation applying non-sulfur purple bacteria. The substrates utilized in the processes were pure glucose, whey permeate and molasses soybean, this is agroindustrial residues. Preliminary tests were performed in penicillin bottles, in batch mode, to verify the production of biogas with: (i) dark fermentation using mixed culture in which it was evaluated the effect of inoculum pre-treatment: heat-shock and acid; (ii) photofermentation of pure cultures and co-culture assays. Based on the results of preliminary tests in reduced scale, it was found out that the pretreatment with heat-shock produced ensured best results, with a productivity of 14,14 mmol H2/L.day. Concerning on the results of photofermentation trials with pure culture and co-culture, it was verified that the results obtained with Rhodopseudomonas palustris assays were better than with Rhodobacter capsulatus and that co-culture system presented the lowest results. In trials that the consumption of molasses soybean was analyzed, it was observed the two strains had the same potential for the production of H2. After preliminary tests, experiments in scale-up were conducted with the purpose of increasing hydrogen production and evaluate the process in function of time, in fed batch mode with isolated, alternating and simultaneous addition of sugar for the two biological routes. Dark fermentation was carried out in anaerobic conditions, using a microbial consortium that obtained best results in the preliminary test in pretreatment. It was observed that fermentation with simultaneous addition of glucose and lactose prometed the highest hydrogen maximum productivity of 168,27 mmol H2/L.day in 24 hours of process. Nevertheless, the alternation fed (glucose and lactose) allowed keeping the culture active with potential to hydrogen production for a period of time superior to 900 hours. At the end of fermentation, the main products were lactic acid and butyric acid, followed by acetic acid, ethanol e propionic acid.