National Algal Biofuels Technology Roadmap, Department of Energy

[ This is the best document of the many I’ve read. If my post Dozens of reasons why the world doesn’t run on algal biofuels didn’t convince you that the scientists are NOT likely to come up with something, get into the weeds and read this 140 page paper about why it’s so hard to make biofuels out of algae. Extracts from this paper follow.. 

Alice Friedemann  author of “When Trucks Stop Running: Energy and the Future of Transportation”, 2015, Springer and “Crunch! Whole Grain Artisan Chips and Crackers”. Podcasts: Practical Prepping, KunstlerCast 253, KunstlerCast278, Peak Prosperity , XX2 report ]

USDOE. May 2010.  National Algal Biofuels Technology Roadmap. Workshop December 9-10, 2008 College Park, Maryland sponsored by the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy Office of the Biomass.   

The term algae can refer to microalgae, cyanobacteria (the so called “blue-green algae”), and macroalgae (or seaweed). Under certain conditions, some microalgae have the potential to accumulate significant amounts of lipids (more than 50% of their ash-free cell dry weight).

A scalable, sustainable and commercially viable system has yet to emerge.

Harvesting & Dewatering

Some processes for the conversion of algae to liquid transportation fuels require pre-processing steps such as harvesting and dewatering. Algal cultures are mainly grown in water and can require process steps to concentrate harvested algal biomass prior to extraction and conversion. These steps can be energy-intensive and can entail siting issues.

Focusing on biofuels as the end-product poses challenges due to the high volumes and relative low values associated with bulk commodities like gasoline and diesel fuels.

Conversion to fuels and products is predicated on a basic process decision point: 1) Conversion of whole algal biomass; 2) Extraction of algal metabolites; or 3) Processing of direct algal secretions. Conversion technology options include chemical, biochemical, and thermochemical processes, or a combination of these approaches.

Three major components can be extracted from algal biomass: lipids (including triglycerides and fatty acids), carbohydrates, and proteins. While lipids and carbohydrates are fuel precursors (e.g., gasoline, biodiesel and jet fuel), proteins can be used for co-products (e.g., animal/fish feeds). Most challenges in extraction are associated with the industrial scale up of integrated extraction systems. While many analytical techniques exist, optimizing extraction systems that consume less energy than contained in the algal products is a challenge due to the high energy needs associated with both handling and drying algal biomass as well as separating out desirable products.

As global petroleum supplies diminish, the United States is becoming increasingly dependent upon foreign sources of crude oil. The United States currently imports approximately two-thirds of its petroleum, 60% of which is used for producing transportation fuels. The rising energy demand in many rapidly developing countries around the world is beginning to create intense competition for the world’s dwindling petroleum reserves.

Advanced biofuels must demonstrate GHG emissions across their life cycle that are at least 50% less than GHG emissions produced by petroleum-based transportation fuels. Significant acreage and productivity will be required for biomass production to generate sufficient feedstock to meet the RFS mandates.

Harvesting is a process step that is highly energy- and capital-intensive.

Extraction of oil droplets from the cells and purification of the oil are also cost-intensive steps.

Low nighttime and winter temperatures limited productivity

One serious problem encountered was that the desired starting strain was often outgrown by faster reproducing, but lower oil producing, strains from the wild.

The costs of these resources can vary widely depending upon such factors as land leveling requirements, depth of aquifers, distance from CO2 point sources, and other issues. Detailed techno-economic analyses underlined the necessity for very low-cost culture systems, such as unlined open ponds (Benemann and Oswald, 1996). In addition, biological productivity was shown to have the single largest influence on fuel cost. Different cost analyses led to differing conclusions on fuel cost, but even with optimistic assumptions about CO2 credits and productivity improvements, estimated costs for unextracted algal oil were determined to range from $59 – $186 per barrel.

Also from 1968-1990, DOE sponsored the Marine Biomass Program, a research initiative to determine the technical and economic feasibility of macroalgae cultivation and conversion to fuels, particularly to substitute natural gas (SNG) via anaerobic digestion (Bird and Benson, 1987). Primary efforts were focused on open ocean culture of California kelp. Similar to the findings of the Aquatic Species Program, researchers concluded that algal-derived SNG would not be cost-competitive with fossil fuel gas.

Based on the information provided at the Workshop, it was determined that a great deal of RD&D is still necessary to reduce the level of risk and uncertainty associated with the algae-to-biofuels process so it can be commercialized.

Overcoming barriers to algal biofuels: technology goals process step R&D challenges

  • Algal Biology
  • Algal Cultivation
  • Harvesting and Dewatering
  • Extraction and Fractionation
  • Fuel Conversion
  • Co-products
  • Distribution and Utilization

The ability of an algal species to secrete fuel precursors may be attractive because it could reduce or skip the cell harvesting step. However, there may be practical problems to consider, such as, if the desired product is volatile, then collection of the atmosphere above the culture will be necessary to isolate it, which will necessitate the use of closed bioreactors. Also to be considered is whether secretion actually makes the product more readily available. For example, although there are algae known to secrete long-chain hydrocarbons (e.g., Botryococcus braunii), they are still associated with the cells in a lipid biofilm matrix, and thus are not free to form an organic hydrocarbon phase in solution. Even if sustainable secretion could be achieved, it is not clear what the effect of a lipid emulsion in an algal culture would be. For example, an abundance of exported lipids could unfavorably alter fluidics properties or provide a carbon source favoring growth of contaminants. Finally, secretion of either intermediates or products into the growth medium could make these compounds vulnerable to contaminating microbes for catabolism.

In some species, addition of supplemental carbon results in increased lipid accumulation, even under mixotrophic conditions where the substrate is not known to be transported into the cell. If the carbon source is utilized by the cell, growth in both light and dark periods is possible, and high cell densities can be achieved. A potential disadvantage of the addition of external carbon sources is the possibility of increased contamination by undesired microbes living off the carbon source.

Many algae are photosynthetic organisms capable of harvesting solar energy and converting CO2 and water to O2 and organic macromolecules such as carbohydrates and lipids. Under stress conditions such as high light or nutrient starvation, some microalgae accumulate lipids such as triacylglycerols (TAG) as their main carbon storage compounds. Certain microalgal species also naturally accumulate large amounts of TAG (30-60% of dry weight), and exhibit photosynthetic efficiency and lipid production at least an order of magnitude greater than terrestrial crop plants. Cyanobacteria and macroalgae, as a general rule, accumulate mostly carbohydrates, with lipid accumulation in macroalgae typically being less than 5% of total dry weight, although concentrations approaching 20% lipid have been reported in some species. Lipids and carbohydrates, along with biologically produced hydrogen and alcohols, are all potential biofuels or biofuel precursors.

When algae are cultivated photosynthetically, the efficiency of photosynthesis is a crucial determinate in their productivity, affecting growth rate, biomass production, and potentially, the percent of biomass that is the desired fuel precursor. Though theoretical biomass productivity values in the range of 100-200 g/ m2/day have been presented, there is no current consensus on the true maximum productivity of algae.

Carbon partitioning in algae is less understood and research on how algal cells control the flux and partitioning of photosynthetically fixed carbon into various groups of major macromolecules (i.e., carbohydrates, proteins, and lipids) is critically needed.

Regardless of the cultivation practices used to maximize light exposure, there remains limitations of algal photosystems regarding light utilization. The majority of light that falls on a photosynthetic algal culture at greater than laboratory scale is not utilized. In high cell density cultures, cells nearer to the light source tend to absorb all the incoming light, preventing it from reaching more distant cells.

Further, the majority of light that falls on algae isn’t used.  At high density, the algae closest to the light absorbs all of it, so the light doesn’t reach more distant cells. Even when exposed to high light, algal photosystems have built-in strategies to prevent the over-absorption of light energy, which can lead to oxidative damage. And a large majority of absorbed incident light is dissipated as heat and could be considered “wasted.” (DOE).

Other abundant polysaccharides, for example alginate found in many brown algae, are considered less suitable for ethanol fermentation because the redox balance favors formation of pyruvate as the end product

Another important consideration in algal strains is the composition and structure of the polysaccharide cell wall. These structures can be an important source of carbohydrates, but like those from plants, must typically be broken down into simpler sugars before conversion into biofuels.

Cell walls can also be a technical barrier, for example, when trying to access DNA for genetic manipulations, or efficiently extracting biofuel precursors from cells in mass culture. As mentioned above, many algal cell walls from different groupings are cellulose based.

The regulation of the synthesis of fatty acids and TAG in algae is relatively poorly understood. This lack of understanding may contribute to why the lipid yields obtained from algal mass culture efforts fall short of the high values (50 to 60%) observed in the laboratory.

It could be a challenge to extrapolate information learned about lipid biosynthesis and regulation in laboratory strains to production strains. Similarly, it will be difficult to use information regarding lipid biosynthesis in plants to develop hypotheses for strain improvement in algae. As an example, the annotation of genes involved in lipid metabolism in the green alga Chlamydomonas reinhardtii has revealed that algal lipid metabolism may be different from that in plants, as indicated by the presence and/or absence of certain pathways and by the size of the gene families that relate to various activities. Thus, de novo fatty acid and lipid synthesis should be studied in order to identify key genes, enzymes and new pathways, if any, involved in lipid metabolism in algae.

Oxidative Stress and Storage Lipids

Under environmental stress conditions (such as nutrient starvation), some algal cells stop division and accumulate TAG as the main carbon storage compound.

Under high light stress, excess electrons that accumulate in the photosynthetic electron transport chain induce over-production of reactive oxygen species, which may in turn cause inhibition of photosynthesis and damage to membrane lipids, proteins, and other macromolecules.

Four biological challenges limiting biohydrogen production in algae have been identified: (a) the O2 sensitivity of hydrogenases, (b) competition for photosynthetic reductant at the level of ferredoxin, (c) regulatory issues associated with the over production of ATP, and (d) inefficiencies in the utilization of solar light energy

Photobioreactor issues

s have suffered from problems of scalability, especially in terms of mixing and gas exchange (both CO2 and O2). Though photobioreactors lose much less water than open ponds due to evaporation, they do not receive the benefit of evaporative cooling and so temperature must be carefully maintained.

Photobioreactors are unlikely to be sterilizable and may require periodic cleaning due to biofilm formation,

In heterotrophic cultivation, algae are grown without light and are fed a carbon source, such as sugars, to generate new biomass. This approach takes advantage of mature industrial fermentation technology, already widely used to produce a variety of products at large scale. Heterotrophic cultivation presents a different set of advantages and challenges compared with photoautotrophic methods. Optimal conditions for production and contamination prevention are often easier to maintain, and there is the potential to utilize inexpensive lignocellulosic sugars for algal growth. Heterotrophic cultivation also achieves high biomass concentrations that reduces the extent and cost of the infrastructure required to grow the algae.

Heterotrophic cultivation is expensive and is likely to compete with other biofuel technologies for feedstock  and availability of suitable feedstocks such as lignocellulosic sugars. Because these systems rely on primary productivity from other sources, they could compete for feedstocks with other biofuel technologies.

It should be noted that, especially in open systems, monocultures are inherently difficult to maintain and require significant investment in methods for detection and management of competitors, predators, and pathogens.

Scale-Up Challenges

The inherent difficulties of scaling up from laboratory to commercial operations present both technical and economic barriers to success.

Systems for large-scale production of biofuels from algae must be developed on scales that are orders of magnitude larger than all current worldwide algal culturing facilities combined. In certain cultivation systems, it will be challenging to maintain algal monocultures on this scale; it may become necessary to understand and manage the communities that will be present. Some members of the community will be of positive value, such as those that can scavenge and recycle nutrients or synthesize essential vitamins. Others will compete for shared resources, and still others will cause culture disruption. One of the more worrisome components of large-scale algae cultivation is the fact that algal predators and pathogens are both pervasive and little understood.

Fungal and viral pathogens are common, although current understanding of their diversity and host range is very limited. Wilson et al., (2009) point out that though there may be between 40,000 and several million phytoplankton species, there have only been 150 formal descriptions of phycoviruses. Chytrid fungi have also been known to cause the collapse of industrial algal cultivation ponds, but very little is known about host specificity and even less is known about host resistance mechanisms. Important questions concerning this threat to large-scale algal cultures include: Nutrient sources and water treatment/recycling are technically trivial and inexpensive at small scales and yet represent major technical and economic problems at commercial scales. Tapping into existing agricultural or municipal waste streams will lower nutrient costs but could introduce unacceptable pathogens, chemical compounds, or heavy metals into the biomass stream

Are agricultural or municipal waste streams—a potentially significant source of nutrients for algal cultivation—actually a liability because of significant reservoirs of algal pathogens and predators?

To what extent will local “weedy” algae invade and take over bioreactors and open ponds?

Continuous monitoring will be necessary in open systems since seasonal variation in competitors, predators, and pathogens is expected.

From a productivity standpoint, supplemental CO2 has long been known to increase algal growth rate, and this area is receiving new attention from the search for renewable, sustainable fuels. New approaches are split between using algae to scrub CO2 from emission gasses and a focus on better understanding the mechanisms of biological CO2 concentration from ambient air siting requirements for efficient algal cultivation may rarely coincide with high-volume point sources of CO2.

Nutrient Sources, Sustainability, and Management

Nutrient supplies for algal cultivation have a sizeable impact on cost, sustainability, and production siting. The primary focus is the major nutrients – nitrogen, phosphorous, iron, and silicon (in the case of diatoms). Nitrogen, phosphorous, and iron additions represent a significant operating cost, accounting for 6-8 cents per gallon of algal fuel in 1987 U.S. dollars. This calculation takes into account a 50% rate of nutrient recycle. Phosphorous appears to be an especially important issue as there have been calculations that the world’s supply of phosphate is in danger of running out (Abelson, 1999).

Because synthetic nitrogen fixation processes utilize fossil fuels (particularly natural gas), costs are tied to fossil fuel prices, and the very large required energy inputs should be accounted for in life cycle analyses.

The final fuel product from algal oil contains no nitrogen, phosphorous, or iron; these nutrients end up primarily in the spent algal biomass. From a sustainability perspective, nutrient recycle may prove to be more valuable than using the spent biomass for products such as animal feed. If the biomass residues are, for example, treated by anaerobic digestion to produce biogas, then most of the nutrients will remain in the digestor sludge and can be returned to the growth system (Benemann and Oswald, 1996). The processes through which these nutrients are re-mobilized and made available for algal growth are not well understood.

Energy to carefully control nutrient levels. Limitation of a key nutrient will have serious impacts on biomass productivity, too much of a nutrient may prove toxic. Unused nutrients pose a problem for waste water discharge. Although economics dictate that the bulk of water derived from the harvesting step must be returned to the cultivation system (where remaining nutrients can feed subsequent algal growth), a certain amount of “blowdown” water must be removed to prevent salt buildup. If this blowdown water contains substantial nitrogen and phosphorous, disposal will become a problem due to concerns of eutrophication of surface waters.

Finding inexpensive sources of nutrients will be important

A potential problem with this approach however is the impact on facility siting. Wastewater treatment facilities, for example, tend to be near metropolitan areas with high land prices and limited land availability, and it is not practical to transport wastewater over long distances.

One of the main advantages of using algae for biofuels production is their ability to thrive in water unsuitable for land crops, such as saline water from aquifers and seawater. At the same time, however, water management poses some of the largest issues for algal biofuels. If not addressed adequately, water can easily become a “show-stopper,” either because of real economic or sustainability problems

With large cultivation systems, water demands will be enormous. For example, a hypothetical 1 hectare (ha), 20 cm deep open pond will require 530,000 gallons to fill. In desert areas, evaporative losses can exceed 0.5 cm per day, which is a loss of 13,000 gallons per day from the 1 ha pond. Though the water used to initially fill the pond can be saline, brackish, produced water from oil wells, municipal wastewater, or other low quality water stream, the water being lost to evaporation is fresh water, and continually making up the volume with low-quality water will concentrate salts, toxins, and other materials in the culture. This can be prevented by adding fresh water—a costly and often unsustainable option—or by disposing of a portion of the pond volume each day as “blowdown.” The amount of blowdown required for salinity control is dependent upon the acceptable salt level in the culture and the salinity of the replacement water.

live cells could adversely affect biodiversity of neighboring ecosystems or result in the dissemination of genetically modified organisms. Sterilization of blowdown water, however, would be a very costly and energy-intensive proposition.

An advantage of closed photobioreactors over open ponds is a reduced rate of evaporation. The added cost of such systems must be balanced against the cost savings and sustainability analysis for water usage for a given location. Note however that evaporation plays a critical role in temperature maintenance under hot conditions through evaporative cooling. Closed systems that spray water on the surfaces or employ cooling towers to keep cultures cool will lose some if not possibly all of the water savings of such systems under these conditions.

Water recycling is essential, but the amount that can be recycled depends on the algal strain, water, process, and location. Some actively growing algal cultures can double their biomass on a daily basis, meaning that half the culture volume must be processed daily. This is an enormous amount of water (260,000 gallons per day in the 1 ha example above). To contain costs, it is desirable to recycle most of that water back to the culture. However, accumulated salts, chemical flocculants used in harvesting, or biological inhibitors produced by the strains themselves could impair growth if recycled to the culture. Furthermore, moving around such large volumes of water is very energy-intensive and can impose a significant cost.

Treatment may be essential for water entering and exiting the process. Incoming water (surface water, groundwater, wastewater, or seawater) may be suitable as is, or may require decontamination, disinfection, or other remediation before use. The blowdown water exiting the process will also most likely require treatment. Disposal of the spent water, which could contain salts, residual nitrogen and phosphorous fertilizer, accumulated toxics, heavy metals (e.g., from flue gas), flocculants, and residual live algal cells, could pose a serious problem, and treatment (e.g., desalination, activated charcoal filtration, etc.) of the recycled stream could be cost-prohibitive.

Understanding the long-term effects of drawing down saline aquifers, including the geology of these aquifers and associations with freshwater systems

Downstream Processing: Harvesting and Dewatering

Conversion of algae in ponds, bioreactors, and off-shore systems to liquid transportation fuels requires processing steps such as harvesting, dewatering, and extraction of fuel precursors (e.g., lipids and carbohydrates). These energy-intensive processes are only now being recognized as critically important. Cultures with as low as 0.02 – 0.07% algae (~ 1 gm algae/5000 gm water) must be concentrated to slurries containing at least 1% algae given the known processing strategies. The final slurry concentration will depend on the extraction methods employed and will impact the required energy input. As the desired percentage of dry biomass increases, energy costs climb steeply. Final slurry concentration also impacts plant location because of transportation, water quality, and recycling issues. A feasible algae-to-fuel strategy must, therefore, consider the energy costs and siting issues associated with harvesting and dewatering.

Harvesting Flocculation and Sedimentation

Microalgae and cyanobacteria remain in suspension in well-managed high growth rate cultures due to their small size (~1 to 30 µm). This facilitates the transport of cells to the photoactive zone through pond or bioreactor circulation. Their small sizes, however, make harvesting more difficult. Flocculation leading to sedimentation occurs naturally in many older cultures. In managed cultures, some form of forced flocculation usually involving chemical additives, is required to promote sedimentation at harvest.

Chemical flocculant recovery techniques are required to minimize cost and control water effluent purity. • The effect of residual flocculant or pH manipulation in recycled water on culture health and stability and lipid production must be understood and controlled. Likewise, the presence of flocculant in further downstream extraction and fuel conversion processes must be understood and controlled. • The environmental impact of flocculant or pH manipulation in released water effluent, and fuel conversion and use must be considered. • Bioflocculation, electroflocculation, and electrocoagulation must be scaled-up with cost and energy analysis.


Solid/liquid filtration technologies are well studied, and filtration without prior flocculation can be used to harvest and dewater algae. Microalgae and cyanobacteria present unique filtration challenges because most strains considered for energy feedstocks have cell diameters less than 10 µm. Filtration is conceptually simple but potentially very expensive.

Centrifugation is widely used in industrial suspension separations and has been investigated in algal harvesting. The efficiency is dependent on the selected species (as related to size). Centrifugation technologies must consider large initial capital equipment investments, operating costs, and high throughput processing of large quantities of water and algae. The current level of centrifugation technology makes this approach cost-prohibitive for most of the envisioned large-scale algae biorefineries. Significant cost and energy savings must be realized before any widespread implementation of this approach can be carried out.

Drying is required to achieve high biomass concentrations. Because drying generally requires heat, methane drum dryers and other oven-type dryers have been used. However, the costs climb steeply with incremental temperature and/or time increases. Air-drying is possible in low-humidity climates, but will require extra space and considerable time.

Seaweeds immediately following harvest can have stones, sand, litter, adhering epifauna and other forms of debris that should be removed before further processing. Screening for debris is considered mandatory, with the degree of screening dependent on the mode of culture and end-use.

A critical gap is the energy requirements of these processes are not only largely unknown but unbounded. This has important implications for plant design to answer simple questions like “What percentage of the total plant energy requirements or what percentage of that made available by algae must be directed toward harvesting and dewatering?”. Ultimately, a unit operations analysis of energy input for a range of dry weight content based on extraction needs is required with consideration of capital equipment investments, operations, maintenance, and depreciation. The cost of harvesting and dewatering will depend on the final algae concentration needed for the chosen extraction method. This will likely be a significant fraction of the total energy cost of any algae-to-fuel process and a significant fraction of the total amount of energy available from algae. A quick and preliminary energy balance example shown below provides some food for thought regarding harvesting and dewatering technologies.

Preliminary Look at Energy Balance

The energy content of most algae cells is of the order of 5 watt-hours/gram if the energy content of lipids, carbohydrates, and proteins and the typical percentage of each in algae are considered. It is possible to estimate the energy requirements in watthours/gram of algae for harvesting, de-watering, and drying as a function of the volume percentage of algae in harvested biomass. The energy requirements for flocculation and sedimentation and the belt filter press are expected to be minimal. However, based on the latent heat of vaporization of water at 0.54 watt-hours/gram, energy balance can become an issue in systems that propose to take algal biomass and concentrate / dry it to enable downstream processing and extraction because of the high volumes of water that must be evaporated away. In spite of gaps in data precluding more detailed analyses, algal biofuel production schemes at scale will likely need to implement innovative technologies and integrated systems in order to overcome this challenge.

Extraction of Products from Algae

While relatively limited volumes of bioproducts are currently produced from algal feedstocks, algal biomass suffers from a lack of well-defined and demonstrated industrial-scale methods for extracting and separating of oils and lipids required for enabling biofuel production. Existing extraction techniques are mainly suitable for analytical- and laboratory-scale procedures, or for the recovery/removal of high-value products. To produce algal biofuels as competitive bulk commodity, extraction techniques employed must be efficient and effective.

Extraction depends on identifying the particular biological component for extraction, which is dependent on the algal species and growth status. Additionally, different harvest process operations (operations could affect extraction processes, as well as the fuel conversion process. While many terrestrial feedstocks can be removed from their environment at total solids >40%, microalgae and cyanobacteria may be cultivated as single cells suspended in water at concentrations below 1% solids.

A shortfall of relevant information on efficient extraction of lipids and oils at larger-scale is limiting the algal-based biofuel development. Laboratory-scale comparisons of extraction of lipids from microalgae and macroalgae have been carried out, but these techniques often rely on freeze dried, pulverized biomass. While considerable knowledge exists for the separation of plant biomass lipid extracts and preparation for conversion to biodiesel, little is known about the scale-up separation challenges for extracted algal lipids.

Current Practices for Lipid Extraction

The basis for lipid extraction from algal biomass is largely in the realm of laboratory-scale processes that serve analytical rather than biofuel production goals.

Mechanical Disruption (i.e., Cell Rupture) Algal biofuel schemes that rely on the accumulation of intra-cellular lipids need an extracting solvent that can (1) penetrate through the matrix enclosing the lipid material, (2) physically contact the lipid material, and (3) solvate the lipid. As such the development of any extraction process must also account for the fact that the tissue structure and cell walls may present formidable barriers to solvent access. This generally requires that the native structure of the biomass must be disrupted prior to extraction. Effective mechanical disruption can help offset the need to use elevated temperature and pressure processes that force the solvent into contact with desired biopolymers. Different methods can be used to disrupt the cell membrane prior to the application of the extraction solvents. Mechanical disruption can include cell homogenizers, bead mills (or bead-beating), ultrasounds, and autoclaving (Mata et al., 2010). Non-mechanical methods include process such as freezing, application of organic solvents, osmotic shock, and acid, base, and enzyme reactions (Mata et al., 2010). The use of microwaves to disrupt cells and increase efficiencies of vegetable lipid and oil extraction is a promising development (Cravotto et al., 2008; Virot et al., 2008), though applications outside of analytical labs are unclear.

Organic Co-solvent Mixtures. The concept of like dissolves like is the basis behind the earliest and well-known co-solvent extraction procedure. After the extraction reaction is complete, water (which is not miscible with chloroform) is added to the co-solvent mixture until a two-phase system develops in which water and chloroform separate into two immiscible layers. The lipids mainly separate to the chloroform layer and can then be recovered for analysis. Chloroform will extract more than just the saphonifiable lipids (i.e., the unsaponifiable lipids such as pigments, lipoproteins, and other lipid and non-lipid contaminants). Consequently, other combinations of co-solvents have been proposed for the extraction of lipids: hexane/isopropanol for tissue; dimethyl sulfoxide/petroleum ether for yeast; hexane/ethanol for microalgae; and hexane/ isopropanol for microalgae. The hexane system has been promoted because hexane and alcohol will readily separate into two separate phases when water is added, thereby improving downstream separations.

To avoid the use of elevated temperature and pressure to push the solvent into contact with the analyte (at the cost of a very high input of energy), disruption of the cell membrane may be necessary.

All the preceding co-solvent systems, however, remain largely bench-scale methods that are difficult to scale up to industrial processes due to the actual solvent toxicity and the low carrying capacity of the solvents (i.e., it is only efficient on biomass samples containing less than 2% w/w lipids).


Presence of Water Associated with the Biomass

The extraction process is affected by the choice of upstream and downstream unit operations and vice versa. The presence of water can cause problems at both ends at larger scales. When present in the bulk solution, water can either promote the formation of emulsions in the presence of ruptured cells or participate in side reactions. At the cellular level, intracellular water can prove to be a barrier between the solvent and the solute.

In this context, the issue of solvent access to the material being extracted is as important as the miscibility of the analyte in the solvent. This is a principal motivation behind the application of extraction techniques at elevated temperatures and pressures.

Separation of Desired Extracts from Solvent Stream Extraction processes can yield undesirable components, such as chlorophyll and non-transesterifiable lipids. Very little information is available on this critical step that is necessary before converting the algal biocrude into finished fuels and products.

Energy Consumption and Water Recycle

For sustainable biofuels production, the following benchmark can be considered: the extraction process per day should consume no more than 10% of the total energy load, as Btu, produced per day.

Attractive targets for this effort, however, are the liquid transportation fuels of gasoline, diesel, and jet fuel. These fuel classes were selected as the best-value targets because 1) they are the primary products that are currently created from imported crude oil for the bulk of the transportation sector, 2) they have the potential to be more compatible than other biomass-based fuels with the existing fuel-distribution infrastructure in the U.S., and 3) adequate specifications for these fuels already exist.

All of the petroleum feedstock that enters a conventional petroleum refinery must leave as marketable products, and this conservation law must also hold true for the algae biorefineries of the future if they are to achieve significant market penetration.

Gasification of the algal biomass may provide an extremely flexible way to produce different liquid fuels, primarily through Fischer-Tropsch Synthesis (FTS) or mixed alcohol synthesis of the resulting syngas. The synthesis of mixed alcohols using gasification of lignocellulose is relatively mature (Phillips, 2007; Yung et al., 2009), and it is reasonable to expect that once water content is adjusted for, the gasification of algae to these biofuels would be comparatively straightforward. FTS is also a relatively mature technology where the syngas components (CO, CO2, H2O, H2, and impurities) are cleaned and upgraded to usable liquid fuels through a water-gas shift and CO hydrogenation

The key roadblocks to using FTS for algae are thought to be similar to those for coal, with the exception of any upstream process steps that may be a source of contaminants which will need to be removed prior to reaching the FT catalyst. FTS tends to require production at a very large scale to make the process efficient overall. However, the most significant problem with FTS is the cost of clean-up and tar reforming. Tars have high molecular weight and can develop during the gasification process. The tars cause coking of the synthesis catalyst and any other catalysts used in the syngas cleanup process and must be removed.

Supercritical processing is a recent addition to the portfolio of techniques capable of simultaneously extracting and converting oils into biofuels. Supercritical fluid extraction of algal oil is far more efficient than traditional solvent separation methods, and this technique has been demonstrated to be extremely powerful in the extraction of other components within algae. This supercritical transesterification approach can also be applied for algal oil extracts. Supercritical fluids are selective, thus providing high purity and product concentrations. Additionally, there are no organic solvent residues in the extract or spent biomass. Extraction is efficient at modest operating temperatures, for example, at less than 50°C, ensuring maximum product stability and quality. Additionally, supercritical fluids can be used on whole algae without dewatering, thereby increasing the efficiency of the process.

The clear immediate priority, however, is to demonstrate that these supercritical process technologies can be applied in the processing of algae, either whole or its oil extract, with similar yields and efficiencies at a level that can be scaled to commercial production. In particular, it must be demonstrated that this process can tolerate the complex compositions that are found with raw, unprocessed algae and that there is no negative impact due to the presence of other small metabolites.

Anaerobic Digestion of Whole Algae

The production of biogas from the anaerobic digestion of macroalgae, such as Laminaria hyperbore and Laminaria saccharina, is an interesting mode of gaseous biofuel production, and one that receives scant attention in the United States. The use of this conversion technology eliminates several of the key obstacles that are responsible for the current high costs associated with algal biofuels, including drying, extraction, and fuel conversion, and as such may be a cost-effective methodology.

It is estimated that industrial-scale ultrasonic devices can allow for the processing of several thousand barrels per day, but will require further innovation to reach production levels sufficient for massive and scalable biofuel production.

Biochemical (Enzymatic) Conversion

Chemical processes give high conversion of triacylglycerols to their corresponding esters but have drawbacks such as being energy-intensive, difficulty in removing the glycerol, and require removal of alkaline catalyst from the product and treatment of alkaline wastewater.

Although enzymatic approaches have become increasingly attractive, they have not been demonstrated at large scale mainly due to the relatively high price of lipase and its short operational life caused by the negative effects of excessive methanol and co-product glycerol. These factors must be addressed before a commercially viable biochemical conversion process can be realized.

Other important issues that need further exploration are developing enzymes that can lyse the algal cell walls; optimizing specific enzyme activity to function using heterogeneous feedstocks; defining necessary enzyme reactions (cell wall deconstruction and autolysin); converting carbohydrates into sugars; catalyzing nucleic acid hydrolysis; and converting lipids into a suitable diesel surrogate.

Catalytic Cracking

The transesterification catalysts presented above are very strong and relatively mature in the field of biofuel production. Although very effective and relatively economical, these catalysts still require purification and removal from the product stream, which increases the overall costs.

All of the processes that take place in a modern petroleum refinery can be divided into two categories, separation and modification of the components in crude oil to yield an assortment of end products. The fuel products are a mixture of components that vary based on input stream and process steps, and they are better defined by their performance specifications than by the sum of specific molecules. As noted in chapter 8, gasoline, jet fuel, and diesel must meet a multitude of performance specifications that include volatility, initial and final boiling point, autoignition characteristics (as measured by octane number or cetane number), flash point, and cloud point. Although the predominant feedstock for the industry is crude oil, the oil industry has begun to cast a wider net and has spent a great deal of resources developing additional inputs such as oil shale and tar sands. It is worth noting that the petroleum industry began by developing a replacement for whale oil, and now it is apparent that it is beginning to return to biological feedstocks to keep the pipelines full.

A major characteristic of petroleum-derived fuels is high energy content which is a function of a near-zero oxygen content. Typical biological molecules have very high oxygen contents as compared to crude oil. Conversion of biological feedstocks to renewable fuels, therefore, is largely a process of eliminating oxygen and maximizing the final energy content. From a refinery’s perspective, the ideal conversion process would make use of those operations already in place: thermal or catalytic cracking, catalytic hydrocracking and hydrotreating, and catalytic structural isomerization. In this way, the feedstock is considered fungible with petroleum and can be used for the production of typical fuels without disruptive changes in processes or infrastructure.

Various refiners and catalyst developers have already begun to explore the conversion of vegetable oils and waste animal fats into renewable fuels. Fatty acids are well suited to conversion to diesel and jet fuel with few processing steps. This process has already provided the renewable jet fuel blends (derived from oils obtained from jatropha and algae) used in recent commercial jet test flights. On the other hand, straight chain alkanes are poor starting materials for gasoline because they provide low octane numbers, demanding additional isomerization steps or high octane blendstocks. Algal lipids can be processed by hydrothermal treatment (basically, a chemical reductive process). Referred to as hydrotreating, this process will convert the carboxylic acid moiety to a mixture of water, carbon dioxide, or carbon monoxide, and reduce double bonds to yield hydrocarbons. Glycerin can be converted to propane which can be used for liquefied petroleum gas. The primary barrier to utilizing algae oils to make renewable fuels is catalyst development. Catalysts in current use have been optimized for existing petroleum feedstocks and have the appropriate specificity and activity to carry out the expected reactions in a cost-effective manner. It will be desirable to tune catalysts such that the attack on the oxygen-bearing carbon atoms will minimize the amount of CO and CO2 lost, as well as the amount of H2 used. Refinery catalysts have also been developed to function within a certain range of chemical components found within the petroleum stream (e.g., metals, and sulfur and nitrogen heteroatoms) without becoming poisoned. Crude algal oil may contain high levels of phosphorous from phospholipids, nitrogen from extracted proteins, and metals (especially magnesium) from chlorophyll. It will be necessary to optimize both the level of purification of algal lipid as well as the tolerance of the catalyst for the contaminants to arrive at the most cost-effective process.


The “guiding truth” is that if biofuel production is considered to be the primary goal, the generation of other co-products must be correspondingly low since their generation will inevitably compete for carbon, reductant, and energy from photosynthesis. Indeed, the concept of a biorefinery for utilization of every component of the biomass raw material must be considered as a means to enhance the economics of the process.

The market for microalgal animal feeds, estimated to be about 300 million US$, is quickly growing. However, it is important to note that since the flue gas from coal-fired power plants that will be used to supply carbon dioxide to the cultures will contain significant amounts of lead, arsenic, cadmium and other toxic elements, the resulting non-oil algal biomass is very likely to be unsuitable for use as an animal feed, particularly given the fact that algae are known to be effective at metal absorption.

Distribution and Utilization

Distribution and utilization are challenges associated with virtually all biofuels. Although the biofuel product(s) from algal biomass would ideally be energy-dense and completely compatible with the existing liquid transportation fuel infrastructure, few studies exist that address outstanding issues of storing, transporting, pipelining, blending, combusting, and dispensing algal biomass, fuels intermediates, biofuels, and bioproducts.

Being intermediate steps in the supply chain, distribution and utilization need to be discussed in the context of earlier decision points, such as cultivation and harvesting. In turn, these logistics through end-use issues influence siting, scalability, and the ultimate economics and operations of an integrated algal biofuels refinery. As a variety of fuel products – ethanol, biodiesel, higher alcohols, pyrolysis oil, syngas, and hydroreformed biofuels – are being considered from algal biomass resources, the specific distribution and utilization challenges associated with each of these possible opportunities is discussed.


Lowering costs associated with the delivery of raw biomass, fuel intermediates, and final fuels from the feedstock production center to the ultimate consumer are common goals for all biofuels. In all cases, biofuels infrastructure costs can be lowered in four ways: • Minimizing transport distance between process units; • Maximizing the substrate energy-density and stability; • Maximizing compatibility with existing infrastructure (e.g. storage tanks, high capacity; delivery vehicles, pipelines, dispensing equipment, and end-use vehicles);

Distribution is complicated by the fact that several different fuels from algae are being considered. Ethanol, biodiesel, biogas, renewable gasoline, diesel, and jet fuels are all possible products from algal biomass. Each of these different fuels has different implications for distributions. Some of these fuels appear to be more compatible with the existing petroleum infrastructure. Specifically, jet-fuel blends from a variety of oil-rich feedstocks, including algae, have been shown to be compatible for use in select demonstration flights. It is also anticipated that gasoline and diesel range fuels from algae will not require significant distribution system modifications during or after processing in the refinery.

First, the stability of the algal biomass under different production, storage, and transport scenarios is poorly characterized, with some evidence suggesting that natural bacterial communities increase the rate of algae decomposition. In the context of a variety of culturing and harvesting conditions differing in salinity, pH and dewatering levels, it is difficult to predict how these factors will influence biomass storage and transport, and the quality of the final fuel product.

Second, an issue that impacts oleaginous microalgae feedstocks is that the transport and storage mechanisms of algal lipid intermediates have not yet been established. It is conceivable that these “bio-crudes” will be compatible with current pipeline and tanker systems. However, it is known that the presence of unsaturated fatty acids causes auto-oxidation of oils, which carries implications for the producers of algae and selection for ideal lipid compositions. It is also known that temperature and storage material have important implications for biodiesel stability. Thus, materials and temperature considerations similar to plant lipids may be possibly taken into account for the storage of algae lipids.

Third, depending on whether it will be dewatered/ densified biomass and/or fuel intermediates that are to be transported to the refinery, conforming to existing standards (e.g., container dimensions, hazardous materials and associated human health impacts, and corrosivity) for trucks, rails, and barges is critical to minimizing infrastructure impacts. The optimal transport method(s) should be analyzed and optimized for energy-inputs and costs, within the context of where the algae production and biorefinery facilities are to be sited. These have been challenging issues for lignocellulosic feedstocks and can be expected to influence the economics of algal biofuels as well.

Considerable infrastructure investments need to be made for higher ethanol blends to become even more attractive and widespread. One issue is that ethanol is not considered a fungible fuel; it can pick up excessive water associated with petroleum products in the pipeline and during storage, which causes a phase separation when blended with gasoline. One possible way to address this is to build dedicated ethanol pipelines; however, at an estimated cost of $1 million/mile of pipeline, this approach is not generally considered to be economically viable. Another possibility is to distribute ethanol blends by rail, barge, and/or trucks. Trucking is currently the primary mode to transport ethanol blends at an estimated rate of $0.15/ton/kilometer. This amount is a static number for low levels of ethanol in the blends (5% to 15%); as the ethanol content in the blend increases, the transport costs will also increase due to the lower energy density of the fuel.

The last remaining hurdle to creating a marketable new fuel after it has been successfully delivered to the refueling location is that the fuel must meet regulatory and customer requirements. Such a fuel is said to be “fit for purpose.” Many physical and chemical properties are important in determining whether a fuel is fit for purpose; some of these are energy density, oxidative and biological stability, lubricity, cold-weather performance, elastomer compatibility, corrosivity, emissions (regulated and unregulated), viscosity, distillation curve, ignition quality, flash point, low-temperature heat release, metal content, odor/taste thresholds, water tolerance, specific heat, latent heat, toxicity, environmental fate, and sulfur and phosphorus content. Petroleum refiners have shown remarkable flexibility in producing fit-for-purpose fuels from feedstocks ranging from light crude to heavy crude, oil shales, tar sands, gasified coal, and chicken fat, and are thus key stakeholders in reducing the uncertainty about the suitability of algal lipids and carbohydrates as a feedstock for fuel production.

Failure of a fuel to comply with even one of the many allowable property ranges within the prevailing specifications can lead to severe problems in the field. Some notable examples included: elastomer compatibility issues that led to fuel-system leaks when blending of ethanol with gasoline was initiated; cold weather performance problems that crippled fleets when blending biodiesel with diesel was initiated in Minnesota in the winter;

Algal Blendstocks to Replace Middle-Distillate Petroleum Products

Petroleum “middle distillates” are typically used to create diesel and jet fuels. The primary algae-derived blendstocks that are suitable for use in this product range are biodiesel (oxygenated molecules) and renewable diesel (hydrocarbon molecules). The known and anticipated end-use problem areas for each are briefly surveyed below.

Oxygenates: Biodiesel

Biodiesel is defined as “mono-alkyl esters of long chain fatty acids derived from vegetable oils or animal fats” (ASTM International, 2009b). Biodiesel has been demonstrated to be a viable fuel for compression-ignition engines, both when used as a blend with petroleum-derived diesel and when used in its neat form (i.e., 100% esters).

The primary end-use issues for plant-derived biodiesel are: lower oxidative stability than petroleum diesel, higher emissions of nitrogen oxides (NOx), and cold-weather performance problems. The oxidative-stability and cold-weather performance issues of biodiesel preclude it from use as a jet fuel. The anticipated issues with algae-derived biodiesel are similar, with added potential difficulties including: 1) contamination of the esters with chlorophyll, metals, toxins, or catalyst poisons (e.g., sulfur and phosphorus) from the algal biomass and/or growth medium; 2) undesired performance effects due to different chemical compositions; and 3) end-product variability.

Hydrocarbons: Renewable Diesel and Synthetic Paraffinic Kerosene

The hydrocarbon analog to biodiesel is renewable diesel, which is a non-oxygenated, paraffinic fuel produced by hydrotreating bio-derived fats or oils in a refinery. Algal lipids can be used to produce renewable diesel or synthetic paraffinic kerosene (SPK), a blendstock for jet fuel. These blendstocks do not have oxidative-stability problems as severe as those of biodiesel, and renewable diesel actually tends to decrease engine out NOx emissions. Nevertheless, unless they are heavily isomerized (i.e., transformed from straight- to branchedchain paraffins), renewable diesel and SPK will have cold-weather performance problems comparable to those experienced with biodiesel. Also, as was the case with algal biodiesel, contaminants and end-product variability are concerns.

Resources and Siting

The development and scale-up of algal biofuels production, as with any biomass-based technology and industry, needs to be analyzed from a site location, as well as from a resource availability and use perspective. Critical requirements—such as suitable land and climate, sustainable water resources, supplemental CO2 supply, and other nutrients—must be appropriately aligned in terms of their geo-location, characteristics, availability, and affordability. To achieve success regarding both technical and economic performance without adverse environmental impacts, the siting and resource factors must also be appropriately matched to the required growth conditions of the particular algae species being cultivated and the engineered growth systems being developed and deployed. The sustainability and environmental impacts of national algae production capacity build-up and operation over time will be important complementary aspects of the siting and resources issues that will also need careful consideration and analysis

Integration with wastewater treatment can play an additional important role in the sourcing of nutrients from both the input wastewater and from possible nutrient recycling from residual algal biomass.

Exhibit 9.2 provides a simple high-level overview of the major resource and environmental parameters that pertain to the algae biofuels production inputs of climate, water, CO2, energy, nutrients, and land. These parameters are of greatest importance to siting, facilities design, production efficiency, and costs. For each parameter, a variety of conditions may be more or less cost-effective for the siting and operation of algal biomass production. Additional resources include materials, capital, labor, and other inputs associated with facilities infrastructure and conducting operations and maintenance.

Heterotrophic production can be characterized as more of an industrial operation with a significant upstream logistics trail associated with the sourcing of the needed biomass derived input feedstocks, whereas photoautotrophic production, in terms of cultivation and harvesting, is more akin to agriculture and serves as the point of origin for the biomass feedstock supply for the downstream value chain. Resource issues for the heterotrophic approach are more largely associated with the upstream supply of organic carbon feedstock derived from commodity crops, selected organic carbon-rich waste streams, and lignocellulosic biomass, thereby sharing many of the same feedstock supply issues with first- and second-generation biofuels. Use of sugars from cane, beets, other sugar crops, and from the hydrolysis of starch grain crops can, after sufficient scale-up of production and demand, lead to the problem of linking biofuel production with competing food and feed markets.

Severe weather will affect water supply and water quality in open systems.

Equally important for photoautotrophic microalgae growth with both open and closed cultivation systems is the availability of abundant sunlight. A significant portion of the United States is suitable for algae production from the standpoint of having adequate solar radiation (with parts of Hawaii, California, Arizona, New Mexico, Texas, and Florida being most promising). The more northern latitude states, including Minnesota, Wisconsin, Michigan, and the New England states, would have very low productivity in the winter months. Growth of algae is technically feasible in many parts of the United States, but the availability of adequate sunlight and the suitability of climate and temperature are key siting and resource factors that will determine economic feasibility.

Preferred Geographic Regions for Algae Production

Exhibit 9.4 GIS-based scoping conducted by Sandia National Laboratories to provide a preliminary high-level assessment identifying preferred regions of the United States for photoautotrophic microalgae production based on the application of selected filter criteria on annual average climate conditions, the availability of non-fresh water, and the availability of concentrated sources of CO2. The climate criteria used to narrow down the geographical regions were: annual average cumulative sun hours = 2800, annual average daily temperature = 55°F, and annual average freeze-free days = 200.

Projections of annual average algae biomass production from the PNNL study show clear patterns relating climate to total biomass growth, with the higher growth regions having gross qualitative similarity to Exhibit 9.4 and the southern tier states showing greatest productivity potential based on the modeling assumptions used. In Exhibit 9.4 (a), the lack of attractiveness of the Gulf Coast region from southeast Texas to northwest Florida is attributed to the lower annual average solar insolation available,

a) Regions with annual average climate conditions meeting selected criteria: = 2800 hour annual sunshine, annual average temperature = 55° F, and = 200 freeze-free days

b) Fossil-fired power plant sources of CO2 within 20 miles of municipal wastewater facilities in the preferred climate region

High annual production for a given species grown photoautotrophically outdoors, however, will require that suitable climatic conditions exist for a major part of the year. Therefore, a critical climate issue for both open and closed photobioreactor systems is the length of economically viable growing season(s) for the particular strains of algae available for productive cultivation. For outdoor ponds, the conventional crop analogy for this is the length of time between the last killing frost in the spring and the first killing frost in the fall. For closed photobioreactors, the conventional crop analog is the greenhouse and the limiting energy and cost needed to maintain internal temperature throughout the seasons.

The primary geographical location factors for determining length of growing season are latitude and elevation, which have major influence on the hours and intensity of available sunlight per day and the daily and seasonal temperature variations. Areas with relatively long growing seasons (for example, 240 days or more of adequate solar insolation and average daily temperatures above the lower threshold needed for economically viable growth) are the lower elevation regions of the lower latitude states of Hawaii, Florida, and parts of Louisiana, Georgia, Texas, New Mexico, Arizona, and California. Other local climate and weather conditions will also have influence.

Water Requirements

Precipitation affects water availability (both surface and groundwater) at a given location within a given watershed region. Areas with higher annual average precipitation (more than 40 inches), represented by specific regions of Hawaii, the Northwest, and the Southeast, are desirable for algae production from the standpoint of long-term availability and sustainability of water supply.

Evaporative loss can be a critical factor to consider when choosing locations for open pond production. Evaporation is a less important concern for selecting locations of closed photobioreactors, although evaporative cooling is often considered as a means to reduce culture temperature. The southwestern states (California, Arizona, and New Mexico) and Hawaii have the highest evaporation rates in the United States, with more than 60 inches annually.

Severe Weather Events and Elements

Severe weather events, such as heavy rain and flooding, hail storms, dust storms, tornadoes, and hurricanes pose serious concerns in the inland regions of the central states, Southwest, Southeast, and coastal areas. These weather events can contaminate an open system environment or cause physical damage to both open and closed systems, and need to be taken into account when looking at prospects for algae production in both inland and coastal regions of the United States.

The marine environment can also be highly corrosive to materials and usually demands both the use of higher quality and more costly materials and greater maintenance.

Water General Water Balance and Management Needs

One of the major benefits of growing algae is that, unlike most terrestrial agriculture, algal culture can potentially utilize non-fresh water sources having few competing uses, such as saline and brackish ground water, or “coproduced water” from oil, natural gas, and coal-bed methane wells (Reynolds, 2003; USGS, 2002). However, for open pond systems in more arid environments with high rates of evaporation, salinity and water chemistry will change with evaporative water loss, thereby changing the culture conditions. This will require periodic blowdown of ponds after salinity build-up, periodic addition of non-saline make-up water to dilute the salinity buildup, the application of desalination treatment to control salinity build-up, or highly adaptive algae that can thrive under widely varying conditions. Open algal ponds may have to periodically be drained and re-filled, or staged as a cascading sequence of increasingly saline ponds each with different dominant algae species and growth conditions. The relatively flat national water withdrawal trend over the past 25 years, following the more than doubling of water demand over the 30 years prior to that, reflects the fact that fresh water sources in the Untied States are approaching full allocation. Growing demand for limited fresh water supplies in support of development and population increase has thus far been offset by increased conservation and by the increased re-use of wastewater. Many of the nations’ fresh ground water aquifers are under increasing stress, and the future expansion of fresh water supplies for non-agricultural use must increasingly come from the desalination of saline or brackish water sources and from the treatment and reuse of wastewater, all of which have increasing energy demand implications

Implementing water desalination would impose additional capital, energy, and operational costs. Disposal of high salt content effluent or solid byproducts, from pond drainage and replacement, or from desalination operations, can also become an environmental problem for inland locations.

Analysis of U.S. Water Supply and Management

Total combined fresh and saline water withdrawals in the United States as of the year 2005 were estimated at 410,000 million gallons per day (Mgal/d), or 460,000 acre-feet per year.  Saline water (seawater and brackish coastal water) withdrawals were about 15% of the total. Almost all saline water, about 95%, is used by the thermoelectric-power industry in the coastal states to cool electricity-generating equipment. In 2005, nearly one-half of the total U.S. withdrawals (201,000 Mgal/d) were for thermoelectric-power generation, representing 41% of all freshwater, 61% of all surface water, and 95% of all saline-water withdrawals in 2005.

Withdrawals for irrigation of crops and other lands totaled 128,000 Mgal/d and were the second-largest category of water use. Irrigation withdrawals represented 31% of all water withdrawals, and 37% of all freshwater withdrawals (Kenny et al., 2009). At the national scale, total combined fresh and saline water withdrawals more than doubled from about 180 billion gallons per day in 1950 to over 400 billion gallons per day in 1980. Total withdrawals since the mid-1980s have remained relatively flat at slightly over 400 billion gallons per day, with the majority (85%) being fresh (Hutson et al., 2004; Kenny et al., 2009). The stress on fresh water supplies in the United States is not restricted to the more arid western half of the country, but is also becoming a local and regional concern at various locations throughout the eastern half of the country, where a growing number of counties are experiencing net fresh water withdrawals that exceed the sustainable supply from precipitation (DOE, 2006b; Hightower et al., 2008; ). Climate change is also recognized as a factor that could have major effect on all sectors of water resources supply and management in the future (USGS, 2009).

Scoping Out Water Requirements for Algae Production

Water use and consumption for algae-based biofuels will depend on the cultivation approach (photoautotrophic/ heterotrophic), with water use in upstream organic carbon feedstock production needing to be part of the heterotrophic assessment. Water use will also depend on the type of growth systems used for photoautotrophic microalgae (open vs. closed vs. hybrid combination), whether evaporative cooling is used for closed systems, and the site-specific details of climate, solar insolation, and weather conditions (cloud cover, wind, humidity, etc.). Also a complicating factor for evaporative water loss in open systems will be the degree of salinity of the water used for cultivation and the local latitude, elevation, ambient temperature variations, solar insolation, humidity, and wind conditions. A significant source of water demand with inland algae production operations could be for the replacement of water continuously lost to evaporation from open cultivation systems.

This will be of greatest impact and concern in water-sparse locations, which also tend to be in the more arid and higher solar resource regions like the Southwest.

The evaporation estimates suggest that water loss on the order of several tens of gallons of water per kilogram of dry weight biomass produced, or several hundreds of gallons of water per gallon of algal biofuel produced, could be a consequence of open system operation in the more arid and sunny regions of the country.

Evaporative water loss associated with algae cultivation can be significantly reduced if closed systems are used.

Unfortunately, quantitative information remains limited on U.S. brackish and saline groundwater resources in terms of their extent, water quality and chemistry, and sustainable withdrawal capacity.

Depth to groundwater is pertinent to the economics of resource development. Along with geological data, depth information determines the cost of drilling and operating (including energy input requirements for pumping) a well in a given location (Maxwell et al., 1985). Suitable aquifers located closer to the surface and nearer to the cultivation site would provide a more cost-effective source of water for algae production than deeper sources located longer distances from the cultivation site. The location, depth, and chemical characterization of saline aquifers in the United States are areas of investigation in need of greater investment. The maps of saline groundwater resources are based on incomplete data that was largely developed by the USGS prior to the mid-1960s.

Carbon Dioxide The Carbon Capture Opportunity in Algae Production Efficient algae production requires enriched sources of CO2 since the rate of supply from the atmosphere is limited by diffusion rates through the surface resistance of the water in the cultivation system. Flue gas, such as from fossil fuel-fired power plants, would be a good source of CO2.

However, algae production does not actually sequester fossil carbon, but rather provides carbon capture and reuse in the form of fuels and other products derived from the algae biomass. Any greenhouse gas abatement credits would come from the substitution of renewable fuels and other co-products that displace or reduce fossil fuel consumption. In addition, at some large scale of algae production, parasitic losses from flue gas treatment, transport, and distribution could require more energy input than the output energy displacement value represented by the algae biofuels and other co-products.

Likely Stationary CO2 Emission Sources

Major stationary CO2 emission sources that could potentially be used for algae production are shown in Exhibit 9.5. The sources shown (NATCARB, 2008) represent over half of the more than 6 billion metric tons of CO2 emitted annually in the United States (EPA, 2009; EIA, 2008 and 2009). Power generation alone (mainly using coal) represents over 40% of the total, or more than 2 billion metric tons per year (EIA, 2008 and 2009).

Barriers to Viable CO2 Capture and Utilization

The degree to which stationary CO2 emissions can be captured and used affordably for algae production will be limited by the operational logistics and efficiencies, and the availability of land and water for algae cultivation scale-up within reasonable geographic proximity of stationary sources.

As an example, a recent analysis suggests that for algae production to fully utilize the CO2 in the flue gas emitted from a 50-MWe semi-base load natural-gas-fired power plant would require about 2,200 acres of algae cultivation area (Brune et al., 2009). The CO2 generated by the power plant can only be effectively used by the algae during the photosynthetically active sunlight hours. As a result, the greenhouse gas emissions offset will be limited to an estimated 20% to 30% of the total power plant emissions due to CO2 off-gassing during non-sunlight hours and the unavoidable parasitic losses of algae production (Brune et al., 2009). Larger coal-fired base-load generators that typically output a steady 1,000 to 2500 MWe of power would each require many tens of thousands of acres of algae production and large volumes of water to provide a similar effective offset of 20% to 30% of the CO2 emitted.

The distance for pumping flue gas to algae cultivation systems will become a limiting factor that requires capture and concentration of CO2 from the flue gas for longer distance transport and distribution.

Photoautotrophic algae will only utilize CO2 during daylight hours when photosynthesis is active. The rate of effective CO2 uptake will also vary with the algae species, biomass growth rate, and details of growth system and incident light conditions. Therefore, the requirements for CO2 supply to enhance algae production, and the matching of CO2 source availability with algal cultivation facilities, is not a simple issue. In addition, it will be necessary to provide a CO2 source that is suitably free of materials potentially toxic to algae.

One outcome of a hypothetical algae production scale-up scenario is the limited quantity of CO2 that would likely be available from stationary industrial point sources (e.g., Exhibit 9.5) within practical transport distances of suitable algae production sites in a given geographical region. This can be expected to constrain the extent to which algal biofuels production can be affordably scaled up within any given region unless other factors drive the investment in expanding the nation’s CO2 pipeline infrastructure.


(Million Metric Ton/Year)

Ag Processing 6.3 140
Cement Plants 86.3 112
Electricity Generation 2,702.5 3,002
Ethanol Plants 41.3 163
Fertilizer 7.0 13
Industrial 141.9 665
Other 3.6 53
Petroleum and Natural

Gas Processing

90.2 475
Refineries/Chemical 196.9 173
Total 3,276.1 4,796


Land Factors for Evaluating Land for Algal Production

Land availability will be important for algae production because either open or closed systems will require relatively large areas for implementation, as is expected with any photosynthesis-based biomass feedstock. Even at levels of photoautotrophic microalgae biomass and oil productivity that would stretch the limits of an aggressive R&D program (e.g., target annual average biomass production of 30 to 60 g/m2 per day with 30% to 50% neutral lipid content on a dry weight basis), such systems would require in the range of roughly 800 to 2600 acres of algae culture surface area to produce 10 million gallons of oil feedstock,

Land availability is influenced by various physical, social, economic, legal, and political factors, as illustrated in Exhibit 9.6.

Physical characteristics, such as topography and soil, could limit the land available for open pond algae farming. Soils, and particularly their porosity and permeability characteristics, affect the construction costs and design of open systems by virtue of the need for pond lining or sealing. Topography would be a limiting factor for these systems because the installation of large shallow ponds requires relatively flat terrain. Areas with more than 5% slope could well be eliminated from consideration due to the high cost that would be required for site preparation and leveling.

Exhibit 9.5 Major stationary CO2 sources in the United States (NATCARB, 2008a) CATEGORYCO2 EMISSIONS NUMBER OF SOURCES (Million Metric Ton/Year) Ag Processing 6.3 140 Cement Plants 86.3 112 Electricity Generation 2,702.5 3,002 Ethanol Plants 41.3 163 Fertilizer 7.0 13 Industrial 141.9 665 Other 3.6 53 Petroleum and Natural Gas Processing 90.2 475 Refineries/Chemical 196.9 173 Total 3,276.1 4,796

Contributing to productivity limits per unit of illuminated surface area is the fact that algal cells nearest the illuminated surface absorb the light and shade their neighbors farther from the light source. Optimizing light utilization in algae production systems includes the challenge of managing dissipative energy losses that occur when incident photons that cannot otherwise be effectively captured and used by the algae in photosynthesis are instead converted to thermal (heat) energy in the culture media and surrounding cultivation system structures. Depending on the algae strain and culture system approach used, the dissipative heat loading can be a benefit in moderating culture temperatures and improving productivity under colder ambient conditions, or can lead to overheating and loss of productivity during hotter ambient conditions.

Relatively large-scale commercial algae production with open ponds for high-value products can serve as a baseline reference, but currently reflect lower biomass productivities in the range of 10 – 20 g/m2 per day. This is significantly lower than the more optimistic target projections for biofuel feedstock of 30 – 60 g/m2 per day.

Land use and land value affect land affordability. By reviewing the more recent economic analyses for algae biomass and projected oil production, the cost of land is often not considered or is relatively small compared to other capital cost. Land that is highly desirable for development and other set-asides for publically beneficial reasons may not be seen as suitable for algae production. The same applies to land highly suited for higher-value agricultural use. Beyond economics, this also avoids the perception and potential conflict of food and feed production versus fuel.

Land cover categories such as barren and scrubland cover a large portion of the West and may provide an area free from other food-based agriculture where algae growth systems could be sited (Maxwell et al., 1985). The availability and sustainability of water supplies in the West will also be a key consideration,

Integration with Water Treatment Facilities

Inevitably, wastewater treatment and recycling must be incorporated with algae biofuel production. The main connections of algae production and wastewater treatment are the following: • Treatment technology is needed to recycle nutrients and water from algae biofuel processing residuals for use in algae production. • Imported wastewater provides nutrients and water to make-up inevitable losses. The imported wastewater would be treated as part of the algae production. • Algae-based wastewater treatment provides a needed service. • Algae-based wastewater treatment can be deployed in the near-term and provides workforce training

For large-scale algae biofuel production, nutrients from wastewater (municipal and agricultural) would be captured by algae and then recycled from the oil extraction residuals for additional rounds of algae production. Nutrient recycling would be needed since wastewater flows in the United States are insufficient to support large-scale algae production on the basis of a single use of nutrients. Inevitable nutrients losses during algae production and processing could be made up with wastewater nutrients, which can also help supplement and off-set the cost of commercial fertilizers for algae production. Supply and cost of nutrients (nitrogen, phosphorus, and potassium) be a key issue for achieving affordable and sustainable scale-up of algae biofuels production.

The major classes of wastewaters to be treated are municipal, organic industrial (e.g., food processing), organic agricultural (e.g., confined animal facilities), and eutrophic waters with low organic content but high nutrient content (e.g., agricultural drainage, lakes, and rivers). Despite a seeming abundance of wastewater and waste nutrients, recycling of nutrients and carbon at algae production facilities will be needed if algae are to make a substantial contribution to national biofuel production. Even with internal recycling, importation of wastes and/or wastewater will still be needed in dedicated algae biomass production facilities to make up for nutrient losses (Brune et al., 2009).

Closed photobioreactors are not emphasized in this wastewater treatment discussion since they are likely to be economical only when also producing high-value products (>$100/kg biomass), which is unlikely when wastewater contaminants are present.

As with other algae production systems, harvesting is a crucial step in wastewater treatment systems. The standard method is chemical addition to achieve coagulation and flocculation, followed by algae separation in dissolved air flotation units or sedimentation clarifiers. The cost of chemical addition ($0.10 – $0.17 per m3 treated) (Maglion, 2008) is high for biofuel production. Nonchemical flocculation processes (bioflocculation and autoflocculation) are far less costly, but research is needed to improve the reliability of these processes

The removal of trace contaminants (e.g., endocrine disrupting compounds such as human hormones and antibiotics from animal facilities) is an area in need of study.

any heavy metals contaminating the algal biomass likely would remain in the waste from biofuel processing, potentially increasing the cost of waste disposal or recycling.

For algae-based treatment of low-organic content wastewaters, CO2 addition or slow atmospheric absorption is essential since inorganic carbon generation from decomposition of organic matter would not be significant.

Co-location of Algal Cultivation Facilities with CO2-Emitting Industries

It is important to point out that amongst the numerous barriers to co-location of algal cultivation facilities with industrial CO2 sources identified at the Workshop and subsequent discussions with electric utilities, an overriding theme was that electric utilities primarily view algae cultivation as a means of CO2 capture as opposed to a method for producing biofuels and co-products.

fossil fired power plants, it is also relevant to other CO2-intensive industries (e.g., cement manufacturing, fossil fuel extraction/refining, fermentation-based industries, some geothermal power production, etc.). The emissions from many of these facilities have higher CO2 concentrations compared to power plant flue gas, which typically ranges from about 5% to about 15%, depending on the type of plant and fuel used.

An important policy question to consider is the value of CO2 absorption by algae in any carbon-credit or cap and trade framework, in that the carbon will be re-released to the atmosphere when algal-derived fuels are combusted. While algae biofuels can be expected to result in a net reduction of overall GHG emissions, the process of capturing flue-gas CO2 to make transportation fuels may not rigorously be considered carbon sequestration.

The quantitative breakdown, introduced earlier in Exhibit 9.5, shows that fossil-fired power plants represent the majority of CO2 emissions from stationary sources.

but, as with baseload coal-fired plants, would also emit CO2 during periods of darkness when it cannot be utilized by the algae through photosynthesis. During those times, the CO2 would be emitted to the atmosphere if not captured and sequestered by other means

Barriers to Co-Location of Algae Production with Stationary Industrial CO2 Sources

  1. Need for nutrient sources: While stationary industrial sources of concentrated CO 2 can potentially provide ample carbon for photosynthesis-driven algal growth, in most cases there will not be a complementary nutrient (N, P, K) supply. Therefore nutrients must be brought in from other sources, or in some cases algal cultivation could be co-located with both stationary CO2 sources and nutrient sources such as wastewater treatment facilities and agricultural waste streams.
  2. Land availability: Suitable and affordable vacant land may not be available adjacent to or near major power plants
  3. Emissions from ponds are at ground level: Regulatory requirements from power plants and other stationary sources are governed by the Clean Air Act, and are based upon point-source emissions from high elevations. The use of flue gas to cultivate algae will involve non-point source emissions at ground level.
  4. Capital costs and operational costs: There exists a need to evaluate capital costs and parasitic operational losses (and costs) for infrastructure and power required to capture and deliver industrial CO2 to ponds and grow/harvest algae. These costs and losses must be minimized and compared to other approaches for the capture and sequestration or reuse of carbon. Current estimates are that approximately 20% – 30% of a power plant’s greenhouse gas emissions can be offset by algae biofuel and protein production. Although often referred to as a “free” resource, the capture and delivery of concentrated CO2 from stationary industrial sources as a supplement to enhance and optimize algae production will not be “free”.
  5. Too much CO 2 near plants for realistic absorption: Large power plants release too much CO 2 to be absorbed by algal ponds at a realistic scale likely to be possible near the power plant facility. The same generally holds true for other stationary industrial sources of CO2 (cement plants, ethanol plants, etc.). Also, CO2 is only absorbed during periods when sunlight is available and photosynthesis is active in the algae.
  6. Maintaining cultivation facilities during utility outages.
  7. Resistance from electric utilities: Electric utilities are not in the fuels business and regulated public utility commissions will be constrained in entering the fuel production arena. Their fundamental objective will be to capture CO2 as opposed to producing biofuels and co-products.

Significant investment is expected to be required to overcome the various technical and economic challenges along each of these pathways, as discussed throughout the Roadmap.

Exhibit 10.4 Scoping the content for Systems Techno-Economic Modeling and Analysis: Key topic areas and issues for the overall algal biofuels supply chain

Algal biofuels remain an emerging field at a relatively immature stage of development.

Siting -Land -Land (cost, location, tilt, geology, soil) – Solar Insolation – Temperatures – Climate/Weather Policy

Algae -Species -Species – Characteristics – Requirements – Performance – GMOs Biology Feedbacks Resources – CO2 / Flue Gas Conditioning- Water or Treatment- Nutrients (NPK) Design Feedbacks Cultivation -Autotrophic -Autotrophic – Heterotrophic – Open systems – Closed systems – Hybrid systems Nutrient Feedbacks Carbohydrates Broader Environment & Economy Conversion Biofuels

Co-Gen Energy Feedbacks Capital Construction, Operations, Monitoring, Maintenance, Replacement Market Externalities: Cost of Energy, Cost of Petroleum & Conventional Fuels, Demand & Price for Co-Products vs. their alternatives, etc.

Other chapters of this Roadmap point out the lack of availability of detailed information about the characteristics of algae themselves and the characteristics (energy requirements and costs) of the systems and processes that are shown in the process flow diagram of Exhibit 10.8. A substantial number of barriers are enumerated and designated as goals to be achieved.

An example of this type of analysis is presented in Exhibit 10.8. Exhibit 10.8 represents a mass and energy balance systems level view of an algal biomass and algal lipid cultivation and extraction system. Inputs to

The value of this kind of systems mass and energy balance assessment is that it can help assess the overall viability of a given algal biomass production system and show what steps in the process are most energy intensive, thus highlighting areas for research and development. The development of mass and energy based systems models can help evaluate different proposed processes for overall viability and examine the sensitivity of different assumptions in individual processes to the overall system.

Geographic Information System (GIS) Visualization and Analysis tools

  • Land and water resources (characteristics, availability, etc.) • Climatic characteristics (temperature, precipitation, solar insolation, etc.) • Water evaporation loss (function of climate, etc.) • CO2 resources (point source emitters, pipelines) • Fuel processing, transport, storage infrastructure • Other infrastructure and environmental features

Several critical resource factors will impact large-scale, sustainable production of microalgae biomass. These include climate and the adequate availability of water, efficiency of water use, availability of suitable land, and availability of supplemental CO2 and other nutrient (N, P, K) supplies.

Producing biofuels that are highly compatible, or totally fungible, with the existing hydrocarbon fuel handling, distribution, and end-use infrastructure would result in easier and more widespread market acceptance. The same would apply to co-products and their potential markets. These and related issues should be an integral part of techno-economic modeling, analysis and LCA for algae, with the appropriate models, tools, and data sets developed and leveraged to provide the necessary assessment

page 102. Recent analysis suggests an upper theoretical limit on the order of ~38,000 gal/ac-yr (263158 acres or 411 square miles)and perhaps a practical limit on the order of ~4,350 – 5,700 gal/ac-yr, based on the expected losses, photosynthetic efficiency, and other assumptions made in the analysis (which include the availability of high solar insolation consistent with lower latitudes and/or high percentage of clear weather conditions, 50% oil content, etc.).  So making 10 billion gallons of algal biofuel to replace 5% of our oil would require about 2,700 to 3,600 square miles of flat land with a very optimistic 50% oil content algae in a sunny area.   to 1754385 to  2298850 acres

  • The average annual insolation is generally the dominant and rate-limiting factor for autotrophic algal productivity, and this factor varies widely across the country among inland, coastal, and offshore sites. This variation will determine the spatial surface area of cultivation systems needed to achieve a set amount of product; it will affect the amount of CO2 that can be captured; and it will affect the amount of culture that will need to be processed on a daily basis. The daily, seasonal, and annual variation in solar insolation, as well as other climate-related factors such as temperature and weather (cloud cover, precipitation, wind, etc.) will also affect both the productivity and reliability of production.
  • Availability, cost, and sustainability of suitable water supplies for algae production will be a key input factor for inland cultivation, and will be heavily dependent on geographical location and local conditions. Areas of the country with the highest solar resource best suited for algae growth also tend to be more arid and subject to more limited water supplies. Under large commercial algae industry build-up scenarios, the amount of water required nationally could begin to approach the same order of magnitude as large scale agriculture, particularly with open systems subject to evaporative loss. Capture and re-use of non-fresh water, in particular, can potentially help fill this need, but will be dependent on the geographical location, availability, and affordable accessibility of such water sources.
  • The supply, availability, and cost of organic carbon feedstock needed as input for heterotrophic microalgae production will play a major role in the commercial viability and extent to which national production capacity can expand using the heterotrophic approach. Sugar from commodity crops and other organic carbon materials from industrial or municipal waste streams can provide bridge feedstock in the near term, but major sustainable scale-up of national production capacity will demand the use of sugars and other suitable organic carbon source materials derived originally from lignocellulosic biomass. As with cellulosic ethanol, the logistics and costs associated with producing, transporting, and appropriately processing lignocellulosic biomass materials in the form of woody and herbaceous energy crops, waste materials from agriculture and forest industries, and municipal waste streams will be location-dependent. The affordability of generating organic carbon feedstock from such materials will also depend on technical advances and processing improvements needed to reduce the cost of lignocellulosic material deconstruction into simple sugars and other organic carbon compounds suitable for feeding heterotrophic microalgae.
  • The supply, availability, and cost of other nutrients (i.e., N, P, K) required as inputs for algae growth will also play a role in commercial viability and extent of industrial build-up. Commercial fertilizer costs are tied closely to the cost of energy supplies (natural gas and petroleum), and can be an appreciable factor in operational costs for algae (Massingale et al., 2008) to the same extent as for large scale commercial agriculture (Huang, 2009; Malcolm et al., 2009). In the absence of nitrogen fixation, algae can require as much, if not more, nitrogen than conventional biomass crops on a mass balance basis (Alexander et al., 2008). Under large commercial algae industry build-up scenarios, the amount of nutrients required nationally could begin to approach the same order of magnitude as large scale agriculture, where recent cost and supply issues have had negative impacts on the industry (Huang, 2009). The capture and reuse of nutrients from various agricultural and municipal waste streams (Woertz et al., 2009) can potentially help supply nutrients for algae production scale-up, but this will be dependent on the geographical location, availability, and affordable accessibility of such nutrient sources.
  • CO2 availability and cost of delivery will play a major role in autotrophic microalgae cultivation scalability and operating expense. As noted here and in chapter 9, it will be advantageous to co-locate cultivation facilities with stationary industrial CO2 sources, but this will not be feasible in all instances and thus, it may be necessary to transport CO2 over some distance. Even in the case of co-location, the size of an autotrophic algae facility will require extensive pipeline infrastructure for CO2 distribution, adding to the cost. The quality of the CO2 source will also play a role for algal growth, and some sources are likely to require more cleanup than others (especially if there are plans for animal feed as a co-product and/or if the CO2 source stream includes contaminants that inhibit algae growth). Algae can be effective at capturing and concentrating heavy metal contaminants (Aksu, 1998; Mehta and Gaur, 2005), such as are present in some forms of flue gas. This could impact the suitability of residual biomass for co-products like animal feed,
  • Land prices and availability can also impact the cost of biofuel production at inland and coastal sites. For offshore sites, the right of access and use, and the associated logistics, risks, and costs of offshore marine operations will have a major impact on costs of production. Cost of site preparation and infrastructure facilities for offshore, coastal, and inland sites will all be location-dependent. It is reasonably straightforward to calculate the impact of the cost of land, and perhaps also for offshore sites, on the overall cost of total algal biomass and intermediate feedstock fraction (e.g., lipids, carbohydrates, proteins, other) production, but for each approach it will likely be an optimum minimum and range of size for a commercial production facility. If it is necessary to distribute the facility over a number of smaller parcels of land or offshore sites, it may not be possible to get the most benefit of economies of scale. The key tradeoffs will be between the cost of overall production (capital and operating costs) versus the matching of affordable production scale to the sustainable and affordable supply of the required input resources with the required output product processing and distribution infrastructure and markets.
  • As in traditional agriculture, the temperature during the growing season will restrict the ability to cultivate specific strains for extended durations. For open systems operating at inland sites in the summer, water evaporation rates will provide some level of temperature control, but evaporation will also add to operating cost (for water replacement and/or for salt management with brackish or saline water.

Conversely, closed systems operating inland can overheat, requiring active cooling that can add prohibitively to the cost of operations. Waste heat and energy from co-located industries or the CO2 source may allow active thermal management for growth during periods of suboptimal (high or low) temperature, but applying this heat or energy to extensive algal cultivation systems will provide the same engineering problems and costs as transporting and distributing CO2.

Life Cycle Analysis (LCA) is a “cradle-to-grave” analysis approach for assessing the resource use and environmental impacts and tradeoffs of industrial systems and processes. LCA is important for assessing relative GHG emissions and other resource utilization (e.g., water, energy) impacts among different approaches to algal biofuels production, and in comparison with fuels based on other renewable and non-renewable feedstocks. LCA is considered to be a key element of the scope of TE modeling and analysis within the context of this roadmap.

The term “life cycle” refers to the major activities in the course of the product’s life-span, from manufacture, use, and maintenance, to final disposal, including the raw material acquisition required to manufacture the product (EPA, 1993). Exhibit 10.11 illustrates the typical life cycle stages considered in an LCA and the typical inputs/ outputs measured.

Algae Production Costs and Uncertainties

Data gathering and validation of technical and economic system performance for an industry that has yet to be commercially realized is one of the biggest challenges for techno-economic analysis.

While most citable sources are quite dated, they also present a wide variability in approach to final costs (from per gallon of algal oil to per kg of “raw” biomass) and illustrate a general lack of demonstrated operating parameters and widely varying basic assumptions on a number of parameters from algal productivity to capital depreciation costs, operating costs, and co-product credits. These shortcomings of the existing literature and modeling knowledge base present a challenge in designing scaled up systems.

The algal biofuels industry is still in its infancy. More specifically, given the current state of this industry, the business strategies of many existing companies are focused on one or more aspects of algae, but not necessarily producing transportation biofuels from cultivated algal biomass at scale.

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2 Responses to National Algal Biofuels Technology Roadmap, Department of Energy

  1. Ivan says:

    Hello Alice,

    Have you looked into hydrothermal liquefaction (HTL) to produce bio crude. If so what are your thoughts about it ?
    (sorry about commenting in the wrong article)

    • energyskeptic says:

      If anything this would lower the energy returned on invested A LOT. The University of Illinois describes this process as “During hydrothermal liquefaction, high moisture biomass is subjected to elevated temperatures (250-350 deg C) and pressures (10-20 MPa) in order to break down and reform the chemical building blocks into a bio-crude oil.” Heating anything to 660 degrees Fahrenheit takes a huge amount of energy! And this is only a tiny part of the dozens of energy-intensive steps, and doesn’t solve the resource issues of enough water, CO2, and so on.

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