Publicação
Polyhydroxyalkanoates production from CO2 using phototrophic mixed cultures
| Resumo: | Two of the current major environmental problems include the rise of CO2 in the atmosphere and plastic pollution, creating the need to implement bio-based and biodegradable plastics on a wider scale. The use of Polyhydroxyalkanoates (PHAs) has emerged as a solution, but de- spite its advantages, the production costs are still too high compared to conventional plastics. This study involved keeping a lab-scale sequencing batch reactor (SBR) with a strictly anaero- bic photosynthetic mixed culture (PMC), in order to try to reduce some of these costs, by re- moving the need of sterilization and aeration. The SBR was maintained with a continuous supply of inorganic carbon and a cyclic supply of sulfide under a feast and famine regime, attaining a biomass concentration of 0.7 ± 0.2 g/L of VSS. A representative full-cycle showed specific consumption rates for sulfides and inorganic carbon of 0.3 mmol SS/Cmmol Xi·d and 1 mmol IC/ Cmmol Xi·d, respectively. The glycogen and PHA contents detected were mini- mal, with an average of 6.2 ± 2.2% GLY/VSS, and a maximum of 3% PHA/VSS. Parallel batch studies evaluated the impact of light intensity on the culture performance. These did not show a linear variation in the rates of consumption of inorganic carbon or sulfides, nor in the production of glycogen or PHA contents. However, in a test performed without light, higher PHA values were detected (10.9 ± 2.2% PHA/VSS) and this could result from the an- aerobic conversion of glycogen into PHA. This suggests that a possible means of increasing PHA production could occur through the implementation of dark/light cycles. Additionally, two samples were tested for a possible new inocula for the SBR. One of them, collected from a creek in Covilhã, which waters are microbially rich in purple bacteria, seemed to be a good candidate as it grew with inorganic carbon and sulfides, and demonstrated visible PHA granules. Finally, due to the limited availability of the gas chromatography (GC) equipment needed for PHA analysis, alternative protocols for detecting PHA were tested. Furthermore, to prevent equipment damage, a series of tests were performed to eliminate any possible sulfur residues from the biomass samples and tried to identify any compounds that could damage the equip- ment. No compound capable of that was found. |
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| Autores principais: | Cardoso, Inês de Araújo |
| Assunto: | Bioreactor Mixed microbial cultures Phototrophic system Biodegradable polymers Polyhydroxyalkanoates CO2 capture |
| Ano: | 2023 |
| País: | Portugal |
| Tipo de documento: | dissertação de mestrado |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade Nova de Lisboa |
| Idioma: | inglês |
| Origem: | Repositório Institucional da UNL |
| Resumo: | Two of the current major environmental problems include the rise of CO2 in the atmosphere and plastic pollution, creating the need to implement bio-based and biodegradable plastics on a wider scale. The use of Polyhydroxyalkanoates (PHAs) has emerged as a solution, but de- spite its advantages, the production costs are still too high compared to conventional plastics. This study involved keeping a lab-scale sequencing batch reactor (SBR) with a strictly anaero- bic photosynthetic mixed culture (PMC), in order to try to reduce some of these costs, by re- moving the need of sterilization and aeration. The SBR was maintained with a continuous supply of inorganic carbon and a cyclic supply of sulfide under a feast and famine regime, attaining a biomass concentration of 0.7 ± 0.2 g/L of VSS. A representative full-cycle showed specific consumption rates for sulfides and inorganic carbon of 0.3 mmol SS/Cmmol Xi·d and 1 mmol IC/ Cmmol Xi·d, respectively. The glycogen and PHA contents detected were mini- mal, with an average of 6.2 ± 2.2% GLY/VSS, and a maximum of 3% PHA/VSS. Parallel batch studies evaluated the impact of light intensity on the culture performance. These did not show a linear variation in the rates of consumption of inorganic carbon or sulfides, nor in the production of glycogen or PHA contents. However, in a test performed without light, higher PHA values were detected (10.9 ± 2.2% PHA/VSS) and this could result from the an- aerobic conversion of glycogen into PHA. This suggests that a possible means of increasing PHA production could occur through the implementation of dark/light cycles. Additionally, two samples were tested for a possible new inocula for the SBR. One of them, collected from a creek in Covilhã, which waters are microbially rich in purple bacteria, seemed to be a good candidate as it grew with inorganic carbon and sulfides, and demonstrated visible PHA granules. Finally, due to the limited availability of the gas chromatography (GC) equipment needed for PHA analysis, alternative protocols for detecting PHA were tested. Furthermore, to prevent equipment damage, a series of tests were performed to eliminate any possible sulfur residues from the biomass samples and tried to identify any compounds that could damage the equip- ment. No compound capable of that was found. |
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