Cost-Effective and Efficient Production of Carbohydrates from an Alkalihalophilic Leptolyngbya sp. in a Photobioreactor with Periodical Mixing

Using sodium bicarbonate (NaHCO3) as the carbon source makes it possible to decouple mixing and carbon supply in microalgae cultivation, and a periodical mixing may be sufficient to support rapid microalgae growth. To test this idea, growth of a screened Leptolyngbya sp. DUT 001 cultured with NaHCO3 was evaluated in a bubbling column photobioreactor. First, the culture medium of this strain was optimized as 25.2 g L–1 NaHCO3 and 0.5 g L–1 NaNO3, in which condition the achieved highest biomass productivity and carbohydrate content were 0.74 g L–1 d–1 and 75.7 ± 1.3%, respectively. Second, the effect of four periodical mixing modes of 6:2, 6:4, 6:6, and 6:10 (bubbling/stopping, s) on microalgae growth was investigated, and these cultures resulted in the highest biomass concentrations of 1.76 ± 0.03, 1.75 ± 0.04, 1.72 ± 0.05, and 1.66 ± 0.04 g L–1, respectively. Correspondingly, the highest carbohydrate contents were 56.5 ± 1.2, 63.0 ± 2.5, 64.7 ± 2.1, and 60.6 ± 2.5%, respectively. However, there was no significant difference between these values and those achieved in the control group with continuous mixing (P > 0.05), which was 1.82 ± 0.06 g L–1 and 59.3 ± 1.3%, respectively. These results showed that it is feasible to use periodical mixing in microalgae cultivation, which may significantly reduce the microalgae biomass production cost.