A New Dawn For Industrial Photosynthesis

A new dawn for industrial photosynthesis
Dan E. Robertson,[pic]1 Stuart A. Jacobson,2 Frederick Morgan,2 David Berry,3 George M. Church,4 and Noubar B. Afeyan3
1Biological Sciences, Joule Unlimited, 83 Rogers Street, Cambridge, MA 02142 USA
2Engineering, Joule Unlimited, 83 Rogers Street, Cambridge, MA 02142 USA
3Flagship VentureLabs, 1 Memorial Drive, Cambridge, MA 02142 USA
4Department ofGenetics, Harvard University, School of Medicine, 77 Ave Louis Pasteur, NRB 238, Boston, MA 02115 USA
Dan E. Robertson, Phone: 617-354-6100, Fax: 617-354-6101, Email: drobertson@jouleunlimited.com.
Contributor Information.
[pic]Corresponding author.
Received October 5, 2010; Accepted January 26, 2011.

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Abstract

Several emerging technologies are aiming to meetrenewable fuel standards, mitigate greenhouse gas emissions, and provide viable alternatives to fossil fuels. Direct conversion of solar energy into fungible liquid fuel is a particularly attractive option, though conversion of that energy on an industrial scale depends on the efficiency of its capture and conversion. Large-scale programs have been undertaken in the recent past that used solar energyto grow innately oil-producing algae for biomass processing to biodiesel fuel. These efforts were ultimately deemed to be uneconomical because the costs of culturing, harvesting, and processing of algal biomass were not balanced by the process efficiencies for solar photon capture and conversion. This analysis addresses solar capture and conversion efficiencies and introduces a unique systemsapproach, enabled by advances in strain engineering, photobioreactor design, and a process that contradicts prejudicial opinions about the viability of industrial photosynthesis. We calculate efficiencies for this direct, continuous solar process based on common boundary conditions, empirical measurements and validated assumptions wherein genetically engineered cyanobacteria convert industriallysourced, high-concentration CO2 into secreted, fungible hydrocarbon products in a continuous process. These innovations are projected to operate at areal productivities far exceeding those based on accumulation and refining of plant or algal biomass or on prior assumptions of photosynthetic productivity. This concept, currently enabled for production of ethanol and alkane diesel fuel molecules, andoperating at pilot scale, establishes a new paradigm for high productivity manufacturing of nonfossil-derived fuels and chemicals.
Keywords: Cyanobacteria, Metabolic engineering, Hydrocarbon, Alkane, Diesel, Renewable fuel, Algae, Biomass, Biodiesel

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Introduction

The capture of solar energy to power industrial processes has been an inviting prospect for decades. Theenergy density of solar radiation and its potential as a source for production of fuels, if efficiently captured and converted, could support the goals of national energy independence. Analyses of photosynthetic conversion have been driven by this promise (Goldman 1978; Pirt 1983; Bolton and Hall 1991; Zhu et al. 2008, 2010). The deployment of solar-based industries for fuels has, however, been limitedby the lack of efficient cost-effective technologies. Projects funded between 1976 and 1996 under the US Department of Energy (DOE) aquatic species program explored phototrophic organisms and process technologies for the production of algal oils and their refinement into biodiesel. The results of these efforts were summarized in a report that delineated the technological barriers to industrialdevelopment (Sheehan et al. 1998).

The traditional photosynthetic fuels process is one wherein triglyceride-producing algae are grown under illumination and stressed to induce the diversion of a fraction of carbon to oil production. The algal biomass is harvested, dewatered and lysed, and processed to yield a product that is chemically refined to an acyl ester biodiesel product. Many companies...