Atmospheric CO2 Enrichment and Delivery (ACED)

Increasing the CO2 concentration in gas supplied to a microalgae growth system can improve its productivity many fold over using atmospheric air.  While flue gas seems a good source of CO2-enriched gas, its usefulness is compromised by transportation costs from the source to the site of microalgae production and its wide range of contaminants that can be toxic to the microalgae and can contaminate fuel or other high-value products.

Having a cost-effective strategy to capture and concentrate atmospheric CO2 for delivery to microalgae-growth systems will overcome both limitations of flue gas.  This will enable the high microalgae productivity needed to meet the significant global demand for high-density liquid trans-portation fuels.  We propose to integrate novel CO2-capture and -delivery technologies, allowing us to boost microalgae productivity and cost-effectiveness no matter the location or the products.

We propose to capture and concentrate CO2 from the atmosphere using Moisture-Swing Sorption (MSS), which takes advantage of unique properties of passive collection to lower the cost of capturing CO2 from air.  The material used operates on a humidity swing and captures CO2 when dry and releases it again when wetted.  At release, the partial pressure of CO2 is increased roughly 100-fold over air, creating an output stream similar to flue gas, but located at the site of microalgae growth and without the contaminants.  This dry-wet reaction cycle is repeatable and can be adapted for continuous operation.
We propose to deliver the concentrated CO2 using special bubble-less gas-transfer membranes, called Membrane Carbonation (MC), which is similar to how hydrogen gas is delivered in the membrane biofilm reactor for treating water contaminated with oxidized pollutants.  Gas delivery is via diffusion through a membrane, which minimizes the loss of CO2, since the CO2 is not sparged.  The CO2 uptake efficiency can be 90% or more with MC.  Furthermore, MC offers more precise control over the pH and inorganic-C (Ci) levels, while eliminating the input of undesired microorganisms from gas delivery.

We will combine MSS and MC to deliver CO2 to microalgae growth systems with high efficiency and at a rate that is high enough to promote high biomass-production rates in closed or open systems, as shown in Figure 1.  The project’s objective is to scale up both approaches and integrate them into a single system that we will test at prototype scale outdoors using various algal strains (Scenedesmus, Chlorella, Synechocystis) that grow optimally with different concentrations of inorganic carbon.

This project is supported by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy Targeted Algal Biofuels and Bioproducts program under Award Number DE-EE0007093.