Aeration and nitrogen modulated growth rate and chemical composition of green macroalgae Ulva sp. cultured in a photobioreactor
2020
Traugott, H. | Zollmann, M. | Cohen, H. | Chemodanov, A. | Liberzon, A. | Golberg, A.
Bottom aeration is a common technology used in macroalgae cultivation. Productivity and chemical composition of macroalgae depend on the air flow rate injected to the cultivating systems through mechanical stimulation, the addition of CO₂, or mass transfer of nutrients. However, detailed information about the different effects and aspects of aeration, which are critical for maximizing the growth of the algae and optimizing its quality, is still lacking. We quantified the effects of aeration rate on the biomass growth rate, protein, starch, and ash contents of Ulva sp., using different combinations of air flow rates and nitrogen concentration in an outdoor photobioreactor. Increasing the air flow from 0.5 L min⁻¹ to 2 L min⁻¹, increased by up to 36% the daily growth rate and the starch content up to 75%, of the Ulva sp. biomass, depending on the fertilization concentration. Protein and ash content were not significantly affected by aeration rates in the tested ranges of aeration for both fertilization with 58 μM and 430 μM of nitrate per week. Protein content increased, and starch decreased with increasing fertilization concentrations. Following the empirical evidence of the combined effect of nitrogen concentration and hydrodynamics we can expect that for increased starch production a cultivation method comprised of two phases could be beneficial: a nitrogen-rich initial phase that leads to higher biomass growth rates, followed by a nitrogen-limited phase with increased aeration for the carbohydrate/starch accumulation.
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