Marine microalgae for outdoor biomass production - a laboratory study simulating seasonal light and temperature for the west coast of Sweden.

At Nordic latitudes, year-round outdoor cultivation of microalgae is debatable due to seasonal variations in productivity. Shall the same species/strains be used throughout the year, or shall seasonal-adapted ones be used? To elucidate this, a laboratory study was performed where two out of 167 marine microalgal strains were selected for intended cultivation at the west coast of Sweden. The two local strains belong to Nannochloropsis granulata (Ng) and Skeletonema marinoi (Sm142). They were cultivated in photobioreactors and compared in conditions simulating variations in light and temperature of a year divided into three growth seasons (spring, summer and winter). The strains grew similarly well in summer (and also in spring), but Ng produced more biomass (0.225 versus 0.066 g DW L-1 d-1 ) which was more energy rich (25.0 versus 16.6 MJ kg-1 DW). In winter, Sm142 grew faster and produced more biomass (0.017 versus 0.007 g DW L-1 d-1 ), having similar energy to the other seasons. The higher energy of the Ng biomass is attributed to a higher lipid content (40 versus 16% in summer). The biomass of both strains was richest in proteins (65%) in spring. In all seasons, Sm142 was more effective in removing phosphorus from the cultivation medium (6.58 versus 4.14 mg L-1 d-1 in summer), whereas Ng was more effective in removing nitrogen only in summer (55.0 versus 30.8 mg L-1 d-1 ). Our results suggesting that, depending on the purpose, either the same or different local species can be cultivated are relevant when designing outdoor pilot studies. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.