Poster – Efficiency of Nordic green microalgae for nutrient removal and resource recovery from wastewater
Ikumi Umetani, Michal Sposob, Olga Tiron
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.
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.