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2 Overview of Algal Biofuel Supply Chain
Pages 27-76

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From page 27...
... It discusses algal strains and the attributes of those strains critical for biofuel production, the photo auto trophic methods for algae cultivation through open-pond and closed photobioreactor systems, the processes for collection and dewatering if necessary, and the processing of algal lipid, biomass, or secreted products into fuels. It provides the basic descriptions of the supply chain components used in later chapters and summarizes some critical process improve ments that could enhance the overall sustainability of algal biofuels.
From page 28...
... For example, species that store polysaccharides can be fermented to yield ethanol, and other biomass processing technologies, such as gasification, pyrolysis, and hydrothermal liquefaction, have shown great utility for the conversion of whole biomass into biofuels. The incipient algal biofuel industry is emerging and evolving from its early foundations in algae cultivation for fish feedstuff and for human nutraceuticals.
From page 29...
... Such reports have spurred investment in intensive research on algal biofuel production. However, such high productivity projections have yet to be obtained in largescale, long-term experiments.
From page 30...
... The potential to enhance the supply chain of algal biofuel through growth of mixed cultures merits additional research to determine the effects on desirable product yield and biomass accumulation (see section Cultivation in this chapter)
From page 31...
... . Many other criteria are important for selecting algal strains for commercial biofuel production, including variables that alter cost in the supply chain that are important for economic viability (for example, AQUAFUEL, 2009)
From page 32...
... Improvements in photosynthesis would lead directly to more prolific production of bio fuels, which would consequently reduce the land, water, nutrient, and energy inputs required. Improve ments to photosynthesis would directly improve the sustainability of algal biofuels.
From page 33...
... · Processability and extractability. This parameter includes factors that influence the ease of extracting algal oil or processing algal biomass to fuels, for example, cell volume, thickness and toughness of the cell wall, the presence of tough fibers (for example, cellulose and silica)
From page 34...
... The understanding of genetics, physiology, and metabolism at present is uneven across the spectrum of genera and species of algae that might have desirable features for algal biofuel production. Major hurdles include the need to develop genetic technologies for new species that have not been domesticated previously and that have desirable characteristics for large-scale cultivation.
From page 35...
... (2004) reviewed macroalgal species as candidates for genomic research and concluded that the red alga Porphyra yezoensis exhibits numerous attributes conducive to further analyses.
From page 36...
... . Transgenic strains could play an important role in biofuel production, and some companies are making major investments in these technologies (for example, the Exxon Mobil alliance with Synthetic Genomics, Inc.; Marler, 2011; Roessler, 2011)
From page 37...
... · Increases in culture density. · Net increase in photosynthetic efficiency.
From page 38...
... Strains that maintain elevated basal oil content might be produced by mutagenesis or genetic engineering. However, the pathways that regulate stress responses -- and key enzymes -- that initiate oil production are insufficiently understood at present.
From page 39...
... 2.1.3.3 Net Increase in Photosynthetic Efficiency A long-time goal, as old as the techniques of genetic engineering itself, is to improve photosynthetic efficiency by such alterations as reducing losses from photorespiration, increasing the substrate selectivity of ribulose-1,5-bisphosphate carboxylase oxygenase (Rubisco) , and enhancing photosystem stability and efficiency.
From page 40...
... take a toll on resources and could threaten the economic sustainability and the future potential of the algal biofuel industry (see section Cultivation in this chapter)
From page 41...
... . 2.2 CULTIVATION Evaluating the sustainability of algal cultivation systems for biofuel production requires examining the various material and energy inputs needed for the cultivation systems to maintain scalable productivity, maximize system robustness, and minimize costs (Figure 2-3)
From page 42...
... . In 2008, the global production of microalgal biomass was estimated to be about 9,000 dry tonnes per year (Benemann, 2008)
From page 43...
... (e) Phyco Biosciences (Edwards, 2010)
From page 44...
... For raceway ponds, a cell concentration of up to 1 gram dry weight per liter can be achieved, and productivities of 10 to 25 grams dry weight per m2 per day have been reported (Shen et al., 2009)
From page 45...
... Productivities of algal biomass in photobioreactors vary with the type of geometric configuration used and the algal species grown (Table 2-3)
From page 46...
... FIGURE 2-6 Triangular external air-lift tubular photobioreactors. SOURCES: Vunjak-Novakovic et al.
From page 47...
... TABLE 2-3 Microalgae Productivities in Photobioreactors Productivity Photobioreactor Volume (L) Microalgal Species (g DW/L/d)
From page 48...
... For example, a treatment for a 60-liter ACCORDION photobioreactor with 45° plate angle and liquid flow rate of 14 liters per minute resulted in algal productivity of 0.30 grams of dry weight per day that was statistically indistinguishable from that of a 1-liter shake-flask control. The ACCORDION photobioreactor is a modular design that can be scaled up by adding modules.
From page 49...
... . FIGURE 2-11 ACCORDION photobioreactor.
From page 50...
... . 2.2.4 Comparison of Open Systems and Closed Systems Table 2-4 compares open-pond systems and closed photobioreactor systems for photoautotrophic microalgae production.
From page 51...
... With the exception of Spirulina and Dunaliella salinas, which are cultivated in open systems under highly selective growing conditions, the lack of competitive advantages of many of the microalgal species being tested for biofuel production in open ponds and their susceptibil ity to culture crashes are concerns. Thus, the low volumetric productivity and susceptibility to contamination could constitute a substantial risk to the economic sustainability of openpond cultivation systems compared to closed photobioreactor systems.
From page 52...
... Note: Net Energy Ratio (NER) = total energy produced/total energy requirement.
From page 53...
... Other aspects of sustainability (for example, economics) would have to be considered in selecting the cultivation systems for algal biofuel production.
From page 54...
... depends on the growth of a particular cultivated algal species, then growing and maintaining that monoculture is critical. Citing Moheimani and Borowitzka (2006)
From page 55...
... . Contamination of open-pond algal cultures by other algal species is unavoidable because the growth conditions inevitably are suitable for the cultivated algal species and other local species.
From page 56...
... . Such strong species dynamics are undesirable because the oscillation of target strain abundance could create strong instability in algal biofuel production rates via changes in algal biomass, lipid content and molecular composition, lipid extractability, and lipid harvestability.
From page 57...
... . Incorporating the ecological advantages of diversity-related, resource-use dynamics into algal biomass production might provide a cost-effective way to improve yield and the robustness of algae cultivation for biofuel production (Stockenreiter et al., 2012)
From page 58...
... In practice, the separation of algae from the growth media and the separation of lipids from algal biomass in a timely manner is energy intensive. Reducing the energy required can be accomplished through improvements in the algal strains, through engineering improvements, and through favorable interplay of the two.
From page 59...
... High concentrations of metals present in residual algal biomass would limit its use as coproducts because of safety concerns. Organic flocculants may be susceptible to anaerobic digestion, removing them from the recycle stream.
From page 60...
... Biodiesel production is a technology that in most variants requires collection of the algal lipids for post processing. Extraction of oil from algal biomass has proven to be difficult.
From page 61...
... Many of the processing options are studied but not described in the literature, making a thorough analysis difficult. Three key parameters influence the algal biofuel supply chain (Figure 2-15)
From page 62...
... 2.3.5.1 Microalgae Harvested with Product Collected for Chemical Processing The harvest of lipid-producing microalgae cultivated for short duration and the chemical processing of algal oil into fuel represent the most commonly discussed method for production of algal biofuels. The expression level of the oil as a fraction of the total biomass determines what processing will be required.
From page 63...
... 2.3.5.3 Microalgae Harvested with Product Collected for Biological Processing Although fermentation of microalgal biomass has been studied (Harun, 2010) , it is not being developed at commercial scale at present.
From page 64...
... is needed to realize the potential of algal biofuels. However, the domestication of algae poses a special challenge as investigation into key biological and ecological aspects of algal biofuel production has lagged far behind the progress in feedstock processing design, system engineering, and life-cycle analyses over the past few decades.
From page 65...
... Identifying which ecophysiological parameters and genes best provide protection against grazers and pathogens at commercial-scale production levels also would be helpful. Improvements in algae cultivation methods and the physical processes used to harvest, dewater, and convert algal biomass into fuels are as important to the sustainable development of algal biofuels as improvements in algal strains.
From page 66...
... This upstream research and development will help inform and guide downstream engineer ing methods and designs for cultivation and processing systems that will enhance the entire algal biofuel production chain. Thus, concerted, complementary efforts in algal domestication and biofuel production will include: ·Development of strategies to improve carbon fixation rates and yields of algal crops at commercial production-level scale.
From page 67...
... Presentation to the NRC Committee on the Sustainable Development of Algal Biofuels on June 13. Atsumi, S., W
From page 68...
... Received by the NRC Committee on Sustainable Development of Algal Biofuels on July 25. Courchesne, N.M.D., A
From page 69...
... Available online at http://www.gevo.com/. Accessed June 17, 2012.
From page 70...
... Presentation to the NRC Committee on the Sustainable Development of Algal Biofuels on August 24. Heaven, S., J
From page 71...
... Presentation to the NRC Committee on Sustainable Development of Algal Biofuels on September 8. Martins, C.A., D
From page 72...
... Received by the NRC Committee on the Sustainable Development of Algal Biofuels on July 6.
From page 73...
... Presentation to the NRC Com mittee on Sustainable Development of Algal Biofuels on September 8. RSB (Roundtable on Sustainable Biofuels)
From page 74...
... 2010. Future prospects of microalgal biofuel production systems.
From page 75...
... 2010. An outlook on microalgal biofuels.


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