Obtenção anaeróbia de etanol em reator em batelada a partir de glicose, xilose e celulose em condição termófila
Data
2017-11-15
Autores
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Biblioteca Digital de Teses e Dissertações da USP
Universidade de São Paulo
Escola de Engenharia de São Carlos
Universidade de São Paulo
Escola de Engenharia de São Carlos
Resumo
Descrição
A biomassa lignocelulósica é uma alternativa atrativa para o aumento na oferta de biocombustíveis, uma vez que é constituída de celulose e hemicelulose. Esses polímeros são constituídos principalmente de unidades menores de glicose e xilose, os quais por meio de bactérias anaeróbias termófilas, podem ser metabolizados em etanol. Portanto, estabeleceu-se o objetivo desse trabalho, em utilizar as principais fontes de carbono da biomassa lignocelulósica (celulose, glicose e xilose), e produzir etanol por meio da ação de consórcio microbiano selecionado a partir de inóculo termófilo e anaeróbio. O inóculo foi submetido a condição de crescimento com variação de pH (2,3,4,5,6,e 7) e variação de dois meios de cultivo em reatores em batelada, visando favorecer bactérias celulolíticas e fermentativas produtoras de etanol. Para a produção de etanol, o pH e meio de cultivo mais adequados foram 7,0 e Meio Thermoanaerobacter ethanolicus, respectivamente. A partir do inóculo enriquecido nas condições nutricionais de pH e meio de cultivo, prosseguiu-se a realização dos ensaios de produção de etanol a partir de celulose, glicose e xilose (1g/L de cada substrato), em pH 7 e meio T. ethanolicus. Os ensaios foram realizados em reator em batelada, em triplicata, a 55 ºC, ambos seguidos de um reator controle, sem adição desses substratos orgânicos. Os rendimentos de etanol foram de 1,73 mol etanol/mol glicose e 1,33 mol de etanol /mol de xilose. Para o substrato celulose obteve-se 1,88 mmol de etanol/g de celulose. Para os reatores controle de glicose, celulose e xilose, no qual o extrato de levedura foi a única fonte orgânica adicionada, a produção de etanol foi 1,27 mmol/L, 0,39 mmol/L e 1,65 mmol/L, respectivamente. Em todos os reatores foi detectado produção de ácido acético, ácido butírico e ácido propiônico. A produção de ácido acético foi de 5,73 mmol/L, 9,73 mmol/L e 14,45 mmol/L, para os reatores de glicose, celulose e xilose, respectivamente. No reator com glicose, observou-se baixo rendimento de hidrogênio (0,31 mol hidrogênio/mol glicose), e nos demais reatores não foi constatado produção desse gás. Em contrapartida, observou-se rendimentos de 6,6 mmol de metano/g de celulose e 0,68 mol de metano/mol de xilose para os respectivos reatores. Dessa forma, pode-se mencionar que em função das características do consórcio microbiano foi possível obter a degradação da celulose e metabolização da glicose e xilose em etanol.
Lignocellulosic biomass is an attractive alternative to increase biofuels proposal, as its composed of cellulose and hemicellulose. These polymers are consisted in individual molecules of glucose and xylose, through some thermophilic bacteria, can metabolize these carbohydrates in ethanol. Therefore, this study reports on using the principals carbon sources of lignocellulosic biomass (cellulose, glucose, and xylose), and producing ethanol through microbial consortium from anaerobic and thermophilic inoculum. The biomass was submitted to variation of pH (2,3,4,5,6, and 7) and two kinds of medium, due to ethanol production in batch reactors. For ethanol production, the optimized pH and medium were 7,0 and Thermoanaerobacter ethanolicus medium, respectively. The enriched culture was being cultivated in pH and medium experiments were used to ethanol production experiments that carried out in batch reactors, from cellulose, glucose and xylose were realized in triplicate and were maintained at 55 °C, in both batches had a control reactor (without these organics substrates). Positive results in ethanol yields were 1,73 mol ethanol/ mol glucose and 1,33 mol ethanol/ mol xylose. In celluloses reactors the microbial consortium was efficient in substrate degradation, however, was obtained lower ethanol yields (1,88 mol ethanol/ g cellulose). In control reactors from glucose, cellulose and xylose, that yeast extract was the unique organic source, ethanol production was 1,27 mmol/L, 0,39 mmol/L e 1,65 mmol/L, respectively. In all reactors were detected acetic, butyric and propionic acids. The acetic acid production was 5,73 mmol/L, 9,73 mmol/L e 14,45 mmol/L in glucose, cellulose and xylose reactors, respectively. For glucoses reactors were observed lower hydrogen production (0,31 mol hydrogen/ mol glucose), in the other reactors did not observed gases production. Instead of the following yields were obtained: 6,6 mmol methane/ g cellulose and 0,68 mol methane/ mol xylose. Taking this into account, microbial consortium enriched had characteristics to degrade cellulose and metabolize glucose and xylose to ethanol.
Lignocellulosic biomass is an attractive alternative to increase biofuels proposal, as its composed of cellulose and hemicellulose. These polymers are consisted in individual molecules of glucose and xylose, through some thermophilic bacteria, can metabolize these carbohydrates in ethanol. Therefore, this study reports on using the principals carbon sources of lignocellulosic biomass (cellulose, glucose, and xylose), and producing ethanol through microbial consortium from anaerobic and thermophilic inoculum. The biomass was submitted to variation of pH (2,3,4,5,6, and 7) and two kinds of medium, due to ethanol production in batch reactors. For ethanol production, the optimized pH and medium were 7,0 and Thermoanaerobacter ethanolicus medium, respectively. The enriched culture was being cultivated in pH and medium experiments were used to ethanol production experiments that carried out in batch reactors, from cellulose, glucose and xylose were realized in triplicate and were maintained at 55 °C, in both batches had a control reactor (without these organics substrates). Positive results in ethanol yields were 1,73 mol ethanol/ mol glucose and 1,33 mol ethanol/ mol xylose. In celluloses reactors the microbial consortium was efficient in substrate degradation, however, was obtained lower ethanol yields (1,88 mol ethanol/ g cellulose). In control reactors from glucose, cellulose and xylose, that yeast extract was the unique organic source, ethanol production was 1,27 mmol/L, 0,39 mmol/L e 1,65 mmol/L, respectively. In all reactors were detected acetic, butyric and propionic acids. The acetic acid production was 5,73 mmol/L, 9,73 mmol/L e 14,45 mmol/L in glucose, cellulose and xylose reactors, respectively. For glucoses reactors were observed lower hydrogen production (0,31 mol hydrogen/ mol glucose), in the other reactors did not observed gases production. Instead of the following yields were obtained: 6,6 mmol methane/ g cellulose and 0,68 mol methane/ mol xylose. Taking this into account, microbial consortium enriched had characteristics to degrade cellulose and metabolize glucose and xylose to ethanol.
Palavras-chave
Ácidos orgânicos e metano, Bactérias celulolíticas, Biomassa lignocelulósica, Digestão anaeróbia, Anaerobic digestion, Cellulolytic bacteria, Lignocellulosic biomass, Methane