PNNL

Abstract

From the Tier II strain screening effort in the PNNL Laboratory Environmental Algae Pond Simulator (LEAPS) photobioreactors (see companion paper in this Special issue), 12 fast-growing microalgal strains were down-selected to be cultivated in outdoor open raceway ponds for field cultivation assessments of biomass productivity (Tier III). In total, 8 pond trials, categorized into cold and warm season groups based on water temperature, were carried out between February and June in 2018, 2019 and 2020. For each season, a benchmark strain, Monoraphidium minutum 26B-AM for the cold season and Scenedesmus obliquus UTEX393 for the warm season, was grown side-by-side with 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, Phaeodactylum triconutum UTEX646 and Tetraselmis striata LANL1001, demonstrated robust growth, enduring stochastic weather changes and invading species. For the warm season trials, Picochlorum celeri WT-CSM/EMRE and Porphyridium cruentum CCMP675 were 39% and 11% more productive than the benchmark with substantially improved culture stability. Compositional analyses on the biomass of the 8 strains showed that the carbohydrate, lipid (measured as fatty acid methyl esters) and protein account for 4.2 – 17%, 3.7 – 16.2% and 27.3 – 49% of the dry matter, respectively.