A comparison of nannochloropsis salina growth performance in two outdoor pond designs: Conventional raceways versus the arid pond with superior temperature management

The present study examines how climatic conditions and pond design affect the growth performance of microalgae. From January to April of 2011, outdoor batch cultures of Nannochloropsis salina were grown in three replicate 780L conventional raceways, as well as in an experimental 7500L algae raceway integrated design (ARID) pond. The ARID culture system utilizes a series of 820cm deep basins and a 1.5m deep canal to enhance light exposure and mitigate temperature variations and extremes. The ARID culture reached the stationary phase 27 days earlier than the conventional raceways, which can be attributed to its superior temperature management and shallower basins. On a night when the air temperature dropped to -9°C, the water temperature was 18°C higher in the ARID pond than in the conventional raceways. Lipid and fatty acid content ranged from 16 to 25 and from 5 to15, respectively, as a percentage of AFDW. Palmitic, palmitoleic, and eicosapentaenoic acids comprised the majority of fatty acids. While the ARID culture system achieved nearly double the volumetric productivity relative to the conventional raceways (0.023 versus 0.013gL ^-1day^-1), areal biomass productivities were of similar magnitude in both pond systems (3.47 versus 3.34gm^-2day ^-1), suggesting that the ARID pond design has to be further optimized, most likely by increasing the culture depth or operating at higher cell densities while maintaining adequate mixing.