PNNL

Abstract

Screening microalgae strains under static light and temperature flask conditions is limited in applicability to predicting biomass productivity in the dynamically fluctuating light and temperature conditions of outdoor pond cultivation environments. We describe a testing pipeline that screens for productivity under climate simulated conditions. A validated, miniaturized Laboratory Environmental Algae Pond Simulator (mini-LEAPS) photobioreactor was used to obtain optimal medium salinities and biomass productivities of microalgae strains collected from cold habitats from the Arctic to the Antarctic. Strains characterized in this effort include: Chlorella antarctica UTEX1959, Chlorella sp. UTEXSNO69, Chloromonas rosae var. psychrophila UTEXSNO11, Phaeodactylum tricornutum UTEX646, and Stichococcus minutus CCALA727. Observed productivities of the characterized strains ranged from 1.74 ± 0.25 to 8.18 ± 0.81 g m-2 day-1 (in ash-free dry weight). For each strain a temperature tolerance profile was generated to identify the most appropriate season(s) for cultivation. Vitamin requirements of P. tricornutum UTEX 646 were determined. The two most promising strains, Chlorella sp. UTEX SNO69 and P. tricornutum UTEX 646, were tested alongside the DISCOVR winter benchmark strain Monoraphidium minutum 26B-AM in outdoor open ponds at the PNNL Algae Testbed (PAT) in Arizona. Under cold-season outdoor pond conditions, Chlorella sp. UTEX SNO69 achieved average areal biomass productivities of 8.21 ± 0.50 g m-2 day-1, not significantly different from that of the benchmark strain (8.52 ± 0.43 g m-2 day-1, p > 0.05). Under spring outdoor pond conditions, P. tricornutum UTEX 646 achieved average areal biomass productivities 10.34 ± 0.27 g m-2 day-1, not significantly different from that of the benchmark (10.07 ± 0.50 g m-2 day-1) under the tested conditions (p > 0.05). The streamlined pipeline was thus demonstrated to successfully characterize productive microalgae strains for outdoor deployment by weeding out algae strains that were not productive under dynamic light and temperature conditions.