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.