Development of processes for the production of PHA by mixed cultures from spent coffee grounds

• Autor(a) principal: Sousa, Raquel Amaral
• 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/10773/32839
• topic: Polyhydroxyalkanoates; Mixed microbial cultures; Spent coffe grounds; Three-step process; Fluorescence in situ hybridization; Quantitative polymerase chain reaction; Next generation sequencing

Worldwide, the concern with pollution and climate changes is dramatically growing. One of the main contributors to these problems are the typical plastics used on a daily basis. In this way, the development of new sustainable products and alternatives to petroleum derivatives is critical. The use of industrial residues as substrate for the production of added-value products by microorganisms is one of the possible alternatives. The present work proposes to produce polyhydroxyalkanoates (PHA) through mixed microbial cultures (MMC) and using spent coffee grounds (SCG) as substrate by using a three-step process. This process includes acidification of SCG to obtain short chain organic acids (SCOAs), selection of a PHA-storing MMC able to use SCOAs and accumulation of PHA. The acidification of SCG occurred after a preliminary hydrolysis step, in a fluidized-bed reactor (FBBR), for the production of SCOAs. Several parameters were tested in order to improve the production of SCOAs, namely, pH control and the organic load rate (OLR). The produced SCOAs reached a maximum concentration of 3.05 gCOD/L after 102 d of operation. This corresponds to an acidification degree of 37% and a composition of SCOAs of 49/13/2/25/11% of acetic, propionic, isobutyric, butyric and valeric acid, respectively, when pH was controlled at 5.0 and the OLR was 1.0 gCOD/L.d. The selection step was performed in a sequencing batch reactor (SBR) under feast and famine conditions. In this way, a selective pressure that allow the survival of PHA-producing organisms is established and the MMC becomes enriched in these bacteria. The SBR was fed with the SCOAs mixture obtained from the FBBR and the effect of parameters as cycle time, sludge retention time (SRT), and OLR was tested. The MMC reached a maximum of 41.3 % of PHA on day 134, producing a copolymer of 3-hydroxybutyrate (HB) and 3- hydroxyvalerate (HV) with 17 % of HV. The microbial community of both systems was analyzed by fluorescence in situ hybridization, quantitative polymerase chain reaction and high-throughput 16S rRNA gene sequencing techniques. In FBBR the phyla Firmicutes, Bacteroidetes, Actinobacteria and Proteobacteria were identified as the main ones. In the case of SBR, the main phyla found were Proteobacteria, Bacteroidetes and Firmicutes. A library of clones was defined, and several ones were identified as PHA-producing microorganisms.