CO2 Mitigation and Renewable Oil from Photosynthetic Microbes: A New Appraisal

Abstract

The only major strategy now being seriously considered for biological mitigation of atmospheric CO2 relies entirely on terrestrial plants. Photosynthetic microbes were the focus of similar consideration in the 1990s. However, two major government-sponsored research programs in Japan and the USA concluded that the requisite technology was not feasible, and those programs were terminated after investing US$117 million and US$25 million, respectively. We report here on the results of a privately funded US$20 million program that has engineered, built, and successfully operated a commercial-scale (2 ha), modular, production system for photosynthetic microbes. The production system couples photobioreactors with open ponds in a two-stage process – a combination that was suggested, but never attempted – and has operated continuously for several years to produce Haematococcus pluvialis. The annually averaged rate of achieved microbial oil production from H. pluvialis is equivalent to <420 GJ ha -1 yr-1, which exceeds the most optimistic estimates of biofuel production from plantations of terrestrial ``energy crops.'' The maximum production rate achieved to date is equivalent to 1014 GJ ha-1 yr-1. We present evidence to demonstrate that a rate of 3200 GJ ha-1 yr-1 is feasible using species with known performance characteristics under conditions that prevail in the existing production system. At this rate, it is possible to replace reliance on current fossil fuel usage equivalent to ∼300 EJ yr-1 – and eliminate fossil fuel emissions of CO2 of ∼6.5 GtC yr-1 – using only 7.3% of the surplus arable land projected to be available by 2050. By comparison, most projections of biofuels production from terrestrial energy crops would require in excess of 80% of surplus arable land. Oil production cost is estimated at $84/bbl, assuming no improvements in current technology. We suggest enhancements that could reduce cost to $50/bbl or less.