DISCOVR strain screening pipeline – Part III: Strain evaluation in outdoor raceway ponds

In our previous studies, as described in the corresponding Part I and II manuscripts in this Special issue, we selected 12 promising microalgae strains from 38 strains for high biomass productivity based on their salinity preferences, temperature profiles, and biomass growth under simulated outdoor conditions. The 12 strains include 6 cold season strains (Micractium reisseri NREL14-F2, Monoraphidium minutum 26B-AM, Monoraphidium sp. MONOR1, Chlorella vulgaris LRB-AZ-1201, Tetraselmis striata LANL1001, Phaeodactylum tricornutum UTEX646) and 6 warm seasons strains (Scenedesmus obliquus DOE0152.z, Scenedesmus obliquus UTEX393, Chlorella sorokiniana DOE1116, Picochlorum renovo NREL39-A8, Picochlorum celeri TG2-WT-CSM/EMRE, Porphyridium cruentum CCMP7765). Because the preceding screening efforts were completed in indoor systems, this study focuses on quantitatively assessing these strains in outdoor raceway ponds to further eliminate those perform poorly under outdoor conditions. The trials presented in this study, categorized as either cold or warm season experiments based on water temperature, were carried out between February and June in 2018, 2019 and 2020. For each season, a benchmark strain, M. minutum 26B-AM for the cold season and S. obliquus UTEX393 for the warm season, was grown side-by-side with the new strains to provide a baseline for comparing strains cultivated under different weather conditions. The results showed that the cold season benchmark, M. minutum 26B-AM, remained the most productive cold season strain, but two new strains, P. triconutum UTEX646 and T. striata LANL1001, demonstrated robust growth in the presence of weather changes and biological contaminants. For the warm season trials, P. celeri TG2-WT-CSM/EMRE and P. cruentum CCMP675 were 39 % and 11 % more productive than the benchmark with substantially improved culture stability. Biomass compositional analyses of the strains showed that the carbohydrate, lipid (measured as fatty acid methyl esters) and protein account for 5.2–20.6 %, 7.2–11.9 %, and 21.7–53 %, of the ash-free dry matter, respectively.