208574065 Biofuels Introduction

8/12/2019 208574065 Biofuels Introduction

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Microalgae Biofuels: A Brief Introduction, John Benemann, January 1, 2009 1

MICROALGAE BIOFUELS: A BRIEF INTRODUCTIONJohn R. Benemann

Summary: The cultivation of microalgae for biofuels in general, and oil production in particular,is not a near-term commercial prospect. Aside from some niche but significant applications inwastewater treatment, this technology still requires a considerable R&D effort. This is due in partto the high costs of even simple algae production systems (unlined, open, paddle wheel-mixed,

raceway-type ponds), in even larger part due to the presently undeveloped nature of algal massculture technologies, from the selection of algal strains that can be stably maintained in the openponds, to their low-cost harvesting, and, most importantly, due to the need to achieve very highproductivities of algal biomass with a high content of vegetable oils or other biofuel precursors,required to cover the high capital and operating costs of algae production. However, R&Defforts to overcome these limitations are justified by the potential of this technology and its non-competition with food crops.

Current Commercial Technology: Microalgae are currently cultivated commercially forhuman nutritional products around the world in several dozen small- to medium-scale productionsystems, producing a few tens to several hundred tons of biomass annually. I estimate total world

commercial microalgal biomass production at about 10,000 tons per year. The main microalgaecurrently cultivated photosynthetically (i.e. with sunlight) for nutritional products are Spirulina,Chlorella, Dunaliella andHaematococcus (Figure 1). Almost half of the microalgae productiontakes place in mainland China, with most of the rest in Japan, Taiwan, USA, India and Australia,with smaller producers in other countries. Almost all commercial producers use open ponds;Figure 2 provides examples of commercial production systems. Microalgae also flourish inmunicipal wastewater treatment ponds (Figure 2.A.1.), where they help in waste purification.However, harvesting of the algal biomass is generally not practiced in such systems, and where itis the chemical flocculants limit further utilization of the algal biomass, even for biofuels (i.e.methane; these algae contain little if any oil). Microalgae are also grown for live aquaculturefeeds in hundreds of systems around the world that individually produce from a few kilos to afew tons of biomass annually. Finally, microalgae nutritional products are also producedcommercially by dark fermentations (using starch or sugar rather than light energy), with a fewthousand tons of algal biomass produced by this route (Chlorellain the Far East and omega-3fatty acids, mainly in the US). This approach has also been proposed by at least one companyfor biodiesel production. However, such dark fermentation processes, using plant-derived sugarsand starches rather than sunlight and CO2, are not further discussed herein. Neither are biofuelsderived from seaweeds (the macroalgae), which will be addressed elsewhere.

Ponds and Photobioreactors. Microalgae cultivation using sunlight energy can be carried outin open or covered ponds, or closed photobioreactors, including tubular, bag and flat platedesigns. Closed systems (Figures 2.C.) are much more expensive than ponds, and present majordesign and operating challenges (overheating, fouling, gas exchange limitations, etc.). Most

importantly, they cannot be scaled-up for individual growth units beyond about a thousandsquare feet (~100 m2), often much less. For biofuels production, which will require systems ofhundreds of acres, this would mean tens of thousands of such units, at high capital and evengreater operating costs. Open ponds, specifically shallow, mixed, raceway ponds (Figure 2B), aremuch cheaper to build and operate, can be scaled to several acres for an individual pond (thoughthe maximal size is presently uncertain), and are the method of choice for commercialmicroalgae production around the world (Figures 2.B). Unfortunately open ponds suffer fromvarious limitations, including more rapid (compared to closed systems) invasions by other algaeand algae grazers, fungi, amoeba, etc. Closed systems have advantages in colder climates,though, on the other hand, they would require cooling for most days, with water spray the only


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practical cooling method, at high water use. Over 98% of commercial algae biomass productionis currently produced with open ponds, even for high value nutritional products selling for overprices hundred-fold more than allowable for biofuels. Almost no information is available on thedesign, operation, yields, and other important aspects of commercial algal production systems, incontrast to the hundreds of publications from academic and government laboratories on algaecultivation with small-scale closed photobioreactors. This has led to a widespread, but incorrect,

perception that the latter are the better and more promising production systems for algal biofuels.

Microalgae Biofuels. Microalgae have been studied for many years for production of hydrogen,(H2), methane, oils (triglycerides and hydrocarbons, for biodiesel, jet fuels, etc.), and bioethanol.Algal H2fuel production has been extensively studied for over thirty years, but no mechanismthat could even conceptually be plausibly scaled-up has as yet been described or demonstrated,even in the laboratory. Thus algal H2production is not further addressed. However, this historyis a salutatory example that not all research leads to favorable outcomes, and that unsuccessfulresearch approaches must be abandoned when their limitations are recognized. Of course, suchrecognition is often difficult for those who have invested a lifetime in such research. Methane(biogas) production was the focus of most of the early work on biofuels from microalgae, whenthese were considered mainly for applications in wastewater treatment. However, the higher

value of liquid transportation fuels - ethanol and oils - focused more attention on these biofuelsafter the 1970s oil shocks. For ethanol production, algal cells would have to accumulate sugarsor starches and then ferment them to produce ethanol at rather high levels (> 4% by volume) toallow for its economic recovery; daunting challenges even for advanced genetic engineeringtechniques. More simple would be the accumulation of starch by microalgae and a subsequentyeast fermentation, as in corn starch ethanol production. Such a process would need to competewith the very low-cost starch or sugar produced by crop plants. However, this approach is not allthat different in concept from the production of algae oils, e.g. triglycerides, the focus of most ofthe current interest in algae biofuels. In brief, some microalgae accumulate large amounts of oil,in particular triglycerides, when subjected to stress conditions (e.g. nitrogen limitation). The keyis to produce such oils at high productivity, which remains to be demonstrated. One species,

Botryococcus braunii,contains about 50% of hydrocarbons, even under normal conditions ofgrowth. Unfortunately it grows very slowly and its large-scale cultivation remains a challenge.Oils or hydrocarbons from microalgae can be converted to green diesel or jet fuel by technologyalready developed for other vegetable oils. The challenge is to produce algal biomass, cheaply.

Algae Strains, Cultivation, Harvesting, Processing.The basic concept for producing oils orother biofuels with microalgae is to use relatively small (in total area) closed photobioreactors toproduce a starter (inoculum) culture, at most 1-2% of the total biomass, to seed larger, severalhundred acres in total area, open ponds. About 20 to 40% of the pond volume must be harvestedon a daily basis (depending on season and other factors). The biomass (a few hundred milligrams/liter) must be concentrated initially by about thirty-fold by a very low-cost harvesting process.Bioflocculation, the spontaneous flocculation-sedimentation of algal cells, using little or no

flocculation chemicals, has been proposed as one promising approach, but still must bedeveloped and demonstrated for each algal species and even strain. The algal strains cultivatedneed to be selected based on many criteria, including oil content, productivity, and harvestability.But these are only some of the essential attributes, which include: resistance to contaminationand grazers, tolerance of high O2and light levels, acceptance of temperature fluctuations, andadaptation to the local water chemistry. After harvesting, further concentration and oil extractionis required. Cell breakage followed by solvent emulsification and recovery with a three phasecentrifuge has been proposed, but cell rupture methods will need to be tested for each case. Othermethods are also possible and this is an active area of R&D. Converting the algal oil to biofuels


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(biodiesel, green diesel, jet fuel) may be the lesser challenge. The residual biomass could beeither dried and sold as animal feed or just as plausibly, converted to biogas for on-site powergeneration, covering parasitic energy needs, with the residual nutrients and carbon recycled tothe ponds. Clearly, much R&D remains to be done, most importantly in how to actually stablyand routinely cultivate the algae in large open ponds and achieve high productivities (see below).

Power Plant CO2Utilization. Central to the concept of microalgal biofuels production is theuse of power plant flue gases or of similar, nearby available, enriched sources of CO2. However,contrary to common belief, CO2use by algal cultures is not a CO2sequestration or greenhousegas abatement process. That can only come from using the algal biofuels to replace fossil fuels.And, of course, any fossil energy expended by the process would reduce such mitigation credits.Thus algal biofuels are no different than biofuels derived from higher plants (that capture CO2from air) or other renewable energy sources. The need for enriched sources of CO2, adds toproduction cost and limits the location of such systems. Indeed, the more plausible approach isto co-locate algal systems with smaller-scale CO2sources, rather than with large centralized coal-fired power plants, as is often proposed, as there CO2distribution may be the limiting factor.

Economics. This is the critical issue, after technical feasibility: the algal production systems

must have low capital and operating costs to compete with other crops and alternative energysources. Most important is the reliable cultivation of algal strains in open ponds, producing oil athigh productivities with a low-cost harvesting process. The lowest plant-gate production cost(e.g. not including costs such as marketing, overheads, R&D, etc.) for commercial algae biomassproduction in the US is about $5,000 per ton dry biomass for the Spirulina(which actually is atype of bacteria, and does not produce oil). Assuming that an algal biomass with 25% oil couldbe cultivated and the oil extracted at a similar cost, this would translate to $20,000/ton of oil, orabout 20-fold higher than even recent (mid-2008) historically high vegetable oil prices. Ofcourse it can be rightly argued that economies of scale for large-scale biofuels production,improved productivities, and even modest advances in the technology could largely overcomethis gap. However, even assuming that high biomass and oil productivities are possible and

stable cultivation achievable, the major problem is likely the irreducible minimal costs of large-scale cultivation systems, including needed infrastructure, harvesting, processing, wastetreatment, water supply, and other support systems required. Prior economic-engineeringfeasibility analyses concluded that for even the simplest open pond, overall system would cost atleast $40,000 per acre ($100,000/ ha), and possibly significantly higher. To this must be addedoperating costs, which are site dependent. Locations with favorable climate, readily availablewater (which can be saline, brackish or wastewater), a nearby and essentially free source of CO 2,nearly flat land, and clay soils (plastic liners would be too expensive), are required. In brief, thisrepresents the current reality, opportunity and challenges of microalgal biofuels production.Again, because of very high costs, and limits to scale-up, closed photobioreactors are notpractical for biofuel production, aside for small-scale seed culture production. In brief, thistechnology requires considerable R&D, with the major, but not the only, challenge being the

achievement of high productivity to justify the unavoidably high capital and operating costs.

Productivity. Assuming that a currently achievable productivity is about 50 mt/ha-yr (~22 t/ac-yr) biomass, with a 25% oil content (e.g. of triglycerides), this is about 14,000 liters oil perhectare-year (~1,500 gal/acre-yr). Even at $1/liter (~$4/gallon) for the raw oil, this would notcover capital costs (assuming $100,000/hectare, see above, and a 20%/year capital charge), letalone any operating costs. As capital costs are already projected at the lowest plausible, a majorimprovement in productivity is required. The goal of at minimum doubling, eventually tripling,what is thought to be currently possible is thus the major R&D objective in this field. Only then


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can microalgae biofuels begin to be competitive with conventional crops, already produced atcosts similar to recent (and likely future) oil prices (~$100/barrel). However, use of oil, starch,sugar or other crops for biofuels is limited by the need to feed the human population. In any case,agriculture can produce but a small fraction of even current transportation fuel demands. Theinterest in microalgae, as for other so-called next-gen biofuels, is that they would not competewith food-feed crops and that large-scale production at higher productivities may be possible.

One promising approach to higher productivities is to develop algal strains with a reduced levelof chlorophyll and other photon capturing pigments: the normally high content of such pigmentsin algal cells results in their mutual shading and inefficient light utilization, reducing overallproductivity. These and other genetic improvements may eventually boost algae oil productionto, possibly, about 5,000 gal/ac-yr. However many productivity claims and projections currentlybeing made exceed this level and are clearly unobtainable; some even violate theoretical limits.

R&D Needs. In brief, the main objectives of R&D in this field are to demonstrate that it isactually possible to mass culture algae at high productivity with a high biofuel yield, andconcomitantly to reduce the cost of algal biomass and fuel production to an acceptable level. Themain issue is how to bridge the gap between the current reality, e.g. the high costs of commercialproduction systems, and the goal of large-scale, low-cost biofuels production, with much higher

productivities than currently achieved. A long list of R&D goals can be formulated, for both theorganisms and the cultivation system. The need is to isolate, screen, select, test (in the laboratoryand outdoors) and genetically improve algal strains for higher oil (or starch) content and overallproductivity (e.g. photosynthetic efficiency), as well as for resistance to competing algae species,grazers, temperature and other environmental factors, etc. A major advantage of microalgae istheir very fast growth rates; they can double in numbers in outdoor mass cultures in a day or less.Although fast growth is not synonymous with high productivity, short generation times willallow much faster development of this technology compared to conventional crop plants, where asingle lifecycle can be months or, for trees, years. Even with this advantage, the development ofalgal strains and cultivation technologies to achieve the high productivities, long-term stability,and low-cost harvesting required for biofuels production will require some years, assuming of

course that it actually proves to be technically and economically feasible. For this, advances inthe organisms, the software, must be combined with advances in hardware, the engineeringdesign of the production system. In particular the ponds, larger than anything operated thus far incommercial cultivation, and the algal harvesting, oil extraction, processing, waste recycling, CO2supply and other system components need to be developed almost from scratch. Again, there isno guarantee that a sufficiently low-cost process can actually be designed and built. However,there are no clear show-stoppers to suggest that either the biological or engineering R&Dcannot eventually succeed. As noted, the fast growth of microalgae suggests that progress, andapplications, could be faster for microalgae than for biofuels derived from higher plants. Still, atbest, it will take some years to establish the feasibility of large-scale algal biofuels production,including the work required to develop protocols for the release of genetically modified algae.

Resource Potential. A major issue is the ultimate production potential for microalgae biofuels.After factoring in all the requirements for algae production, from suitable climate, flat land, claysoils, water and CO2resources, even a cursory analysis would suggest that visions of enormousalgae farms populating the deserts of the U.S. Southwest or Sahara are misguided. Even though,counter-intuitively, less water is used by algae grown in open ponds than by conventional crops,and brackish-saline water sources can be used by algae, water will be a limiting factor in many,even most, locations. Still, sufficient resources would likely be available, such that algal biofuels,even if they cannot replace petroleum as some proponents argue, could, if the R&D is successful,make a plausibly significant contribution to the global goal of renewable energy production.


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Wastewater Treatment.A short-cut to algal biofuels development is to co-produce the biofuels,such as vegetable oils, with other, higher value co-products, or with wastewater treatment. Sucha development pathway would allow this technology to advance and mature, to the point wherethe biofuels could become an ever more important component, and eventually the main output.The nearest-term opportunity for practical applications is in wastewater treatment, in particularmunicipal wastewater treatment. Microalgae ponds are already used in such applications, wherealgae provide O2for bacterial breakdown of waste organic matter, and in turn use the liberatedCO2(Figure 2). However, this technology is currently limited by the lack of a reliable, low-costalgal harvesting process. A bioflocculation- settling process appears promising, but remains to beperfected and demonstrated with a full-scale system. This would allow using microalgae inwastewater treatment to remove nutrients (nitrogen, phosphates), and achieve a higher level oftreatment while generating more biomass, and thus biofuels and greenhouse gas reductions, thancurrent conventional, energy intensive, wastewater treatment processes. This would also allowrecycling these fertilizers, with major environmental and economic benefits.

Conclusions. Although algal biofuels still require a great deal of R&D, the prospect of a highlyproductive process, able to use land and water resources not suitable for conventional crops,justifies a continuing investment into this technology. Even if some current projections andproponents are excessively optimistic, and near-term achievements prove disappointing, theseshould not detract from the long-term potential of this technology and the need to carry out therequired R&D. Potential applications in wastewater treatment alone would justify such efforts.

Addendum:On January 7, 2009 a test flight by Continental Airlines used a mixture of biojetfuelthat included a small amount (2.5%) derived from algae oil procured by Sapphire Co. from algaegrown by Cyanotech Corp. in Hawaii (Fig. 2B1). This test proved the technical feasibility ofalgal biojet fuels. Their practical and economic production must now be developed.

FIGURE 1. MICROGRAPHS OF COMMERCIALLY CULTIVATED ALGAL SPECIESSpirulina is acyanobacteria, the other three are green algae (chlorophyceae)

A. Spirulina(Arthrospiraplatensis) B.Dunaliella salina

C. Chlorella vulgaris D. Haematococcus pluvialis


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FIGURE 2. EXAMPLES OF COMMERCIAL MICROALGAL PRODUCTION SYSTEMS

2.A. Large open, unmixed ponds, for wastewater treatment andDunaliella salinaproduction.2.A.1. Wastewater treatment ponds - so-called oxidation ponds - are not true algae

production ponds because algae productivity is not maximized and the biomass produced israrely harvested, and, when harvested, the chemical flocculants interfere with conversion of thebiomass to biofuels. A few waste treatment ponds use mixed, raceway designs, see Figure 2B,which have great potential for application in combined wastewater treatment-biofuels productionprocesses.

2.A.2.Dunaliella salinaproduction in Australia uses very large saline evaporation ponds(>100 acres each), with these algae dominating naturally in >100 g/l of salt. However such openunmixed ponds produce biomass at very low productivities (10 cm) flexible bag type reactors. Many other designs have been used in pilot scaleproduction, including various types of flat plate reactors, hanging bag reactors, hemispherical

dome reactors (these also used in one commercial plant, see Figure 2.C.2 left), and other types.

Figure 2.A.1. Oxidation Pond for Wastewater Figure 2. A.2. Dunaliella salinaponds inTreatment(Napa, California, total ~300 acres) Australia (Cognis-Betatene ponds in S.Note: ponds on top are salt evaporation ponds. Australia. Each pond ~100 acres in size).


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Fig. 2.B.1. Commercial microalgae production in open raceway paddle-wheel mixed ponds.A. Left; Earthrise Nutritionals, LLC, California. Production of Spirulina, Ponds ~ 1 acre.B

. Right: Cyanotech Co., Hawaii, producingHaematococcus pluvialis(red ponds) and Spirulina.

Fig 2.B.2. Additional examples of commercial open pond production systems.A. LeftH. pluvialisproduction in raceway paddle wheel mixed ponds (Parry Nutraceuticals,ndia). B. Right: Chlorellaproduction in circular ponds (Chlorella Industries, Japan).I

Figure 2.C. Left:Haematococcus pluvialisproduction, hemispherical photobioreactors(Fuji Co., Hawaii) (dome ~1 meter diameter). Right:Haematococcus pluvialisproduction,tubular photobioreactors (each tube is about 100 m long, 5 cm diameter(Algatech Co., Israel).


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SOME REPORTS BY THE AUTHOR AVAILABLE ON THE WEB

Benemann, J.R.; Goebel, R.P.; Weissman, J.C.; Augenstein, D.C. 1982. Microalgae as asource of liquid fuels. Final technical report USDOE OERhttp://www.osti.gov/bridge/product.biblio.jsp?query_id=0&page=0&osti_id=6374113

Benemann J.R. and W.J. Oswald. Final Report to US DOE NETL, 1996 Systems andEconomic analysis of microalgae ponds for conversion of CO2 to biomass At:http://www.osti.gov/bridge/servlets/purl/493389-FXQyZ2/webviewable/493389.pdf

Benemann, J.R., 2002 A Technology Roadmap for Greenhouse Gas Abatement withMicroalgae. Report to the U.S. Department of Energy, National Energy Technology Laboratory,and the International Energy Agency Greenhouse Gas Abatement Programme,http://www.co2captureandstorage.info/networks/Biofixation.htm

Sheehan, J., Dunahay, T., Benemann, J., Roessler, P., Weissman, J. 1998. Look Back at theU.S. Department of Energy's Aquatic Species Program: Biodiesel from Algae; Close-Out

Report. NREL Report No. TP-580-24190 http://www.nrel.gov/docs/legosti/fy98/24190.pdf

SOME PRESENTATIONS AVAILABLE ON THE WEB

Benemann, J., Open ponds and Closed Photobioreactors Comparative Economics 5th AnnualWorld Congress on Industrial Biotechnology & Bioprocessing, April 30, 2008 Chicago, Illinois.www.bio.org/ind/wc/08/breakout_pdfs/20080430/Track1_ContinentalA/Session9_230p400pm/Benemann

_Continental_A_Wed.pdf

Benemann, J., Overview: Algae Oil to Biofuels, NREL-AFOSR Workshop, Algae Oil for JetFuel Production, Arlington, VA, February 19, 2008, www.nrel.gov/biomass/pdfs/benemann.pdf

Lundquist, T., and J. Benemann, Using CO2 and Algae to Treat Wastewater and ProduceBiofuel Feedstock March 23 2007 First Western Forum on Water and Energy Sustainability,U.C. Santa Barbara www2.bren.ucsb.edu/~keller/energy-water/4-2%20Tryg%20Lundquist.pdfBenemann, J., Microalgae Biofuels, EECA Biofuels Conf., April 24, 2007, Wellington, NewZealand www.eeca.govt.nz/eeca-library/renewable-energy/biofuels/summary/john-benemann.pdfBenemann, J., Photosynthesis, Algae, CO2 and Bio-Hydrogen, GCEP Energy WorkshopApril 27, 2004, Stanford Univ. http://gcep.stanford.edu/events/workshops_biomass_04_04.html

John R. Benemann, Ph.D.Benemann Associates andMicroBio Engineering3434 Tice Creek Dr. No.1Walnut Creek, CA 94595Phone (925) 352 3352Fax (925) 944 [email protected]
http://www.osti.gov/bridge/searchresults.jsp?Author=%22Benemann,%20J.R.%22http://www.osti.gov/bridge/searchresults.jsp?Author=%22Goebel,%20R.P.%22http://www.osti.gov/bridge/searchresults.jsp?Author=%22Weissman,%20J.C.%22http://www.osti.gov/bridge/searchresults.jsp?Author=%22Augenstein,%20D.C.%22http://www.osti.gov/bridge/product.biblio.jsp?query_id=0&page=0&osti_id=6374113http://www.nrel.gov/docs/legosti/fy98/24190.pdfhttp://www.bio.org/ind/wc/08/breakout_pdfs/20080430/Track1_ContinentalA/Session9_230p400pm/Benemann_Continental_A_Wed.pdfhttp://www.bio.org/ind/wc/08/breakout_pdfs/20080430/Track1_ContinentalA/Session9_230p400pm/Benemann_Continental_A_Wed.pdfhttp://www.bio.org/ind/wc/08/breakout_pdfs/20080430/Track1_ContinentalA/Session9_230p400pm/Benemann_Continental_A_Wed.pdfhttp://www.bio.org/ind/wc/08/breakout_pdfs/20080430/Track1_ContinentalA/Session9_230p400pm/Benemann_Continental_A_Wed.pdfhttp://www.nrel.gov/docs/legosti/fy98/24190.pdfhttp://www.osti.gov/bridge/product.biblio.jsp?query_id=0&page=0&osti_id=6374113http://www.osti.gov/bridge/searchresults.jsp?Author=%22Augenstein,%20D.C.%22http://www.osti.gov/bridge/searchresults.jsp?Author=%22Weissman,%20J.C.%22http://www.osti.gov/bridge/searchresults.jsp?Author=%22Goebel,%20R.P.%22http://www.osti.gov/bridge/searchresults.jsp?Author=%22Benemann,%20J.R.%22

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