R.J. van Tatenhove-Pel
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Plastic is completely immersed in our society, but due to its numerous negative effects on the planet and human health, bio-based alternatives are in high demand. Polyhydroxyalkanoates (PHAs) are bio polymers synthesized by microorganisms as a carbon and electron reserve under unbalanced growth. PHAs have similar properties to conventional plastics, but their biocompatibility and biodegradability give them an improved environmental footprint. In order to achieve cost-effective PHA production, sequencing batch reactor (SBR) enrichment strategies utilizing mixed microbial cultures (MMC) fed with waste streams are of particular interest. A promising strategy in MMC PHA production is the nutrient decoupled feeding strategy, with with high PHA accumulating cultures can be obtained in a single-step process. This work further characterized the metabolic behavior and PHA storage per formance of C/N decoupled enrichment cultures in five SBRs operated at varying carbon-to-nitrogen (C:N) and exchange ratios (ER). Stable and reproducible PHA accumulation of 59 wt% was achieved at a C:N of 40 molC/molN and a ER of 50%. Increasing the ER to 75% led to the highest achieved PHA content of this study, 77 wt%. The experimental performance was, however, substantially de creased compared to expectations based on theoretical and data-driven models. Investigation revealed important process parameters for further optimization. Specifically, the time of harvest, as well as the impact of harvest on the experienced C:N ratios by the culture. The most notable result of this study was the strong indication of the presence of a nitrogen storage metabolism in at least two of the five enrichment cultures. Specifically, the data pointed to the capacity for nitrogen accumulation during the famine phase and subsequent delayed growth in the feast phase. This behavoir was characterized by high nitrogen uptake rates paired with the formation of nitrogen rich, non-PHA organic solids in the famine phase. Furthermore, approximately half of the total dry cell weight (DCW) increase occurred during the nitrogen absent carbon phase. Nitrogen accumulation is predominantly thought to occur in specialized cyanobacteria and has not been described before in PHA enrichment cultures. It is therefore considered a novel metabolic insight.
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Plastic is completely immersed in our society, but due to its numerous negative effects on the planet and human health, bio-based alternatives are in high demand. Polyhydroxyalkanoates (PHAs) are bio polymers synthesized by microorganisms as a carbon and electron reserve under unbalanced growth. PHAs have similar properties to conventional plastics, but their biocompatibility and biodegradability give them an improved environmental footprint. In order to achieve cost-effective PHA production, sequencing batch reactor (SBR) enrichment strategies utilizing mixed microbial cultures (MMC) fed with waste streams are of particular interest. A promising strategy in MMC PHA production is the nutrient decoupled feeding strategy, with with high PHA accumulating cultures can be obtained in a single-step process. This work further characterized the metabolic behavior and PHA storage per formance of C/N decoupled enrichment cultures in five SBRs operated at varying carbon-to-nitrogen (C:N) and exchange ratios (ER). Stable and reproducible PHA accumulation of 59 wt% was achieved at a C:N of 40 molC/molN and a ER of 50%. Increasing the ER to 75% led to the highest achieved PHA content of this study, 77 wt%. The experimental performance was, however, substantially de creased compared to expectations based on theoretical and data-driven models. Investigation revealed important process parameters for further optimization. Specifically, the time of harvest, as well as the impact of harvest on the experienced C:N ratios by the culture. The most notable result of this study was the strong indication of the presence of a nitrogen storage metabolism in at least two of the five enrichment cultures. Specifically, the data pointed to the capacity for nitrogen accumulation during the famine phase and subsequent delayed growth in the feast phase. This behavoir was characterized by high nitrogen uptake rates paired with the formation of nitrogen rich, non-PHA organic solids in the famine phase. Furthermore, approximately half of the total dry cell weight (DCW) increase occurred during the nitrogen absent carbon phase. Nitrogen accumulation is predominantly thought to occur in specialized cyanobacteria and has not been described before in PHA enrichment cultures. It is therefore considered a novel metabolic insight.