Effect of medium recycling, culture depth, and mixing duration on D. salina growth

Abstract

Microalgal cultivation is currently stifled by various constraints. In winter, additional losses are incurred due to lower productivities. Here, effects of medium recycling to conserve water use, paddle wheel mixing duration to reduce power consumption and culture depth on growth of Dunaliella salina (MUR 8) cultivated in raceway ponds during the Austral winter season was studied. Ponds were operated semi-continuously at 0.18 m depth to study the effect of medium recycling on the growth and productivity. One pond served as a control without recycling (NMR) which was replenished with fresh medium after each harvest while the other served as a test variable with medium recycling (MR). In parallel, two ponds were also operated to investigate the effects of culture depth on the growth and productivity with one pond being operated at of 0.11 m (LD) and the other at 0.18 m (HD). Subsequently, a comparison of 24 h paddle wheel mixing (24MX) against 12 h daytime paddle wheel mixing (12MX) was also performed in 2 m2 raceway ponds. Our results showed that medium recycling, paddlewheel mixing time and pond depth did not have significant effects on μmax, biomass, lipids, and carotenoid productivity of Dunaliella salina. However, carotenoids: chlorophyll a ratio were significantly higher in LD treatments in comparison with HD treatments. Areal productivities were also higher in HD treatments compared to LD treatments. Medium recycling, paddlewheel mixing time and pond depth also had no significant effect on the photosynthetic parameters: Fv′/Fm′, rETRmax and Ioptimum. However, α was higher in HD treatments compared to LD treatments. NPQmax was also higher in 24MX treatments compared to 12MX treatment. In here we demonstrated that medium recycling and reduced paddle wheel mixing could be employed as viable cost and energy saving methods in the cultivation of Dunaliella salina during the Austral winter season.