This post quantifies claims in my algae geoengineering proposal, now in the last week of public voting at the MIT Climate Colab Competition. Microalgae Cultivation Using Offshore Membrane Enclosures for Growing Algae (OMEGA) (1) states that NASA’s OMEGA project sought to sustain a target microalgae productivity of 20 grams per square meter per day, in line with the average productivity cited by Putt et al (2). A gram per square meter equals a tonne per square kilometer. An average of 20 grams per square meter per day gives dry weight algae yield above 7000 tonnes per square kilometer per year in tropical zones of year-round operation. At the scale of the global climate considered for geoengineering, we emit about 30 gigatonnes of CO2 per year. For algae farms to utilise all anthropogenic CO2 would therefore require 3 million square kilometers of production area, or about 1% of the total world ocean area of 361 million km2. The high productivity level shows why algae is potentially better as a geoengineering carbon dioxide removal method than other crops which achieve lower yield. This technology is still in early days. The NASA trial achieved yield of only 14 grams on average, 70% of Putt’s figure, but yields will increase as systems are optimised. To illustrate the uncertainty of best technology, the algae production method in the OMEGA lab used LLDPE plastic tubes which appear somewhat different from the flat membrane concept initially described by Dr Jonathan Trent at his TED Talk on Energy from floating algae pods (3). Fixing a tonne of carbon requires 3.66 tonnes of CO2, given atomic weights of oxygen (16), carbon (12), and CO2 (44). A review of algae field trials by Doucha et al (4) states “It was estimated that about 50% of flue gas decarbonization can be attained in the photobioreactor and 4.4 kg of CO2 is needed for production of 1 kg (dry weight) algal biomass.” The figure of 4.4 kg appears to involve loss of about 2.6 kg of CO2 to the air, given that the NASA review paper states that algae is 50% carbon, so 1 kg of algae contains 0.5 kg of carbon, which only requires 1.8 kg of CO2. The relevant figure for CDR is the amount of CO2 actually removed from the system, ie 1.8 kg of CO2 per kg of algae. My proposal suggests a target of 2% of the world ocean for algae farming. This would enable half of the algae to be sold for fuel and other products, and half to be sequestered in recoverable or usable form for CDR. This would drive the atmosphere back towards its previous stable CO2 level and reverse local ocean warming and acifidication while enhancing biological diversity and abundance. As well, it would replace the need for ecologically harmful land based mining operations. This large algae production scale is a medium term goal, based on maintaining current energy consumption level and methods. The geoengineering result includes the objective of ‘banking’ most of the produced algae, either in bags on the sea floor, in construction materials, or in closed loop electric power production, as well as cooling of critical locations such as the Gulf Stream and Australia’s Great Barrier Reef. Robert Tulip 1. Microalgae Cultivation Using Offshore Membrane Enclosures for Growing Algae (OMEGA), Patrick Wiley, Linden Harris, Sigrid Reinsch, Sasha Tozzi, Tsegereda Embaye, Kit Clark, Brandi McKuin, Zbigniew Kolber, Russel Adams, Hiromi Kagawa, Tra-My Justine Richardson, John Malinowski, Colin Beal, Matthew A. Claxton, Emil Geiger, Jon Rask, J. Elliot Campbell, Jonathan D. Trent*,Journal of Sustainable Bioenergy Systems, 2013, 3, 18-32 doi:10.4236/jsbs.2013.31003, published March 2013 (http://www.scirp.org/journal/jsbs), 2. R. Putt, et al., “An Efficient System for Carbonation of High-Rate Algae Pond Water to Enhance CO2 Mass Transfer,” Bioresource Technology, Vol. 102, No. 3, 2011, pp. 3240-3245. doi:10.1016/j.biortech.2010.11.029 3. Jonathan Trent: TED http://www.ted.com/talks/jonathan_trent_energy_from_floating_algae_pods.html 4. J. Doucha, F. Straka and K. Lívanský, “Utilization of Flue Gas for Cultivation of Microalgae Chlorella sp.) in an Outdoor Open Thin-Layer Photobioreactor,” Journal of Applied Phycology, Vol. 17, No. 5, 2005, pp. 403-412. doi:10.1007/s10811-005-8701-7 CoLab: http://climatecolab.org/web/guest/plans/-/plans/contestId/20/planId/1303631
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