Microalgae for Greenhouse Gas Abatement

AMBIENTE TPOINT 1/2003 Microalgae for Greenhouse Gas Abatement An international R&D opportunity Paola Pedroni/EniTecnologie John Benemann La possi...
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AMBIENTE

TPOINT 1/2003

Microalgae for Greenhouse Gas Abatement An international R&D opportunity

Paola Pedroni/EniTecnologie John Benemann

La possibilità di catturare e riutilizzare la CO2 emessa da sorgenti concentrate mediante coltivazioni intensive di microalghe rappresenta un’opzione innovativa ed ecocompatibile per mitigare le emissioni di gas serra derivanti dalla combustione delle fonti fossili e per produrre biofuels rinnovabili. Il raggiungimento di adeguati target di convenienza economica richiede attività di ricerca sia di base che applicata a lungo termine. Combinando la cattura della CO2 fossile con servizi ambientali aggiuntivi, come per esempio il trattamento di acque di scarto, è possibile attendersi l’applicazione di tali sistemi biologici in un arco temporale più breve. Per promuovere lo sviluppo tecnologico e l’utilizzo di processi di biofissazione nella mitigazione delle emissioni di gas serra, EniTecnologie e il DoE statunitense hanno organizzato un Network Internazionale, che opera sotto l’egida dell’IEA GHG R&D Programme, e comprende industrie e organizzazioni governative operanti nel settore energetico. EniTecnologie partecipa attivamente a tale network con una propria attività di ricerca focalizzata sulla conversione della biomassa algale a vettori energetici rinnovabili. Mankind is just beginning to recognize both the necessity and increasing urgency to reduce emissions of fossil fuelderived greenhouse gases, principally CO2. Global warming and greenhouse gas (GHG) abatement can, 24

however, not be considered in isolation of the other problems and challenges that our technological societies have created during their economic development, from resource depletion to ecosystem destruction. The solution to these challenges is best summarized by the concept and goal of “sustainability”. Technology development in GHG abatement must not only look for short-term solutions, such as those involving capture and sequestration of CO2, but also promote technologies, in particular solar energy-based processes, which can provide for more sustainable economies. In this respect, biological processes for GHG abatement, through CO2 fixation into biomass and then conversion to biofuels, deserve attention, as photosynthesis is already widely used and is in principle, even if not yet in practice, a highly efficient solar energy converter. Globally, biological processes, such as forest growth, already abate a significant fraction of fossil and other GHG emissions resulting from human activities. Also the human impact on ecosystems, in terms of appropriation or disturbance of primary productivity, that is CO2 fixed into biomass, exceeds our use of fossil fuels by a large factor. Biological processes afford many different mechanisms and approaches to fossil GHG abatement, principally through the production of biofuels to replace fossil fuels, but also through carbon sequestration in soils and replacement of chemicals, fertilizers and other products presently derived from fossil fuels. The major R&D challenge is to increase the practical efficiency of the photosynthetic process, to minimize their footprint, and also to reduce their overall costs.

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Figure 1: commercial microalge production facility (Cyanotech Corp., Kona Hawaii)

Figure 2: power plant for CO2 supply in microalgae production (Cyanotech Corp., Kona Hawaii)

Microalgae Biotechnology

Hawaii, with the red ponds being cultures of Haematococcus and the green ones of Spirulina. This plant also operates a small power plant (2 MWe), run on biodiesel, which provides the CO2 required by the microalgae cultures, as well as power for its own use and sale to the local grid (figure 2). This is a first example of a completely CO 2-neutral microalgae production operation, as the biodiesel does not contribute to GHG emissions. However, for fossil CO2 abatement, more than neutrality is desired, and some additional fossil fuel-sparing product or process must be an output from such an operation. The first major R&D effort in developing microalgae biotechnologies, about 50 years ago, was an international cooperation between the U.S., Germany and Japan to develop algal mass cultures for production of human foods. Pioneering work at the University of California Berkeley demonstrated microalgae pond systems for practical wastewater treatment, leading to the proposal to use power plant flue gas CO2 to produce additional algal biomass from wastewaters and convert it to biofuels [1]. The energy crisis of the 1970’s gave impetus to R&D of this concept, with emphasis on the harvesting of the

Microalgae are microscopic plants, typically growing in water and able to reproduce rapidly, often doubling in as little as a day. A major reason for the interest in microalgae for GHG abatement is that their cultivation requires a concentrated source of CO2, such as power plant flue gases, as, unlike higher plants, microalgae ponds cannot capture CO2 from the air. Over ten thousand species of microalgae are described, but only a handful are presently commercially cultivated: Spirulina, a filamentous blue green alga, Chlorella, Dunaliella and Haematococcus, the last three being unicellular green algae. The first two species are produced for food supplements the last two for their pigment content, specifically beta-carotene and astaxanthin, which gives farmed salmon fish their natural color. Production plants are now operating in the U.S., China, India, Australia and other countries, most using raceway-type ponds with paddle wheel mixing. Figure 1 shows a microalgae production plant in

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algal biomass from wastewater ponds through spontaneous flocculation and settling [2]. During the 1980’s the U.S. Department of Energy supported considerable R&D, under the “Aquatic Species Program”, for the production of algal oils (biodiesel) in large-scale, dedicated systems. This effort culminated in the operation of a 0,2 hectare pilot plant in Roswell, New Mexico that demonstrated the ability to grow selected algal strains with high CO2 utilization efficiency in large, low cost, open raceway ponds mixed with paddle wheels [3]. However, engineering cost analyses concluded that for economic feasibility such stand-alone processes required very high biomass productivities, approaching the limits of solar conversion efficiencies, among many other favorable engineering and process assumptions [4]. During the 1990’s a very large R&D effort on microalgae for utilization of power plant flue gas CO2 and GHG abatement was carried out in Japan, sponsored by RITE (Research for Innovative Technologies of the Earth) and emphasizing the use of closed photobioreactors of various designs, in particular optical fiber-based designs and co-production of high value products. These R&D efforts were discontinued by the end of the decade, in large part because of the unfavorable economic projections for such approaches. Closed photobioreactors, of any design, are presently much too expensive for applications dealing with microalgae GHG abatement, wastewater treatment or similar processes. Indeed, in the commercial production of microalgae, open ponds, mostly of the raceway-type mixed with paddle wheels (figure 1), have proven to be the only cost-effective production method. Even with such ponds, current production costs for Spirulina, with some 2,000 tons produced annually world-wide, are about U.S.$ 5,000/ton. Costs would drop by over ten-fold if larger scale systems were deployed, with individual unlined earthen ponds of several hectares, and if higher productivities could be achieved and lower cost harvesting methods developed. 26

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R&D Network for microalgae biofixation To advance the near- and long-term development and applications of microalgae for biofixation of CO2 and GHG emissions reductions, EniTecnologie and the U.S. DoE, with assistance from the IEA GHG R&D Programme, have organized the “International Network on Biofixation of CO2 and Greenhouse Gas Abatement with Microalgae”. EniTecnologie hosted a workshop on this topic at Monterotondo facility in January 2001, attended by over thirty experts in microalgae biotechnology and representatives of interested corporations and agencies. The consensus of the participants was that microalgae have significant potential for achieving the high productivities and low costs required for GHG abatement [5]. The Network became operative in June 2002 and present members include, in addition to EniTecnologie and U.S. DoE, Arizona Public Services, a U.S. electric utility; ENEL Produzione Ricerca; EPRI, a U.S. R&D organization serving electric utilities; ExxonMobil; the Gas Technology Institute, carrying out R&D in support of the gas industry and Rio Tinto, an international mining company. Other members expected to join this year. These companies and organizations, all with an interest in promoting R&D and practical applications in this field, have joined together to more effectively use limited resources and expertise, to avoid duplication, and promote R&D coordination and cooperative efforts. The objectives of the Network are to develop and demonstrate the technical and economic feasibility of such technologies and initiate some practical applications within this decade.

The R&D roadmap The first task of the International Network was to develop an R&D Roadmap. A Roadmap provides a structured R&D planning process by identifying the

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CO2 INPUTS CONCENTRATED CO2 SOURCES ● ● ●

Power plants Industries Others

PROCESSES MULTIFUNCTIONAL for MITIGATING GHGs ● ● ● ●

ALGAL STRAINS ● ● ● ● ●

Selection Genetics Metabolism Physiology Pond ecology SCIENCE

OUTPUT PRODUCTS

Biofuels/co-products Waste treatment Nutrient recycling Reduced fossil fuel use

MICROALGAE MASS CULTURE SYSTEMS ● ● ● ●

Ponds/Inoculum CO2 Supply/Transfer Harvesting Processing ENGINEERING

FOSSIL FUEL-SUBSTITUTING or SPARING PRODUCTS ● ● ●

CH4, ethanol, biodiesel, H2, hydrcarbons Fertilizers, biopolymers Reclaimed water

PROCESS DESIGNS and ECONOMICS ● ● ● ●

Design/Cost analysis Resource assessments: land, water etc. GHG mitigation accounting Markets and local/global impact for GHG Mitigation ANALYSIS

Figure 3: R&D Roadmap

scientific and technological developments needed to achieve a specific strategic goal. Most importantly, the roadmapping effort involves consensus building among technical experts of the most plausible processes and the critical R&D needs that can meet the goal. The consensus developed during the Monterotondo Workshop and subsequent organizational and technical meetings is that the preferred R&D pathway to the development of microalgae biofixation processes is to make these, at least initially, part of multipurpose processes which provide additional services, such as wastewater treatment and higher value co-products, in addition to their GHG abatement functions. The schematic in figure 3 provides an overview of the elements considered for the development of the Roadmap. Major R&D objectives that must be addressed in the development of such processes are the stable mass culture of selected microalgae strains in large open ponds, the low-cost harvesting of the algae biomass,

and the achievement of high productivities, above 100 tons/hectare/year. The cultivation system for such processes would be raceway earthen ponds. Closed photobioreactors can be useful in the production of required algal inoculum, which has to be grown from a laboratory seed cultures through successive stages of increasing scale under more controlled conditions than possible in open ponds. The R&D Roadmap [6], proposed the development of four general microalgae biofixation/GHG abatement processes that encompass the plausible near- to mid- term opportunities for practical applications: 1. municipal wastewater treatment using CO2, with production and reduced energy CH 4 consumption; 2. treatment of animal and other agricultural/food wastes, with production of biofuels and fertilizers; 3. use of nitrogen fixing microalgae and nutrient recycling for agricultural applications; 27

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4. co-production of biofuels and large volume/higher value products (biopolymers, animal feeds, etc.). All these conceptual processes require similar production systems, e.g., raceway pond, paddle wheel-mixed, using CO2 from power plants or similar concentrated sources, producing renewable biofuels, in addition to other functions, such as wastewater treatment and higher value (than fuels) co-products. GHG abatement derives not only from the renewable biofuels produced from the algal biomass, but also from reduced energy consumption, compared to alternatives, and even secondary GHG (e.g. CH4) reductions. All four approaches could be plausibly economically feasible through near- to mid-term R&D, and would be of sufficient scale, both as individual processes and in aggregate, to achieve significant GHG abatement, regionally and globally. These processes have to address essentially similar basic and applied research issues: maintenance and stability of algal strains in outdoor pond cultures; development of large-scale production of inoculum; microalgal physiology under highly variable and extreme environments; maximization of productivity, that is solar conversion efficiencies; development of low-cost harvesting processes of the algal biomass; efficient conversion of the algal biomass to biofuels (CH4, H2, biodiesel, ethanol, even hydrocarbons); integration with additional co-products and coprocesses; engineering designs of large-scale open ponds and the supporting systems (e.g. CO 2 injection); evaluation of resources and GHG mitigation impact, that is to say how many megatons of fossil CO2 abatement could microalgae processes provide, both regionally and globally.

Activities for innovation The R&D challenges in microalgae biofixation of CO2 and GHG abatement require multidisciplinary skills and a critical mass to allow a broad coverage of the many R&D topics, as well as a diversity of 28

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approaches and projects that cannot be encompassed by any single organization. The Network provides the structure and the mechanism by which the required expertise can be integrated, the critical mass reached and the research projects coordinated, to help focus R&D efforts on most promising approaches. EniTecnologie is actively working and collaborating with other organizations in this innovative technology, also with a in-house R&D project developed as part of CO 2 sequestration options for clean and renewable fuel production. References 1. Oswald, W. J. and Golueke, C. G., (1960), Adv. Appl. Microbiol. 11, 223 – 242. 2. Benemann, J. R., Koopman, B. L., Weissman, J. C., Eisenberg, D. M. and Goebel, P. (1980). “Algae Biomass: Production and Use”, pp. 457-496, G. Shelef and C. J. Soeder (editors) Elsevier, Amsterdam. 3. Sheehan, J., Dunahay, T., Benemann, J. R. and Roessler, P. (1998). “A Look Back at the U.S. Department of Energy’s Aquatic Species Program - Biodiesel from Algae”. National Renewable Energy Laboratory, Golden, CO, 80401 NERL/TP-580-24190. 4. Benemann, J. R. and Oswald W. J., (1996). “Systems and Economic Analysis of Microalgae Ponds for Conversion of CO2 to Biomass”, pp. 260. Final Report, Pittsburgh Energy Technology Center. 5. IEA GHG R&D Programme, (2001). Workshop on “Formation of an International Network on Biofixation of CO2 and GHG Abatement with Microalgae”. Report PH4/1, March 2001. 6. Benemann, J. R., Roadmap Report. 2003.

John Benemann’s profile John Benemann is an independent consultant living in Walnut Creek, California. He has worked for many agencies and Companies around the world in the fields of biological energy production. His research career, mostly at the University of California Berkeley, has concentrated on microalgae processes for energy production and wastewater treatment. He is presently Manager of the “International Network on Biofixation of CO2 and Greenhouse Gas Abatement with Microalgae”.