Circular economy: bioethanol production from pulp and paper industry wastes

• Autor(a) principal: Gonçalves, Manuel João Afecto
• Data de Publicação: 2021
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/33577
• topic: Bioethanol; Circular economy; Fermentation; Pulp and paper industry; Kraft pulp; Yeast recycling; Yeast extract

High quantities of wastes are generated by the pulp and paper industry every day, such as the wood barks which are lignocellulosic materials. The lignocellulosic biomass, mainly composed of cellulose, hemicelluloses, and lignin, is a primordial feedstock for biofuels production due to its renewable properties and high carbon source. Bioethanol is the major biofuel produced worldwide and its production goes through several steps: the pretreatment, the hydrolysis, the fermentation, and lastly a distillation and purification step. These processes have high associated costs which oppress this production at an industrial scale. The circular economy applied to the pulp and paper industry, through the integration of a bioethanol producing biorefinery, may be a promising approach to decrease the overall bioethanol production costs, due to the feedstock availability and the implemented technologies to process the lignocellulosic biomass. The main objective of this work was to study the production of bioethanol from the enzymatic hydrolysate of Eucalyptus globulus barks kraft pulp, namely this process improvement by reducing the overall costs associated. Therefore, urea and Fermaid O™ were studied as economical alternatives to replace or reduce yeast extract utilization. Also, the spent yeast from the fermentation broth was studied for reutilization as supplementation, through the production of yeast extract by autolysis, and as inoculum (in successive fermentations). The fermentation using the produced yeast extract presented the highest ethanol performance in the Erlenmeyer assays, testing different supplementations. Comparing the results with produced yeast extract, and commercial yeast extract, there is an improvement of the maximum ethanol concentration from 45.31 ± 1.24 g L-1 to 48.26 ± 0.94 g L-1, of the productivity from 1.59 ± 0.04 g L-1 h-1 to 1.82 ± 0.04 g L-1 h-1 and of the ethanol yield from 72.72 ± 1.32 % to 76.73 ± 4.53 %. The scale-up to a bioreactor provided the highest ethanol concentration of 61.05 g L-1. This study indicates that bioethanol production from E. globulus barks kraft pulp hydrolysates could be viable by implementing a circular economy model into the pulp and paper industry. However, several optimizations are still required to improve the yields obtained and increase the profits of this production.