Evolutionary engineering: production of bioplastics using waste

• Autor(a) principal: Rosmaninho, Margarida Monteiro
• 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/10773/32761
• topic: Polyhydroxyalkanoates; Mixed microbial cultures; Three-step process; Acidogenic fermentation; Dynamic aerobic feeding; Industrial waste; Spent coffee grounds

Conventional plastics play a crucial role in society and have a negative impact on the environment and, therefore, bioplastics, such as polyhydroxyalkanoates (PHAs), become sustainable alternatives due to their biocompatibility and biodegradability. In this work, the production of PHAs by mixed microbial cultures (MMC) from an industrial waste, following a circular economy logic was studied. The valorization of a waste from the coffee industry, spent coffee grounds (SCGs) was another aim of this work. SCGs are a cheap raw material, constituted by high amounts of organic compounds, such as polysaccharides and lipids, and are, therefore, considered as a good substrate for biotechnological processes. In this work, the production of PHAs followed the three-step process: first, acidogenic fermentation (AF) of SCGs occurs, then the selection of a MMC with PHAs accumulation capacity and, finally, the accumulation of biopolymer. The application of a pre-treatment facilitated the process of AF that ran in a fluidized bed biofilm reactor (FBBR). Acetic, propionic, and butyric acids were the most produced short-chain organic acids (SCOAs), and valeric acid appeared in lower concentrations. The maximum concentration of SCOAs produced was 3.25 gCOD/L, and the maximum acidification levels were 58±3.0% and 37±3.5% for the supplied sugars and the total organic carbon available, respectively. The selection step occurred in a sequential discontinuous reactor (SBR) and the operating conditions tested allowed selecting a stable PHA-accumulating MMC. Two pseudo-stationary states (PSS) were possible to define and a maximum PHAs content of 40.0 % of a copolymer of hydroxybutyrate and hydroxyvalerate was obtained, thus demonstrating the good accumulation capacity of MMC. In the last step of the work, three accumulation tests were performed in which different substrates supplied to the selected MMC were tested. The test performed with the FBBR effluent showed a maximum accumulation of 60.8 % and a volumetric yield of 0.252 gPHA/L.h. This work demonstrated the potential of SCGs as substrate to produce PHAs by MMC, opening the possibility of its implementation at the industrial level.