MICROALGAE BIOFIXATION PROCESSES:

Applications and Potential Contributions to

Greenhouse Gas Mitigation Options

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MICROALGAE BIOFIXATION PROCESSES: Applications and Potential Contributions to Greenhouse Gas Mitigation Options

Date

May 2006

Prepared by TNO Built Environment and Geosciences

Toon van Harmelen Hans Oonk

Order no.

36562

Prepared for the

International Network on Biofixation of CO2 and Greenhouse Gas Abatement with Microalgae operated under the International Energy Agency Greenhouse Gas R&D Programme

Sponsored by

EniTecnologie S.p.A., San Donato Milanese, Milan, Italy

Keywords

Microalgae Biofixation CO2 mitigation Regional and Global Potential

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Preface

This report has been carried out from June 2005 to March 2006 for the International Network on Biofixation of CO2 and Greenhouse Gas Abatement with Microalgae (Biofixation Network) under the auspices of the IEA Greenhouse Gas R&D programme and the sponsorship of EniTecnologie S.p.A. (Milan, Italy). Preparation of this report was supervised by Paola Maria Pedroni (Project Manager, EniTecnologie and Chair of the Biofixation Network) and Angela Manancourt, Harry Audus and John Gale (IEA Greenhouse Gas R&D Programme) and has been carried out with the advice and assistance of John R. Benemann (Manager of the Biofixation Network). The authors would like to thank them for their valuable discussions and contributions. The results, conclusions and opinions in this report are solely those and responsibility of the authors and do not necessarily reflect the views of the performing, sponsoring or supervising organisations. Frontispiece: Open, raceway, paddle wheel mixed Spirulina production ponds

(Earthrise Nutritionals, LLC, Calipatria, California, USA). Growth ponds about 0.4 hectare or 4,000 m2 each (courtesy of Amha Belay)

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demonstrated in practice and will require considerable R&D. More critically, the projected capital costs for such algal production systems are high (close to US$

Executive summary

This report provides an independent assessment of the applications and potential contributions to greenhouse gas (GHG) abatement of microalgae biofixation processes. It is intended as a strategic tool for R&D personnel and managers, policy makers, and others who need to broadly evaluate the various technology options for GHG abatement, as well as related environmental and sustainability issues. This assessment, carried out on both a regional and global scale, is based on technology plausibly available in the near- to mid-term (2010 to 2020) for practical applications of microalgae in biofuels production. The most plausible immediate applications are in conjunction with advanced wastewater treatment processes, for removal and recovery of nitrogen and phosphorous, thus allowing the re-use of these plant nutrients in agriculture. Microalgae are microscopic plants that typically grow suspended in water and carry out the same photosynthesis process as higher land plants (crops and trees): the conversion of water, CO2 and sunlight into O2 and biomass. Microalgae have been extensively studied in the USA, Japan, and elsewhere for over 50 years for food and feed production, wastewater treatment, generation of biofuels (biogas, biodiesel, hydrogen, and ethanol), nutritional supplements, and, more recently, for CO2 capture from power plant flue gases for GHG abatement. A rapidly growing algae industry, in Japan, USA, India, China, among others, is currently producing over 10,000 tons annually of microalgal biomass, mostly in open ponds and mainly for nutritional supplements. Most of these systems cultivate the algae in raceway-type open ponds mixed with paddle wheels and generally are supplied with CO2 to increase productivity. In addition, many thousands of algal ponds, mostly small but some large (> 100 hectares) are also used around the world for wastewater treatment. However, in these waste treatment applications CO2 fertilisation is presently not practiced and the algal biomass is typically not harvested, or in the few cases where harvested, the biomass is not beneficially used. The most important advantages of microalgae biofixation processes in GHG abatement are: their ability to directly use fossil CO2 (from power plant flue gases and similar sources), their potentially much higher productivities than higher land or other aquatic plants, their high nutrient contents (allowing for nutrient capture in waste treatment), and their use of resources, such as brackish, saline, and wastewaters, as well as clay, hardpan, alkaline and salty soils, not suitable for conventional agriculture. Development of microalgae technologies is helped by the very short generation times (one day or even less) of these microscopic plants and the relative simplicity and scalability of their hydraulic production systems, allowing for faster process development at smaller scales than possible with higher plants. Current technological limitations of microalgae production processes include the harvesting process (due to their small cell sizes), the relatively high cost of the cultivation systems and the generally undeveloped nature of this technology. There is renewed interest in microalgae for biofuels production, based on the presumed very high productivities of microalgae cultures, projected at well above 100 tons of biomass (as dry organic matter) per hectare per year (ton/ha/yr), and high yields of biodiesel and other biofuels. However, these projections still must be

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CO2 or flue gases, with the biomass harvested by flocculation and settling.

100,000 per hectare) compared to the capital costs for establishment of new land plants cultivation (well below US$ 10,000 per hectare). Thus, even with high productivities, microalgae biomass production will be more expensive than higher plants. It must therefore be justified based on the quality of the biomass produced, allowing easier conversion to desired biofuels and the co-production of higher value products. The small “footprint” of such high productivity systems allows for more efficient use of scarce land resources and reduces environmental impacts. The use of otherwise underutilised land, water and nutrient resources, could even justify the long-term (>20 years) development of such technologies solely for biofuels production, even with the relatively, to higher plant biomass systems, high capital and operating costs currently projected. In the near-term (5 to 10 years) R&D for microalgae biofuels production can most plausibly be considered in conjunction with wastewater treatment. In this case the economics are based on the alternative technologies currently employed, in particular the activated sludge process for municipal wastewaters. Microalgae waste treatment processes substitute solar energy for the fossil fuels used in such conventional wastewater treatment processes. Thus they reduce fossil CO2 emissions by both reducing fossil energy use compared to conventional processes as well as by producing renewable biofuels. This report focuses on the global potential of microalgae processes for GHG abatement in conjunction with wastewater treatment, both municipal and agricultural (animal husbandry), as this is the nearest-term application of such technologies. Practical applications in wastewater treatment could also lead the way to further applications in the production of biofertilisers, higher value co-products and, possibly, in the long-term, to stand-alone, dedicated, biofuel production processes. The near-term applications would provide the starting point for such mid- and longer-term applications: Near Term Mid Term Long Term 5 – 10 years 10 – 20 years 20+ years Waste treatment Higher value Dedicated biofuels- processes co-products only systems The main results and conclusions of this report are summarised as follows: Microalgae and CO2 abatement • Biological, including microalgae, photosynthesis-based processes are solar

energy converters that produce a storable form of renewable energy, biomass. Microalgae processes, unlike higher plants that capture CO2 from the atmosphere, require enriched sources of CO2, such as power plant flue gases. Microalgae biomass can be converted to liquid and gaseous fuels, but, due to its very high moisture and nitrogen content, cannot be combusted or used in thermochemical conversion processes.

• Microalgae biofixation processes for large-scale, low-cost production of

biofuels and GHG abatement, would involve cultivation of selected algal strains in large, open, raceway-type, paddle wheel mixed ponds, fertilised with

• Microalgae biofixation processes for GHG abatement that could be developed in the near- to mid-term (by 2020) could combine utilisation of fossil and other concentrated CO2 sources with municipal or agricultural wastewater treatment, the recycling of nutrients as fertilisers and the production of renewable fuels. For some wastewaters the co-production of higher value products, such as biopolymers or animal feeds, can also be considered. In the mid- to long-term, such co-products may economically justify such processes without need for a waste treatment function.

• An approximate overall estimate is that production of one ton of microalgae

biomass produced during wastewater treatment reduces the equivalent of one ton of fossil CO2 emissions, based on both the biofuels derived from the algal biomass and the GHG reductions compared to conventional wastewater treatment processes, as well as fertilisers and other potential co-products, currently derived from fossil fuels.

Economic viability • Microalgae biofixation technologies involve designs and operations similar to

that of wastewater treatment and also mechanised agriculture and can be applied in developing countries, as evidenced by the widespread applications of commercial microalgae production technologies in China and India.

• With R&D advances, specifically low-cost harvesting by spontaneous settling,

“bioflocculation”, and doubling of current productivity, through CO2 fertilization and improved strains, microalgae-based wastewater treatment processes would be economically viable in the near-term for municipal and some agricultural applications, in favourable climates and locations.

• Co-production of high-value/large-market co-products, such as biopolymers

and animal feeds, will require achieving significantly higher productivities, possibly twice those necessary for cost-effective wastewater treatment processes.

• Among the R&D advances required for economic viability of such co-

products are the development of algal strains that exhibit high biomass productivity and that can also be cultivated in open ponds.

• Single purpose microalgae processes, solely for production of fuels (i.e.

biodiesel, methane, ethanol, etc.) would require long-term R&D and very favourable site and process assumptions.

Production potentials • Microalgae production processes systems are limited to locations with

generally flat land and in favourable climates, roughly those with average annual temperatures of 15oC, found between 37° north and south latitude.

• Within these climatically favoured areas, based on nutrients (nitrogen)

available in the wastewaters from humans, pigs and dairy cattle, about 350 million tons (Mtons) of algal biomass could be produced annually in 2020.

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intensive CO2 abating power generation technology and contrary to the case for CO2 capture and storage technologies.

• These theoretical potentials will be constrained by technical factors such as terrain (relatively flat land is required for algal ponds), and need for sufficiently dense human or animal populations for wastewater availability.

• The CO2 required for algal growth can be provided by flue gases from power

plants, including on-site use of biogas derived from the wastes and algal biomass produced.

• Wastewaters from about 30,000 people or about 5,000 pigs or 1,200 dairy

cows are required for a minimum economic scale of about 10 hectares of algal ponds.

• The resource potential for microalgae production will be limited in many areas

due to unfavourable conditions, such as low average human and animal population densities and mountainous terrain (high elevations). However, the relatively low spatial resolution of the available data plausibly results in some underestimates for some of these resource potentials.

• Applying these constraints with the available data to the theoretical global

potential result in a “technical” potential of about 90 million tons of CO2 avoided per year: 40 million tons from municipal wastewaters, 30 million tons from dairy and 20 million tons from pig wastes. These treatment systems will require about one million hectares in total area, distributed over several tens of thousands of individual sites in several continents.

• The largest technical potential is in Asia (somewhat over half of the total),

with America and Africa dividing the remainder. • Fertiliser from nitrogen-fixing microalgae (cyanobacteria) could add 10

million ton in CO2 abatement for each one million tons of nitrogen fertiliser produced, representing about 1% of the chemical fertilisers produced globally.

• Higher value/large market algal products, such as specialty animal feeds and

biopolymers, could contribute additional, but presently highly uncertain, amounts to GHG abatement. However, practical development of even a single such co-product could plausibly achieve tens of millions of tons of GHG abatement annually.

• In summary, the global technical potential for microalgae GHG abatement

technologies available by 2020, after constraining the theoretical potential by the above listed technical factors, is estimated to be in the order of 100 million ton/year of fossil CO2 reduction, based on using a significant fraction of the wastewater resources available, but with only a token contribution from the potential for production of fertilisers and other higher value co-products.

Comparison with other CO2 abatement options • Microalgae could achieve biomass productivities of above 100 ton/ha/yr,

reducing the system “footprint” to as low as one tenth that of conventional biofuels production processes.

• GHG abatement with microalgae, as for other biofuels processes, becomes

more competitive with increasing energy prices, stronger than more capital

• In addition to biofuels production, use of microalgae in wastewater treatment

and for higher value co-products also reduces GHG emissions through reduction in energy use, compared to the alternatives in wastewater treatment (e.g. activated sludge processes).

• The favourable climatic environments, the relatively simple technological

characteristics, and the already present application of commercial algae production, make microalgae technologies particularly suitable for developing countries and Clean Development Mechanism (CDM) projects for GHG abatement under the United Nations Framework Convention for Climate Change (UNFCCC). Under certain conditions the CO2 emission rights of these projects can be bought and accounted by countries that have emission reduction obligations. Therefore, CDM can provide a clear path to exploit the value of avoided CO2 emissions by microalgae in developing countries.

• Single-purpose microalgae biofuels production processes could have a large

potential for GHG abatement, but its technical and economic viability is presently uncertain and will require long-term (>2020) development.

Overall conclusions Microalgae biofixation is potentially a globally significant and economically viable technology for CO2 abatement in the climatically warmer and sunnier regions of the world, mostly in developing countries. The present analysis is global and therefore not able nor intended to disqualify any local area for potentially profitable microalgae production. Near-term applications are in conjunction with wastewater treatment and fertiliser recycle and production. It is estimated in this report that such processes could provide about 100 million tons of CO2 abatement annually by 2020. In the mid-term, within 15 to 20 years, processes might be developed that integrate biofuels production with higher value/large market co-products, such as biopolymers and animal feeds. In the longer-term, dedicated biofuels-only production processes may be feasible, greatly expanding the contribution of this technology to the goal of global greenhouse gas abatement. Microalgae biofixation therefore deserves inclusion in technology portfolios for GHG abatement, wherever climatic, land, water and other resources are favourable.

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Contents PREFACE.............................................................................................................................1

EXECUTIVE SUMMARY..................................................................................................2

CONTENTS..........................................................................................................................7

1. AN ASSESSMENT OF MICROALGAE BIOFIXATION PROCESSES .............8 1.1 MICROALGAE BIOFIXATION PROCESSES......................................................................8 1.2 THE BUSINESS CASE REPORT....................................................................................10 1.3 STRUCTURE OF THIS REPORT ....................................................................................10

2. MICROALGAE AND CO2 ABATEMENT ...........................................................11 2.1 GHG MITIGATION OPTIONS AND CO2 SEQUESTRATION ............................................11 2.2 BASIC PROCESSES OF MICROALGAE PRODUCTION AND CO2 ABATEMENT .................13 2.3 CONCLUSIONS ON MICROALGAE AND CO2 ABATEMENT ...........................................17

3. TECHNO-ECONOMIC PERFORMANCE ..........................................................18 3.1 KEY PRODUCTION FACTORS......................................................................................18 3.2 COSTS AND REVENUES..............................................................................................18 3.3 CONCLUSIONS ON ECONOMIC VIABILITY ..................................................................22

4. REGIONAL RESOURCE POTENTIALS & APPLICATION OPPORTUNITIES.............................................................................................................23

4.1 ASSESSMENT OF MICROALGAE PRODUCTION POTENTIALS ........................................23 4.2 THEORETICAL RESOURCE POTENTIALS FOR MICROALGAE PRODUCTION ON WASTES 23 4.3 CONSTRAINTS ON PRACTICAL MICROALGAE PRODUCTION........................................28 4.4 TECHNICAL POTENTIALS FOR MICROALGAE PRODUCTION ON WASTES......................30 4.5 ADDITIONAL APPLICATIONS OF MICROALGAE IN GHG ABATEMENT.........................34 4.6 CONCLUSIONS ON REGIONAL RESOURCE POTENTIALS...............................................36

5. OUTLOOK ON CO2 ABATEMENT BY MICROALGAE PROCESSES..........37 5.1 THE GLOBAL POTENTIAL FOR MICROALGAE CO2 ABATEMENT..................................37 5.2 COMPARISON WITH OTHER CO2 ABATEMENT OPTIONS .............................................38

6. REFERENCES .........................................................................................................41 7. AUTHENTICATION...............................................................................................42 APPENDIX A. TECHNO-ECONOMIC PERFORMANCE........................................43

APPENDIX B. RESOURCE POTENTIAL...................................................................45

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1. An assessment of microalgae biofixation processes 1.1 Microalgae biofixation processes Microalgae are microscopic plants (Figure 1.1) which typically grow suspended in water and carry out the same photosynthesis process as higher land plants (crops and trees) – the conversion of water CO2 and sunlight into O2 and biomass. Unlike higher land plants, these microscopic plants have no vascular system for nutrient and water transport, but make up for that by having a very large surface to volume ratio. This is a fundamental factor in their mass culture and applications, as large surface areas per unit biomass allows for rapid uptake of nutrients, including CO2, by simple diffusion, at much faster rates than possible for larger plants. Thus, seaweeds, or macroalgae, with their much greater mass and smaller surface area exposed to the water environment, where diffusion constants are three orders of magnitude lower than in air, become rapidly limited for nutrients, in particular CO2, when grown in mass culture. Only very large, and unaffordable, inputs of mixing energy (to increase turbulence) allow high productivity of seaweeds in mass culture, a fundamental, but often overlooked, limitation of macroalgae, and other aquatic plants (both fresh and saltwater).

Figure 1.1. Examples of microalgae (from left): Botryococcus braunii (a

hydrocarbon producing colonial green alga) Chlamydomonas reinhardtii (a unicellular green alga), Spirulina and Anabaena (both filamentous cyanobacteria)

A small but rapidly growing algae industry, in Japan, USA, India, China, among others, is currently producing about 10,000 dry tons of microalgal biomass almost all in open ponds (Frontispiece) and mainly for nutritional supplements. Some microalgae production systems also use enclosed photobioreactors or covered ponds, but these represent only a tiny fraction of the overall production. Many thousands of algal ponds, some quite large (> 100 hectares, or one million square meters, about 250 acres), are also used around the world for wastewater treatment (Figure 1.2). Microalgae biomass can also be used for production of biofuels. Such applications, as for other biofuels, results in replacement of fossil fuels and, thus, fossil CO2 abatement1. The potential advantages of microalgae in greenhouse gas (GHG) abatement are their ability, indeed need, for using CO2, most plausibly from power plant flue gases introduced into the ponds, and their potentially much higher productivities compared to those obtained with higher plants. Further advantages are their ability

1 In this report, CO2 abatement or mitigation and greenhouse gas abatement are used interchangeably, in most cases being reduction in fossil CO2 emissions but also referring to equivalent non-CO2 greenhouse gas reductions. This report only uses only SI units and all costs are given in 2005 U.S. dollars, $, or euros, €.

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to use resources not suitable for agriculture or forestry, such as brackish, saline, and wastewaters, as well as clay, hardpan, and sodic soils. The research and development (R&D) of microalgae technologies is helped by the very short generation times of these microscopic plants and the relatively simplicity of their hydraulic production systems. These allow for faster process development at smaller scales than is possible with higher plants. The disadvantages of microalgae, are their small sizes, which make harvesting challenging, the relatively, to higher plants, high cost of the cultivation systems, and the relatively undeveloped nature of this technology. On balance, the advantages of microalgae mass cultures can outweigh their disadvantages, most plausibly in the near-term where their innate capabilities are most usefully: in recovery of nutrients from wastewaters and capture of CO2 from flue gases. Microalgae have been extensively studied in the USA, Japan, and elsewhere for over 50 years for food and feed production, wastewater treatment, biofuels production (biogas, biodiesel, hydrogen, etc.), higher value products, nutritional supplements, and, more recently, CO2 capture from power plant flue gases for production of biofuels as a method for GHG abatement. As noted above, practical applications have been already achieved in some areas, however a great deal of uncertainty remains about the use of microalgae for GHG abatement. For example, U.S. projections made during the 1980’s for microalgae fuels suggested that most of the U.S. oil imports could be replaced by microalgae produced biodiesel. More recently, H2 production by microalgae has become a preferred route to solar hydrogen production while biodiesel production by microalgae has started to receive renewed attention. However, most such projections assume major technological breakthroughs, resulting in extraordinarily high productivity and greatly reduced costs, and also very favourable assumptions about the availability of water, suitable land, near-by CO2 sources, infrastructure and other resources.

Figure 1.2. Wastewater treatment ponds, note approximately 6 hectare channel-

type pond (Hollister, California) (Photo courtesy Bailey Green) Major biotechnical and engineering challenges must be solved in the development of microalgae-based processes for GHG abatement, most importantly maximising biomass productivity, to allow achievement of the full potential of this technology.

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processes and puts these results in the context of other CO2 abatement options.

1.2 The Business Case report This report presents a first-cut assessment of the global potential of microalgae technologies for GHG abatement focusing on their near-to mid-term applications in wastewater treatment of human (municipal) and animal (agricultural) wastes. This report is intended as a strategic tool for R&D personnel and managers, policy makers, and others who need to broadly evaluate the various technology options for GHG abatement, as well as related environmental and sustainability issues. Its aim is to develop both a methodology and an initial estimate of the applications and global potential for GHG abatement of microalgae-based technologies. The main objectives of this report are: (1) To evaluate the resource potential, on a regional and global scale, available in

the mid-term (year 2020), for GHG abatement with microalgae technologies, and techno-economic performance (costs and benefits) assuming an increasing R,D&D (research, development & demonstration) effort over the next decade.

(2) To place microalgae biofixation processes with other GHG mitigation options;

based on their abatement potential, cost, state of development and R&D needs. (3) Identify contexts in which microalgae systems can be competitive with other

technologies, taking into account combined co-processes and co-products in addition to fossil CO2 mitigation through renewable biofuels production

The major output of this Business Case report is an assessment of the potential contribution of multipurpose microalgae processes to GHG mitigation and the circumstances and regions where this technology can become competitive.

1.3 Structure of this report Chapter 2 briefly introduces CO2 capture and sequestration and other GHG abatement options, and microalgae biofixation processes for CO2 mitigation. Chapter 3 analyses and assesses the techno-economic performance of microalgae biofixation processes to address the issue of whether such processes can be economically viable within current and potentially future scenarios of energy costs and global actions to reduce GHG emissions. Chapter 4 analyses and evaluate the potentials for algal biomass production and the resulting CO2 abatement for different near- to mid-term (by year 2020) opportunities to apply microalgae technologies, specifically for both human and animal wastewater treatment processes within the climatically favourable land area (37o Latitude, north and south). First, the theoretical resource potential is estimated and then different factors (e.g. availability of suitable land, animal and human populations, etc.), are estimated to reduce the theoretical to a technical (practical) potential. Chapter 5 summarises the overall costs and global potentials of microalgae

2. Microalgae and CO2 abatement 2.1 GHG mitigation options and CO2 sequestration The large-scale, unconstrained use of fossil fuels and the extensive degradation of the biosphere (due to deforestation, soil carbon oxidation, etc.) have resulted in major increases in atmospheric CO2 levels (Figure 2.1), which, along with other GHGs, have started to impact the world climate. Policy makers are responding in various ways to tackle this problem, in particular by supporting R&D in novel technologies to reduce GHG emissions, particularly CO2, to the atmosphere.

Figure 2.1. The global carbon cycle and human effects on this cycle (source:

UNEP). There are a number of options to reduce GHG emissions, which can be divided into the following major categories, roughly in order of increasing costs: • Increasing energy efficiency in all sectors, through improved technology and

also by demand-side reductions through incentives, regulations, and taxation • Reducing non-CO2 greenhouse gases through a whole palette of mitigation

options, including, for example, the recovery of CH4 containing gases from landfills and the thermal or catalytic reduction of N2O in nitric acid or adipic acid tail-gases

• Fuel switching to low carbon fuels, e.g. replacing coal with natural gas.

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tonne CO2 in Africa and Southeast-Asia up to US$ 5 per tonne in Eastern Europe, and higher costs in OECD countries (up to US$ 25 per tonne). However, these

• Reducing deforestation and managing soil carbon storage in agriculture forestry, and in conjunction with sustainable biofuel production processes

• Renewable energy sources such as solar, wind, hydro, and biofuels, which do

not generate net atmospheric CO2. Microalgae systems are a subset of biofuel production processes.

• CO2 capture and storage (CCS) with CO2 captured from power, ammonia,

cement, and other plants, and then stored in depleted oil or gas wells, aquifers, coal beds, or oceans

• Nuclear power, if proliferation, safety, waste disposal, etc., issues are solved • Hydrogen as energy carrier promises greater end-use efficiency from fuel cells,

but must still be produced from other energy sources – fossil, nuclear or solar. None of these options is likely to be able to avoid climate change by itself. The emissions of fossil CO2 are interwoven to such a large extent with our economies that no single option can solve this global problem. Biological processes are generally recognised as having great potential for GHG abatement. Note in Figure 2.1 that the biological carbon (C) cycle is well over one order of magnitude larger than fossil CO2 emissions. Currently humanity, directly or indirectly, is already appropriating or impacting over half of the primary productivity on this planet. Thus, even modest alterations in the management of ecosystems, from agriculture and forests to rangelands and aquatic environments, could be of major importance in implementing countermeasures to global warming. Microalgae biofixation of CO2 and conversion of the algal biomass to renewable biofuels is one of the many potential biological options for GHG abatement. Microalgae mass cultures can directly capture CO2 from power plants and beneficially re-use it to produce biofuels or higher value products. However, there is no fundamental difference between capturing CO2 from air or a power plant flue gas, the essential aspect is the production of renewable biofuels that can substitute for fossil fuels. Biological technologies for fossil CO2 abatement Terrestrial sequestration through prevention of deforestation, aforestation and reforestation results in carbon-storage. Aforestation (planting trees where none existed before, at least in recent history) and reforestation (replacing recently destroyed forests) is a relative cost-effective way to reduce atmospheric CO2 levels. These can compensate for CO2 emissions at remote locations, the CO2 emissions trading option. The potential of these options is rather high: the IPCC report (2001) estimates that reducing deforestation over an area of 138 million ha, promoting natural forest regeneration over 217 million ha, and implementing a global aforestation/reforestation programme of 345 million ha, for a total of 700 million ha, would allow accumulation of 220 to 320 gigatons (Gtons) of CO2 in the forest biomass and soils, up to about 2050. Available land area seems not to be limiting. Costs for aforestation/reforestation depend on local conditions, in particular costs of land and its alternative uses. The IPCC estimates costs of only about US$ 1 per

costs may be underestimates: for example, Davison and Freund (2000) report costs of about US$ 20 per tonne CO2 equivalents for large-scale aforestation in Mexico, including opportunity costs (the lost income, e.g. land rent, from alternative uses), monitoring and administration. Of course, aforestation and reforestation are not permanent solutions: within 50 to 100 years, the above ground carbon accumulation slows down and, on average, even can partially reverse, as forests approach maturity. The long-term solution, and indeed a near-term option, is biomass energy, converting wood and other biomass to renewable biofuels, such as wood chips to replace coal, including in co-firing with coal, and biofuels, such as ethanol from conversion of starches, sugars and, potentially, cellulosic biomass, as well as other biofuels such as methane, hydrogen or biodiesel, produced from a variety of plant biomass resources and conversion technologies. Actually, the costs of renewable biofuels are already competitive with fossil fuels in many local situations using current technology. Cost curves for biomass exhibit large ranges, due to many opportunities for small-scale applications at modest costs and fewer opportunities for large-scale applications at higher costs. However, optimistic forecasts abound and technology availability to actually produce and convert the biomass is sometimes wrongly assumed. One major issue is that achieving even a fraction of the global potential for biofuels production will require many, relatively large-scale (>1,000 hectares) and long-term (> 20 years) pilot/demonstration projects to establish biomass productivities and perfect harvesting and conversion technologies. As discussed below, algal technologies, being modular and less sensitive to local conditions, can be developed with much smaller and shorter term pilot projects. Proposals to use the oceans for large-scale CO2 storage have not had much traction with either ocean scientists, policy makers or the public. Physical and biological processes, such as iron fertilisation to enhance phytoplankton (microalgae) growth in iron deficient areas, are fraught with uncertainties, not all of which are technical in nature. Growing algae (seaweeds) in oceans for GHG abatement is also problematic. Thus in this report we only address microalgae processes using land-based technologies.

2.2 Basic processes of microalgae production and CO2 abatement The simplified schematic in Figure 2.2 illustrates the basic concept of microalgae biofixation. It will be briefly outlined by addressing the key process components.

Figure 2.2. Schematic overview of a microalgae biofixation process

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photosynthetic efficiency in mass culture ponds have to be developed and maintained in outdoor mass culture ponds. This might be achieved through an

The technology Microalgae are grown in open raceway, mechanically mixed (typically with paddle wheels) ponds, supplied with all the nutrients required by the algae to grow: CO2, N (as ammonia or nitrate), P (as phosphates), and a variety of minor elements, including Fe, S, Mg, Mn, Ca, etc. Municipal, agricultural and some industrial wastewaters can provide these required nutrients, although they are typically limited in their carbon content in relation to other nutrients, principally N and P. Suitable water sources can be fresh, brackish, saline or even hypersaline. For cost-reasons, large (one hectare in size or larger) clay-lined ponds, open to the atmosphere, would be used. The maximum practical size and channel width of such ponds is not yet established. Only one paddle wheel is required even for very large ponds, but channel width is typically constricted at the paddle wheel to reduce its size, as it is a significant capital cost factor. The ponds would be operated at a depth of typically about 30 cm and with a mixing velocity of about 20 to 30 cm/sec. Photosynthesis by the algae results in a rapid accumulation in the ponds of dissolved O2, typically to two to three-fold air saturation, which can be inhibitory to many algal species, in particular when the CO2 supply is limiting. CO2 utilization by the algal culture can increase the pH to above 9, a sign of CO2 limitation. CO2 and nutrients supply CO2 is transferred into the ponds by means of sumps and diffusers, with counter-current flow to maximise bubble residence time and minimise head-losses and sump depth, particularly important when dealing with power plant flue gases. CO2 supply stations are located typically upstream from the paddlewheels, with one paddle wheel per pond sufficient even for large ponds. Other nutrients are fed into the ponds as needed. In the case of wastewaters, some, but rarely all, of the required CO2 can come from the aerobic breakdown of organic wastes by action of naturally present bacteria, which in turn depend on the O2 produced by the algae. The bacteria also break down organic N and P, which can then be used by the algae, with algae and bacteria thus living in a commensal relationship. CO2 can be supplied from a concentrated source, either pure CO2, if available on-site at low cost (< US$ 20/ton), which is seldom the case, or from the flue gas of a local power plant. Algal pond systems are best located where sources of CO2 are available essentially on site, such as at wastewater treatment plants, landfills, small distributed power plants, or even larger power plants. If remotely sited from such sources, pure CO2 would need to be generated and transported to the algal farm, an overall much more expensive option even considering that it is easier to inject pure CO2 into the ponds compared to flue gas. Thus this option can be ignored for now. Algal productivity The potential for very high biomass productivities by algae cultures is perhaps the strongest argument for microalgae technology in GHG abatement. If indeed achievable, renewable biofuels production by microalgae would require much less footprint than any other biofuel production process. A goal of 100 ton/ha/yr of organic dry weight biomass is projected to be achievable in the near- to mid-term, about 50% higher than present technology, and even higher productivities should be possible in the longer-term. To achieve this goal, strains that exhibit increased

adaptation process that uses of the outdoor pond environment to select strains with desired attributes, which are then genetically improved in the laboratory. Such attributes include, among others, sustained growth outdoors, high areal productivity (g of organic matter dry weight /illuminated surface/time), production of desired co-products, harvestability, etc. The cultivation of selected algal strains also requires an inoculum production system, which would involve a series of closed photobioreactors of increasing size and decreasing sophistication (e.g. costs), with about a ten-fold scale-up for each of the six or more stages of inoculum production. Harvesting Harvesting has been a major challenge for microalgae technologies. Wastewater treatment plants, and even some commercial microalgae production facilities for high value nutritional products, use chemical flocculation followed by dissolved air floatation. However, these are much too expensive for GHG abatement. A high priority for R&D is the process of bioflocculation, in which the algae essentially harvest themselves, by first flocculating (single cells aggregating in clusters or flocs) after being removed from the paddle wheel mixed pond environment, and then sinking to form a dense mass (large flocs settle much faster than individual cells or small flocs). Filamentous cyanobacteria, such as Spirulina or Anabaena (Figure 1.1), can also be relatively easily harvested with backwashed 25-50 µm mesh rotating screens (“microstrainers”). Technologies such as bioflocculation-sedimentation or microstraining, produce a biomass slurry of only a few percent solid (typically 3-5%). Further concentration may be required depending on the conversion process to the biofuels and other products desired. Biomass conversion to biofuels and other products Conversion or extraction of the harvested and concentrated algal biomass for biofuels and higher value co-products presents additional challenges. Algal biomass is generally most readily and immediately converted by the process of anaerobic digestion to biogas, a mixture of roughly 50/50 methane and CO2. Covered lagoons as used in swine and dairy waste anaerobic digestion, and have been proposed as the lowest cost technology for microalgae digestion, although achieving an acceptable conversion efficiency for biomass from some algal strains still remains to be demonstrated. Ethanol, biodiesel and even hydrocarbons can also be obtained from algal biomass: ethanol by yeast fermentation of algal biomass high in starches, biodiesel from algal biomass with a high content of vegetable oils, and hydrocarbons by the unique Botryococcus braunii, (Figure 1.1) which produces up to half its weight as pure hydrocarbons. However, cultivation of algal biomass high in starch, oil or hydrocarbons, at high productivity, will require longer-term R&D than for biogas production. (H2 production is discussed later). In all cases, the residue remaining after extraction of these biofuels would be subjected to anaerobic digestion to recover the remaining energy content as biogas. The residue from the anaerobic digesters contains all the nutrients present in the biomass (up to 10% N and 1% P) and can be used as fertiliser. In the long-term, this residue could even be recycled to the micro-algae ponds to allow additional algal biomass production, beyond what is possible with only the wastewater input.

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higher costs compared to other biomass systems, these processes would rely for

CO2 abatement Microalgae biofixation of CO2 from flue-gases is only the first step in the abatement of this GHG: CO2 mitigation stems primarily from the conversion of the algal biomass to renewable fuels, directly substituting for fossil fuels, or the replacement of fossil fuel-based products. The actual fossil fuel being replaced, coal or natural gas, will make a difference in GHG abatement. In the case of coal, CO2 abatement is higher, about twice, than if natural gas is being substituted. This depends on local circumstances and cannot be readily generalized. Also the disposal of sludges from conventional treatment plants (e.g. into landfills, incineration, soil application, etc.) will also affect GHG balances. However, in wastewater treatment, the major factor in GHG abatement is the energy use in conventional treatment technologies, though these can vary widely, from relatively low energy technologies (e.g. oxidation ponds, trickling filters) to the high energy inputs of extended activated sludge processes (used for tertiary treatment, that is N removal). Uncertainties are also inherent in assigning a GHG abatement value to fertiliser recovery and re-use. Algal biomass (units always given dry weight organic matter) generally contains about 46% carbon, and about one third of this can be transformed into methane gas by the process of anaerobic digestion. Thus, if the biogas produced is used to replace fossil natural gas of input in a power plant, this would abate approximately 0.5 tons of CO2, assuming, realistically, a somewhat lower efficiency in the use of biogas compared to natural gas. However, this abatement would be more than doubled if any one of the above discussed factors were considered: abatement of coal-fired (rather than natural gas) power generation, energy savings compared to conventional wastewater treatment, or reduction in fossil fuel use compared to production of fertiliser or other energy intensive products. In some cases, as for waste treatment operations, a higher multiplier is applicable for converting tons of algal biomass to tons of CO2 abatement, as conventional wastewater treatment processes (e.g. activated sludge, in particular when used for nutrient removal) use more energy, and generate more GHG emissions, than the fuel that can be derived from the algal biomass produced. Other non-CO2 greenhouse gases could also be considered in such an analysis. However, in recognition of the many uncertainties and likely practical limitations for implementation of such systems, we use in the present analysis a single factor of 1 ton of algal biomass = 1 ton of CO2 avoided. Multipurpose processes In the Technology Roadmap, developed for the Biofixation Network (Benemann, 2003), four related multipurpose microalgae biofixation processes were outlined: • Municipal waste water treatment with CO2 utilisation and methane production • Agricultural waste treatment with fertilisers, feeds and biofuel co-production • Biological nitrogen fixation for organic biofertilisers and biofuels co-production • Biofuels co-production with high volume/value co-products (e.g. biopolymers) All these processes would use the same standard paddle wheel mixed raceway pond already used extensively in commercial algal mass cultures and wastewater treatment, though, as already noted above, larger pond sizes, higher productivities and lower costs will need to be attained. Even with such improvements, due to their

their economic viability, in the foreseeable future, on products and services additional to renewable biofuel production and GHG abatement functions. Actually, the need for co-products is also true in many cases for higher plant biomass systems: for example corn-ethanol production would not be feasible (even with current government subsidies) in the U.S. without an animal feed by-product. Microalgae productivity The over-riding issue in microalgae GHG abatement is the productivity of the algal biomass, in terms of tons per hectare per year. This is, of course, also the over-riding issue for all biomass systems, forestry and agriculture, but is particularly critical to microalgae systems, whose high capital and operating costs demand the highest possible productivities. Indeed, microalgae have the potential for very high productivities, and a major goal of the Biofixation Network in the near-term is to demonstrate productivities of 100 ton/ha/yr and above in outdoor cultures, representing an over 50% increase compared to the current achievable. This is, along with the other technical assumptions discussed above (e.g. harvesting and processing of the algal biomass), a key assumption underlying this analysis (see also Appendix A for further discussion). 2.3 Conclusions on microalgae and CO2 abatement • A portfolio of different GHG abatement options, acting both at regional and

global scale, is needed to tackle climate change; no dominant technologies will be able, singly or even in combination, to accomplish the task alone

• Biological photosynthesis-based processes, that capture and store carbon/CO2 in plant biomass and produce renewable biofuels, are fundamentally different from CO2 capture and storage concepts where CO2 is disposed through an energy-intensive process. Their economics improve with increasing energy prices, while the converse is true for CO2 capture and storage technologies

• Microalgae biofixation of CO2 and conversion of algal biomass to biofuels is one of the many biological options for GHG abatement that re-uses CO2 and provides renewable energy

• Microalgae biofixation processes can be multipurpose, they can combine fossil CO2 capture and renewable energy production with additional environmental services (wastewater treatment) and co-products (animal feeds, fertilisers, etc.) that abate other GHGs and conserve fossil energy

• Each ton of microalgae biomass produced, is equivalent to about one ton of CO2 abated

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biomass produced is assumed for the wastewater treatment function.

3. Techno-economic performance 3.1 Key production factors The engineering design for large-scale ponds does not present major uncertainties or R&D issues. For example, the use of power plant flue gas CO2 for microalgae cultivation has been amply demonstrated and does not represent a significant impediment. NOx and SOx, present in the flue gas, dissolve in the water and are neutralised by the alkaline environment, with the nitrogen used by the algae. The transfer, storage, outgasing, pH effects and periodicity of CO2 supplied to the algal ponds can be well enough calculated to allow projections of an overall CO2

utilisation efficiency up to 90% for pure CO2, and somewhat less for flue gas. However, the experience with the design and the operation of large-scale (>1 ha) unlined raceway ponds is limited, and their hydraulic behaviour is not easily predictable from small-scale ponds. Thus, the design and operation of large-scale, unlined ponds presents some uncertainties that need to be addressed in the future. However, the major challenges in microalgae biofixation processes are related to the mass cultivation of the algae themselves. As discussed above and in Appendix A, the key performance parameters of microalgae biofixation systems for GHG abatement are: • Availability or transport of flue gas and/or waste water to the ponds • Land price / costs / suitability / availability • Algal productivity / harvestability / processing • Product values: biofuels, GHG abatement, reclaimed water, fertilisers, other

co-products In the present chapter, the relative weight of these key parameters on the general economic feasibility of microalgae biofixation technologies is analysed. 3.2 Costs and revenues The broad range of costs and revenues of microalgae production systems are summarised in Table 3.1. Both costs and revenues are highly dependent on different site-specific factors, which makes the cost-evaluation of microalgae-based processes difficult. Thus, a range of costs, from more to less favourable, that includes the likely uncertainties are given in Table 3.1. In all cases, a key assumption underlying these estimates is the achievement by these processes of a productivity at least of 100 ton of algal biomass/ha/yr. Revenues Wastewater treatment can be of little or of considerable value, depending on site-specific environmental regulations, water resources, nature of the wastewater, alternative technologies, etc. In developed countries, the value of reclaimed water can be substantial, similar or higher than the assumed co-products. In developing countries, the alternative to wastewater treatment by microalgae processes often is not an activated sludge process, but no treatment at all. Again, this would be very site- and country-specific. In the best case, a value of € 200/ton for the algal

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1,250/ton. The co-products in the raw biomass (prior to processing), are assumed to

Table 3.1. Best, worse and median estimates of costs and revenues for key elements of microalgae production chain (for 100 ton/ha/yr productivity)

Worse case

Median case

Best case

Production chain element

Basis for Calculation Remarks

[€/ton algae or CO2]

Revenues

Reclaimed water Fertilisers OR

Water treatment, 2500 m3/ton algae valued at 0 to 0.08 €/m3 0 to 50 €/t algae for fertiliser

Depends on location Only for waste Treatment

€ 0

€ 0

OR

€ 120

€ 30

OR

€ 200

€ 50

OR

High value co-products

0 or 20 % of biomass at € 750 and 1250 €/ton of co-product

No fertiliser credit applies

€ 0

€ 150

€ 250

Fuel produced Assuming a recovery of 12 GJ/ton algae (2 barrels oil/ton)Reduce 20% for co-products

Assume € 35/ 60/75/barrel of oil equivalent

€ 70 € 100 € 120

Avoided CO2 0 to 50 €/ton CO2 abatement (Reduce 20% if co-products)

1 t CO2 = 1 t algal biomass

€ 0 € 30 € 50

Total Revenues

Using high value products OR reclaimed water & fertiliser, not both

Worse case is for fuel-only production

€ 70

€ 280

€ 420

Costs

Land High/medium/low cost for land at 100, 20 and 0 k€/ha

Charged at 5% per year

€ 50 € 10 € 0

Pond investment 100 k€/ha at 10% to 15% capital cost and 4 to 8% annual depreciation, 1-2% other

Capital charge ranges from 15 to 25% over 20 years

€ 250 € 180 € 160

Operation costs 50 -100 k€/ton O&M € 100 € 70 € 50

CO2 transport to pond system site

0 to 40 €/ton CO2 used (= algae biomass), for transport & compression, average case

Depending on location

€ 40 € 10 € 0

Risk premium 0 to 10% contingency added to total costs

Avoid for nth plant built

€ 45 € 10 € 0

Total costs € 485 € 280 € 210

TOTAL REVENUES MINUS COSTS

€ -415

€ 0

€ 210

High value co-products, such as biopolymers and specialty animal feeds, when produced, are assumed to have a value of about € 1,000/ton, ranging from € 750 to

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if not more, in an updated and more conservative analysis applicable to wastewater treatment and other multi-product systems discussed above. Here we use a capital

represent 20% of the algal biomass, thus providing a value of € 200/ton, ranging from € 150 to 250/ton biomass. This allows a sufficiently high value to enhance revenues, and also a large enough potential market to be of relevance in GHG abatement. Considering recent and historical fluctuations and changes in energy prices, and local circumstances, the value of the biofuel produced by microalgae systems is no more certain than for the other process outputs. Depending on future world market prices, the biofuel value of the recoverable energy from algal biomass (about 12 GJ/ton, equivalent to 2 barrels of oil per ton of algae) ranges from about € 70/ton (at 2003 prices) to € 120/ton algae, based on an energy (fuel) recovery and a plausible future range of oil prices from € 45 to 75/barrel oil. (Note that algal biomass high in oils may have a higher fuel yield, but then would also have proportionally lower biomass productivity, thus not changing this analysis). Another potential revenue comes from any recovered fertiliser or, in the case of N2-fixing algae (cyanobacteria), actually de novo (new) produced fertiliser. Fertiliser revenues are even more uncertain than biofuel revenues, due to local conditions (demand, transportation distances), and can be estimated in the range from € 0 to € 50/ton of algae for the residual biomass after fuel extraction, based on a 10% content of N and neglecting other fertiliser values (e.g. phosphate content, etc.). As for co-products and wastewater treatment, not all microalgae-based processes would allow the recovery of fertiliser values or their monetary valuation, though in some cases (e.g. use in organic agriculture) these values could be quite high. Finally, the GHG abatement value of such processes has to be considered. Microalgae biofuels and co-products will directly substitute for fossil fuels and save non-renewable fossil energy. As discussed in Chapter 2, on average about 1 ton of CO2 emissions can be avoided for each ton of algae produced. Again, this is highly variable, depending on the biofuel produced, the fossil fuel displaced, and the energy savings realised in the production of co-products or wastewater treatment compared to current fossil fuel-based technologies. Currently in Europe, one ton of CO2 avoided is worth about € 20-30/ton. However, in developing countries or the USA, the value is currently much lower, e.g. well below € 5/ton. With strictly regulated climate policies, it is likely that the price could rise up to € 50/ton CO2 avoided by the year 2020, the time horizon of this report. In a stand-alone microalgae system, where biofuel is the only product, the revenues would be only the biofuel output and GHG abatement. Costs Costs include land, capital costs of ponds, ancillary costs (harvesting, processing, water supply, infrastructure, etc.) and operating costs. Assuming flat land, clay soils (no percolation) and raceway-mixed ponds, capital costs of about US$ 60,000 per hectare were estimated (1996 US $, Benemann and Oswald, 1996), including earthworks, paddle wheels, carbonation stations and piping, harvesting (bioflocculation-sedimentation), and minimal infrastructure (utilities, roads, drainage, etc.). These were projected for large systems (>100 hectares) and individual growth ponds of several hectares. Operating costs were estimated at the time in the order of US$ 50/ton. These costs would likely to rise by a factor of two,

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cost of € 100,000/ha and a median operating costs of € 70/ton of biomass (range € 50 to 100, see also Appendix A). A capital cost of € 100,000/ha is a first order approximation, optimistic for some cases and a likely upper bound for others. It does not include land costs, which can range from negligible to the near prohibitive (€ 0 to € 100,000/ha). Depreciation could range from 8% down to 4% per year, that is over a 12.5 to 25 year period, the latter being realistic for earthworks and other fixed structures that have relatively little wear and long life, with operating costs (maintenance) covering most upkeep costs. Other fixed capital-related expenses (e.g. taxes, insurance) should also be relatively modest, about 2%. Cost of capital itself would be expected be relatively small if part of a waste treatment process, but higher if not, plausibly ranging from 10% to 15% per year. Land, however, does not depreciate and would be charged at a much lower annual rate, here given at 5% per year. Operating costs would likely vary by a factor of two, from € 50 to 100, as mentioned above. It should be noted that in this analysis only the cost of the algae production, not the additional cost incurred for waste treatment (e.g. influent pumping, primary sludge treatment, disinfection, etc.) or specialty products (extractions and purification) is included. Since microalgae biofixation is a relatively new technology, at least as herein envisioned, additional contingencies, a “risk premium” are also appropriate, in addition to those already included in the cost analyses, up to 10% interest (cost of capital), or € 50 per ton algae, though for the best case (assuming a mature technology) no such contingency is included. Economic viability The economics of microalgae systems are highly sensitive to the assumptions made about costs and revenues, with the difference between the best and worst case assumptions being over € 600/ton of algal biomass. It should also be noted that even with the most favourable assumptions about algae production costs (€ 210/ton) and revenues for biofuels (€ 120/ton algae) and GHG abatement (€ 50/ton algae), the process would still not be economically feasible. Thus, fuel-only algal systems are not plausible, at least not in the foreseeable future and additional revenues are required, either from wastewater treatment or higher value co-products. However, as they cannot be applied in combination, their revenues are not added together in Table 3.1. For example, in the case of co-products, no fertiliser value can be assigned, as fertilisers either have to be recycled or added to the operating costs. Also, for such co-products, a 20% reduction in biofuel outputs and GHG abatement applies. For the case of nitrogen fixing algae, a net fertiliser value of € 40/ton of algae would makes this co-product option appear economically competitive. However, there would be a productivity penalty for nitrogen fixation. For the median case, values that balance revenues and costs were chosen, demonstrating that an economically viable process is possible with reasonable assumptions about capital and operating costs and output values (for biofuels, GHG abatement and fertilisers), and with some additional revenues from the co-products or waste treatment services. Of course, these are only examples of plausible costs and revenues, and a wider range for all these parameters is possible, depending on specific locations and cases.

A more detailed economic analysis is beyond the scope of this report, which aims primarily at estimating the global potential of these technologies for GHG abatement. However, the above suggests that to expand the potential of algal production systems in addition to wastewater treatment and associated fertiliser recovery and production, it is important to identify and generate high volume/high value co-products from microalgae biomass that could provide a significant revenue (> € 100/ton algae). High value animal feeds (e.g. high in pigments or omega-3 fatty acids) are plausible, as are industrial biopolymers (polysaccharides). This should be a high priority for future R&D, but are difficult to evaluate at the present time in terms of future resource potential. The issue addressed in the remainder of this report is the global potential of microalgae processes for GHG abatement with wastewater treatment as the co-service. A brief comparison of microalgae systems to other GHG abatement processes is provided first.

3.3 Conclusions on economic viability • Once developed, operating microalgae biofixation processes requires a rather

low technology from an engineering point-of-view, making these systems suitable for developing countries

• Economic cost-benefits analyses indicate that microalgae biofixation processes can be economically viable if expected R&D advances are achieved

• Co-processes (wastewater treatment) or higher value/large market co-products (fertilisers, animal feed or biopolymers) are needed to make these systems economically viable, ruling out stand-alone microalgae processes devoted only to biofuel production, at least in the near- to mid-term

• A 50%+ increase of the current achievable annual productivity to 100 ton biomass/ha is a key assumption and a pre-requisite for the economic viability of microalgae-based processes for GHG abatement

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4. Regional resource potentials & application opportunities 4.1 Assessment of microalgae production potentials In this chapter, the global production potentials for microalgae biofixation processes and its regional distribution based on wastewater treatment are estimated for the year 2020 in a number of steps. First, the availability of the two main resources for the production of algae is assessed, these being suitable climatic conditions and waste nutrient resources. Based on these resources, the global and regional theoretical potential is assessed, which indicates the amount of microalgae that can technically be produced. The full theoretical potential will not be realised in practice due to a number of practical constraints that limit the economic feasibility of the technology. These constraints include production factors such as suitable flat and low cost land, infrastructure and power availability, and CO2 supply. Based on the theoretical potential and the availability of these key production factors, technical production potentials are estimated for different regions in the world. Besides these considerations on the supply part of the microalgae technology, possible limitations in the demand for certain produced products are also considered. It is assumed that if the required resources, production factors and product demand are available, then the technical potentials for microalgae biofixation processes are in practice economically feasible. 4.2 Theoretical resource potentials for microalgae production on wastes Climatic resources The major parameter limiting algal production processes is climate, as defined by temperature, sunlight and moderate seasonality. Locations with suitable climatic conditions encompass areas with annual average temperatures of 15°C or higher, as shown in Figure 4.1.

Figure 4.1. Suitable climatic conditions for microalgae processes are approximated by annual average temperatures of 15 °C or higher (in orange and red), included in the blue rectangle outlining the area between 37° north and south latitude (source: IPCC [10])

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Only the areas that meet the temperature criteria, are used in the further assessments below, dealing with additional resources requirements (wastes, land, and CO2). This is a somewhat arbitrary, and in future reiterations, climatic constraints should be used that emphasise minimum winter and night-time temperatures, which are the actual limiting factors, rather than average conditions. Overall waste nutrient resources Resources considered as most suitable for the initial application of microalgae mass cultures for renewable energy production and GHG abatement are human, animal and some industrial wastes that contain sufficient nutrients (principally nitrogen and phosphorous) for algal growth. Microalgae, due to their high N and P content (up to about 10% and 1%, respectively) can absorb large amounts of such nutrients, making them uniquely suited for waste treatment, specifically for nutrient removal. The traditional function of microalgae in wastewater treatment is to provide for waste oxygenation, to reduce biological oxygen demand, BOD, by means of their in situ O2 production. Of course, these wastes have to be liquid and collected in amounts that allow operation of a reasonable size algae facility. The amount of nitrogen in human sewage is about 3 kg N per capita per year in the selected geographical area. Although this figure is somewhat affected by the food composition and therefore is region-specific (see also animal waste in Appendix B), it is a globally valid and even conservative. It translates to a potential of 30 kg of algal biomass per capita-year, or, approximately, 3,000 persons per hectare of treatment ponds, assuming a 100 ton/ha/yr productivity, based on the fact that the average N levels in the biomass would be about 9%. This is generally similar to the loading rates (people/ha) of current sewage treatment ponds (facultative ponds), which, however, reduce only BOD (biological oxygen demand, that is the biodegradable organic component of the wastes), but do not achieve nutrient removal. In general, sufficient P is present to make N the limiting nutrient, once CO2 is supplied, but P as well can captured and removed essentially completely, in the process. Similar arguments hold for pig and dairy cow wastes, with selected nitrogen excretion factors as reported in Table 4.1. Table 4.1. Number of individuals (people, pigs and dairy cows) in areas with

suitable climatic conditions and annual N excretion per individual Type Individuals

in suitable climates [million]

Excretion factor

[kg of N per year]

Data source

People 3,125 3 FaoStat database

Pigs 272 16 IPCC Reference manual

Dairy cows 98 70 IPCC Reference manual

For a minimum scale of 10 hectare algae pond, human waste (sewage) sewer systems would have to collect wastes from populations of about 30,000 people. For animal wastes only concentrated animal feedlots that use flush systems, typically dairies and pigs, would be suitable for such applications. Although much more animal than human waste is produced, the former is generally not available in as large amounts and as centralized as the latter. From the above, operations with 5,000 pigs and only 1,200 dairy cows could be candidates for such algal-based waste treatment processes. However, the value of animal wastewater treatment is much lower than for m ess stringent applicable waste disposal regulations com uman) wastes. However, the potential for managing and recy es is relatively higher, due to their proxim such concentrated animal operations to control odo in objective of waste treatment), reuse water, and control nutrie croalgae technology relatively favourable for such applications. Other waste resources idered: aquacultural, food processing and industrial. Aquaculture produces a large am stes, and for some operations the application of mi ent using paddle wheel raceway ponds appears very favour ing in southern U.S. and intensive shrimp farm ere excessive nutrients and organics need to be managed, could nology. Some food processing facilities could also be ca ndustrial wastewaters would contain sufficient nutrients for culture. They may represent opportunities for ma e development of microalgae technology at local level. of these applications will significantly change the present asses and pig wastes. Spatial distribution of nutrient resour The next issue addressed is the entration of waste generators, people, pigs and dairy co le areas. Without a sufficient density of such resour es are not viable. Data on numbers and areal density (indi people (1990), pigs and dairy cows (1985) in various loc lly differentiated grid from the Edgar GHG emis is allows the calculation and presentation of spatially ntials. These are “theoretical potentials”, in the sense that ounts makes it theoretically croalgae biofixation technologies. Of course, this does not consider yet the actual practical availability, economics or other limiting factors, such as land, CO2 etc. (see below). The theoretical resource potentials of municipal wastewaters, pig and dairy cow wastes are graphically presented in Figure 4.2. For each cell, the annual waste production is calculated in terms of tons of N. Low nitrogen production levels are indicated by yellow, followed by green for higher and red for highest potential, of 20,000 ton N per cell, corresponding to 1,600 kg and above of waste N per km2. This equals 500 persons, or 100 pigs or 25 dairy cows per km2. The total theoretical potential is made up by all coloured areas.

unicipal wastewaters, due to lpared to municipal (h

cling fertiliser valuity to agricultural areas. The need by

urs (often the mant discharges, make mi

can also be consount of wa

croalgae-based waste treatmable. For example, catfish farm

ing in many countries, whuse this tech

ndidates, but only a few imicroalgae mass

rket niches relevant for thHowever, none

sment based on human, dairy

ces

location and concws, in the climatically suitab

ces, the biofixation processviduals per km2) of

ations are available in a spatiasion database (Edgar 2005). Th

differentiated resource pote the presence of such resources in sufficient am

possible to apply mi

25

Pig

Dairy

Municipal

Figure 4.2. Graphical presentation of the global theoretical potential of

microalgae biofixation based upon municipal wastewater (1990 - green), dairy cow wastes (1985 - brown) and pigs wastes (1985 - red) in the suitable climatic zone

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Highly populated areas with large municipal waste water potentials are particularly present in India, south of China, middle of Indonesia and the south of Nigeria. Furthermore, very large and densely populated cities such as Rio de Janeiro, Mexico City and Cape town are visible as red spots. Here are the large resource potentials that dominate the picture, although all other (smaller) potentials are included in this estimate as well. It should be noted that for large urban areas, the resource potential for human wastes would mostly not be available, except at the periphery, due to limitations of affordable land area. In the suitable climate zone, very high pig production densities are found in southern China. In addition, Philippines, central Asian countries, south of Brazil, Mexico, south of Spain and Italy have considerable intensive pig production. High densities of dairy cows are found in the north and south of India and also south of Brazil. Central India, Mexico, Kenya, Tanzania, Morocco, south of Spain and Italy also have considerably intensive dairy cow production. However, in most areas only limited numbers of both pigs and dairy cows are presently kept in very intensive and concentrated operations potentially suitable for algal technologies. Africa almost completely lacks industrialised pig or dairy production. Thus, any estimate for the integration of microalgae biofixation processes with animal wastewater treatment may be presently an overestimate, although the world-wide trend is towards larger, more concentrated operations. Total (theoretical) resource potential The spatially distributed theoretical potentials (e.g. based on the total populations in climatically suitable regions) are translated into projections for the year 2020 using, as a scenario, the growth rates from an IPCC study (Nakicenovic 2000). Values from the B1 scenario were considered, foreseeing an open global economy with an orientation towards equity and sustainable development. The scenario forecasts that, on average, the population in Asia and in the world grows by 50% over the period 1990-2020 (1.4% per annum). Since it is expected that the population will have more food per head in 2020 compared to 1990, we estimated for both dairy cows and pigs a growth of 2% per year, resulting in a growth of 100% over the period 1985-2020. Resource potentials projected for the year 2020 are summarised by continent in Table 4.2. The global theoretical resource potential is 350 million tons of algal production (200 in 1990), based on the nutrient content of the total human, dairy cow and pig wastes in the climatically suitable areas. For humans, 140 million ton of algal potential amounts to about 4.5 billion people, the population in 2020 in the climatically suitable regions. Similarly, the estimate of the total animal wastes theoretically available for microalgae-based wastewater treatment is equivalent to 0.55 billion pigs and 0.2 billion dairy cows.

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waste treatment systems.

Table 4.2. Theoretical resource potentials by continent in 2020 [million ton of algae or CO2 avoided per year] based on total waste N nutrient available (only areas with 15 °C annual average temperature of Figure 4.1 are included)

Continent Municipal

wastewater [Mton algae]

Dairy cow wastes

[Mton algae]

Pig wastes

[Mton algae]

Total

[Mton algae] Africa 28 31 3 62 America 20 46 23 89 Asia 84 53 56 193 Europe 2 3 3 7 Middle East 2 1 0 3 Oceania 7 2 2 11 Total 142 137 87 366

Here again it becomes clear that Asia has the largest theoretical potentials in all categories. More evident is now the second largest municipal wastewater potential: in Africa followed by south and central America. Furthermore, in south and central America is located the second largest dairy cow waste potential (closely trailed by Africa) and pig waste potential.

4.3 Constraints on practical microalgae production The theoretical resource potentials discussed above was calculated on the basis of total available nitrogen resources from humans and target animals located in the areas with suitable climate. However, only a fraction of this theoretical potential can be, realistically, exploited because of other limiting factors. Specifically, three factors that will likely limit the application of these systems were analysed: the availability of sufficient flat land, the availability of affordable land, and the availability of sufficient people to provide infrastructures (e.g. power) and CO2 resources. Spatially differentiated data are not available for these constraints. Therefore, the following approximations and proxies were used in the analysis: a) The global availability of flat land is approximated by land located at 500

meter altitudes or lower (source: Go Spatial [9]). This is highlighted in colour in Figure 4.3. This constraint excludes some areas with large theoretical potential in China and India due to the high altitude suggesting limited flat land areas.

b) The global availability of low cost land is approximated by areas with

moderate (lower than 250 persons per km2) population densities (source: Columbia University of New York [5]). This available land is calculated at the highest available resolution (15 x 15 minutes, i.e. 28 x 28 km). It means that in general very large cities are not accounted as having available land, although less populated areas nearby may contribute. The land availability is coloured in Figure 4.4. Besides large cities, the most highly populated areas in India and south China are assumed to have little land available for microalgae-based

Figure 4.3. Availability of flat land (green) located at altitudes lower than 500 m

(source: [9])

Figure 4.4. Availability of low-cost land (purple) approximated by population

densities smaller than 250 persons per km2 (source: [5])

Figure 4.5. Availability of sufficient infrastructure (green) approximated by

population densities higher than 25 persons per km2 in suitable climatic conditions (source: [7])

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Figure 4.6. Global areas suitable for practical production of microalgae on

wastes (pink) as a result of the combination of the constraints on the theoretical production factors by availability of flat, low cost land and infrastructure (population density) with the right climatic conditions

c) The global availability of CO2 supply, power, and other infrastructure is

approximated by a population density of more than 25 persons per km2. Thus moderately to highly populated areas are regarded as close to a power plant of sufficient size to supply CO2 and that areas with low population densities are assumed to have limited access to CO2 supplies and other infrastructures (such as power). This factor was calculated at a lower resolution, which is a grid of 1 by 1° (111 x 111 km), in order not to exclude areas with low population densities near highly populated areas (source: Edgar [7]). These areas are attractive for microalgae technology on the basis of land availability (lower population densities at a more detailed grid). From Figure 4.5, CO2 supply is assumed to be available in populated areas and becomes a constraint only in low population density areas.

Locations that fulfil all three constraints discussed above, in addition to climatic requirements, are deemed here as having the highest economic potential from a resource perspective for microalgae biofixation processes integrated with wastewater treatment. These locations are reported in Figure 4.6 which shows that the large areas of central and south America, Africa and Australia do not fall into this category. To what extent this lowers the theoretical potential depends on the correlation with the resource potentials. This issue is addressed next.

4.4 Technical potentials for microalgae production on wastes The critical issue in assessing the technical (practical) potential of microalgae systems for renewable energy production and GHG abatement is the economics of such processes. Here we assume that if required resource and production factors are available (e.g. nutrients, climate, land, infrastructures), as outlined above, then these processes will potentially be practical, that is economic, based on the data in Table 3.1. Furthermore, for simplicity, it is assumed that the identified suitable land area will be so also for the year 2020. Obviously, this is the case for climate conditions and the availability of flat land. For the availability of low cost land, the calculated area might be an overestimation, while the opposite is true for the

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availability of infrastructures, energy and CO2 supply. These requirements are to some extent contradictory: high population densities both help and hinder the establishment of these technologies. This would reduce some of the uncertainties of the analysis, and the overall estimate of the suitable area appears appropriate. Figure 4.7 summarises the regions where these production factors are available and shows the global distribution of the technical potential for people, dairy cows and pigs. Table 4.3 summarise the results by continent in absolute and relative numbers respectively, that is millions of tons of algal biomass produced and as % of the theoretical potential available in the area. In addition, a sufficient density of wastewater production is demanded for the economic realisation of the theoretical potential. We consider a minimum density of 25 persons, 1 dairy cow or 5 pigs per km2. This means that in each grid cell of 111 x 111 km (1 degree latitude) at least 300,000 people (or 60,000 pig or 12,000 dairy cows) have to be present for the economic production of microalgae. Algae ponds would produce at least 10,000 ton of biomass in 1 km2. Table 4.3. Technical production potentials by continent in 2020 as million tons

of algae (=CO2 avoided) per year and as % of the theoretical potential

Continent Municipal

wastewater Mton (%)

Dairy cow waste

Mton (%)

Pig waste

Mton (%)

Total

Mton (%) Africa 9 34% 4 14% 0 3% 14 24% America 6 28% 7 15% 3 15% 16 18% Asia 21 25% 17 32% 15 27% 53 27% Europe 1 34% 1 40% 1 32% 3 35% Middle East 1 32% 0 25% 0 0% 1 30% Oceania 4 52% 0 0% 0 15% 4 39% Total 41 29% 30 22% 20 23% 90 25%

In summary, from Table 4.3, the technical annual production potentials in 2020 are 40 million ton/year from municipal wastewater, 30 million ton/year from dairy wastes and 20 million ton/year from pig wastes, giving a total algae production or CO2 abatement of 90 million ton/year, representing overall about 25% of the theoretical (maximum) potential in the favourable climatic areas (Table 4.2). Municipal and animal wastewater potentials are limited to a quarter of their potential by the combined constraints of lack of populated areas and land availability (flat and cheap). Africa is not densely populated, but it scores well in Nigeria and Egypt. Economic production potentials of municipal wastewaters in India and China are by far the largest, but account only for about a quarter of theoretical production potentials, since land availability is a limitation in the densely populated areas. Oceania has the relatively most favourable production factors, but the totals are low due to the limited population.

Figure 4.7. Graphical presentation omicroalgae biofixation based upon the theowastewater (1990 - greewastes (red - 1985) in cand regional constraints

g

y

Pi

Dair

Municipal

32

f the global technical production potential of processes integrated with waste treatment retical resource potentials of municipal n), dairy cow wastes (1985 - brown) and pigs ombination with suitable climatic conditions in economic production factors

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Technical production potentials of dairy cow and pig manure in Africa and Central

ue. Finally, even low population areas will have many settlements of more 0,000 people who would have (at least in the future) sewerage and thus need stewater treatment.

On the other hand, many other factors will likely limit the practical applications of these technologies in many local situations much more than predicted by the above constraints. In summary, these and other uncertainties are likely to cancel out to some extent on a global scale and provide a reasonable global estimate, even if they do not predict local situations well. In other words, local and regional assessments should not consider the constraints used herein for a global estimate as

and South America are only 15% or less of the theoretical resource, considering minimum animal and population densities as proxies for infrastructures. Also important in these countries is that approximately half of the land area is not suitable due to higher elevations. The opposite is true for Asian and European countries where 30% to 40% of the theoretical resource potential seems to be technically available for practical production. Again, the largest economic production potentials are found in India and southern China, covering 50% of the global economic production potential, followed by America with a quarter of the world’s economic potential.

Discussion of the technical potential analysis for waste-grown microalgae

ount of microalgae production will be determined by the demand for the products that can be produced. The demand for renewable fuels is assumed to be

The am

more li

greater in all cases than the biofuels that could be produced by algae. Higher value products could be transported some distance. Fertilisers and animal feeds have a

mited transportation radius, but would likely be produced and used near the algal processes. Therefore, it is assumed that the demand for products will pose no major additional constraints on the technical potential. It must, again, be pointed out that there are many limitations with the present analysis. In brief, it will likely both overestimate and underestimate several important aspects the potential of microalgae production. However, improving on this estimate of the technical potential of this technology would be difficult as site-specific studies would be difficult to extrapolate to a global resource potential and a higher resolution geographic analysis does not seem possible at present. In any event, they would be beyond the scope of the present study. It can be reasonably argued that the potential of India and China might be an overestimate and that others regions are likely underestimated, based on the methodology used. For example, elevations above 500 m will certainly reduce land availability, but will not prevent establishment of such systems, and may not even be a major restriction until much higher elevation. Similarly, land affordability, a major constraint for municipal wastewaters, is likely not well represented by the constraints imposed by human population densities shown in Figure 4.4. Also, municipal wastewater treatment systems are generally government functions and land is sometimes more available for these than for private activities. Finally, availability of CO2 sources is not a major constraint for the present systems. For

ple, the wastes themselves can provide all the CO2 required, if power is on site from the biogas produced and the CO2 is recycled. Power or

ls produced from such systems are in universal demand, so the demand is not

examgenerated biofuean issthan 3for wa

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fertilisers. Replacement of even 1% of the roughly 100 million tons of N fertiliser

pre-emptive, no region or location should be excluded a priori from consideration, as long as it is located in a favourable climate. In conclusion, we believe that the overall global estimate for a technical potential of about 90 million tons of algae biomass grown on human and animal wastes is reasonable.

4.5 Additional applications of microalgae in GHG abatement Microalgae fertiliser production The above estimation of the global potential for microalgae GHG abatement addressed only the first two (municipal and animal waste treatment) of the four multipurpose processes outlined in the Technology Roadmap by Benemann (2003). The other two involve the production of N fertilisers and of higher value co-products. Fertiliser production by microalgae is envisioned as a relatively simpler process than wastewater treatment: conventional plant fertilisers (P, K, Fe, and other minor nutrients) are used to cultivate filamentous or colonial N2-fixing heterocystous cyanobacteria in open ponds. The main advantage here is that these algae experience little or no competition and thus their maintenance in the ponds is not a major issue. Further, these algae are easily harvested, solving the other of the two major technical problems in algal mass cultures. The main disadvantage is that the process of N2 fixation itself requires considerable metabolic energy, just as the Haber-Bosch process requires fossil fuels. Indeed, it appears that a similar conversion factor can be considered for both, 3 tons less CO2 would be fixed by the algae per ton of N produced. On this basis, as the N content of the algal biomass is 10%, N2-fixation would reduce biomass productivity by about 30%, or from the herein projected 100 /ha/yr to about 70 ton/ha/yr. However, the lower overall cost of such a process, would still bringing it in line with the economic estimates in Table 3.1. Based on a general use rate for intensive agriculture of 200 kg of N fertiliser per hectare, one hectare of algae ponds could supply the fertiliser of 35 hectares of crop plants, a very reasonable trade-off of crop production for local fertiliser production. Of course, as for other algal biomass, methane can be produced by anaerobic digestion of the biomass, prior to the use of the residuals as biofertilisers. Thus, where there is a need for fertiliser and where otherwise favourable conditions prevail, this is a technology that can be considered as a near-term application in this global estimate of the potential for microalgae GHG abatement. Of course, in this case a local supply of an enriched CO2 source would be required (the recycling of CO2 from the combustion of the biogas generated from the algal biomass would not be sufficient). However, as such systems would be located in agricultural areas, there should be no lack of availability of additional biomass suitable for co-digestion with the algae, and this should not present a significant limitation. The need for N fertiliser is also not a limiting factor, in particular as the increasing price of fossil fuels greatly increases the production and transportation costs of

currently produced would amount to 10 million tons of algal biomass and an equivalent amount of CO2 abatement, based on the methane and N fertiliser contributions. An analysis of the world crop production in the climatically favoured areas, in particular of intensive irrigated agriculture, such as rice production, would be of interest. However, even without such, it is clear that the potential of microalgae de novo fertiliser production is for millions of tons of N fertiliser and thus tens of millions of tons of CO2 avoided. A more precise estimate of the potential of this specific application of microalgae in GHG abatement does not appear reasonable at present. It should be noted that the recycling of N (and P, etc,) nutrients from the algal biomass produced in conjunction with wastewater treatment already represents several million tons of additional fertilisers that would be recycled to agriculture. Of course, some, even most, of the fertiliser content in animal manures is already recycled with current waste management practices on a global basis. Higher value microalgae products In the above discussion, the higher value, large market products that can be potentially produced from microalgae were identified as specialty animal feeds and biopolymers. Several specific products can be considered for practical applications in the near- to mid-term, which would fit the requirement of providing significant GHG abatement credit, for examples animal feeds high in protein and carotenoids (pigments) or omega-3 fatty acids, and biopolymers of various types. However, none have been developed to the point that they can form a basis for specific predictions of GHG abatement potential. It is certainly plausible, given even some modest economic encouragement, that this type of product and technology could be developed in the mid-term. However, any speculation on the potential for such a technology is somewhat premature. Of course, the markets for such products are large, and would amount in the tens of millions of tons of algal biomass, and much of the biomass produced would be a residue that could be used to produce biofuels. The products themselves would likely provide significant GHG abatement, compared to current production of such animal feeds or biopolymers. It should be noted that even a modest 10 million ton estimate for such a technology represents a 100-fold higher production level than all current microalgae production systems around the world. However, as global production of microalgae, mainly for food supplements and specialty feeds, has expanded almost ten-fold in the past dozen or so years, such expansion of this industry is not beyond the plausible.

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4.6 Conclusions on regional resource potentials • Suitable climatic conditions for microalgae are roughly in the area between

37° north and south latitude, corresponding to annual average temperatures above about 15°C

• A minimum scale of 10 hectares algae pond for waste treatment requires the wastewaters from about 30,000 people or from about 5,000 pigs or 1,200 dairy cows

• In the climatically favoured areas, the global theoretical resource potential amounts to 350 million tons of algal production in 2020 (200 in 1990), based on the nutrient (N) content of the total wastes of humans, dairy cows and pigs

• Large areas of central and south America, Africa and Australia are not suitable for algae production due to constraints of available flat land, low cost land (particularly for municipal wastewater) and lack of infrastructures, such as power and CO2 supply (especially for animal waste)

• Globally, annual technical potentials are 40 million ton of CO2 avoided from municipal wastewater, 30 million ton from dairy waste and 20 million ton from pig waste, giving a total algae production or CO2 abatement of 90 million ton per year

• Asia (about 50 million ton), America and Africa (about 15 million ton each) have the largest annual technical potentials

• Fertiliser production with nitrogen-fixing microalgae (cyanobacteria) could potentially add 10 million ton algal biomass production and CO2 abatement annually, for each 1% global market share of synthetic N fertiliser displaced.

• The potential exists for additional tens of millions of tons of microalgae co-production of higher value/large market co-products, such as specialty animal feeds and biopolymers

• Based on achieving stated R&D goals, the global technical potential for microalgae production and overall GHG abatement can thus be estimated to be in the order of 100 million ton/year by 2020

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5. Outlook on CO2 abatement by microalgae processes 5.1 The global potential for microalgae CO2 abatement In summary, we estimate that by the year 2020 microalgae biofixation processes could annually produce in the order of 100 million tons of algal biomass, of which the majority would likely come from wastewater systems treating human and animal waste conversion processes, and with additional GHG abatement possible from fertiliser production and higher value/large market co-products. This is, of course, only a first order estimate, which is fundamentally dependent on the further development and demonstration of the underlying technology. Some of the estimates could, and likely are, on the high side. For example, the conclusion that the sewage generated from 1.5 billion people, 20% of mankind in 2020, could be suitable for treatment with microalgae ponds has to be considered optimistic. On the other hand, the potential for fertiliser production and higher value co-products may err somewhat on the conservative side, as, if the right technology and co-products were to be developed, they could produce several tens of million tons annually of algal biomass. Thus, in conclusion, we believe that a 100 million ton CO2 abatement scenario for microalgae- based multipurpose processes is overall defensible and realistic in the context of the potential of this technology and the uncertainties inherent in any such assessment. The above analysis also fits into the general methodologies and level of precision for estimates of other GHG abatement technologies. Although we have not provided any probabilistic ranges for our estimates, the lower bound would be quite low, while the upper bound could certainly be several-fold higher. Of course, this analysis is based on many assumptions, both internal to the process (e.g. productivity, costs) as well as external (prices of energy, value of products and services). In particular, many site-specific parameters for land, climate and resources, will affect these results. Finally, we have not addressed herein the potential for microalgae-based fuel-only processes, such as for biodiesel production, or processes based on alternative production technologies, such as closed photobioreactors, or processes that produce H2 and thus do not require CO2 (or if they do would recycle it internally). Despite large R&D investments into all of these approaches in the past, at least relative to the approaches advocated herein, these were excluded from the present analysis because they all are considered to be long-term options, with limited potential in any near- to mid-term R&D effort (Benemann, 2003). This is also illustrated by the techno-economic performance analysis (Table 3.1), which suggests that without the revenues from co-products or co-processes microalgae technology is not likely economically viable. In any event, the most plausible route to the development of more advanced microalgae technologies, will be through demonstrations of the feasibility of the multipurpose processes discussed herein.

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energy options since these compare the most closely with microalgae technology.

5.2 Comparison with other CO2 abatement options Footprint The efficient use of land is an important aspect of the potential success of, specifically, biological CO2 mitigation options. As discussed herein (also see Benemann, 2003), the near-term goal of microalgae technology is to achieve a productivity of 100 ton/ha/yr corresponding to an equivalent amount of CO2 abatement. An even higher productivity is considered feasible in the longer-term. According to the IPCC (2001), reforestation has a potential of less than 5 tons CO2 avoided per hectare per year (over a 100 year project life-time), while biomass energy systems are estimated at 10 tons CO2 avoided per hectare-year, although plausible technological advances make it likely that this could be doubled in the long-term. In brief, microalgae have a potential footprint of only one tenth the size of most other biomass energy systems. Of course, this does not apply to all cases: in the tropics sugar cane and some other high yield crops can exhibit much higher productivities than the global average, but these opportunities are limited. In an increasingly crowded and land-limited world, footprint is a major consideration for any biofuel and GHG abatement technology. Some technologies will have much smaller footprints, of course, such as photovoltaics, but these are not directly comparable with microalgal or biofuel processes. The main conclusion is that microalgae have a footprint of only one tenth the size of most other biomass systems. Energy price sensitivity The techno-economic analysis in Chapter 3 pointed out that energy prices are very important for the profitability of microalgae technology. At present, high energy prices and general expectations of increasing prices over time, represent an advantage of microalgae technology, as it is for other renewable energy options. Important here is the relative position of microalgae as a renewable energy producing technology compared to other renewable energy producing technologies. Also, with rising world energy prices, microalgae, producing biofuel, will increase its revenues while all fossil fuel-based processes with CO2 capture and storage options will increase in costs. Even other renewable energy options, such as solar, wind and hydro, will not enjoy such a large increase in revenues, since their economics are more connected to large investment costs. In brief, biofuel-producing options, among which microalgae processes, have a most favourable quality with respect to high world energy prices and become, under these circumstances, relatively more profitable than non-biological CO2 abatement options. Comparison to other GHG abatement technologies In Figure 5.1, microalgae multipurpose processes assessed in this report are put in the context of different energy related technologies for GHG abatement that were compared by the IPCC Working Group III in terms of costs, potential of implementation by 2010 and 2020 and probability of realisation. We selected

39

realisation of the technical potential of microalgae is not too probable for the years

Figure 5.1. Microalgae processes assessed in this report (in blue) in the context of

an IPCC overview (2001) on energy-related CO2 abatement options in terms of costs and potentials for the years 2010 and 2020

Figure 5.1 shows that the costs of energy related options which are considered for CO2 abatement range from negative (thus having benefits) to 400 US$ per ton of avoided carbon. Also the potentials vary from smaller than 20 million ton CO2 avoided per year (solar for coal and biomass for gas) to larger than 200 million ton CO2 avoided per year (e.g. wind energy). Also, the probability of realising the level of potential varies from very unlikely to probable. All these technologies are included in the research portfolio for GHG mitigation, since none of the options has large enough potential and high enough probability to combat climate change by itself. On the basis of the assessment made in this report, we conclude that microalgae biofixation processes fit in this portfolio of energy related GHG abatement options. The technical potential is comparable with some of the other options. Actual

MicroalgaeMicroalgae

2010 and 2020 but in this regards microalgae technology does not represent an exception in the assessment of CO2 abatement technologies. In fact, the economic viability of microalgae biofixation technology is better than that of almost all other options. Assuming successful technology development and applied in the right circumstances, microalgae biofixation technology can even be profitable. CDM matches with microalgae The not too complex technological characteristics, the present application of commercial algae production and wastewater treatment in developing countries and their favourable climatic and other circumstances for economically viable operation of microalgae biofixation technologies make this CO2 abatement technology especially suitable for Clean Development Mechanism (CDM) projects under the United Nations Framework Convention for Climate Change (UNFCCC). These are CO2 mitigation projects in (developing) countries without a greenhouse gas mitigation target. The CO2 emission rights of these projects can, under certain conditions and at the price of reimbursing additional costs, be accounted by countries that have emission reduction obligations. One important condition that microalgae can fulfil easily is the condition of ‘additionality’ which means that the CO2 mitigation would not take place without the (microalgae) project. Also, projects have to be attractive for local people regardless of CO2 abatement. Furthermore, avoidance of CO2 emissions must be accountable. These criteria can be met by microalgae based processes. In case the CO2 “poor” products, such as biofuel or biofertiliser, are directly applied in a country that has an emission target, a CDM construction is not needed to account the CO2 abatement. CDM is particularly valuable if the produced fuel or other products, and herewith the CO2 mitigation, takes place in the developing country and has to be transferred to a country that has an emission objective in order to cash the value of the CO2 mitigation. In case of heavy and not too valuable products, this is certainly a more profitable route. For microalgae biofixation

40

projects it is a clearly defined way to exploit the value of avoided CO2 emissions. Overall conclusion The overall conclusion is that microalgae biofixation technology is, in the context of greenhouse gas abatement, a potentially viable and significant technology for CO2 abatement in the climatically warmer and sunnier regions of the world with sufficient flat land available, with near-term (before 2020) application in conjunction with waste treatment, fertiliser production and higher value/large market co-products. The largest potentials are found in developing countries, although the present analysis is global and therefore not able nor intended to disqualify any local area for potentially profitable microalgae production.

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6. References

1. Benemann J.R., Oswald, W.J., Systems and Economic Analysis of Microalgae Ponds for Conversion of CO2 to Biomass, Final report to the Department of Energy, Pittsburgh Energy Technology Centre, 21 March 1996

2. Benemann J.R., Augenstein D.C., Weissman, J.C., 1982a, Microalgae as a source of liquid fuels, appendix: technological feasibility analysis, final report, US DOE, unpublished; in: a look back at the aquatic species program – technical review

3. Benemann J.R., Utilization of carbon dioxide from fossil fuel - burning power plants with biological system. Energy conversion and management 34(9/11), 999-1004, 1993

4. Benemann J.R., Biofixation of CO2 and greenhouse gas abatement with microalgae – Technology Road Map, 2003

5. Columbia University of New York, global population densities for the year 1995 at 15 x 15 minutes from http://sedac.ciesin.org/plue/gpw/index.html? oceania.html&2

6. Davidson, J. and P. Freund, Comparison of sequestration of CO2 by forests and capture from power stations. IEA Greenhouse Gas R&D Programme, Chelteham, UK, 2000.

7. Ecofys & TNO-NITG: Global carbon dioxide storage potential and costs, Report, no EEP-02001, 2002

8. Edgar Greenhouse gas emission database, global data set on dairy cattle, pigs and population at 1 degree provided by J.J. Olivier and J. Peters (RIVM)

9. Faostat database, grand total protein per capita per year for 2002 at http://faostat.fao.org/

10. Go Spatial Ltd, global elevation data set from http://www.gospatial.com/

11. IPCC data distribution centre, global mean temperature data set by month at 0.5 degree for 1981-1990 from http://ipcc-ddc.cru.uea.ac.uk/

12. IPCC Third Assessment Report, Climate Change 2001: Mitigation, 2001

13. Nakicenovic, N., Alcamo, J., Davis, G., de Vries, B., Fenhann, J., Gaffin, S., Gregory, K., Grübler, A., et al., 2000. Special Report on Emission Scenarios: A Special Report of Working Group III of the Intergovernmental Panel on Climate Change, Cambridge University Press, Cambridge

14. Revised 1996 IPCC Guidelines for National Greenhouse Gas Inventories: Reference Manual, 2001

15. Spiewak I., 2004: Cleaner fossil fuel technologies for CO2 reduction, capture and sequestration, report No. E/149, Opet, Israel

16. Weissman, J.C., R.P. Goebel, Benemann, J.R., Photobioreactor Design: Comparison of Open Ponds and Tubular Reactors, Bioeng. Biotech., 31: 336-344, 1988

17. Weissmann J.C., Tillett D.T., 1992: Design and Operation of an outdoor Microalgae test-facility; large scale systems result, Aquatic Species project FY 1989-1990, NREL, Golden CO., NREL/MP-232-4174

7. Authentication

Commissioned by:

EniTecnologie S.p.A

Names of researchers:

Toon van Harmelen Hans Oonk Hans van der Brugh

Timing of the project:

June 2005 to May 2006

Signature:

Drs. A.K. van Harmelen project leader

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43 43

Appendix A. Techno-economic performance

Assumptions on technological development Techno-economic performance of microalgae biofixation processes is based assuming a successful future R&D of algae-related technology, in particular: • development of improved techniques for mass culture and maintenance of

specific algae species/strains. A modest inoculum system (<5% of costs) is assumed to allow mass culture of selected strains

• increased productivities (solar energy conversion efficiency) by means of improved algal strains. Productivities of 100 ton/ha/yr (average biomass composition: 45% C, 10% N, 1% P) is feasible at 35°Latitude or below

• algal biomass harvesting is feasible at low-cost by spontaneous flocculation-settling (bioflocculation). Harvesting is 95% efficient for a spontaneous flocculation-settling cycle of 12-24 hours

• conversion of the algal biomass to renewable biofuels (anaerobic digestion or others, as feasible). Methane recovery with lightly mixed covered digester equals 75% of the biomass higher heating value, other fuels can also be derived also, with anaerobic digestion recovering any remaining fuel value to this level.

• effective nutrient (nitrogen and phosphates) uptake and removal from wastewaters; Nutrient removal based on variable N and P in biomass and low residual N or P levels

• low-cost engineering designs: (i) construction of large (> 1 ha) open, unlined ponds, including flue gas CO2 transfer and capture, mixing, infrastructures, and

e possible with capital costs € 100,000/ha (ii) use of flue gas from l power plant (8-12% CO2) with an overall 80% efficiency. A

assumed to be available to supply maximum ents (iii) large-scale (> 40 hectares) algal ponds allows for

economies of scale and cost-effective operations (iv) energy for operations (mixing, CO2 transfer, harvesting, pumping) is at maximum 20% of gross outputs; (v) annualised costs range from about 20%-33% of capital costs (10 to 15% capital charges, 10 to 25 year average depreciation, 5%-10% operations);

• operation of the overall process to achieve multiple process goals, including GHG abatement

harvesting ara conventionapower plant of sufficient size isflue gas requirem

Table A.1. Overview of technical parameters that characterise microalgae biofixation processes

Parameter Value Remarks/reference

Algal biomass composition 45% C (in dry biomass) 10% N (dry) 1% P (dry)

Algae N content may vary from 4 to 10%, P from 0.3 to 1.2%

Wastewater utilisation/reclaimed water production

2.5 m3 wastewater per kg of algal biomass (dry)

assuming 40 g m-3 Nkj in wastewater (Dutch average waste water composition, Oonk, 2004)

CO2 utilisation

1.7 kg CO2 per kg algal biomass (dry)

0.7 kg CO2 m3

wastewater

95% overall CO2 efficiency (CO2 uptake in algal biomass/CO2 fed to the system) is attainable (Weissmann and Goebel, 1988)

Algal biomass productivity 55 Mg ha-1 y-1 annual productivity achieved. Projected 100-300 Mg ha-1y-1, >70 Mg ha-1y-1 algae containing 40% lipids 160 bbl oil ha-1y-1

Achieved, also 30 g m-2 d-1 peak productivity, see Weissmann and Tillett, 1992. Projected productivity by future systems (Benemann, 1982, Benemann and Oswald, 1996)

Energy & products 240 kg CH4 per ton of algae upon anaerobic digestion (660 m3 biogas)

assuming about 80% dissimilation of organic material in anaerobic digester

10 kg P and 100 kg N per ton of algae in anaerobic digestor residue

obtained as a solution in water

100-300 kg specific products per ton of algae

e.g. 10% of polyhodroxybutyrate; 30 wt % lipids is feasible

CO2 mitigation upon utilisation

1 kg CO2 per kg algae biomass processed in anaerobic digestion

Benemann, 2003

3.5 kg CO2 per kg N in residue of anaerobic digestion, when used as a fertiliser (~0.35 kg CO2 per kg algal biomass into the anaerobic digester)

Benemann, 2003

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Appendix B. Resource potential

Table B.1. Tentative default values for nitrogen excretion per head of animal per

region (kg/animal/yr) a(from the Revised 1996 IPCC Guidelines for National Greenhouse Gas Inventories: Reference Manual, 2001)

Table B.2. Grand total nitrogen excretion per capita per year (from Faostat)

Continent kg nitogen per capita per year

Relevant for microalgae / (sub)tropical climate

Africa 2.6 Yes Asia 2.9 Yes Central America 3.3 Yes Europe 4.2 North America 4.2 Oceania 4.0 Yes South America 3.2 Yes Developed countries 4.2 Developing countries 2.7 Selected for this study 3

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