A strategy to increase the production of extracellular polymeric substances. Industrial valorization of Cyanocohniella Calida and its application in microplastic removal

• Autor(a) principal: Gomes, Ricardo André Ferreira
• Data de Publicação: 2022
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10400.13/4941
• topic: Cyanobacteria; Cyanocohniella calida; Exopolysaccharides; Microalgae; Microplastics; Bioflocculation; Cianobactérias; Exopolissacáridos; Microalgas; Microplásticos; Biofloculação; Applied Biochemistry; .; Faculdade de Ciências Exatas e da Engenharia; Domínio/Área Científica::Engenharia e Tecnologia::Engenharia Química; Domínio/Área Científica::Ciências Naturais::Ciências da Terra e do Ambiente; Domínio/Área Científica::Engenharia e Tecnologia::Engenharia Química

Microplastics (MPs) are present in all types of water, proving to be a risk to both environment and human health. These contaminants also may affect the algal industry, leading to significant economic losses. Therefore, creating sustainable and efficient removal methods is essential. Microbial exopolysaccharides (EPS) have demonstrated an ability to remove water contaminants. Their network-like appearance structure encourages particle agglomeration. This work's goals are: (i) to propose an industrial operation strategy to enhance EPS Cyanocohniella calida production; (ii) evaluate the cyanobacteria EPS behaviour in the presence of MPs; (iii) and verify the EPS bioflocculant potential, in view of its industrial valorisation. The response surface methodology (RSM) was employed to find better conditions for EPS production. The developed model evaluated the number of days(0-7), nitrogen concentration (2.5-10 g/dm3 ), phosphorous concentration (0.5-2 g/dm3 ), and ratio (1:1-1:14) (cyanobacteria/culture medium). The best conditions were 7 days of production, with 10 g/dm3 of nitrogen, 0.98 g/dm3 of phosphorus, and a biomass/culture medium ratio of 1/6.87, for an EPS production efficiency of 113 mg/dm3 . C. cf. calida was placed in MPs-contaminated water at low (0.05 mg/dm3 ) and high (5 mg/dm3 ) concentrations, under static and aerated conditions, and in two distinct growth stages (exponential and stationary). Higher EPS production (231 mg/dm3 ) was achieved in the exponential growth stage under aerated conditions and when exposed to environmental concentrations of MPs (0.05 mg/dm3 ). To determine the bioflocculant activity of the produced EPS in water highly contaminated with MPs (2 g/dm3 ), the type of cation present, its concentration, pH, salinity, and EPS/MPs ratio were examined. The highest bioflocculation rates (82%) were obtained in freshwater with an EPS/MPs ratio of 1/5, 0.05% (w/w) Fe3+ , pH 3.5 ± 0.1, a temperature of 25 ± 2 °C, and an EPS solution with a concentration of 400 mg/dm3 . Thus, C. cf. calida demonstrates (i) high potential as an EPS producer; (ii) EPS production stimulation in the presence of MPs-contaminated water; and (iii) the EPS produced is an efficient, suitable, and environmentally friendly solution to remove MPS from contaminated water for use in the algal industry.