Produção e destoxificação de hidrolisado ácido de bagaço de cana-de-açúcar visando a otimização de leveduras fermentativas
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Data
2020-11-27
Autores
Candido, João Paulo [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
O etanol de segunda geração (E2G) tem perspectiva de se tornar uma importante alternativa bioenergética. O desenvolvimento dessa tecnologia está associada à utilização de materiais lignocelulósicos, com destaque para subprodutos agrícolas e agroindustriais dos quais são extraídos açúcares fermentesíveis, principalmente xilose e glicose. A hidrólise ácida despolimeriza a hemicelulose contida nestes materiais liberando principalmente xilose. Subsequentemente a celulose é convertida em glicose por hidrólise enzimática. Contudo, os processos químicos para despolimerização da hemicelulose e para alteração da estrutura da celulose produzem compostos tóxicos, como, derivados do furano, fenólicos e ácidos orgânicos, que podem ser prejudiciais à fermentação. Desta forma, este estudo busca destoxificar o hidrolisado ácido de bagaço de cana-de-açúcar utilizando diferentes materiais adsorventes, avaliar a viabilidade celular após a destoxificação, quantificar o rendimento fermentativo utilizando Saccharomyces cerevisiae (PE-2) e Scheffersomyces stipitis (NRRL Y-7124), além de caracterizar quimicamente a vinhaça e avaliar sua biodegradação (Bartha e Pramer, 1965) e toxicidade mediante ensaios com Lactuca sativa e Daphnia similis. A fração líquida obtida do hidrolisado ácido (HA) (pH 5.5) de bagaço de cana-de-açúcar foi utilizada como fonte de pentoses (17.70 g L-1) e melaço (ME) de cana-de-açúcar como fonte de hexoses (47.00 g L-1). Diferentes concentrações ácidas foram utilizadas na hidrólise do bagaço de cana-de-açúcar (1-5% m/v H2SO4). Foram utilizados os adsorventes: carvão ativado, argila, hidrotalcita e células ativas e inativas de S. cerevisiae and S. stipitis, em concentrações que variaram (1 – 8 % m/v). A fermentação foi conduzida sob 48 h com cultura isolada e cultura mista (S. cerevisiae e S. stipitis). Subsequentemente as vinhaças (vinhaça sem o processo de destoxificação e com o processo de destoxificação) provenientes da fermentação etanólica foram avaliadas sob diferentes concentrações de condicionamento em solo (2,5; 5,0 e 10,0 %) para estudo da biodegradabilidade. O teste de toxicidade foi realizado em concentrações que variaram de 1,5 a 10 %. Resultados de crescimento celular e viabilidade permitiram selecionar as concentrações mais efetivas de adsorventes (4 e 8 % m/v), com destaque para o adsorvente biológico (células ativas de PE-2) que apresentaram remoção de 66 % de furfural, 51 % de 5-hidroxi-metil-furfural (5-HMF) e produtividade alcoólica de 23,5 g L-1 (48 h) quando foi utilizado substrato com HA e ME na presença PE-2 e NRRL Y-7124. Os ensaios de caracterização química indicam alta carga orgânica e mineral nas amostras de vinhaças, compatíveis com a vinhaça de etanol de primeira geração, que sob determinadas condições (condicionamento no solo a 2.5 %) possibilita alta eficiência na biodegradação (> 80 %). Bioensaio com L. sativa sinaliza que a vinhaça proporciona crescimento radicular quando administrada sob baixa concentração (≤ 2,5 %), e toxicidade aguda com 50 % de imobilização para D. similis em concentração na ordem de 4,5 %. Este estudo indica que o uso de adsorventes contribuiu para melhorar a qualidade do hidrolisado, com enfase para o uso do adsorvente biológico, que proporcionou melhores taxas de crescimento cellular, redimento fermentativo e para nos ensaios de biodegradação e toxicidade. Estes dados indicam uma importante aplicação deste material adsorvente na destoxificação de hidrolisado ácido de bagaço de cana de açúcar.
Second generation ethanol has the prospect of becoming an important bioenergy alternative. The development of this technology is associated with the lignocellulosic materials' use, with emphasis on agricultural and agroindustrial by-products from which fermentable sugar are extracted, mainly xylose and glucose. The acid hydrolysis depolymerizes the hemicellulose releasing mainly xylose. Subsequently, the cellulose can be converted into glucose by enzymatic hydrolysis. However, the acid hydrolysis produces toxic compounds, such as furan derivatives, phenolics, and organic acids, which are harmful to fermentation. This study seeks to detoxify the sugarcane bagasse acid hydrolyzate using different adsorbent materials, evaluate cell viability before and after detoxification, quantify the fermentative yield using Saccharomyces cerevisiae (PE-2) and Scheffersomyces stipitis (NRRL Y-7124), besides, chemically characterizing vinasse and evaluating its biodegradation (Bartha and Pramer, 1965) and toxicity through tests with Lactuca sativa and Daphnia similis. The liquid fraction obtained from the acid hydrolyzate (HA) (pH 5.5) from sugarcane bagasse was used as a source of pentoses (17.70 g L-1 ) and molasses (ME) of sugarcane as a source of hexoses (47.00 g L-1 ). Different acid concentrations were used in the hydrolysis of sugarcane bagasse (1 – 5 % m/v H2SO4). The adsorbents were used: activated carbon, clay, hydrotalcite and active and inactive cells of S. cerevisiae and S. stipitis, in concentrations that varied (1 – 8 % m/v). The fermentation was carried out under 48 h with isolated culture and mixed culture (S. cerevisiae and S. stipitis). Subsequently, vinasse (vinasse without the detoxification process and with the detoxification process) from ethanolic fermentation was evaluated under different concentrations of soil conditioning (2.5, 5 and 10 %) to study biodegradability and tests of toxicity. Results of cell growth and viability allowed to select the most effective concentrations of adsorbents (4 and 8 % m/v), with emphasis on the biological adsorbents that showed 66 % removal of furfural, 51 % of 5-hydroxy-methyl-furfural (5–HMF) and alcoholic productivity of 23.48 g L-1 in 48 h when substrate with HA and ME was used in the presence of PE–2 and NRRL Y–7124. The chemical characterization tests indicate a high organic and mineral load in the samples of vinasse, compatible with first generation ethanol vinasse, which under certain conditions (soil conditioning at 2.5 %) allows high efficiency in biodegradation (> 80 %). Bioassays with L. sativa indicate that vinasse provides root growth when administered at low concentration (≤ 2,5 %), and acute toxicity with 50 % immobilization for D. similis in a concentration of 4.5 %. This study indicates that the use of adsorbents contributed to improve the quality of the hydrolyzate, with an emphasis on the use of biological adsorbent, which provided better rates of cell growth, fermentative productivity and for biodegradation and toxicity tests. These data indicate an important application of this adsorbent material in the detoxification of acid hydrolyzate from sugarcane bagasse.
Second generation ethanol has the prospect of becoming an important bioenergy alternative. The development of this technology is associated with the lignocellulosic materials' use, with emphasis on agricultural and agroindustrial by-products from which fermentable sugar are extracted, mainly xylose and glucose. The acid hydrolysis depolymerizes the hemicellulose releasing mainly xylose. Subsequently, the cellulose can be converted into glucose by enzymatic hydrolysis. However, the acid hydrolysis produces toxic compounds, such as furan derivatives, phenolics, and organic acids, which are harmful to fermentation. This study seeks to detoxify the sugarcane bagasse acid hydrolyzate using different adsorbent materials, evaluate cell viability before and after detoxification, quantify the fermentative yield using Saccharomyces cerevisiae (PE-2) and Scheffersomyces stipitis (NRRL Y-7124), besides, chemically characterizing vinasse and evaluating its biodegradation (Bartha and Pramer, 1965) and toxicity through tests with Lactuca sativa and Daphnia similis. The liquid fraction obtained from the acid hydrolyzate (HA) (pH 5.5) from sugarcane bagasse was used as a source of pentoses (17.70 g L-1 ) and molasses (ME) of sugarcane as a source of hexoses (47.00 g L-1 ). Different acid concentrations were used in the hydrolysis of sugarcane bagasse (1 – 5 % m/v H2SO4). The adsorbents were used: activated carbon, clay, hydrotalcite and active and inactive cells of S. cerevisiae and S. stipitis, in concentrations that varied (1 – 8 % m/v). The fermentation was carried out under 48 h with isolated culture and mixed culture (S. cerevisiae and S. stipitis). Subsequently, vinasse (vinasse without the detoxification process and with the detoxification process) from ethanolic fermentation was evaluated under different concentrations of soil conditioning (2.5, 5 and 10 %) to study biodegradability and tests of toxicity. Results of cell growth and viability allowed to select the most effective concentrations of adsorbents (4 and 8 % m/v), with emphasis on the biological adsorbents that showed 66 % removal of furfural, 51 % of 5-hydroxy-methyl-furfural (5–HMF) and alcoholic productivity of 23.48 g L-1 in 48 h when substrate with HA and ME was used in the presence of PE–2 and NRRL Y–7124. The chemical characterization tests indicate a high organic and mineral load in the samples of vinasse, compatible with first generation ethanol vinasse, which under certain conditions (soil conditioning at 2.5 %) allows high efficiency in biodegradation (> 80 %). Bioassays with L. sativa indicate that vinasse provides root growth when administered at low concentration (≤ 2,5 %), and acute toxicity with 50 % immobilization for D. similis in a concentration of 4.5 %. This study indicates that the use of adsorbents contributed to improve the quality of the hydrolyzate, with an emphasis on the use of biological adsorbent, which provided better rates of cell growth, fermentative productivity and for biodegradation and toxicity tests. These data indicate an important application of this adsorbent material in the detoxification of acid hydrolyzate from sugarcane bagasse.
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Palavras-chave
Adsorvente biológico, Etanol hemicelulósico, Etanol de segunda geração, Materiais lignocelulósicos, Degradação respirométrica, Adsorbents biologics, Hemicellulosic ethanol, Lignocellulose materials, Second generation etanol, Lignocellulose materials, Respirometric degradation