Sugar Beet as an Energy Crop | SpringerLink

Sugar Tech (September and December 2010) 12(3–4):288–293 DOI 10.1007/s12355-010-0041-5

REVIEW ARTICLE

Sugar Beet as an Energy Crop Lee Panella

Received: 3 September 2010 / Accepted: 26 November 2010 / Published online: 27 January 2011 Ó Society for Sugar Research & Promotion 2011

Abstract The combination of volatility in the oil market and finite oil resources and the effect on global climate change from the addition of CO2 to the atmosphere as a result of burning fossil fuels has increased the interest in sustainable energy generation from renewable biofuels. Most 1st generation biofuels in current production are liquid with bioethanol the product of fermentation. Sugar beet provides an abundance of sucrose, which is easily fermented by many microbes and on a per hectare basis; sugar beet is one of the most efficient sources of ethanol, however storage of harvested roots is problematic. Most studies have indicated sustainable biofuels have reduced greenhouse gas emissions (GHG) when compared to petroleum based fuels. Bioethanol from sugar beet reduces GHG comparably or superiorly to maize or sugarcane. There also are other biofuels from fermentation, including biomethanol, biobutanol ETBE, biomethane, and biohydrogen, many of which are more energy dense than ethanol. Storage of sugar beet is a problem that could be solved by ensilage and anaerobic digestion producing a biogas, which could yield more energy per hectare than bioethanol. As the global economy moves away from fossil fuels, sugar beet will play an increasing role in the adoption of more sustainable energy generation. Keywords Beta vulgaris Feedstock Renewable energy Biofuel Sustainable energy

L. Panella (&) Sugarbeet Research Unit, Crops Research Laboratory, USDA-ARS, NPA, 1701 Centre Ave, Fort Collins, CO 80526, USA e-mail: [email protected]

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Introduction The combination of volatility in the oil market and finite oil resources and the effect on global climate change from the addition of CO2 to the atmosphere as a result of burning fossil fuels has increased the interest in sustainable energy generation from renewable biofuels. At present, approximately 10% of the primary global energy demand is met using biomass (Antoni et al. 2007). Some of this is from primary biofuels (i.e., unprocessed biomass) but increasingly secondary (processed biomass) biofuels are being used (FAO 2008). Secondary biofuels often are divided into 1st generation (with a feedstock of seeds, grains, or sugars), 2nd generation (from lignocellulosic biomass) and sometimes 3rd generation (from algae and seaweed) (Nigam and Singh 2010; Larson 2006). Currently, only 1st generation biofuels are widely produced, with the wide adoption of 2nd generation biofuels requiring 5–10 years before the technology is available to economically produce them commercially (Larson 2006; de Wit and Faaij 2010). Because one of the main purposes of developing biofuels is the reduction of greenhouse gases (GHG), some sort of tools or sustainability metrics need to be used to compare biofuels’ ability to reduce GHG. Once such metric is life cycle analysis (LCA), which is an attempt to measure the total GHG effects generated from the production of a product (biofuel) including the entire process from extraction of the raw materials to the end of their use (Menichetti and Otto 2009). Other metrics include Life Cycle Energy Balance, quantity of fossil energy substituted (per unit area), co-product energy allocation, life cycle care balanced, changes in land use, and integrated environmental assessment (Menichetti and Otto 2009; Silva Lora et al. 2010; Demirbas 2009). There is a strong need to use metrics that are based on international standards, do not put

Sugar Tech (September and December 2010) 12(3–4):288–293

developing nations at a disadvantage and focus on the global good (FAO 2008). Most 1st generation biofuels in current production are liquid (either bioethanol or biodiesel) with the biodiesel coming from oil seed crops or palm oil, and bioethanol the product of fermentation (Antoni et al. 2007; de Vries et al. 2010; FAO 2008). Sugar beet provides an abundance of sucrose, which is easily fermented by many microbes. The amount of sucrose extracted per hectare is dependent on three factors, the weight of the beets harvested, the percentage sucrose in those beets, and the amount of the sucrose that is extractable. The root of the sugar beet may contain 20% sucrose by fresh weight (fw). However the amount extracted is less (15.3% average from the U.S. crop 2000–2009) (USDA-ERS 2010) because some cations (e.g., Na? and K?) or amino nitrogen compounds (e.g., betaine and glutamine) interfere with the extraction of sucrose (McGinnis 1982). After the sucrose has been extracted, the remaining juice is molasses. The molasses from one tonne (t = Mkg) of sugar beet (fw) weighs about 20 kg and is approximately 50% sucrose (Shapouri et al. 2006). Pulp or marc remains after the sucrose and molasses have been extracted from the crop. The pulp represents the 22–28% of the dry mass of the sugar beet root that is not solubilized during the sugar beet extraction process (Scott and Jaggard 1993) and is fermentable. Beet tops have feed value, but are usually left in the field at harvest. Amounts range from 4.6 to 7.5 t/ha (Scott and Jaggard 1993).

Present Situation The conversion of sucrose to ethanol is a simple process requiring only yeast fermentation, whereas producing ethanol from maize, wheat or other cereal grains e.g., requires enzymes to convert starch to sugars (Antoni et al. 2007; Jacobs 2006). However harvested sugar beet is a root and more difficult to store than a cereal grain. Cereal grains (primarily wheat) were feedstock to more than 50% of the 3.7 billion liters (l) of EU ethanol produced in 2009. Sugar beet was the next most common feedstock. Although ethanol production in Europe is growing, Brazil and the United States are by far the largest producers of ethanol. In 2007, the U.S. (24.5), Brazil (21.3) and the European Union (1.7) produced 47.5 billion liters, over 90% of the global bioethanol production (Biofuels Platform 2008). On a per hectare basis, sugar beet is one of the most efficient sources of ethanol. It has been calculated that sugar beet produces between 100 and 120 l/t (fw) of ethanol through the fermentation process (110 l/t (FAO 2008), 103.5 l/t (Shapouri et al. 2006), 117 l/t (Panella and Kaffka 2010). The dry weight equivalent of one tonne of sugar beet (fw) has been calculated to contain about 3.89 GJ of

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energy (Tzilivakis et al. 2005). Ethanol has an energy content of 21.2 MJ/l (Schmer et al. 2008), which would be give an energy value of 2.44 GJ/t sugar beet (fw), assuming production of 115 l/t when converted to ethanol. FAO (2008) calculates 5,060 l/ha yield for sugar beet compared with a 1,960 l/ha yield for maize or 952 l/ha for wheat, using a global estimate of average yield (46 t/ha for beet, 4.9 t/ha for maize, 2.8 t/ha for wheat). Von Felde (2008) has estimated that anaerobic digestion methods for whole beets to produce bio-methane would produce 137% more energy than would fermentation of sugar beet to ethanol. Yield estimates in the in FAO (2008) study are low when compared to yields in Western Europe or the United States. Sugarbeet production in Europe varies by region but in a 2 year study (2003–2004) looking at variation in root yield of nine genotypes over five European regions, the lowest average yielding region, East (Hungary, Czech Republic, Austria, Poland), was over 60 t/ha (Hoffmann et al. 2009). The South region (Spain, Italy, Turkey) averaged over 110 t/ha. In the United States 10-year (2000–2009) production yields (typically lower than measured on experimental plots) averaged from 48 t/ha in the Upper Midwest (Minnesota, North Dakota) to 70 t/ha in the Far West (primarily Idaho, with small acreage in Oregon, Washington, and California) (USDA-ERS 2010). Ten year averages (1998–2007) in the Imperial Valley where sugar beet is grown as winter beet were 89 t/ha, with the record yield of 142 t/ha in 2004 on a 30 ha field (Panella and Kaffka 2010; Kaffka 2009). As seen in yield averages from the United States and Europe, for winter beet grown in Mediterranean, sub tropical, and arid tropical climates, when irrigation water is available, yield potentials are very high. This is because the crop is grown for 210–300 days, sown late summer and harvested the following late spring and summer. A 100 t/ha crop yielding 115 l/t (fw) ethanol, would have a 11,500 l/ ha ethanol yield, almost three fold FAOs estimate for ethanol production from high-yielding maize in the U.S. (3,751 l/h based on a 9.4 t/ha maize yield) (FAO 2008). LCA is one of the methods used to determine GHG effects generated from substitution of biofuels for fossil fuels. LCAs follow international standards that provide the framework for conducting these studies (ISO 14040:2006 and 14044:2006) (Menichetti and Otto 2009), which are increasingly important because they are used by governmental agencies to design laws promoting or mandating the use of biofuels (US EPA 2007). Most LCA studies (e.g., (Menichetti and Otto 2009; Larson 2006) have indicated that 1st generation biofuels (bioethanol or biodiesel) have reduced GHG when compared to petroleum based fuels (gasoline or diesel). Most Sugar beet LCA studies have focused on conditions present in central European, where most commercial bioethanol production from sugar beet

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occurs (Balat and Balat 2009; Merkes 1996; Halleux et al. 2008; Menichetti and Otto 2009). Bioethanol from sugar beet reduces GHG comparably or superiorly to maize or sugarcane (Table 5.1, p. 85 in Menichetti and Otto (2009) compares maize, sugar cane, wheat and sugar beet). Sugar beet production in central Europe is different from production in many other parts of the world. It is primarily a rainfed agricultural system in a moderate continental climate. Although yields are high, they do not approach the yields of winter beet in the Southern European areas (Hoffmann et al. 2009). It has been noted that LCA studies need to quantify differences among crops, environments, cropping systems, and conversion technologies (Kaltschmitt et al. 1997; Larson 2006; FAO 2008). Small amounts of nitrous oxide (N2O), a more potent GHG than CO2, are released from soils by agriculture. The amount released is dependent on cropping practices associated with fertilization, use of manure, or cover cropping (Smeets et al. 2009); however, it is a 300 times more potent GHG than CO2, and, therefore monitoring its release in the atmosphere is important. Smeets et al. (2009) concluded that sugar beet and sugar cane were effective in reducing N2O emissions compared with maize; however, the authors stressed that management of crop nutrition, especially optimization of nitrogen fertilization was crucial in reducing N2O emissions from the soil. Increasing resource use efficiency, where it occurs, will be critical in reducing GHG through the use of sugar beet and sugar beet coproducts for biofuels in the future (Kaffka 2010; Merkes 1996).

Future Needs and Developments As we move into the twenty-first century and move away from non-sustainable fossil fuels to more sustainable biofuels, 1st generation liquid biofuels will continue to play an important part in converting away from an oil-based transport system. I believe that sugar beet will play an important role as a feedstock in the production of bioethanol. Most of the European bioethanol production is in France, followed by Germany and Spain. However, there is interest in exploring or expanding the use of sugar beet as a bioethanol feedstock in a number of European countries, such as Ireland (Power et al. 2008), but especially in Eastern European nations (Kondili and Kaldellis 2007) including Slovenia (Krajnc et al. 2007) and Serbia (Dodic et al. 2009). In the Americas, Brazil (from sugar cane) and the U.S. (from maize) are the major ethanol producers and users. Globally, there is a strong interest in Asia in the use of sugar beet as one of a number of potential bioethanol feedstocks—Turkey (Iço¨z et al. 2009), Japan (Hatano et al. 2009; Koga et al. 2009; Koga 2008) China (Tian et al.

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2009), and India (Srivastava et al. 2008). Because storing the harvested roots is a large impediment to using sugar beet as a bioethanol feedstock, climates where sugar beet can be cultivated both as spring or fall sown crops, will be the most attractive areas for biofuel production because the crop can be harvested daily most of the year. If biofuel production were via anaerobic digestion, sugar could be ensiled to extend the processing (Klocke et al. 2007). Nonetheless, in the long run, even the most optimistic scenarios do not see bioethanol (especially from 1st generation feedstocks) replacing the fossil fuel now used in the transport sector (FAO 2008; de Vries et al. 2010; de Wit et al. 2010). If it were possible to convert the entire U.S. grain yields to bioethanol that would fill only 18% of the demand for automotive fuel in the U.S. (Brown 2009). With rapidly expanding fleets of personal vehicles in India and China, I think we must see the transport sector transitioning from fossil fuel to liquid biofuels and hybrid technology and then to an increasingly electric based system (Brown 2009). Important Influences in the Twenty-First Century What are the most important influences in the twenty-first century that will impact the adoption of biofuels to replace fossil fuels, especially in relation to the use of sugar beet as a feedstock? Sustainability will be a key consideration. As discussed above, LCAs are currently used to measure the direct impact of the adoption of sustainable energy technologies to replace fossil fuels but they will continue to evolve taking into account more indirect effects and be more sensitive to both political and economic impacts, as well as environmental impacts (Bram et al. 2009; de Vries et al. 2010; Demirbas 2009; Henke et al. 2005; Kretschmer et al. 2009; Silva Lora et al. 2010; Tao and Aden 2009). A key factor effecting the use of sugar beet (and many other crops) is the development rate of advanced technologies (2nd generation lignocellulosic feedstocks), which is hard to predict but offers very sustainable alternatives to some of the food crops now being used as feedstocks (de Wit et al. 2010; de Wit and Faaij 2010) Another resource requirement, which is receiving increased scrutiny is the water needed (or water footprint) for bioenergy crop production (Gerbens-Leenes et al. 2009; Hoogeveen et al. 2009). Gerbens-Leenes et al. (2009) found sugar beet and potato more efficient than maize and sorghum as sources for biofuels in most regions of the world. However, once sugar beet is irrigated, as it is in most areas where winter beet is grown (Morillo-Velarde et al. 2001; MorilloVelarde and Ober 2006), its water footprint also grows (Gerbens-Leenes et al. 2009) and may impact regions with fast growing populations dependent on irrigated food production (Hoogeveen et al. 2009).


As the global population moves toward the projected 8–10 billion people in 2050 the discussion of whether to grow potential food crops for biofuels will intensify (Naylor et al. 2007; Cassman and Liska 2007). There is serious concern that the use of crop land will both cause the grassland and forest to be brought into cropping and, thereby, both threaten food security and cause environmental damage (Searchinger et al. 2008; FAO 2008). Although there is still uncertainty about the impacts of using abandoned agricultural land (Campbell et al. 2008), or different cropping systems (Kim et al. 2009), this is a continuing dialog (de Wit and Faaij 2010; Goldemberg and Guardabassi 2009; Sanderson 2006), and a balance must be found (Young 2009). This is not just a challenge for biofuels; if we are to feed a growing global population and maintain biodiversity in a sustainable manner, agricultural research must be focused on increasing global food production per hectare while reducing inputs (Sachs et al. 2010)—a formidable challenge! Breeding an Energy Beet In most regions over the next few years economic conditions will require a ‘‘dual purpose’’ sugar beet—one that may be grown as a sugar crop as well as an energy crop. However, in those areas were sugar beet is used only as biofuel feedstock, different criteria will become import. There is certainly discussion of this (von Felde 2008; Hoffman 2008) but many of the criteria will depend on the conversion technology used to produce biofuels, which is changing (Balat et al. 2008; Dodic et al. 2009; Rankovic et al. 2010). Earlier studies have shown that if biomass yield is the most important parameter, crossing fodder beet and sugar beet in hybrid combination will yield more biomass (Doney and Theurer 1984; Theurer et al. 1987). These studies must repeated with modern germplasm in the environments were the energy beet would be grown, most likely areas where high-yielding winter beets might be adapted (Hoffmann et al. 2009; Panella and Kaffka 2010). Sugar beet breeding companies have already begun or are discussing in house breeding programs for energy beets. Where Will Sugar Beet Fit in the Biofuels Scenario Current technology is looking at ethanol as the primary fermentation product of sugar beet. There are, however, other choices for an end biofuel, including biomethanol, biobutanol ETBE, biomethane, and biohydrogen, many of which are more energy dense than ethanol (Antoni et al. 2007; Sanderson 2006; Zhang et al. 2007). Storage of sugar beet is a problem that could be solved by ensilage and anaerobic digestion (Weiland 2003; Klocke et al. 2007), producing a biogas, yielding more energy per hectare than

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bioethanol (von Felde 2008). Once 2nd generation liquid biofuels come online, there still will be niche markets for specialty fuels form locally grown crops with high conversion efficiency; sugar beet might be an excellent feedstock to produce products such as jet fuel (Kozak and Laufer 2009). The introduction of a $30/t carbon tax, or cap and trade system in the United States has been predicted to reduce the beet sugar production by 87% because of the extensive use of coal to power processing factories (Taylor and Koo 2010). One solution to this cost would be using the sugar co-products—pulp or marc and molasses (Sutton and Doran Peterson 2001; Kozak and Laufer 2009; von Felde 2008)—to generate biomethane to provide the energy to process the sugar. There may be a trend in beet sugar processing to make the processing energy neutral— much as we see in sugar cane processing today. We may see adoption of small factory based onsite energy production from renewable biofuels. Only about 2% of the globally produced sucrose (or sucrose derivatives) currently are used as a source for value-added feedstock chemicals (Eggleston 2008). Sugar beet pulp contains very little lignin, consisting of approximately equal amounts of hemicellulose and pectin (Harland et al. 2006). Sucrose and all of these compounds can be used as feedstocks for several important industrial feedstock chemicals; and there is tremendous potential to expand this market (Turley 2008; van Beilen 2008). As the global economy moves away from fossil fuels, sugar beet will play an increasing role in the adoption of more sustainable energy generation.

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