Ikumi Umetani
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Microalgae biotechnology can strengthen circular economy concepts in the wastewater treatment sector. This study investigated the Norwegian microalgae strains of Tetradesmus wisconsinensis, Lobochlamys segnis, and Klebsormidium flaccidum for their efficiency in nutrient removal. Their biomass productivity and compositions were evaluated for bioenergy and bi-products development. In the laboratory batch experiment with synthetic municipal wastewater, all strains accomplished total removal of nitrogen and phosphorus. L. segnis removed all NH4+ and PO43− (initial concentration of 28 and 15 mg/L, respectively) earliest among others. T. wisconsinensis biomass was superior in total carbohydrates content (40%) and fatty acid profile that imply biorefinery potential. The fatty acid (TFA) content was the highest in L. segnis (193 ± 12 mg/g dry cells), while K. flaccidum accumulated fatty acids that consisted largely of polyunsaturated fatty acids (82% of TFA). The highest protein level was measured in K. flaccidum (53%). Observed variations in biomass components can be used for a strategic production of targeted compound in resource recovery scenarios for biofuel generation.
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This report shows results from an experiment where it was investigated whether a powder of freeze-dried microalgae (Phaeodactylum tricornutum) had a biostimulating effect on the growth and content of nutrients and antioxidants in basil (Ocimum basilicum). The effect of the microalgae powder was tested as a supplement to either mineral fertilizer or a commercial organic fertilizer. We found no significant effect on the yield of applied microalgae powder, but there was a tendency for a higher yield with added microalgae powder for the treatment with organic fertiliser. This may be due to additional nitrogen supply with the microalgae powder. With mineral fertiliser, there was the opposite tendency, highest yield without microalgae powder. The only statistically significant effect of the microalgae powder was an increase in the concentration of boron for the treatment with organic fertiliser. This was probably an effect of a significant additional supply of boron with the microalgae biomass. There was a tendency for an increased concentration of copper with the addition of microalgae powder with both mineral and organic fertiliser, although the additional copper supply with the microalgae powder was small. With organic fertiliser, there was also a tendency towards increased phosphorus and potassium concentrations with the addition of microalgae powder. This could be a biostimulating effect as the additional phosphorus and potassium supply with the microalgae powder was small, but as mentioned, the effect was not statistically significant. We found no significant differences between the treatments for total antioxidant content.
Sammendrag
Three strains of chlorophyte microalgae indigenous in Norway were studied regarding their potential for nutrient removal and resource recovery from wastewater. The nutrient uptake, growth, and cell composition (total proteins and carbohydrates) were monitored under a controlled batch environment for 14 days. Additionally, the fatty acids were analyzed at the end of the study. The fastest nutrient removal was achieved by Lobochlamys segnis F12 that used up NH4+ (28 mg L-1) and PO43- (15 mg L-1) after 4 days. Similar PO43- uptake was achieved by Tetradesmus wisconsinensis H1 while its NH4+ uptake took 2 days longer. Both strains showed a higher specific growth rate (1.1 day-1) than Klebsormidium flaccidum NIVA-CHL80 (0.55 day-1). The highest biomass (1.276 ± 21 mg L-1) and carbohydrates content (40%) were achieved by T. wisconsinensis. K. flaccidum was characterized by superior protein content (53 ± 4%). In terms of total fatty acids production both K. flaccidum and L. segnis were favored (184 ± 6 and 193 ± 12 mg g-1 dry cells), especially with their high polyunsaturated fatty acid content (82 and 67%, respectively). The fatty acids of K. flaccidum consisted mainly C18:2 n-6 (73% of the total). L. segnis had a preferable n3 to n6 ratio (1.3) in their fatty acid profile. The proteins and carbohydrates content changed in all strains depending on the growth stage. Therefore, resource recovery scenarios could be further optimized for a specific cell component production combined with an appropriate strategy for nutrient removal from wastewater.
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Forfattere
Ikumi Umetani Eshetu Janka Wakjera Michal Sposób Christopher Jonathan Hulatt Synne Kleiven Rune BakkeSammendrag
Bicarbonate was evaluated as an alternative carbon source for a green microalga, Tetradesmus wisconsinensis, isolated from Lake Norsjø in Norway. Photosynthesis, growth, and lipid production were studied using four inorganic carbon regimes: (1) aeration only, (2) 20 mM NaHCO3, (3) 5% (v/v) CO2 gas, and (4) combination of 20 mM NaHCO3 and 5% CO2. Variable chlorophyll a fluorescence analysis revealed that the bicarbonate treatment supported effective photosynthesis, while the CO2 treatment led to inefficient photosynthetic activity with a PSII maximum quantum yield as low as 0.31. Conversely, bicarbonate and CO2 treatments gave similar biomass and fatty acid production. The maximum growth rate, the final cell dry weight, and total fatty acids under the bicarbonate-only treatment were 0.33 (± 0.06) day−1, 673 (± 124) mg L−1 and 75 (± 5) mg g−1 dry biomass, respectively. The most abundant fatty acid components were α-linolenic acid and polyunsaturated fatty acids constituting 69% of the total fatty acids. The fatty acid profile eventuated in unsuitable biodiesel fuel properties such as high degree of unsaturation and low cetane number; however, it would be relevant for food and feed applications. We concluded that bicarbonate could give healthy growth and comparative product yields as CO2.