Publicação
Development of an organic culture medium for Chlorella vulgaris
| Resumo: | The commercial value of microalgal biomass can be explored for various applications, such as human nutrition. Chlorella vulgaris, is one of the few species that are currently approved as food ingredient and supplements. In recent years, trends in the food industry have led to an increased demand for natural, healthy, sustainable and quality assured food. A growing niche market is the production of organic food products, due to the increasing awareness of customers nowadays. This work aims at developing and establishing an effective organic culture medium for industrial production of autotrophic and heterotrophic microalgal biomass. Initially, a preliminary study in 1.5 L airlift reactors was performed to determine the most promising organic substrates (OS). Starting with 2 mmol L-1 of nitrates and ammonia in the final growth medium, the highest biomass productivities were obtained in OS.4 (0.033 g L-1 d-1) and OS.1 (0.028 g L-1 d-1). After the elemental analysis of the OS was performed, a culture medium was developed to meet the nutrient needs of Chlorella. Once the culture medium was optimized with the ideal concentration of each solution, it was tested at autotrophic pilot and industrial scale, namely, 125 L green wall panels and a 10 m3 tubular photobioreactor. Obtained results revealed that both organic and inorganic culture media displayed the same growth pattern. Interestingly, organic microalgae biomass presented good physicochemical properties with a significantly higher content of proteins compared to the control inorganic medium. Since heterotrophic cultivation is a more suitable approach to “seed” (inoculum) the autotrophic production photobioreactors, a heterotrophic medium was optimized using an organic carbon source (molasse). Following the optimization of sucrose inversion in molasse at 45 O C, pH 5.8 and 0.015 mg mL-1 of enzyme, the carbon source was optimized by testing different concentrations. From the study conditions, 5 g L-1 of glucose showed higher biomass productivity (0.07 g L-1 h-1) but at 10 g L-1 glucose the growth was inhibited. Afterwards, the N concentration was optimized using the previously optimized autotrophic growth medium. In this context, different N concentrations were tested (1, 5 and 10 mmol L-1 of N). The highest volumetric productivities were obtained at 5 and 10 mmol L-1 of N (0.023 ± 0.002 and 0.025 ± 0.001 g L-1 h-1 respectively). Following the optimization of the C and N concentrations a fed-batch growth on a 7 L bench top fermenter denoted that heterotrophic growth can be used for inoculum production. In this experiment, approximately 13.1 g L-1 of biomass dry weight were achieved, however, further optimization of the fed-batch operation will enable a significant improvement of the final biomass productivities. |
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| Autores principais: | Machado, Adriana Salomé Amaro |
| Assunto: | Organic biomass Chlorella vulgaris Autotrophic; Heterotrophic Biochemical composition Biomassa biológica Chlorella vulgaris Autotrófica Heterotrófico Composição bioquímica |
| Ano: | 2017 |
| País: | Portugal |
| Tipo de documento: | dissertação de mestrado |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade do Minho |
| Idioma: | português |
| Origem: | RepositóriUM - Universidade do Minho |
| Resumo: | The commercial value of microalgal biomass can be explored for various applications, such as human nutrition. Chlorella vulgaris, is one of the few species that are currently approved as food ingredient and supplements. In recent years, trends in the food industry have led to an increased demand for natural, healthy, sustainable and quality assured food. A growing niche market is the production of organic food products, due to the increasing awareness of customers nowadays. This work aims at developing and establishing an effective organic culture medium for industrial production of autotrophic and heterotrophic microalgal biomass. Initially, a preliminary study in 1.5 L airlift reactors was performed to determine the most promising organic substrates (OS). Starting with 2 mmol L-1 of nitrates and ammonia in the final growth medium, the highest biomass productivities were obtained in OS.4 (0.033 g L-1 d-1) and OS.1 (0.028 g L-1 d-1). After the elemental analysis of the OS was performed, a culture medium was developed to meet the nutrient needs of Chlorella. Once the culture medium was optimized with the ideal concentration of each solution, it was tested at autotrophic pilot and industrial scale, namely, 125 L green wall panels and a 10 m3 tubular photobioreactor. Obtained results revealed that both organic and inorganic culture media displayed the same growth pattern. Interestingly, organic microalgae biomass presented good physicochemical properties with a significantly higher content of proteins compared to the control inorganic medium. Since heterotrophic cultivation is a more suitable approach to “seed” (inoculum) the autotrophic production photobioreactors, a heterotrophic medium was optimized using an organic carbon source (molasse). Following the optimization of sucrose inversion in molasse at 45 O C, pH 5.8 and 0.015 mg mL-1 of enzyme, the carbon source was optimized by testing different concentrations. From the study conditions, 5 g L-1 of glucose showed higher biomass productivity (0.07 g L-1 h-1) but at 10 g L-1 glucose the growth was inhibited. Afterwards, the N concentration was optimized using the previously optimized autotrophic growth medium. In this context, different N concentrations were tested (1, 5 and 10 mmol L-1 of N). The highest volumetric productivities were obtained at 5 and 10 mmol L-1 of N (0.023 ± 0.002 and 0.025 ± 0.001 g L-1 h-1 respectively). Following the optimization of the C and N concentrations a fed-batch growth on a 7 L bench top fermenter denoted that heterotrophic growth can be used for inoculum production. In this experiment, approximately 13.1 g L-1 of biomass dry weight were achieved, however, further optimization of the fed-batch operation will enable a significant improvement of the final biomass productivities. |
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