Using polyethylene glycol to promote Nannochloropsis oceanica growth with 15 vol% CO 2 .

CO ₂ capture with microalgae has been put forward in response to global concern on greenhouse gas emission. However, the short residence time and slow diffusion of CO ₂ in water limits the growth of microalgae. In order to improve CO ₂ transfer from gas phase to liquid phase and utilization by algal cells, polyethylene glycol 200 (PEG 200) was used as CO ₂ absorbent to promote growth of Nannochloropsis oceanica with the bubbling of 15 vol% CO ₂ . Total inorganic carbon (TIC) absorbed in culture medium remained constant at 5.6 mM when 15 vol% CO ₂ was bubbled continuously. PEG 200 in the medium provided additional CO ₂ absorption from 0.6 to 4.8 mM when PEG 200 concentration increased from 0.5 to 4 mM. The specific growth rate of N. oceanica reached the maximum (1.41 d ^-1 ) with 1 mM PEG 200 in culture medium, which was 21.5% higher than the specific growth rate without PEG 200. About 79% of the increase in biomass was attributed to the increased TIC with more CO ₂ dissolution in culture medium because of PEG 200, and about 21% was attributed to PEG 200 itself utilized as an organic carbon source. In conclusion, PEG 200 as a CO ₂ absorbent can effectively capture flue-gas CO ₂ for algal growth.
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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