The Path Forward for Biofuels and Biomaterials

This is a review on biofuels and biomaterials in general written by Arthur J. Ragauskas, Charlotte K. Williams, Brian H. Davison, George Britovsek, John Cairney, Charles A. Eckert, William J. Frederick Jr., Jason P. Hallett, David J. Leak, Charles L. Liotta, Jonathan R. Mielenz, Richard Murphy, Richard Templer, Timothy Tschaplinski.
Biomass represents an abundant carbon-neutral renewable resource for the production of bioenergy and biomaterials, and its enhanced use would address several societal needs. Advances in genetics, biotechnology, process chemistry, and engineering are leading to a new manufacturing concept for converting renewable biomass to valuable fuels and products, generally referred to as the biorefinery. The integration of agroenergy crops and biorefinery manufacturing technologies offers the potential for the development of sustainable biopower and biomaterials that will lead to a new manufacturing paradigm.

We are apt to forget the gasoline shortages of the 1970s or the fuel price panic after Hurricane Katrina, but these are but harbingers of the inevitable excess of growing demand over dwindling supplies of geological reserves. Before we freeze in the dark, we must prepare to make the transition from nonrenewable carbon resources to renewable bioresources. This paper is a road map for such an endeavor.

Among the earliest drivers of chemical and biochemical research were the benefits to be gained from converting biomass into fuels and chemical products. At the beginning of the 20th century, many industrial materials such as dyes, solvents, and synthetic fibers were made from trees and agricultural crops. By the late 1960s, many of these bio-based chemical products had been displaced by petroleum derivatives (1). The energy crisis of the 1970s sparked renewed interest in the synthesis of fuels and materials from bioresources. This interest waned in the decades that followed as the oil price abated. However, this meant that global consumption of liquid petroleum tripled in the ensuing years (2). Indeed, energy demand is projected to grow by more than 50% by 2025, with much of this increase in demand emerging from several rapidly developing nations. Clearly, increasing demand for finite petroleum resources cannot be a satisfactory policy for the long term.

Hoffert et al. and others have provided a global perspective on these energy challenges and their relationship to global climate stability. As these authors point out, future reductions in the ecological footprint of energy generation will reside in a multifaceted approach that includes nuclear, solar, hydrogen, wind, and fossil fuels (from which carbon is sequestered) and biofuels. These concerns have also been advanced by the recent Joint Science Academies_ statement to the Gleneagles G8 Summit in July 2005, Global Response to Climate Change, which asserts that the warming of the planet can be attributed to human activities and identifies the need for action now to pinpoint costeffective steps to contribute to substantial and long-term reductions in net greenhouse gas emissions.

Shifting society's dependence away from petroleum to renewable biomass resources is generally viewed as an important contributor to the development of a sustainable industrial society and effective management of greenhouse gas emissions. In the United States, bioethanol derived primarily from corn contributes ~2% to the total transportation fuels mix; another ~0.01% is based on biodiesel. The U.S. Department of Energy has set goals to replace 30% of the liquid petroleum transportation fuel with biofuels and to replace 25% of industrial organic chemicals with biomass-derived chemicals by 2025. The European Union Directive 2003/30/EC ("the Biofuels Directive") adopted in 2003 targeted 2% of all petrol and diesel transport fuels to be biomass-derived by December 2005 and 5.75% by December 2010. This directive was motivated by concerns to ensure the security of the European energy supply, environmental sustainability, and achievement of Kyoto Protocol targets. These biomaterials and biofuels production targets are certainly achievable; Parikka has reported the current sustainable global biomass energy potential at 10²⁰ joules per year, of which ~40% is currently used.

Given these accomplishments, a key question is "When will biorefineries be ready to make a major contribution?" One answer, coming from a forum at the 27th Symposium on Biotechnology for Fuels and Chemicals, was that some applications are ready now, but their impact will be limited with current technologies and feedstocks. We need commercialization and policy support for current and near-term opportunities to grow the industry from its present base. Equally important, we need research and development to increase the impact, efficiency, and sustainability of biorefinery facilities. The current production and use of bioethanol and biodiesel processes are a starting point. It is our belief that the next generational change in the use of bioresources will come from a total integration of innovative plant resources, synthesis of biomaterials, and generation of biofuels and biopower (Fig. 1).

Fig.1: The fully integrated agro-biofuel-biomaterial-biopower cycle for sustainable technologies.

Innovative Plant Design via Accelerated Domestication

"More, Bigger, and Better," the mantra of modern consumerism, also summarizes— ironically—the goals of research aimed at modifying plant species for use in sustainable biomass production. Interrelated plant traits such as higher yield, altered stature, resilience to biotic and abiotic challenge, and biomass composition will increase industrial crop value in terms of biofuels and biomaterials. The challenge is to weave these different strands of research into an integrated production strategy.

Currently, the global yield for all biomass crops, including woody and herbaceous crops growing in temperate and subtropical regions, varies from ~8 dry Mg ha^-1 year^-1 (for willow in Sweden) to 10 to 22 dry Mg ha^-1 year^-1 (for short-rotation woody crops in the United States). Some commercial plantations in Brazil have reported up to 20 dry Mg ha^-1 year^-1. A conservative global biomass average would be ~10 dry Mg ha^-1 year^-1, although some small-scale field trials have reported four times this level of biomass production. The grand challenge for biomass production is to develop crops with a suite of desirable physical and chemical traits while increasing biomass yields by a factor of 2 or more. Although many annual crops benefit from centuries of domestication efforts, perennial species that could play a central role in providing a renewable source of feedstock for conversion to fuels and materials have not had such attention to date. Doubling the global productivity of energy crops will depend on identifying the fundamental constraints on productivity and addressing those constraints with modern genomic tools (Fig. 2).

Fig.2: Overview of plant traits that can be targeted by accelerated domestication for enhanced plant biomass production and processing.

An obvious target is manipulation of photosynthesis to increase the initial capture of light energy, which at present is less than 2%. Recently, this approach has had some success using engineered genes from plants and photosynthetic bacteria. For example, ribulose-1, 5-bisphosphate carboxylase-oxygenase (RuBisCO), the plant enzyme that converts CO₂ to organic carbon by carboxylation during photosynthesis, also conducts a competing, less efficient oxygenation reaction. When an inorganic carbon transporter gene from cyanobacteria was expressed in plants, the more efficient carbonfixing photosynthetic reaction of RuBisCO was favored. In another approach, the cyanobacterial versions of two rate-limiting enzymes in the chloroplast’s carbon-fixing "dark reaction" were overexpressed in tobacco, resulting in an elevated rate of photosynthesis and increased plant dry weight.

In addition to manipulating photosynthesis to increase the initial capture of light energy, the manipulation of genes involved in nitrogen metabolism has also been a successful approach to increasing biomass. For example, in a 3-year field trial of transgenic poplar (P. tremula X P. alba) overexpressing a glutamine synthase gene (GS1), tree height increased to 141% that of control plants by the third year of the study. The potential of GS1 for engineering biomass increase is further emphasized by results showing that quantitative trait loci for yield in maize and maritime pine map to the location of GS1. Similar possibilities are evident in the overexpression of a bacterial glutamate dehydrogenase, which increased the biomass of tobacco plants under both laboratory and field conditions.

Much research has been devoted to protecting food and fiber supplies from biological and environmental stress by transferring genetically engineered versions of plant defense genes to crop plants. By this method, different plant lines have been generated that, relative to controls, grow at elevated rates under drought and high- and low-temperature stress; they also survive pathogen attack. Furthermore, plants typically invest considerable energy in making reproductive structures, and if flowering can be delayed or prevented, this energy may be transferred into increasing the overall biomass of the plant. In addition, by delaying or shortening the winter dormancy of plants, the growth phase of plants can be extended; regulators for this process are being investigated.

Additional research has revealed the coregulation of lignin and cellulose biosynthesis in several studies. Repressing a single lignin biosynthetic gene, 4-CL, resulted in a reduction in lignin content with a concomitant increase in cellulose, an effect that can be amplified by cotransformation of multiple genes. Conversely, an Arabidopsis CESA3 mutant, impaired in cellulose biosynthesis, had altered lignin synthesis. In several cases, manipulation of the expression of lignin biosynthesis genes resulted in alteration in lignin structure rather than alteration in quantity. Because the efficiency of biomass conversion depends on hydrolyzing agents gaining access to plant polysaccharides, alteration of plant cell wall structure could yield important advantages. For example, when the lignin biosynthesis gene CCR is down-regulated in poplar, the cellulose component of the plant cell wall is more easily digested by the bacterium Clostridium cellulolyticum, and twice as much sugar is released. The intensive genetic engineering used to alter lignin structure and content with the goal of improving wood and papermaking quality shows the potential of these approaches. In summary, advances in plant sciences and genetics are providing researchers with the tools to develop the next generation of agroenergy/ material crops having increased yield and utility tailored for modern biorefinery operations.

Biomaterials from Biorefineries

These advances in plant sciences will need to be captured in subsequent biorefinery operations. In essence, the modern biorefinery parallels the petroleum refinery: An abundant raw material consisting primarily of renewable polysaccharides and lignin (Fig. 3) enters the biorefinery and, through an array of processes, is fractionated and converted into a mixture of products including transportation fuels, co-products, and direct energy.

Fig.3: Key global biomass resources from agricultural residues, wood, and herbaceous energy crops.

The power of the biorefinery concept is supported by economies of scale and by efficient use of all incoming bioresources. A key aspect of the biorefinery concept is the imbalance between commodity chemical needs and transportation fuels. Using the petroleum industry as an illustrative example, ~5% of the total petroleum output from a conventional refinery goes to chemical products; the rest is used for transportation fuels and energy. Most visions for integrated biorefineries do not expect this ratio to change.

The paradigm shift from petroleum hydrocarbons to highly oxygen-functionalized, bio-based feedstocks will create remarkable opportunities for the chemical processing industry. For example, the use of carbohydrates as chemical raw materials will eliminate the need for several capital-intensive, oxidative processes used in the petroleum industry. Biomass carbohydrates will provide a viable route to products such as alcohols, carboxylic acids, and esters. These natural products are also stereo- and regiochemically pure, thereby reducing dependence on expensive chiral catalysts and complex syntheses that are currently required to selectively install chemical functionality in petrochemicals.

Bio-based feedstocks are already having an impact on some practical applications, including solvents, plastics, lubricants, and fragrances. Bio-derived plastics such as polylactic acid are attracting attention, in part because of their biological compatibility and hydrolytic degradation, which enables them to successfully replace petrochemicals as well as open up new applications. Polylactic acid is currently manufactured on a million-kilogram scale in the United States and on a smaller scale in Europe and Japan. This process ferments corn dextrose to produce lactic acid that is subsequently dimerized, polymerized, and used in several applications, including food packaging and the apparel industry. The production of lactic acid by fermentation is economically competitive with its chemical synthesis from acetaldehyde and hydrogen cyanide. Further reductions in cost are expected with improvements in the fermentation process and the use of waste agricultural materials as feedstocks. Another example is the production of 1,3- propanediol by the fermentation of carbohydrates. This process is being exploited to supplement the use of petrochemically derived 1,3-propanediol to make poly(trimethylene terephthalate), a polymer fiber with properties related to nylon and polyethylene terephthalate. These commercially viable processes do, however, require purified feedstocks. The major impediment to biomass use is the development of methods to separate, refine, and transform it into chemicals and fuels.

One of these steps, separation, currently accounts for 60 to 80% of the process cost of most mature chemical processes. As we progress from the oil refinery to the biorefinery, the challenges associated with separation will change, but not diminish, in importance. In the petroleum industry, distillation is the unit operation that dominates the refinery separation scheme. For chemicals derived from biomass, this dominance will be transferred to solventbased extraction. This is a result of the nonvolatile nature of most biomass components and the fact that other separation techniques, such as chromatography or membranes, do not yet have the same economies of scale.

Future biorefinery operations will first extract high-value chemicals already present in the biomass, such as fragrances, flavoring agents, food-related products, and high-value nutraceuticals that provide health and medical benefits. Once these relatively valuable chemicals are extracted, the biorefinery will focus on processing plant polysaccharides and lignin into feedstocks for bio-derived materials and fuels. This requires the development of innovative separation and depolymerization process chemistries. Supercritical CO₂, nearcritical water, and gas-expanded liquids are well suited to these challenges. These tunable solvents offer distinct green chemistry processing advantages that could be exploited in the processing of renewable bioresources. Supercritical fluids exhibit outstanding transport properties coupled with highly tunable solvent properties (such as solvent power and polarity) and ease of solvent removal. Near-supercritical fluids are also highly tunable and generally offer better transport than liquids and better solvent power than supercritical fluids. Gasexpanded liquids are mixtures of a gas with an organic liquid such as methanol or acetone; in our context the gas is CO₂, which is completely miscible with most organics. These solvents exhibit highly tunable solvent power, as small pressure changes yield large changes in composition, and they give much greater solubilities and operate at much lower pressures than supercritical fluids. All of these solvents result in advantages for downstream processing in terms of product purification and/or catalyst recycling.

Water is arguably the most environmentally benign and food-safe solvent that can be used in chemical synthesis. However, the range of water-soluble substrates is quite limited, making ambient water an unsuitable medium for many chemical syntheses. Near-critical water (200^o to 300^oC) exhibits a reduction in dielectric constant (20 to 30) and density (0.7 to 0.8 g/cm³) relative to ambient water; its ability to dissolve both nonpolar organic molecules and inorganic salts is comparable to that of the popular organic solvent acetone. In addition, under these conditions, the dissociation constant of water into hydroxide and hydrogen ions rises by more than three orders of magnitude, so that near-critical water also acts as a selfneutralizing acid or base catalyst, eliminating salt waste generation. Further, the use of near-critical water in place of organic solvents greatly simplifies product isolation, as nonpolar products are insoluble after cooling. The utility of this medium has been demonstrated for a diverse group of organic syntheses. High-temperature water has already been proposed for the depolymerization of cellulosic waste materials in the Biometics process for producing levulinic acid.

The sugars in the biorefinery process can be transformed into building-block chemicals by fermentation as well as by enzymatic and chemical transformations. The key building block chemicals will include ethanol, C3 to C6 carboxylic acids (e.g., hydroxypropanoic acid, glucaric acid), and alcohols such as glycerol and sorbitol. It is noteworthy that the current cost of many carbohydrates and their derivatives is already competitive with petrochemicals and solvents such as toluene, aniline, and acetaldehyde. The U.S. Department of Energy recently published a comparative study on the top 12 chemicals from carbohydrate biomass, identifying several particularly promising compounds including sorbitol, levulinic acid, and glycerol. The effective production and use of these chemicals rely on the development of innovative enzymatic and catalytic green chemistries that will yield a viable range of new bioderived products.

Biofuels: Biopower from Biorefineries

After extracting value-added chemicals from biomass in the early stages of a biorefinery, the separations and chemical operations will need to be shifted to the production of biofuels. Today’s bioethanol plant process relies largely on the fermentation of starch from corn in the United States or from sugar cane in Brazil. Enhancing the cost structure of bioethanol generation has moved research attention away from plant grains and more toward corn stovers, trees, and other low-cost agricultural and municipal waste materials. These biomaterials typically have higher amounts of cellulose and hemicellulose, and their efficient, cost-effective depolymerization remains a key challenge in their use.

One important tool in reducing the cost of this depolymerization is pretreatment of lignocellulosics to make the biomass matrix more accessible to enzymes. The tailoring of chemical and physical pretreatments for specific biomass resources is a field of growing interest and practicality. These pretreatment benefits are leveraged with recent research efforts that have reduced the cost of cellulase by a factor of 5 to 10. Future cost reductions in bioprocessing will be accomplished by combining cellulase/hemicellulase treatments with other process steps. For example, researchers have proposed combining cellulase production with the fermentation steps via modified microorganisms capable of both cellulase production and ethanol fermentation, which could provide just-in-time delivery of the optimal mixture of the hydrolytic enzymes.

The endogenous production of such polysaccharide hydrolyase enzymes could also be coupled with enhanced plant biomass production made possible by recent advances in molecular farming. Exogenous depolymerization enzymes used in the bioethanol process could be replaced with plants that are capable of synthesizing these enzymes in situ. Carbohydrate depolymerase enzymes, such as cellulase, could be triggered for plant biosynthesis when an inducer is applied to the plant. A signal sequence from a cell wall protein could be spliced onto the cellulase gene to ensure that the cellulase synthesized by the plant is localized to the plant cell wall. The cellulase signal sequence-coding region would be attached to a chemically induced promoter that would switch on the cellulase gene. Once the modified cellulase transgene is introduced into a host plant, seeds could be produced, planted, and cultivated normally. Just before harvest, the crop would be sprayed with the chemical inducer. The cellulase would then be produced and transported to the cell wall, where it would start to break down the cellulose. After harvesting, the residual plant material would be collected and transported to a biorefinery, during which the in situ–generated cellulase would continue to depolymerize cellulose to glucose. An added feature of this approach is that additional depolymerization enzymes could be brought to bear for further, no-cost conversion of plant polysaccharides to mono- or oligosaccharides, facilitating subsequent separation or fermentation operations.

Currently, the fermentation of a mixture of hexoses and pentoses is inefficient because no wild organisms have been found that can convert all sugars at high yield into ethanol. Recently, several groups have made great advances in this field by genetically modifying microorganisms. One promising strategy has been to take a natural hexose ethanologen and add the pathways to convert other sugars. This strategy has been effective in adding pentose conversion to Saccharomyces cerevisiae and to Zymomonas mobilis. The other primary strategy has been to modify a host capable of converting multiple sugars to produce only ethanol from glycolysis. Other remaining microbiological challenges include the need to understand and manipulate ethanol and sugar tolerance and resistance to potential inhibitors generated in presaccharification treatments. Solutions to these issues also will need to accommodate the variability in biomass resources.

Biological processing is not the only refining approach, however. Although biological protocols of converting polysaccharides to bioethanol are among the most developed process technologies available for biofuels, other burgeoning chemical technologies are being pursued and present promising alternatives. These biofuels technologies are centered on the removal of oxygen from carbohydrates to obtain oxygenated hydrocarbons. As summarized in Fig. 4, controlled elimination of water from sugars has been extensively studied and can provide 5-hydroxymethyl-2-furfural (HMF), levulinic acid, and other organic acids.

Fig.4: Dehydration-decarboxylation chemistry of hexoses.

Although these materials are too polar for direct liquid fuel applications, they could be used as a resource for subsequent conversion to alternative fuels. For example, controlled decarboxylation and dehydration of hexoses could yield structures such as valerolactone or 2- methylfuran. These relatively nonpolar compounds could be considered as components for novel gasoline blends, which are typically dependent on ~C5 to C10 hydrocarbons. The controlled decarboxylation and dehydration of sugars is an essential objective of this process, as overdehydration will lead to polymeric materials that have little value as biofuels. These proposed products will not provide a viable diesel supplement because diesel fuel typically relies on C12 to C20 hydrocarbons. Given the higher vapor pressure requirements of diesel fuel, these issues could be addressed by subsequent dimerization of HMF, valerolactone, or related compounds, which will increase the chain length of these biodiesel precursors.

Dumesic and co-workers recently demonstrated the potential of this pathway. Using a catalytic system containing both acidic and noble metal catalysts, they were able to dehydrate and hydrogenate an aqueous stream of sorbitol to hexane. They also showed that an aldol-crossed condensation between HMF and acetone leads to C9 to C15 alkanes when performed under a hydrogen atmosphere in the presence of a Pt/SiO₂-Al₂O₃ catalyst. This field of study is ripe for further rapid advances as the revolution in catalysis, computational modeling, and combinatorial chemistry will lead to a suite of catalytic systems that will facilitate the conversion of biomass polysaccharides to liquid alkanes and oxyalkanes for fuel applications.

For the biorefinery approach to be widely applicable, the lignin component of lignocellulosics must also be addressed. Residual lignin from paper pulping is now burned for heat and power, but lignin thermal-cracking studies using temperatures of ~250^o to 600^oC have demonstrated the potential of generating low molecular weight feedstocks for further processing. These high temperatures suggest that the use of cracking catalysts could lower conversion temperatures and provide improved control over product distributions. Shabtai et al. have highlighted this potential in a process whereby a two-stage catalytic reaction with lignin produces a reformulated, partially oxygenated gasoline-like product. Lignin is first depolymerized by a base-catalyzed treatment into a series of low molecular weight phenolic compounds. This mixture is then subjected to hydroprocessing, which primarily yields a mixture of alkylbenzenes useful as a potential liquid biofuel.

This pyrolysis approach to biofuels from lignin is also being pursued with biomass in general, with and without a catalyst; it provides about 58 to 77% conversion of biomass to a condensable gas, 13 to 28% noncondensable gases, and 6 to 13% char formation. The condensable gases can be refined to fuels and chemicals, and the noncondensables can be steam-reformed to synthesis gas (syngas), a mixture of CO and H₂, which can also be used to produce fuels and chemicals.

Regardless of which process technologies are incorporated into a biorefinery, almost all will generate some waste products that will be intractable and difficult to convert to valueadded biomaterials or biofuels. These spentbiomass residues will contain fragments from lignin, residual carbohydrates, and other organic matter. This residue will need to be treated in an environmentally compatible manner, with the smallest ecological footprint. Such wastes and residues offer important energy sources within the biorefinery, given their chemical energy content, and are an ideal candidate for thermochemical conversion to syngas. Syngas is an intermediate in the production of ammonia, methanol, and Fischer-Tropsch hydrocarbons. Production of syngas from coal, natural gas, and other carbonaceous sources is well established. Coal is normally gasified in entrained-flow reactors at temperatures exceeding 1400^oC at 20 to 70 bar. Biomass is more reactive than coal and is usually gasified at temperatures between 800^o and 1000^oC at 20 to 30 bar.

The greatest challenge in producing syngas from biomass is the need to avoid poisoning the noble metal catalysts used in the subsequent downstream conversion to fuels and chemicals. Potential problem products are the alkali metals, halides, sulfur gases, and especially the tars. A high quantity of tar is produced as the organic components of biomass decompose. Evolution of tar from primary to tertiary species is rapid, but tertiary tar species are degraded slowly to CO and H₂ by water vapor or CO2 at temperatures below 1100^oC. Catalytic conversion of tar in raw syngas to CO and H₂ is practiced, but the quantities of tar that must be converted are large, and robust catalysts that are insensitive to alkali metals, halides, sulfur, and nitrogen need to be developed.

Chloride, the predominant halide in biomass, is converted to HCl or submicrometer aerosols of potassium and sodium during gasification, which poses a corrosion issue. Most of the alkali metal chlorides are removed by filtering the cooled syngas. Sulfur gases can be removed by absorption. Remaining alkali metal chlorides and sulfur gases are removed by reaction with ZnO in a packed-bed filter. Although these advances in syngas purification technologies are necessary for the catalytic conversion of syngas to other fuels or chemicals, they add further complications and increase the overall cost. Anaerobic fermentation of syngas into biofuels is a promising competing technology that is far more tolerant of tar and trace contaminants than noble metal catalysts. Development of enhanced bioagents, reactor designs with improved mass transfer of the syngas into the liquid phase, and enhanced gas and liquid separation methods are needed if the biochemical route is to become economically viable. As these challenges are addressed, the final component of the integrated biorefinery will become available, and the resulting residue products from the biorefinery will become a valuable resource for biopower, biofuels, and biomaterial generation.

Concluding Remarks

In view of changing world energy needs, a research road map for the biorefinery of the 21st century is vital. This biorefinery vision will contribute to sustainability not only by its inherent dependence on sustainable bioresources, but also by recycling waste, with the entire process becoming carbon neutral. It leverages our knowledge in plant genetics, biochemistry, biotechnology, biomass chemistry, separation, and process engineering to have a positive impact on the economic, technical, and environmental well-being of society.

An integrated biorefinery is an approach that optimizes the use of biomass for the production of biofuels, bioenergy, and biomaterials for both short- and longterm sustainability. The demands of future biorefineries will stimulate further advances in agriculture in which tailored perennial plants and trees will provide increasing amounts of bioresources, as highlighted in the "Billion-Ton" report. The advances in plant science will certainly be influenced by societal policies, land use practices, accelerated plant domestication programs, and research funding to develop this vision. Nonetheless, given humanity’s dependence on diminishing nonrenewable energy resources, this is a challenge that must be addressed—and we need to get on with it

Bioenergy FAQs

By the U.S. Department of Energy. The USDE has compiled a list of bioenergy queries with answers: some general questions, the use and availability of biofuels, production and technology, programmatic focus and investments and incentives.

What is biomass?

Biomass is any organic material made from plants or animals. Domestic biomass resources include agricultural and forestry residues, municipal solid wastes, industrial wastes, and terrestrial and aquatic crops grown solely for energy purposes.

Biomass can be converted to other usable forms of energy and is an attractive petroleum alternative for a number of reasons. First, it is a renewable resource that is more evenly distributed over the Earth's surface than are finite energy sources, and may be exploited using more environmentally friendly technologies.

Agriculture and forestry residues, and in particular residues from paper mills, are the most common biomass resources used for generating electricity and power, including industrial process heat and steam, as well as for a variety of biobased products. Use of liquid transportation fuels such as ethanol and biodiesel, however, currently derived primarily from agricultural crops, is increasing dramatically.

What are biofuels?

Biofuels are any fuel derived from biomass. Agricultural products specifically grown for conversion to biofuels include corn and soybeans. R&D is currently being conducted to improve the conversion of non-grain crops, such as switchgrass and a variety of woody crops, to biofuels.

The energy in biomass can be accessed by turning the raw materials of the feedstock, such as starch and cellulose, into a usable form. Transportation fuels are made from biomass through biochemical or thermochemical processes. Known as biofuels, these include ethanol, methanol, biodiesel, biocrude, and methane.

What is ethanol? What is the difference between E10 and E85?

Ethanol is the most widely used biofuel today. Also known as ethyl alcohol or grain alcohol, it can be used either as an alternative fuel or as an octane-boosting, pollution-reducing additive to gasoline. It is an alcohol fuel made from sugars and starch found in plants. In the U.S., ethanol is primarily produced from the starch contained in grains such as corn, grain sorghum, and wheat through a fermentation and distillation process that converts starch to sugar and then to alcohol.

Currently, a majority of ethanol is made from corn, but new technologies are being developed to make ethanol from other agricultural and forestry resources such as:

1. corn stover (stalks and residues left over after harvest);
2. grain straw;
3. switchgrass;
4. quick growing tree varieties, such as poplar or willow; and
5. municipal wastes.

Ethanol can be blended with gasoline in varying quantities to reduce the consumption of petroleum fuels, as well as to reduce air pollution. It is increasingly used as an oxygenate additive for standard gasoline, as a replacement for methyl t-butyl ether (MTBE), which is responsible for groundwater and soil contamination.

Most of today's commercially available vehicles can run on blends of E10, a blend of 10 percent ethanol and 90 percent gasoline, or lower. E10 is the most common low concentration blend. Many areas of the country mandate its use as a replacement for MTBE.

Ethanol can be blended with gasoline to create E85, a blend of 85 percent ethanol and 15 percent gasoline. Due to the corrosive affects of E85, because of its high alcohol content, traditional vehicles cannot use E85. Flex fuel vehicles (FFVs) have engines modified to accept higher concentrations of ethanol. Such flexible-fuel engines are designed to run on any mixture of gasoline or ethanol with up to 85 percent ethanol by volume.

What is biodiesel?

Biodiesel is a clean burning alternative fuel produced from domestic, renewable resources such as new and used vegetable oils and animal fats. Biodiesel is primarily produced through base catalyzed transesterification. Biodiesel is simple to use, biodegradable, nontoxic, and essentially free of sulfur and aromatics. Biodiesel can be blended at any level with petroleum diesel.

What are biobased products?

Today, petroleum is refined to make chemical feedstocks used in thousands of products. Many of these petroleum-based feedstocks could be replaced with value-added chemicals produced from biomass to then manufacture clothing, plastics, lubricants, and other products.

Biobased chemicals and materials are commercial or industrial products, other than food and feed, derived from biomass feedstocks. Biobased products include green chemicals, renewable plastics, natural fibers and natural structural materials. Many of these products can replace products and materials traditionally derived from petrochemicals, but new and improved processing technologies will be required.

What is biopower?

Biopower, or biomass power, is the use of biomass to generate electricity, or heat and steam required for the operation of a refinery. Biopower system technologies include direct-firing, cofiring, gasification, pyrolysis, and anaerobic digestion.

Most biopower plants use direct-fired systems. They burn biomass feedstocks directly to produce steam. This steam drives a turbine, which turns a generator that converts the power into electricity. In some biomass industries, the spent steam from the power plant is also used for manufacturing processes or to heat buildings. Such combined heat and power systems greatly increase overall energy efficiency. Paper mills, the largest current producers of biomass power, generate electricity or process heat as part of the process for recovering pulping chemicals.

How much biofuels are produced in the U.S. today?

According to the Renewable Fuels Association, the U.S. produced 5.4 billion gallons of ethanol in 2007. As of March 2008, U.S. ethanol production capacity was at 7.2 billion gallons, with an additional 6.2 billion gallons of capacity under construction.

As of January 2008, annual U.S. biodiesel production capacity was 2.24 billion gallons according to the National Biodiesel Board.

Use and Availability of Biofuels

Where can I buy biofuels?

Ethanol blends of E10 (10% ethanol, 90% gasoline) can be and are sold at gasoline fueling stations across the U.S. Ethanol in higher blends, such as E85, is also sold at gasoline fueling stations across the U.S., but requires modified fueling equipment.

Similarly, some diesel fueling stations across the U.S. also supply biodiesel in various blends.

Are biofuels more expensive than their petroleum-based counterparts?

Because the cost of any type of fuel - gasoline, diesel, ethanol, biodiesel - varies over time due to a variety of market, political, and production factors, it is difficult to say at any one time whether or not biofuels are sold for more or less than traditional petroleum-based fuels in the marketplace. On average, biofuels are generally comparable to traditional fuels in sales price, although they may be higher or lower at times, depending on gasoline and diesel prices. The non-monetary benefits of biofuels - such as environmental, national security, and local economy benefits - may also be taken into consideration by the consumer, even if they are not reflected in the cost of biofuels versus traditional fuels.

Will I get lower gas mileage with ethanol-blended fuels than with traditional gasoline?

The ethanol blends used today have little impact on fuel economy or vehicle performance:

• Ethanol has the highest octane rating of any fuel
• On a gallon-for-gallon basis, ethanol delivers less energy than gasoline. However, today's vehicles are designed to run on gasoline blended with ethanol in small amounts (up to 10%) with no perceptible effect on fuel economy
• Flex-fuel vehicles designed to run on higher ethanol blends experience reduced miles per gallon, but these engines can be tuned to minimize detrimental effects on fuel economy

Can ethanol be transported, stored, and dispensed within existing petroleum infrastructure?

Lower ethanol blends, such as E10, are currently mixed with gasoline and transported, stored, and dispensed in existing infrastructure. Higher ethanol blends, such as E85, however, require separate infrastructure because E85 cannot be used in all vehicles, and because E85 can corrode some materials. In many cases, existing petroleum fuel infrastructure can be used to transport and store E85, as long as they are properly cleaned and the fuels are not mixed. Special E85-compatible pump dispensers are available, and can be incorporated into existing fueling stations. The National Renewable Energy Laboratory, U.S. Department of Energy, and National Ethanol Vehicle Coalition jointly published the Handbook for Handling, Storing, and Dispensing E85, which contains more detail on this issue.

Production and Technology

How are biofuels created from plant material?

How a fuel is produced from plant materials can depend on a variety of factors, including the feedstock (or biomass plant material) being used and the fuel one desires to produce. For more information on the types of biomass feedstock available and the types of fuels that can be produced from them see the Office of the Biomass Program Biomass Feedstocks website.

Ethanol and biodiesel are the two most common types of biofuels. There are two primary types of conversion methods used to produce ethanol from biomass resources:biochemical conversion and thermochemical conversion . Biochemical conversion refers to the process where biomass is separated into its component parts, starch and cellulose. In water, both starch and cellulose can be broken down further to multiple sugars, which can than be fermented to produce ethanol. Thermochemical conversion heats the feedstock with no oxygen to produce synthesis gas (syngas). The syngas can be fermented to produce ethanol.

In the U.S., biodiesel is produced from the oil in soy beans, canola, and other agricultural products. The oils from the plant material are reacted with methanol to produce methyl esters (commonly known as biodiesel) and glycerin. For every 100 lbs of biodiesel produced approximately 10 lbs of glycerin is produced; glycerin is an ingredient in hand lotions and soaps.

Does the U.S. have enough biomass resources to displace petroleum with biofuels without negative impacts to the food supply?

A joint study conducted by the Departments of Energy and Agriculture, the Billion Ton Study (PDF 5.5 MB), estimates that 1.3 billion tons of biomass feedstock is potentially available in the U.S. for the production of biofuels. This is enough biomass feedstock to displace approximately 30 percent of current gasoline consumption on a sustainable basis.

Both the U.S. Department of Agriculture's (USDA) Chief Economist (PDF 53 KB), as well as the National Corn Growers Association, have recently testified to Congress that they do not foresee proposed increases in ethanol production having a negative impact on the availability of corn and other grains for food purposes.

The development of technologies to convert cellulosic feedstocks (or non-grain based resources that are not used for food purposes, such as switchgrass, agricultural residues, and wood resources) will make it possible to produce biofuels at levels that will meet the various goals described above from feedstocks that are not competing with other uses.

What other materials can be produced from biomass?

Biomass can be used to produce any number of common products based on the feedstock (or biomass plant material) chosen. Specific products include but are not limited to plastics, polymers, carpets, fabrics, detergents, fabrics, and lubricants.

The Office of the Biomass Program "Top Value Added Chemicals from Biomass (Volume 1)" study (PDF 1.4 MB) provides an extensive list of potential products and intermediate chemicals that can be commercially produced from biomass.

Does ethanol require more energy to produce than it delivers as a fuel?

Each gallon of corn ethanol produced today delivers as much as 67 percent more energy than is used to produce the ethanol. The amount of energy used to produce corn ethanol has decreased significantly over the last two decades due to improved farming techniques, more efficient use of fertilizers & pesticides, higher-yielding crops, and advances in conversion technologies.

The focus of the Biomass Program is on the development of cellulosic biofuels. Cellulosic ethanol has an even higher energy balance than corn ethanol, delivering four to six times as much energy as is necessary to produce it.

Does ethanol result in more or less greenhouse gas emissions than gasoline?

Ethanol results in fewer greenhouse gas (GHG) emissions than gasoline. The higher the amount of ethanol blended with gasoline the lower the resulting GHG emissions. Cellulosic ethanol has the potential to reduce GHG emissions by up to 86 percent. Click here for more information on the environmental benefits of biofuels.

Use of ethanol can, however, increase the emissions of some air pollutants due to the fossil energy inputs used for farming and biofuels production. Such emissions can be reduced by using improved farming methods and renewable power in the production process.

Programmatic

What is the R&D focus of the Office of the Biomass Program?

The R&D focus of the Biomass Program is on the development of the integrated biorefinery, which includes both biological and thermochemical conversion processes. Currently, the Program is organized to address the technological R&D needs of each stage in the biorefinery: sustainable feedstock production & logistics, biochemical conversion, thermochemical conversion, and integrated biorefinery development.

Feedstock R&D is focused on ensuring a sustainable biomass supply and on the reduction of biomass harvesting and storage costs. Biochemical conversion R&D is currently the highest priority for the program; it is focused on reducing the cost of producing mixed sugars by overcoming the difficulty of separating biomass into its components (cellulose and lignin). The thermochemical conversion R&D focus is developing technologies that convert the residues from the biochemical conversion process into fuels, heat and chemicals. The focus of integrated biorefinery R&D is the development of cost-effective cellulosic biorefineries.

Additional information on the Office of the Biomass Program R&D focus can be found at the Office of the Biomass Program.

With the President's announcement of the Advanced Energy Initiative (AEI) (PDF 2.6 MB) in the 2006 State of the Union address, and the Twenty in Ten (PDF 50 KB) initiative in the 2007 State of the Union Address, the primary focus of the Program has shifted to achieving the goals of the these initiatives as they relate to alternative fuels.

What is the President's Advanced Energy Initiative?

During the 2006 State of the Union Address, the President announced the Advanced Energy Initiative (AEI). The AEI aims to reduce the nation's reliance on foreign sources of energy by addressing two areas: 1) Changing the way we fuel our vehicles, and 2) Changing the way we power our homes and businesses.

AEI Goals for the way we fuel our vehicles are:

• Develop advanced battery technologies that allow a plug-in hybrid-electric vehicle to have a 40-mile range operating solely on battery charge.
• Foster the breakthrough technologies needed to make cellulosic ethanol cost-competitive with corn-based ethanol by 2012.
• Accelerate progress towards the President's goal of enabling large numbers of Americans to choose hydrogen fuel cell vehicles by 2020.

AEI Goals for the way we power our homes and businesses are:

• Complete the President's commitment to $2 billion in clean coal technology research funding, and move the resulting innovations into the marketplace.
• Develop a new Global Nuclear Energy Partnership (GNEP) to address spent nuclear fuel, eliminate proliferation risks, and expand the promise of clean, reliable, and affordable nuclear energy.
• Reduce the cost of solar photovoltaic technologies so that they become cost-competitive by 2015, and expand access to wind energy through technology.

What is the President's Twenty in Ten Initiative?

During the 2007 State of the Union Address, the President announced the "Twenty in Ten", an effort to reduce U.S. gasoline usage by 20 percent in the next ten years. America will reach the President's goal by:

1. Increasing The Supply Of Renewable And Alternative Fuels By Setting A Mandatory Fuels Standard To Require 35 Billion Gallons Of Renewable And Alternative Fuels In 2017 – Nearly Five Times The 2012 Target Now In Law. In 2017, this will displace 15 percent of projected annual gasoline use.
2. 2. Reforming and Modernizing Corporate Average Fuel Economy (CAFE) Standards for Cars and Extending the Current Light Truck Rule. In 2017, this will reduce projected annual gasoline use by up to 8.5 billion gallons, a further 5 percent reduction that, in combination with increasing the supply of renewable and alternative fuels, will bring the total reduction in projected annual gasoline use to 20 percent.

Investment and Incentives

What resources or incentives are available to support biofuels development?

There are a number of Federal tax credits and refunds available for the production, blending, sale, or use of biofuels. See the IRS Fuel Tax Credits and Refunds page for specifics on the incentives available and how to apply.

The Department of Energy Office of Energy Efficiency and Renewable Energy's Alternative Fuels Data Center tracks both Federal and State incentives for transportation-related topics, such as alternative fuels and vehicles, air quality, and fuel efficiency.

There are also a variety of state incentives available for renewable energy in general, many of which are biomass-related. The Database of State Incentives for Renewables and Efficiency has information by state.

The Department of Energy makes funding for research and development related to biofuels available via competitive solicitations. All opportunities are publicly available through Grants.gov or the DOE E-Center.

The National Biomass Initiative tracks both State and Federal biomass-related funding opportunities.

What companies are involved in biomass energy/biofuel production?

The best resource for information on both biodiesel and ethanol producers are their respective industry associations:

• The National Biodiesel Board
• The Renewable Fuels Association
• The Biobased Manufacturers' Association
• Other biomass energy trade associations are linked on the OBP website.

The Biomass Program at DOE and the USDA - DOE Biomass Initiative do conduct some projects with industry research partners, awarded via independently assessed competitive solicitations.

Have biofuels been successful in other countries?

Yes, biofuels have been commercially successful in several other countries. Brazil (ethanol) and Germany (biodiesel) are two examples. In Brazil, "Eighty percent of 2005 production (ethanol) is anticipated to meet national demands (transportation fuels)."i In Germany, the last ten years consumption and production of biodiesel has increased several fold. In 2004, 1.18 million tones were produced, up 45 percent from 2003 and an additional 500,000 tonnes are planned for 2005.

Biogas: Cleaning and Uses

By Mahendran Navaratnasamy, Agriculture Stewardship Division, Jim Jones, Bio-Industrial Development, Bruce Partington, Rural Utilities Division of the Agriculture and Rural Development, Alkberta. Biogas consists of methane (CH₄) and carbon-dioxide (CO₂) along with some trace gases such as water vapour, hydrogen sulphide (H₂S), nitrogen, hydrogen and oxygen.

Carbon dioxide and trace gases such as water vapour and H₂S must be removed before the biogas can be used because:

• the hydrogen sulphide gas is corrosive
• water vapour may cause corrosion when combined with H2S on metal surfaces and reduce the heating value

Uses

Biogas is mostly used as a fuel in power generators and boilers. For these uses, the H₂S content in biogas should be less than 200 parts per million (ppm) to ensure a long life for the power and heat generators.

Biogas can also be upgraded to pipeline natural gas quality for use as a renewable natural gas. This upgraded gas may be used for residential heating and as vehicle fuel.

When distributing the biogas using pipelines, Canadian oil and gas pipeline standards may become applicable. According to Canadian oil and gas pipeline standards, the H₂S content shall not exceed 4.6 ppm at 0° C. The CO₂ level should be lower than two per cent (CH₄> 95 %).

Removing water vapour is easier than removing CO₂ and H₂S from biogas. A condensate trap at a proper location on the gas pipeline can remove water vapour as warm biogas cools by itself after leaving the digester.

Producing pipeline gas quality requires the use of advanced and expensive technologies. The cost of cleaning and producing pipeline quality gas (renewable natural gas) is $3 to 6/GJ and $6 to 12/GJ, respectively.

The following sections include brief information about these technologies as well as about using biogas as a transportation fuel.

CO₂ Removal

Carbon dioxide is soluble in water. Water scrubbing uses the higher solubility of CO₂ in water to separate the CO₂ from biogas. This process is done under high pressure and removes H₂S as well as CO₂. The main disadvantage of this process is that it requires a large volume of water that must be purified and recycled.

Polyethylene glycol scrubbing

This process is similar to water scrubbing; however, it is more efficient. It also requires the regeneration of a large volume of polyethylene glycol.

Carbon molecular sieves

The carbon molecular sieve method uses differential adsorption characteristics to separate CH₄ and CO₂. This adsorption is carried out at high pressure and is also known as pressure swing adsorption. For this process to be successful, H₂S should be removed before the adsorption process.

Membrane separation

There are two membrane separation techniques:

• high pressure gas separation
• gas-liquid adsorption

The high pressure separation process selectively separates H₂S and CO₂ from CH₄. Usually, this separation is performed in three stages and produces 96 per cent pure CH₄.

Gas liquid adsorption is a new development and uses microporous hydrophobic membranes as an interface between gas and liquids. The CO₂ and H₂S dissolve while the methane (in the gas) is collected for use.

H₂S Removal

Biological desulphurization

Natural bacteria can convert H₂S into elemental sulphur in the presence of oxygen and iron. This can be done by introducing a small amount (two to five per cent) of air into the head space of the digester. As a result, deposits of elemental sulphur will be formed in the digester. Even though this situation will reduce the H₂S level, it will not lower it below that recommended for pipeline-quality gas.

This process may be optimized by a more sophisticated design where air is bubbled through the digester feed material.

It is critical that the introduction of the air be carefully controlled to avoid reducing the amount of biogas that is produced.

Iron/iron oxide reaction

Hydrogen sulphide reacts readily with either iron oxide or iron chloride to form insoluble iron sulphide.

The reaction can be exploited by adding the iron chloride to the digester feed material or passing the biogas through a bed of iron oxide-containing material. The iron oxide comes in different forms such as rusty steel wool, iron oxide pellets or wood pellets coated with iron oxide.

The iron oxide media needs to be replaced periodically. The regeneration process is highly exothermic and must be controlled to avoid problems.

Activated carbon

Activated carbon impregnated with potassium iodide can catalytically react with oxygen and H₂S to form water and sulphur. The reaction is best achieved at 7 to 8 bar (unit of pressure) and 50°to 70° C. Activated carbon beds also need regeneration or replacement when saturated.

Scrubbing and membrane separation

As discussed in the section on CO₂ removal, the CO₂ and H₂S can be scrubbed by water, polyethylene glycol solutions or separated using the membrane technique.

Biogas as Transportation Fuel

Using the upgraded biogas for automotives is similar to using natural gas. In Canada, there are about 20,000 natural gas vehicles in use. This transportation fuel can either be in the form of compressed natural gas (CNG) or liquefied natural gas (LNG).

When CNG is used as a transportation fuel it is generally referred to as natural gas for vehicles (NGV). Typical vehicles require modification to run on natural gas. The cost of modification is about $6,000 and depends on the size of the vehicle.

Certified natural gas compressors for refueling the vehicles (known as vehicle refueling appliances or VRAs) are commercially available. These allow refueling at home or work. Your local natural gas company may provide information on different brands of refueling equipment and equipment providers.

Advantages

• CNG burns cleanly
• CNG engines make less noise than do diesel engines
• nitrogen oxide emission is very low
• natural gas users can take advantage of on-site refuelling units located at their home or business
• CNG is less likely to cause contamination than is gasoline in the event of leak or spill

Disadvantages

• high cost ($3-6/GJ) to clean the biogas
• reduced driving range
• less cargo space

Summary

Traces of impurities are present in biogas. Removal of these impurities (such as water vapor, CO₂ and H₂S) is essential prior to using as fuel for various applications. It is possible to upgrade biogas to pipeline-gas quality using the above discussed techniques. The upgraded biogas may be termed as renewable natural gas and has similar applications as natural gas.

References

NRCAN 2007. Vehicle and Fuel Availability.

IEA 2001. Biogas and More: Systems Market Overview of Anaerobic Digestion.

For additional information, check the following web pages:

Anaerobic Digesters Agdex 768-1
Anaerobic Digesters: Frequently Asked Questions, Agdex 768-2
Biogas Energy Potential in Alberta, Agdex 768-3
Integrating Biogas, Confined Feedlot Operations and Ethanol Production, Agdex768-4
Biogas Distribution – Rural Utilities Division of Alberta Agriculture and Rural Development .
Incentives for Biogas Production – Alberta Bioenergy Producer Credit Program.

New Mechanism to Produce Energy from Biomass

Scientists from the Carlos III University of Madrid (UC3M) have developed a system that can improve the efficiency of the conversion process of biomass to fuel gas that will contribute to the production of energy in a more sustainable manner.

One of the challenges that chemical engineers face is placing solid materials in contact with gases to generate certain reactions.

One of the options is to use a fluidised bed, consisting of a vertical cylinder with a perforated plate inside where solid particles are introduced using pressurised air.

This way, the solid particles are suspended, and behave much like boiling water. Solids behaving like a liquid depend on the speed of the air stream, making it key to achieving the desired behaviour.

With insufficient air, the particles don’do not move, but with too much the opposite happens, and they are carried away by the air stream.

Fluidised beds have relevant environmental applications because they allow the gasification of biomass to produce energy. That is, producing fuel gas from crushed biomass which can then be used for energy production.

According to one of the authors of the study, Mercedes de Vega from the Energy System Engineering Group of the department of Thermal and Fluid Engineering of the UC3M, using fluidised beds as chemical reactors allows for a more efficient conversion by achieving high mixing degrees and high exchange rates of mass and heat.

This renewable source has great potential in Spain, especially in processes of co-combustion, direct combustion, and gasification.

The applications are mainly industrial, open to be used in motors for the production of electricity, in gas turbines, drying processes, as well as in the pharmaceutical industry for the treatment of powder.

Greater Efficiency

The study analyses the behaviour of a new bed designed with a rotating base.

The base consists of a perforated plate where holes represent just one per cent of its total area.

The study evaluates the performance of this new design, considering the increase in pressure and the quality of the fluidisation.

It also analyses the effect of the rotation speed of the perforated plate on the performance of the fluidised bed.

This type of beds can usually present problems such as agglomeration of solid particles and points of high temperature.

But one of the most important conclusions determined that the rotating perforated plate reduces these problems by maintaining a very uniform fluidisation.

The researchers now propose, for future investigations, to study different rotation speeds over 100 revolutions per minute, and to alter the configuration of the holes in the plate.

Celia Sobrino, author of the study, states that the new rotating distribution plate produces smaller bubbles inside the fluidised bed and distributes them better, while improving the efficiency of the conversion in gasification applications.

The study 'Fluidization of Group B particles with a rotating distributor' carried out by the Energy System Engineering Group of the department of Thermal and Fluid Engineering of the Carlos III University of Madrid has been published in the journal Powder technology.

What is Really Needed to Make Biogas Work?

Biogas production through anaerobic digestion is a technology option that has received increasing attention throughout North America over the past number of years, Cedric MacLeod from MacLeod Agronomics told the Banff Pork Seminar this year.

2008

Introduction

The technology, of course, is not novel, and was intensively explored during the 1970’s energy crunch/boom depending on which side of the market one was on. As oil and gas prices plummeted during the 1980’s so did interest in biogas production from organic residual materials, known in some circles as ‘organic wastes’. This represents one of the key factors that must be considered in biogas system planning and assessment efforts. Biogas production is not a cheap source of energy, however, the adoption of anaerobic digestion technology provides a number of valuable products, some of which have been assigned value in today’s society, and some that have not. The pros and cons of biogas production in Canada will be further discussed in the context of industry growth in select regions of the country and contrasted with efforts being expended in select EU member states.

What is Biogas?

Anaerobic digestion (AD) is a naturally occurring microbial process that converts organic material into a mixture of methane, carbon dioxide and trace gases in a warm environment free of oxygen, hence anaerobic digestion. Many of the by-products produced from primary agricultural production or food processing are suitable for AD treatment. Livestock manures are a preferred feedstock, but tend to be relatively low in energy density compared to products such as food processing or slaughterhouse wastes, or energy crops such as corn or cereal crop silage. AD technology is used quite extensively in the food processing industry as the waste streams from these operations are often high strength (high Biological Oxygen Demand) and difficult to process. Treatment in a biogas plant reduces the strength of the residuals stream, allowing for more effective clarification, and the product of AD treatment (biogas) provides a source of on-site thermal or electrical energy production. This represents one of those win-win situations often discussed in reference to environmental management technologies, ‘treat your wastes efficiently and get energy for the effort’.

Past and Current Technology Adoption around the World

Active anaerobic treatment has been used for centuries by various societies. Centuries ago, the Chinese used deep, cone shaped in-ground lined pits to store animal and human manures, food wastes and other organics and collected the methane gas that was emitted for use as a cooking and heating fuel. This approach has lasted throughout the centuries and thousands of family-based digesters operate in China, India and other developing countries today. In the more recent past, London’s street lamps were built as an extension of the city’s below ground sewage transportation network and the ‘swamp gas’ that was emitted from the sewers was burned to light the way for evening passers by.

The world energy crunch of the 1970-80’s brought anaerobic waste treatment to the modern industrial world as oil and natural gas prices reached record levels. More than 100-biogas plants were constructed in North America during this period, many of which still stand as relics of the effort, but few continue to produce useful biogas. These early installations failed due to a number of factors including overbearing or poorly conceived engineering efforts, lack of understanding of the complexities of operating a biogas plant, and/or the physical, chemical and biological process at work in the anaerobic reactor.

Further to the technical challenges that were faced by early AD pioneers, as the price of hydrocarbon fuels returned to their pre-OPEC oil embargo prices, early interest in perfecting the industrial biogas energy production concept was largely diminished.

Despite societies’ disregard for the environmental (cost) benefits that AD systems can provide, the concept was not completely lost in the 1980s.. Many individuals involved in the original North American AD push continued to work towards perfecting the technology despite low oil, coal and gas prices. Early programs such as AgSTAR, a collaborative effort between the US Departments of Environment, Energy and Agriculture have promoted the installation of on-farm biogas plants as demonstration and learning sites. More recently Agriculture and Agri-Food Canada’s Energy Cogeneration from Agricultural and Municipal Wastes program provided funding to a number of Canadian biogas installations to collect system performance data to verify that biogas plants can be effectively operated in Canada’s cold northern climate.

Many European countries have successfully ushered in a modern age of green energy production with the creation of effective renewable energy policies. Germany, despite having large coal reserves is by far the world leader in biogas plant design and construction. Other European nations such as Denmark, Austria, Switzerland, Italy and Ireland have followed the German lead, installing policies that place an appropriate value on biogas energy production which has encouraged significant investment in the sector.

Making Biogas Work

To identify the policy, cash incentive and/or economic reality environments in which a thriving biogas industry may evolve, it is important to consider how biogas has gained a foothold in exemplary regions around the world.

Policy

Policy is an extremely important driver in the development of a successful biogas sector within a given region. Greenhouse gas management is playing an increasingly important role in policy development and is one of the key selling points for the development of biogas energy policy. Elevated power purchase rates for biogas derived electrical energy often include a few cents per kilowatt hour produced to reflect the reduced GHG emissions that result from treating organic residual (waste) products using anaerobic digestion. Often policy makers are intrigued by the ability of a biogas system to turn odorous, nuisance products into quality fertilizer and renewable energies.

Germany is the most common reference for how a thriving biogas industry can be stimulated with renewable energy policy. With a goal of eliminating nuclear power from the power generation system, Germany placed a high value on a host of renewable energies, and established power purchase rates that reflected the costs of producing each type of renewable energy individually. Initial feed-in tariff rates for biogas power did not provide enough incentive to spurn the widespread adoption of biogas power generation, but rather promoted the construction of a small number of large industrial facilities. While a success in terms of gaining some biogas production momentum, subsequent revisions of renewable energy laws allowed for the construction of much smaller biogas plants, 100-250 kWh generation capacity, and small independent power producers to operate biogas plants in a profitable position.

Roughly 1200-MW of biogas energy generation capacity has been installed to date in Germany. Upwards of 4,000-AD systems are currently operating, many designed to operate using biomass energy crops such as corn or winter rye silage, which significantly boost power output, compared to manure only systems.

Cash Incentives

There are typically two options for biogas industry support that have been adopted by world biogas leading nations, support biogas energy prices as described above, or make the energy cheaper to produce by subsidizing construction costs.

Germany has chosen to support the growth of the renewable sector through mandated power purchase rates, or feed-in tariff rates. Lawmakers there produced the Renewable Energy Sources Act which put in place specific rules that German utilities were obligated to follow. These rules included a predetermined feed-in tariff rate that in some cases for biogas plant operators results in a payment of nearly $0.28CAD/kWh produced. The Act also stated that if renewable power was produced, the utilities had no option but to buy it, no questions asked and no arguing about the purchase price.

Several Canadian provinces have installed renewable power purchase programs that would apply to biogas power production. Purchase prices, or top up incentives can range from a low of $0.04CAD/kWh to a high of $0.14CAD/kWh for power placed on the grid during peak consumption periods.

The US based AGSTAR program has provided grant funding for the development of biogas plants across the US. A number of state programs have also been designed around the grant-based incentive option, however, there have been recent developments in the development of feed-in tariff rates for biogas energy production in Michigan and other states. Ontario, Alberta and Manitoba to a much smaller extent, are currently offering grant based AND feed-in tariff incentives to stimulate biogas plant construction in their respective regions.

The EVER evolving carbon trading programs should not be discounted as a potential source of income in biogas plant feasibility analysis. A 600-sow farrow-to-finish operation located in Red Deer Alberta would produce enough biogas to operate a 50-kW generator continuously. Table 1 provides a brief analysis on the value of carbon offsets that might be created by installing a biogas plant at a 600-sow unit.

Table 1. Biogas Plant Greenhouse Gas Reduction and Value Estimate
	Baseline GHG Emissions (MT CO2e)	Digester GHG Emissions (MT CO2e)	GHG Reduction (MT CO2e)	Carbon Offset Value*
Methane (CH4)	640	40	600	$9000
Nitrous Oxide (N2O)	500	350	150	$2250
Total	1140	390	750	$11250
* Based on $15/MT CO2e

Economic Reality

Where there’s coal, there’s cheap energy!! It is certainly difficult for some to consider paying at least $11/MWh if not $14-17/MWh for biogas generated electricity when coal consuming regions boast $4/MWh prices for energy delivered to the doorstep. Seldom considered are the hidden costs of dirty power generation however, and true economic realities are simply not reported. Coal-fired power plants produce constant emissions of mercury, nitrogen and sulphur dioxides, particulate matter and of course carbon dioxide GHG emissions. Applying an environmental degradation fee, or estimating the costs to the health care system to address respiratory illness linked to coal burning emissions, is extremely challenging. Unfortunately, society seems quite happy to accept that there is a social and environmental cost to nonrenewable power generation, and simply continue to pay $0.04kWh on the power bill each month. If society would like to see enabling technologies such as anaerobic digestion take hold, it needs to become less complacent and place value where value is due. Clean water and clean air will support vibrant economies, despite higher energy costs. If the energy system status quo does not change, increasingly, our provincial and federal budgets will be consumed with healing people and the environments in which we live as opposed to supporting a quality living experience for Canadian citizens.

Biogas power plants in provinces such as Quebec, Manitoba and British Columbia will compete directly with hydro power for a share of the electricity market. Despite having significant livestock herds, and significant quantities of biogas feedstock (manure) available, these provinces also boast vast hydro resources, one of the least expensive sources of electrical energy available. Support through appropriate policy development is essential in these regions if a biogas industry is expected to flourish.

Although quite often overlooked in the discussion of enabling renewable energy production, energy efficiency will be extremely important to the success of the biogas industry. It is widely understood by energy management experts that individual Canadians use roughly twice as much power as necessary to enjoy current standards of life. If appropriate steps were taken by consumers to reduce energy use by one-half of current consumption, energy consumers could then afford to pay TWICE as much for electrical energy, without increasing the cost of living. Biogas plants would likely dot the entire provincial landscape if the sale price of biogas energy increased to $20/MWh, a price not unreasonable if the concept of energy efficiency were intimately embraced by governments and energy consumers.

Conclusion

No one definitive solution exists for ‘Making Biogas Work’. Government programs and policy development have been the cornerstones of successful biogas industries to date, not the economic realities. This is not to say that biogas energy cannot compete on a straight economics basis, but competing energy sources need to endure the same full life-cycle economic analysis, including both direct and in-direct costs, that often discredits a fledgling distributed biogas energy industry.

In conclusion, the following benefits of anaerobic digestion treatment of organic residual products is offered, each with a socio-enviro-economic benefit that may or may not be assigned a dollar value:

• Increased rural community infrastructure investment
• Rural job creation and increased municipal tax revenue
• Reduced powerline losses due to more distributed power generation
• Reduced GHG emissions from renewable power generation and enhanced waste management
• Improved plant nutrient (fertilizer) cycling, decreased nutrient runoff and leaching losses
• An increasingly diverse and reliable renewable energy sector

Biogas will likely not become a stand alone, financially viable energy source until appropriate value is assigned to these benefits.

Developments in Biofuels; Implications for Livestock Production

As the manufacture of biofuels grows, questions are being asked as to whether such a strategy can be supported without putting unacceptable pressure on the food supply chain, writes John Pinkeye, Ensus Biofuels, in the proceedings from the 42nd University of Nottingham Feed Conference.

This paper critically assesses the arguments and looks in particular at the impact of biorefining wheat in Europe to both provide a new source of protein concentrate for the animal feed sector, and support the growth of Bioethanol as a substitute for gasoline/petrol.

In order to respond to the challenge of global warming, transport fuels are a priority for action; they are the source of over 18per cent of Greenhouse Gas (GHG) emissions in the EU and are notable as the only significant source of GHG which are increasing. Whilst more efficient cars and new technologies will inevitably contribute to meeting this challenge, the use of biofuels is an essential element of the strategy to decarbonise transport fuels. Biofuels vary in their contribution to saving carbon. Manufactured in the right way and using the right feedstock, biofuels can reduce GHG by at least 50per cent compared to fossil fuels Refs 2 and 3.

Conventionally, land has been used to meet the world's food requirements, while other sources such as oil, coal and gas have been used to meet energy and transport fuel requirements. In other words, today's sun has been used to feed the world and yesterday's sun (over millions of years) has been used to meet the world's energy and fuel needs. The challenge now is to use land and today's sun to meet not only the world's food needs but also its requirements for energy and transport fuel requirements. The critical question is whether this can be done without putting undue pressure on the planet's food supply chain and land use.

Bioethanol is manufactured through the fermentation of sugars. Today this is done by accessing sugars directly (sugar cane and beet) or by breaking down the starch in grains such as wheat to sugar. Biorefineries for the manufacture of bioethanol from cereals also produce a co-product of protein rich animal feed (DDGS) as well as carbon dioxide. Previous studies that have compared the biofuel yields from alternative crops have almost entirely ignored the credit for high protein co-products, such as DDGS from grain crops.

In meeting our food requirements, growing protein in sufficient quantities and concentrations is critical. Although cereal crops such as wheat and maize are very efficient at converting the sun's energy, the concentration of protein is too low for animal feed. Soy meal is widely used as a supplement to raise protein levels and Europe today imports about 35 million tonnes of soy meal to use as an animal feed supplement.

However soy makes inefficient use of land and of the sun's energy producing only 2.5 tes/ha, compared to a yield of 7.7 tes/ha for wheat in NW Europe. When cereals are biorefined to make bioethanol, the protein in the co-product DDGS is at a much higher concentration than in the original cereal and can replace soy meal. This means that cereals produce high protein feedstocks as well as low carbon biofuel, thus creating the opportunity for much more effective use of land.

Thus at current yields, the use of cereals to produce bioethanol could enable more effective use of the land by growing a greater proportion of crops which are more efficient at converting the sun's energy to food and biofuel products. The use of bioethanol DDGS to replace soy meal could therefore enable large scale EU production of biofuel from wheat and maize of 35mt/yr with only a small net increase in the global arable land area. With continued increases in cereal yields, the bioethanol can be obtained with no increase or even a decrease in global cropland area.

For example with sustainable higher cereals yields and an increased land use of 4 million ha, the supply of biofuel cereals in the EU could be increased by about 110 million tonnes per year (mtes/yr) by 2020. This would enable production of about 44 mtes/yr of bioethanol in the EU, which could replace more than 8per cent of the EU road transport fuels consumption. The increased protein production from the DDGS would reduce EU import of soy meal by 18 mtes/yr and would reduce the area required for growing soy in South America by 6 million ha. There would result in a net decrease in land area of 1.5 million ha. This is not the whole story. The above analysis only considers wheat grain.

When growing wheat a similar amount of straw and stalks are also produced, ca 8 tonnes/hectare, of which half is harvested and is available for use to generate energy, either for power generation, or biofuel. In fact when this is taken into account wheat has the potential to be a very effective way of meeting the world's food, fuel and energy requirements and is more effective than ligno-cellulosic energy crops on arable land.

In summary therefore, this paper shows that biorefining wheat to biofuels is a much more efficient process than has been generally recognised, which uses little if any net new land, and which, far from competing with food, actually makes a very valuable contribution to the food industry by virtue of providing an alternative source of feed protein concentrate.

Not only does this substantially help the food industry cope with future growth, it also makes a massive environmental contribution by reducing the pressure on tropical land, some of which is heavily associated with continued deforestation. The paper also shows that Europe's capacity to source biofuels from its indigenous cereal production is substantial, with the ability to meet the targets currently being proposed in the European Renewable Energy Directive draft legislation, with minimal if any need for imports or development of costly so called second generation ligno-cellulosic technology.

September 2008

Articles on Biogas

Biogas plant to power 50 streetlights

T. Madhavan

— Photo: A. Muralitharan

NOVEL VENTURE: Elected representatives and officials of the Tiruneermalai town panchayat inspecting the plant.

CHENNAI: A Rs. 6.15-lakh biogas plant, utilising human waste, is nearing completion at Durga Nagar under the Tiruneermalai town panchayat in Kancheepuram district.

The town panchayat, which is funding the non-conventional energy project, began work on the 25-cubic metre plant on a trial basis in December 2006. It is likely to be completed in a fortnight.

According to site engineers, night soil from 240 housing units of the TNHB housing colony will be deposited in a sump.

After the biological changes, the sludge will generate methane gas. This will be piped to a power generator, which will power streetlights in the area.

"Power generation from the plant will be 3 kva, sufficient for providing power to 50 lights for five hours," says R. Devadoss, Executive Officer of the town panchayat. After treatment, the wastewater and sludge can be utilised for gardening.

According to officials of the Directorate of Town Panchayat, this is the first plant of its kind in Kancheepuram district. It is planned to extend the non-conventional energy model to other areas.