Carbon dioxide capture by algae
D. Moreira & J. Pires in Atmospheric carbon dioxide capture by algae: Negative carbon dioxide emission path (2016) provide a comprehensive review of technologies to remove CO2, a key greenhouse gas (GHG) associated with climate change, global warming and increased health risks. The authors expand on technologies that go beyond carbon sequestration to physical removal of CO2 from our atmosphere by algae using Negative Emissions Technology (NETS). Although NETS include direct geoengineering methods of capturing CO2 as well as other indirect biological methods, one of the most viable options is Bioenergy with Carbon Capture and Storage (BECCS): photosynthetic organisms use the CO2 to make biomass followed by conversion to bioenergy, then storage of the resulting CO2 in aquifers, depleted oil gas field or coal seams, or recirculation back into algal production. The authors review both macroalgae (seaweeds) and microalgae BCCS technologies then present some funded projects.
Carbon dioxide capture by macroalgae or seaweeds
Macroalgae or seaweeds make up only 0.05% of the biomass available on the earth yet can provide 50-71% of the world’s storage of carbon (Chung et al., 2011). Indeed, the authors highlight that the main challenge to BECCS is the cost and capacity for storage of the CO2. The authors also highlight predictions made by Azar et al. (2013) that global temperatures could reduce by 0.06°C per decade with large-scale implementation of BECCS to reach 9% macroalgae afforestation in shallow coastline areas (N’Yeurt et al., 2012). This technology holds far more promise than carbon taxation which only offers, at best, carbon neutral goals. Hence, their emphasis on negative emissions propels further research into macroalgae’s role to reduce ocean acidification, dissolved CO2 in oceans and gaseous CO2 in our atmosphere. Although atmospheric CO2 concentrations rise by 2 ppm/year, BECCS can potentially reduce this by 100ppm in 30 years if no fossil fuels are used (Azar et al, 2013). The authors also identify other benefits of macroalgae cultivation including biogas production, integrated plant and fish cultivation, and bioactive compound extraction for pharmaceutical, cosmetic and nutritional use.
Carbon dioxide capture by microalgae
Likewise, carbon dioxide capture by microalgae provide the same benefits in CO2 reduction but hold more promise for bioenergy production and wastewater treatment. Numerous models allign microalgae biorefineries close to fossil fuel refineries to capture flu GHG’s (Figure 1). Microalgae such as Anabaena and Chlorella vulgaris can double their cell concentration in a few hours and contain ten-fold the energy conversion than land plants (Cheah et al., 2015). The bioenergy comes either from high lipid concentrations extracted from the microalgae for biofuel or anaerobic digestion to produce biogas. The fuel can be high grade enough to use in aviation and space exploration.
Finally, the authors provide results of research projects of carbon dioxide capture by algae. They highlight examples from the EU based Seventh Framework Program such as Biowalk4BioFuels (2012) that used macroalgae in biowaste energy recovery systems, biogas production and reduction in GHG emissions. The authors also describe the C-fast (Carbon negative Fuels derived from Algal and Solar Technologies) project through Computational Modelling Cambridge Ltd., U.K., which is still ongoing.
Essentially, algae contain far more potential than land plants to reduce CO2 emissions from both our atmosphere and oceans and have the added benefits of bioenergy, waste water management, nutrient pumping and bioactive compounds. The authors provide hope with research that predict emission negative outcomes which is paramount in our efforts to reduce GHG’s, possibly reverse climate change and save the planet we love.
File:Glowing Kelp Forest (17540493521).jpg. (2019, February 25). Wikimedia Commons, the free media repository. Retrieved 04:57, May 28, 2019 from https://commons.wikimedia.org/w/index.php?title=File:Glowing_Kelp_Forest_(17540493521).jpg&oldid=340515346.
Allen, J., Unlu, S., Demirel, Y., Black, P., Riekhof, W. (2018). Integration of biology, ecology and engineering for sustainable algal-based biofuel and bioproduct biorefinery. Bioresources and Bioprocessing, 5:47.
Moreira, D., & Pires, J. C. M. (2016). Atmospheric CO2 capture by algae: Negative carbon dioxide emission path. Bioresource Technology, 215, 371–379.