Produção biotecnológica de hidrogênio a partir do glicerol, bioproduto da produção do biodiesel
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2016-08-23
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Universidade Estadual Paulista (Unesp)
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A produção de biodiesel levou ao aumento do coproduto gerado desse processo, o glicerol bruto, que devido ao seu excesso, tem ganhado interesse nas transformações biotecnológicas visando à formação de produtos com valor agregado, sendo H2 de maior interesse. Este estudo avaliou o potencial da bioconversão do glicerol bruto, proveniente da produção de biodiesel a partir de óleo de cozinha usado, a hidrogênio por meio de consórcios de bactérias anaeróbias fermentativas. O glicerol bruto foi submetido ao pré-tratamento ácido (pH 3,0, HCl 1,0M) para converter sabões solúveis, considerados inibitórios ao crescimento microbiano, à ácidos graxos insolúveis. Consórcios bacterianos provenientes de estação de tratamento de água residual industrial (I) e sanitária (II e III), além da cultura pura Enterobacter sp. (inóculo IV) foram utilizados como inóculos e reativados em meio de cultivo, pH 7,0, a 37°C por 7 dias, sob condições anaeróbias. Para a obtenção de consórcios bacterianos produtores de H2, o pré-tratamento nos inóculos I, II e III foi realizado por meio do choque térmico (100°C por 15 minutos) com posterior enriquecimento por diluições seriais em meio PYG modificado e pH 5,5. Bacilos Gram positivos e formadores de endósporos foram predominantes. Os consórcios enriquecidos que apresentaram melhores desempenhos quanto à geração de H2, (I) e (II), foram utilizados para as realizações de ensaios, em batelada, em proporções crescentes de glicerol bruto pré-tratado. Nos ensaios de geração de H2, 20% do meio reacional era composto pelos inóculos (I) e (II), separadamente, em meio PYG modificado, mantidos a 37°C, pH inicial 5,5, headspace de N2 (100%) sob as seguintes condições: (a) 10 g DQO L-1 de glicerol bruto pré-tratado e 10 g DQO L-1 de glicerina; (b) 4 g DQO L-1 de glicerina e 16 g DQO L-1 de glicerol bruto pré-tratado e (c) 20 g DQO L-1 de glicerol bruto pré-tratado. Os rendimentos de H2 foram de 2,21, 1,63, 0,83, 1,05, 0,57 e 0,31 mol H2 mol-1 glicerol, respectivamente para Ensaio (I)-a (envolvendo o inóculo (I) sob a condição a), Ensaio (I)-b, Ensaio (I)-c, Ensaio (II)-a (envolvendo o inóculo (II) sob a condição a), Ensaio (II)-b e Ensaio (II)-c, com o consumo de glicerol de 26,9%, 45,8%, 56,2%, 31,7%, 59,0% e 91,0% para os respectivos ensaios citados. Foi detectado principalmente etanol em maior concentração em todos os ensaios envolvendo o inóculo (I), bem como para o inóculo (II) envolvendo os ensaios (II)-a e b, e ácido butírico em maior concentração no ensaio (II)-c. Por meio da análise de biologia molecular, a abundância relativa da ordem Clostridiales para o inóculo (I) e (II) foi, respectivamente, 91,81% e 94,70%, bem como de representantes da família Peptostreptococcaceae com alta abundância relativa para ambos os inóculos, de 85,29% e 70,26% para inóculo (I) e (II) respectivamente. Foi realizado um ensaio comparativo com cultura pura Enterobacter sp. com 20 g DQO L-1 de glicerol bruto pré-tratado e o rendimento obtido foi de 0,13 mol H2 mol-1 glicerol. Além disso, a cultura pura mostrou-se ser mais sensível nos ensaios de geração de hidrogênio devido à presença de contaminantes no glicerol bruto. Os resultados de geração de H2 envolvendo consórcios foram eficientes do ponto de vista em que foram atingidos rendimentos equivalentes, ou até mesmo superiores, aos reportados por outros trabalhos, mostrando que é possível obter hidrogênio por meio do glicerol bruto proveniente de transesterificação do óleo de cozinha usado.
The biodiesel production has led to increase co-product generated in this process, the crude glycerol, which due to its excess, has gained interest in the biotechnological transformations for aimed at formation of value-added products, considering H2 the most interest bioproduct. This study evaluated the potential of bioconversion of crude glycerol from the biodiesel production from used cooking oil, to generate hydrogen through consortia of fermentative anaerobic bacteria. The crude glycerol has been subjected to the acid pretreatment (pH 3.0, 1.0M HCl) to convert soluble soaps, considered inhibitory to microbial growth, to insoluble fatty acids. Consortia from sewage treatment of industrial waste (I) and sanitary waste (II and III), and the pure culture Enterobacter sp. (inoculum IV) were used as inocula and reactivated in growth medium, pH 7.0, at 37°C for 7 days, under anaerobic conditions. To obtain H2-producing bacterial consortia, pretreatment in inocula I, II and III was carried through the thermal shock (100°C for 15 minutes) with subsequent enrichment by serial dilutions in modified PYG and pH 5.5. Gram positive bacillis and spores-forming were predominant. The enriched consortia that showed better performances for the H2 generation, (I) and (II), were used for the assays, in batch mode, varying concentrations in increasing proportions of the crude glycerol pretreated. In the H2 generation assays, 20% of the reaction medium was composed of inoculum (I) and (II) separately in modified PYG medium, kept at 37 ° C, initial pH 5.5, headspace N2 (100%) under the following conditions: (a) 10 g COD L-1 crude glycerol pretreated and 10 g COD L-1 glycerine; (b) 4 g COD L-1 of glycerin and 16 g COD L-1 crude glycerol pretreated and (c) 20 g COD L-1 crude glycerol pretreated. H2 yields were 2.21, 1.63, 0.83, 1.05, 0.57 and 0.31 mol H2 mol-1 glycerol, respectively, for the Assay (I)-a (involving the inoculum (I) under the condition a), Assay (I) -b, Assay (I)-c, Assay (II)-a (involving the inoculum (II) under the condition a), Assay (II) -b Assay (II)-c with glycerol consumption of 26.9%, 45.8%, 56.2%, 31.7%, 59.0% and 91.0% for the respective assays cited. Ethanol was mainly detected in a higher concentration in all assays involving the inoculum (I), as well as for the inoculum (II) involving the assays (II)-a and b, and butyric acid in higher concentrations in the assay (II)-c. Through molecular biology, the relative abundance of the Clostridiales order for the inoculum (I) and (II) were, respectively, 91.81% and 94.70% as well as the Peptostreptococcaceae family showed high relative abundance for both inocula of 85.29% and 70.26% for inoculum (I) and (II) respectively. A comparative assay with a pure culture Enterobacter sp., with 20 g COD L-1 crude glycerol pretreated and the yield obtained was 0.13 mol H2 mol-1 glycerol was performed. In addition, the pure culture was shown to be more sensitive to hydrogen generation assays due to the presence of contaminants in the crude glycerol. The results of generation of H2 evolving consortia were efficient from the point of view that equivalent yields have been achieved, or even superior, to those reported by other studies showing that it is possible to obtain hydrogen by crude glycerol from cooking oil transesterification used.
The biodiesel production has led to increase co-product generated in this process, the crude glycerol, which due to its excess, has gained interest in the biotechnological transformations for aimed at formation of value-added products, considering H2 the most interest bioproduct. This study evaluated the potential of bioconversion of crude glycerol from the biodiesel production from used cooking oil, to generate hydrogen through consortia of fermentative anaerobic bacteria. The crude glycerol has been subjected to the acid pretreatment (pH 3.0, 1.0M HCl) to convert soluble soaps, considered inhibitory to microbial growth, to insoluble fatty acids. Consortia from sewage treatment of industrial waste (I) and sanitary waste (II and III), and the pure culture Enterobacter sp. (inoculum IV) were used as inocula and reactivated in growth medium, pH 7.0, at 37°C for 7 days, under anaerobic conditions. To obtain H2-producing bacterial consortia, pretreatment in inocula I, II and III was carried through the thermal shock (100°C for 15 minutes) with subsequent enrichment by serial dilutions in modified PYG and pH 5.5. Gram positive bacillis and spores-forming were predominant. The enriched consortia that showed better performances for the H2 generation, (I) and (II), were used for the assays, in batch mode, varying concentrations in increasing proportions of the crude glycerol pretreated. In the H2 generation assays, 20% of the reaction medium was composed of inoculum (I) and (II) separately in modified PYG medium, kept at 37 ° C, initial pH 5.5, headspace N2 (100%) under the following conditions: (a) 10 g COD L-1 crude glycerol pretreated and 10 g COD L-1 glycerine; (b) 4 g COD L-1 of glycerin and 16 g COD L-1 crude glycerol pretreated and (c) 20 g COD L-1 crude glycerol pretreated. H2 yields were 2.21, 1.63, 0.83, 1.05, 0.57 and 0.31 mol H2 mol-1 glycerol, respectively, for the Assay (I)-a (involving the inoculum (I) under the condition a), Assay (I) -b, Assay (I)-c, Assay (II)-a (involving the inoculum (II) under the condition a), Assay (II) -b Assay (II)-c with glycerol consumption of 26.9%, 45.8%, 56.2%, 31.7%, 59.0% and 91.0% for the respective assays cited. Ethanol was mainly detected in a higher concentration in all assays involving the inoculum (I), as well as for the inoculum (II) involving the assays (II)-a and b, and butyric acid in higher concentrations in the assay (II)-c. Through molecular biology, the relative abundance of the Clostridiales order for the inoculum (I) and (II) were, respectively, 91.81% and 94.70% as well as the Peptostreptococcaceae family showed high relative abundance for both inocula of 85.29% and 70.26% for inoculum (I) and (II) respectively. A comparative assay with a pure culture Enterobacter sp., with 20 g COD L-1 crude glycerol pretreated and the yield obtained was 0.13 mol H2 mol-1 glycerol was performed. In addition, the pure culture was shown to be more sensitive to hydrogen generation assays due to the presence of contaminants in the crude glycerol. The results of generation of H2 evolving consortia were efficient from the point of view that equivalent yields have been achieved, or even superior, to those reported by other studies showing that it is possible to obtain hydrogen by crude glycerol from cooking oil transesterification used.
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Palavras-chave
Bioprodução de Hidrogênio., Consórcio Microbiano, Enterobacter sp, Fermentação, Glicerol bruto, Óleo de Cozinha Usado