esearchers have developed a new inexpensive and environmentally friendly technique to deliver carbon dioxide to microalgae, according to a study at the University of Melbourne. The technique involves a novel combination of solvent absorption, membrane desorption and microalgal cultivation to capture carbon dioxide and convert it to a lipid-rich biomass.
In the system, carbon dioxide is absorbed into a potassium carbonate solvent and this gas is desorbed directly into the microalgal medium via a non-porous polydimethyl siloxane (PDMS) hollow fiber membrane. This single step approach provides a paradigm shift in the cost of carbon delivery to the microalgae, say the researchers, as the very large reboiler energy demand of standard carbon capture solvent regeneration is avoided, as is the energy associated with gas compression.
Specifically, the use of a 20 wt% potassium carbonate solvent with 0.2, 0.5 and 0.7 CO2 loading was evaluated as a mechanism to deliver carbon dioxide to cultures of a salt tolerant Chlorella sp. microalgae. In all cases, accelerated growth of Chlorella sp. was observed, relative to a control.
The use of carbonate solutions of 0.5 and 0.7 loading resulted in the highest volumetric productivity (0.38 g L−1 d−1) and biomass concentration (1.8 g L−1) by completely avoiding carbon limitation of the cultures.
“In this work, we have found a way to purify the carbon dioxide and to supply it to the microalgae for a much more moderate cost and using a lot less energy,” said Sandra Kentish, lead author of the study.
The new technique purifies the carbon dioxide that is in power station flue gases by absorbing it into a liquid, according to the researchers. The liquid is then pumped through hollow fiber membranes that appear like long drinking straws. These membranes can be placed into the microalgae beds.
“The CO2 moves directly from the liquid into the microalgae culture by permeating through the fiber walls,” said Dr. Greg Martin, coauthor of the study. “Aside from being a cheaper approach, our research has shown that the microalgae grow faster than in other work done to date.”