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A procura global por energia e produtos materiais têm vindo a crescer imenso. As principais fontes de energia e produtos químicos são os combustíveis fósseis, recursos altamente poluidores do ambiente, que levantam questões importantes não só a nível ambiental, mas como também económico e social. Esta dependência dos combustíveis fósseis pode levar a uma potencial crise energética no futuro quando estes começarem a esgotar. Para combater isto é necessário encontrar e utilizar recursos mais sustentáveis. A biomassa lignocelulósica é uma alternativa bastante promissora. A biomassa lignocelulósica está presente em grandes quantidades e oferece diversas opções para a produção de bioenergia. A produção de biocombustíveis renováveis e sustentáveis, como é o caso do bioetanol ou do biodiesel, a partir de biomassa está a ganhar interesse global. Os biocombustíveis trazem benefícios do ponto de vista ambiental e económico. O bioetanol produzido a partir de biomassa renovável, surge como um combustível sustentável, mais limpo, ambientalmente seguro, neutro em carbono e uma alternativa verde para o combustível fóssil. Este trabalho teve como objetivo principal valorizar a biomassa lignocelulósica (palha de milho) resultante da fitorremediação de um solo contaminado com metais pesados como o zinco (Zn) e o cádmio (Cd), através da otimização do processo de obtenção de açúcares usados na produção de bioetanol. O processo de produção de bioetanol inclui três etapas fundamentais: o pré-tratamento da biomassa de forma a aumentar a eficiência dos processos seguintes; a hidrólise, que converte a celulose e a hemicelulose da biomassa lignocelulósica em açúcares; e a fermentação, que utiliza microrganismos para converter esses açúcares em etanol. Este estudo focou-se na otimização das etapas de pré-tratamento com ácido diluído e de hidrólise enzimática, sendo a palha de milho a biomassa lignocelulósica, algumas provenientes de solos contaminados com metais pesados e outra palha servindo de controlo. De forma a otimizar estas etapas foi usada a metodologia de Delineamento Composto Central Rotacional (DCCR). Neste método foram usados três pontos centrais e estudadas 3 variáveis independentes, a saber: para o pré-tratamento ácido, a temperatura do banho (T), o tempo de reação (t) e a concentração do ácido (CA); e para a hidrólise enzimática, a temperatura do banho (T), o tempo de reação (t) e a quantidade de enzima (E). A resposta analisada em ambos os casos foi a soma dos açúcares (SA) obtidos, após leitura com cromatografia líquida de alta eficiência. Na otimização do prétratamento foram realizados 51 ensaios no total. Para a otimização da hidrólise foram executados 34 ensaios. As condições ótimas para o pré-tratamento com ácido clorídrico diluído foram determinadas para as biomassas utilizadas neste estudo, que se passam a enumerar: para a biomassa do solo de Controlo uma temperatura de 86,8 °C, tempo de reação de 6,6 horas e uma concentração do ácido de 3,2% v/v, foi considerado ótimo e previu-se um resultado de 16,4 g/L de açúcares (resultado experimental de validação de 15,2 g/L); para a biomassa do solo de Estarreja foi considerado ótimo uma temperatura de 86,7 °C, tempo de reação de 6,9 horas e uma concentração do ácido de 3,6% v/v e previu-se um resultado de 11,4 g/L de açúcares (resultado experimental de validação 12,0 g/L); por último para a biomassa do solo da Panasqueira foram determinados uma temperatura de 86,6 °C, tempo de reação de 7,3 horas e uma concentração do ácido de 3,6% v/v, como sendo as condições ótimas e previu-se um resultado de 13,5 g/L de açúcares (resultado experimental de validação 12,5 g/L). Para a hidrólise enzimática com Accellerase 1000, só se procedeu à análise das palhas dos solos de controlo e Panasqueira. A biomassa do solo de controlo apresentou as condições ótimas como sendo temperatura igual a 54 °C, tempo de reação de 30,3 horas e volume de enzima de 2,5 mL, com um resultado previsto de 17,2 g/L de açúcares (resultado experimental de validação 16,8 g/L) e a biomassa do solo da Panasqueira apresentou temperatura igual a 43 °C, tempo de reação de 38,5 horas e volume de enzima usado de 3 mL como condições ideais, com um resultado previsto de 17,6 g/L de açúcares (resultado experimental de validação 17,5 g/L).
The global demand for energy and material products has been growing immensely. The main sources of energy and chemicals are fossil fuels, highly polluting resources for the environment that raise important issues not only at an environmental level, but also economically and socially. This dependence on fossil fuels could lead to a potential energy crisis in the future when fossil fuels start to run out. To combat this, it is necessary to find and use more sustainable resources. Lignocellulosic biomass is a very promising alternative. Lignocellulosic biomass is present in large quantities and offers several options for the production of bioenergy. The production of renewable and sustainable biofuels from biomass, such as bioethanol or biodiesel, is gaining global interest. Biofuels bring benefits from an environmental and economic point of view. Bioethanol produced from renewable biomass offers opportunities for a sustainable, cleaner, environmentally safer, carbon neutral fuel and a green alternative to fossil fuel. The main objective of this work is to value the lignocellulosic biomass (corn stover) resulting from the phytoremediation of a soil contaminated with heavy metals such as zinc (Zn) and cadmium (Cd), by optimizing the process of obtaining sugars used in production of bioethanol. The bioethanol production process includes three fundamental steps: pre-treatment of biomass in order to increase the efficiency of the following processes; hydrolysis, which converts cellulose and hemicellulose from lignocellulosic biomass into sugars; and fermentation, which uses microorganisms to convert these sugars into ethanol. This study focused on optimizing the steps of pre-treatment with dilute acid and enzymatic hydrolysis, using corn stover as lignocellulosic biomass, produced using soils contaminated with heavy metals (Panasqueira and Estarreja) and from noncontaminated soil, that served as a control. In order to optimize these steps, the Central Composite Rotational Design (DCCR) methodology was used. In this method, three central points were used and 3 independent variables were studied, namely: for the acid pretreatment, the bath temperature (T), the reaction time (t) and the acid concentration (CA); and for enzymatic hydrolysis, the bath temperature (T), the reaction time (t) and the amount of enzyme (E). The response analyzed in both cases was the sum of sugars (SA) obtained, after analyzing with high performance liquid chromatography. In optimizing the pre-treatment, 51 experiments were performed in total. To optimize the hydrolysis, 34 experiments were performed. The optimal conditions for pre-treatment with dilute hydrochloric acid were determined for the biomasses used in this study, which will now be listed: for the biomass from Control soil, a temperature of 86,8 °C, reaction time of 6.6 hours and an acid concentration of 3.2% v/v was considered optimal and a result of 16.4 g/L of sugars was predicted (experimental validation result of 15.2 g/L); for the Estarreja biomass, a temperature of 86.7 °C was considered optimal, a reaction time of 6.9 hours and an acid concentration of 3.6% v/v and a result of 11,4 g/L was predicted of sugars (experimental validation result 12.0 g/L); finally, for the Panasqueira biomass, a temperature of 86.6 °C, a reaction time of 7.3 hours and an acid concentration of 3.6% v/v were determined as the optimal conditions and a result of 13.5 g/L of sugars (12.5 g/L experimental validation result). For enzymatic hydrolysis with Accellerase 1000, only control and Panasqueira straws were analyzed. The control biomass presented the optimal conditions as being a temperature equal to 54 °C, a reaction time of 30.3 hours and an enzyme volume of 2.5 mL, with a predicted result of 17.2 g/L of sugars (result experimental validation 16.8 g/L) and the Panasqueira biomass had a temperature of 43 °C, a reaction time of 38.5 hours and a volume of enzyme used of 3 mL as ideal conditions, with a predicted result of 17.6 g/L of sugars (experimental validation result 17.5 g/L).
The global demand for energy and material products has been growing immensely. The main sources of energy and chemicals are fossil fuels, highly polluting resources for the environment that raise important issues not only at an environmental level, but also economically and socially. This dependence on fossil fuels could lead to a potential energy crisis in the future when fossil fuels start to run out. To combat this, it is necessary to find and use more sustainable resources. Lignocellulosic biomass is a very promising alternative. Lignocellulosic biomass is present in large quantities and offers several options for the production of bioenergy. The production of renewable and sustainable biofuels from biomass, such as bioethanol or biodiesel, is gaining global interest. Biofuels bring benefits from an environmental and economic point of view. Bioethanol produced from renewable biomass offers opportunities for a sustainable, cleaner, environmentally safer, carbon neutral fuel and a green alternative to fossil fuel. The main objective of this work is to value the lignocellulosic biomass (corn stover) resulting from the phytoremediation of a soil contaminated with heavy metals such as zinc (Zn) and cadmium (Cd), by optimizing the process of obtaining sugars used in production of bioethanol. The bioethanol production process includes three fundamental steps: pre-treatment of biomass in order to increase the efficiency of the following processes; hydrolysis, which converts cellulose and hemicellulose from lignocellulosic biomass into sugars; and fermentation, which uses microorganisms to convert these sugars into ethanol. This study focused on optimizing the steps of pre-treatment with dilute acid and enzymatic hydrolysis, using corn stover as lignocellulosic biomass, produced using soils contaminated with heavy metals (Panasqueira and Estarreja) and from noncontaminated soil, that served as a control. In order to optimize these steps, the Central Composite Rotational Design (DCCR) methodology was used. In this method, three central points were used and 3 independent variables were studied, namely: for the acid pretreatment, the bath temperature (T), the reaction time (t) and the acid concentration (CA); and for enzymatic hydrolysis, the bath temperature (T), the reaction time (t) and the amount of enzyme (E). The response analyzed in both cases was the sum of sugars (SA) obtained, after analyzing with high performance liquid chromatography. In optimizing the pre-treatment, 51 experiments were performed in total. To optimize the hydrolysis, 34 experiments were performed. The optimal conditions for pre-treatment with dilute hydrochloric acid were determined for the biomasses used in this study, which will now be listed: for the biomass from Control soil, a temperature of 86,8 °C, reaction time of 6.6 hours and an acid concentration of 3.2% v/v was considered optimal and a result of 16.4 g/L of sugars was predicted (experimental validation result of 15.2 g/L); for the Estarreja biomass, a temperature of 86.7 °C was considered optimal, a reaction time of 6.9 hours and an acid concentration of 3.6% v/v and a result of 11,4 g/L was predicted of sugars (experimental validation result 12.0 g/L); finally, for the Panasqueira biomass, a temperature of 86.6 °C, a reaction time of 7.3 hours and an acid concentration of 3.6% v/v were determined as the optimal conditions and a result of 13.5 g/L of sugars (12.5 g/L experimental validation result). For enzymatic hydrolysis with Accellerase 1000, only control and Panasqueira straws were analyzed. The control biomass presented the optimal conditions as being a temperature equal to 54 °C, a reaction time of 30.3 hours and an enzyme volume of 2.5 mL, with a predicted result of 17.2 g/L of sugars (result experimental validation 16.8 g/L) and the Panasqueira biomass had a temperature of 43 °C, a reaction time of 38.5 hours and a volume of enzyme used of 3 mL as ideal conditions, with a predicted result of 17.6 g/L of sugars (experimental validation result 17.5 g/L).
Description
Keywords
Bioetanol Biomassa lignocelulósica Contaminantes metais pesados Fitorremediação Otimização Palha de milho Bioethanol Corn stover Heavy metal contaminant Lignocellulosic biomass Optimization Phytoremediation