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Published on: August 8, 2018
Optimizing calcium and magnesium in seawater medium with high bicarbonate concentration for efficient growth and
Xiang Du1, Chenba Zhu2, Zhanyou Chi1
1MOE Key Laboratory of Bio-Intelligent Manufacturing, School of Bioengineering, Dalian University of Technology, Dalian 116024, China.
Abstract:
Microalgae cultivation using high bicarbonate concentration in seawater medium triggers CaCO3 precipitation due to pH elevation, contaminating the photobioreactor and reduce biomass productivity. It is necessary to control Ca2+ and Mg2+ concentration in appropriate range to allow microalgae rapid growth without precipitation, followed by effective self-flocculation for harvesting. This study optimized this concentration range as 0.5-1.0 mmol L-1 for Ca2+ and 2.5-5.0 mmol L-1 for Mg2+. With this concentration, subsequent pH adjustment to 11 induced > 90 % self-flocculation efficiency. Also, outdoor cultivation in floating photobioreactors utilized treated seawater with optimized Ca2+ and Mg2+ concentration achieved productivity of 9.36 g m-2 day-1, which is 112 % higher than untreated seawater (4.42 g m-2 day-1). The optimized process reached the goal of higher biomass productivity without precipitation and efficient harvesting. On the other hand, microalgae-induced precipitation may serve as potential carbon sink, contributing to ocean-negative carbon emissions.
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