Ikumi Umetani
Research Scientist
Abstract
Cultivation of microalgae has gained significant interest as an alternative protein source, potentially becoming a target commodity recovered from microalgae-based wastewater treatment. This study examined a semi-continuous cultivation strategy to optimize protein accumulation of the indigenous freshwater chlorophytes, Lobochlamys segnis and Klebsormidium flaccidum, and simultaneously remove nutrients from wastewater efficiently. A strain-specific regime was made based on a fixed biomass concentration at the start of 24-h cultivation cycle, i.e., a constant initial cell density, which regulated harvesting and fresh medium supply volume according to the dilution rate. Six cultivation cycles were conducted in lab-scale 1L reactors with a synthetic municipal wastewater. Lobochlamys segnis and K. flaccidum grew exponentially in all cycles. The biomass productivity was 573 and 580 mg L–1 day–1, in which the total protein consisted of 62 and 45% of dry cell weight (dw), respectively. When a culture medium deficient in nitrogen and phosphorus was used, protein level was significantly reduced. L. segnis consumed all NH4+ and PO43– supplied by the medium replacement, giving the removal rate of 9.2 and 5.2 mg L–1 day–1. Whereas K. flaccidum removed 13.8 mg L–1 day–1 NH4+ without completing PO43– removal. The amino acid profile of both strains was characterized by glutamic acids content (4–5% dw). We concluded that the designed cultivation regime would support a constant biomass production with stable and high protein content, along with an efficient removal of nutrient from the wastewater.
Abstract
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.
Abstract
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.