Impact of seasonal variations on Nannochloropsis oculata phototrophic productivity in an outdoor pilot scale raceway

Abstract : This study investigated the impact of seasonal variations on the productivity of Nannochloropsis oculata culture, cultivated in an outdoor pilot scale open pond raceway over 16 months. The 2.5 m3 pilot (i.e. water depth of 20 cm) was operated under phototrophic conditions in a simulated marine environment at 50 g.L−1 of salinity. Results revealed that culture growth rates, doubling times and productivity were highly impacted by weather conditions with a good reproducibility of seasonal features. During summer, growth rate (i.e. 0.15 d−1) was higher than in winter (i.e. +300%) and in spring-autumn (i.e. +40%). Average areal productivities were higher during summertime (i.e. 13.2 t.ha−1.y−1 or 3.61 g.m−2.d−1) compared to those of winter (i.e. +264%) and autumn-spring conditions (i.e. +90%). Monthly correlation analysis revealed also a significant correlation between productivity and weather conditions (i.e. higher than 0.85), especially during culture periods not affected by microbial contamination, while daily correlation analysis showed that microalgae have a relative long-time spread response (i.e. about 10 days) to change in weather conditions. Therefore, the monthly approach appeared more suitable for considering weather effects over microalgae culture