Chapter 3 Bioethanol Production From Corn and Wheat Food, Fuel, and Future C H A P T E R 45Bioethanol Production From Food Crops http //dx doi org/10 1016/B978 0 12 813766 6 00003 5 Copyright © 2019 E[.]
C H A P T E R Bioethanol Production From Corn and Wheat: Food, Fuel, and Future Sujit K Mohanty*, Manas R Swain** *Iowa State University, Ames, IA, United States **DBT-IOC Center for Advance Bio-energy Research, Faridabad, India 3.1 INTRODUCTION In addition to United States and Brazil, in past few decades, many other countries around the globe are gradually emerging as global players in renewable fuel ethanol production sector by using starchy and sugar-rich feedstocks For example, countries, such as China and Canada, are producing ∼845 million gal (∼3.2 billion L) and ∼436 million gal (1.65 billion L) of fuel ethanol, respectively, from various starchy feedstocks, such as corn, cassava, wheat, and rice (Table 3.1), while countries, such as India, France, Germany, and Australia, are producing about 1 billion L, 1 billion L, 750 million L, and 500 million L, respectively, primarily from sugar-rich feedstock, such as sugarcane, molasses, sugar beet, and wheat (RFA, 2017) Thus, it is evident that corn and wheat are not only the top choices across the globe as the first-generation feedstocks for bioethanol production, but are also expected to remain so for decades to come Therefore, it is becoming increasingly Corn and wheat are grown and utilized not only as food and feed, but also as feedstocks for generation of renewable fuel ethanol Production of fuel ethanol through biological fermentation of sugars extracted from sugar-rich crops (such as sugarcane) and starchy crops (such as corn and wheat) is a technically matured and commercially successful story, while those from lignocellulosic materials are still in early developmental/trail phases For instance, global leaders in fuel ethanol production, such as the United States and Brazil produce about 15.25 billion gal (∼57.7 billion L) and 7.3 billion gal (∼27.6 billion L) of fuel ethanol annually primarily from starchy feedstocks, such as corn and wheat, and sugar-rich feedstock, such as sugarcane, respectively (Table 3.1) This clearly indicates the pivotal role these starchy and sugar-rich feedstocks play, particularly corn and wheat, in the global fuel ethanol production scenario Bioethanol Production From Food Crops http://dx.doi.org/10.1016/B978-0-12-813766-6.00003-5 45 Copyright © 2019 Elsevier Inc All rights reserved 46 3. Bioethanol Production From Corn and Wheat: Food, Fuel, and Future TABLE 3.1 World Fuel Ethanol Production by Country or Region (in Million Gallons) Country 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 World 13,123 17,644 20,303 23,311 22,404 21,812 23,429 24,570 25,682 26,504 USA 6521 9309 10,938 13,298 13,948 13,300 13,300 14,300 14,806 15,250 Brazil 5019 6472 6578 6922 5573 5577 6267 6190 7093 7295 Europe 570 734 1040 1209 1168 1179 1371 1445 1387 1377 China 486 502 542 542 555 555 696 635 813 845 Canada 211 238 291 357 462 449 523 510 436 436 Rest of the world 315 389 914 985 698 752 1272 1490 1147 1301 Source: Data taken from Renewable Fuels Association (www.ethanolrfa.org/wp-content/uploads/2017/02/Ethanol-Industry-Outlook-2017.pdf) and the US Department of Energy Alternative Fuels Data Center (www.afdc.energy.gov/data/) 3.2 CORN AND WHEAT-BASED ETHANOL PRODUCTION: GLOBAL SCENARIO important to not only understand the global production scenario of these starchy feedstocks, but also the biotechnological processes developed so far and the socioeconomic issues involved in their utilization to fully comprehend the current global perspective of renewable fuel ethanol generation along with its future implications This chapter primarily focuses on these aspects of corn and wheatbased fuel ethanol production Global production of corn is estimated to be about 40.8 billion bushels in the year 2016–17 (Fig. 3.1) This corresponds to approximately about 1.04 billion metric tons of corn (given 1 bushel approximately equals to 56 pounds or say 1/40th of a metric ton) Among all the major FIGURE 3.1 (A) Major corn producing countries in the world with their total production in 2016–17 in million bushels (MB) and its share (in percentage) in total global production (B) Distribution of corn usage in USA in various application sectors Source: Data taken from (A) US Department of Agriculture, Foreign Agricultural Service (USDA FAS), Grain: World Markets and Trade, January 12, 2017 (B) US Department of Agriculture, Economic Research Service (USDA ERS), Feed Outlook, January 17, 2017 ProExporter Network, Crop Ending, August 31, 2017 47 3.2 Corn and wheat-based ethanol production: global scenario corn producing countries, the United States tops the list with a major share of ∼37%, which is little more than one-third of total corn production in the world, followed by China and Brazil with ∼21.2% and 8.3%, respectively (Fig. 3.1) Global corn production has sharply increased in the past few decades owing to its newly found applications in renewable liquid fuel (bioethanol) production industry (Table 3.2) Consequently, the global fuel ethanol production has also increased significantly in recent years; in fact, it has almost doubled between the years 2007 and 2016 (Table 3.2) If we particularly analyze the fuel ethanol production scenario in the United States, which produces ethanol primarily from corn, the overall ethanol production has almost tripled during these 10 years (Table 3.1) In the year 2016–17, the United States alone used about 28.9% of its total corn harvest (Fig. 3.1), which is about 4.38 billion bushels of corn, to produce over 15 billion gal of ethanol fuel (Table 3.1) The same rapid growth in ethanol production is also observed in China and other countries that primarily use corn and wheat as feedstock for ethanol production This clearly indicates that there is not only a rapid growth in global corn production but also its utilization as feedstock in fuel ethanol industry across the globe with the United States emerging as the leader in this sector The United States is the top ethanol producer in the world with 15,250 million gal of fuel ethanol produced according to 2016 estimations This account for about 58% of overall global fuel ethanol production (Fig. 3.2), which was estimated to be about 26,504 MG Interestingly, most of this fuel ethanol comes from cornstarch as feedstock (Fig. 3.2) To be precise, almost 95% of the total fuel ethanol produced in the United States in the year 2016, which is about 14,490 MG, came from cornstarch feedstock and a minor section from wheat (3%) This implies that the United States tops the global chart not only in corn production, but also in fuel ethanol production because of its choice of using corn and wheat as feedstock for ethanol production The availability of low-cost feedstock in sufficient quantities year-round is always a great advantage for any biotechnological process economically and the United States is a good example of that Brazil is the second largest producer of fuel ethanol in the world with 27% of total global TABLE 3.2 Global Corn Production and Yield From 2015–17 (in Million Metric Tons) Production (million metric tons) Yield (metric tons per hectare) Country/region 2015/16 2016/17 2017/18 projected 2015/16 2016/17 2017/18 projected World 969.49 1070.51 1036.90 5.43 5.83 5.70 USA 345.51 384.78 362.09 10.57 10.96 10.72 China 224.63 219.55 215.00 5.89 5.97 6.14 Brazil 67.00 98.50 95.00 4.19 5.61 5.37 European Union 58.75 61.14 61.60 6.35 7.11 7.03 Argentina 29.00 41.00 40.00 8.29 8.37 8.16 Mexico 25.97 27.40 25.00 3.60 3.65 3.50 India 22.57 26.00 25.00 2.56 2.71 2.63 Rest of the world 196.06 212.14 213.21 — — — Source: Data taken from Foreign Agricultural Services/USDA Office of Global Analysis For a more detailed table of data see https://apps.fas.usda.gov/ psdonline/circulars/production.pdf 48 3. Bioethanol Production From Corn and Wheat: Food, Fuel, and Future FIGURE 3.2 Schematic showing global fuel ethanol production in 2017 and its distribution among major ethanol producing countries in the world with their total production in million gallons (MG) and share in global production (%) Right: Major sources of starchy feedstocks for fuel ethanol production in USA Source: Data taken from Renewable Fuels Association (www.ethanolrfa.org/wp-content/uploads/2017/02/Ethanol-Industry-Outlook-2017.pdf) and the US Department of Energy Alternative Fuels Data Center (www.afdc.energy.gov/data/) production, which accounts to about 7295 MG of ethanol (Table 3.1) However, the major source for fuel ethanol is sugar-rich feedstock sugarcane and to a less extent from starchy crops like corn and wheat (Chum et al., 2014) Furthermore, it is interesting to note that though China shares 21% of the global corn production (Fig. 3.1) and uses corn to produce fuel ethanol, but it contributes only 3% to the global fuel ethanol production (Fig. 3.2) Thus, corn being such a widely popular and highly successful agricultural produce worldwide, and with such high content of starch, fiber, protein, and oil, it has not only found usage as food, livestock rations, and feedstock for renewable fuel ethanol production, but also in many other industrial sectors responsible for production of diverse coproducts (Sharma et al., 2016), such as: 3.2.1 Advantages of Using Corn as Feedstock: One Source, Many Products Food and feed: To produce high-fructose syrup (corn syrup), beverages, alcohols, table cornstarch, sweetener, and animal feed in the form of dry distillers grains (DDGs) and salsa made from by-products Polymers: For production of polylactic acid polymers, which are sustainable versions of fibers and plastics, biodegradable styrofoam, and so on Being a starchy crop with high amounts of fiber, proteins, and oils, corn has found its application not only in food and feed industry, but also in production of bulk chemicals, such as fuel ethanol, fibers, and sweeteners A thorough analysis of the chemical composition of a shelled corn reveals that it is composed of starch (72%), fiber (9.5%), protein (9.5%), and oils (4.3%) (Mosier and Illeleji, 2006) It is estimated that, one bushel (i.e., 56 pounds) of corn is known to provide up to 31.5 pounds of cornstarch or 33 pounds of sweeteners (high fructose corn syrup), or 22.4 pounds of polylactic acid fibers/polymers, or alternatively, one bushel of 49 3.2 Corn and wheat-based ethanol production: global scenario corn approximately provides 2.8 gal of ethanol along with about 17.5 pounds of DDGs via drymilling process, or 13.5 pounds of gluten feed (with 20% protein), 2.6 pounds of gluten meal (60% protein), and 1.5 pounds of corn oil via wet-milling process (http://www.worldofcorn com/#one-bus hel-of-corn-can-provide) This rough estimate helps to quantitatively understand the significance of corn as a commercially relevant feedstock with the possibility of obtaining diverse products from a single source with an average of about 130, 90, and 70 million metric tons, respectively (Table 3.3) Unlike corn, which is mostly produced in the United States and China, wheat production is well distributed across the globe and is mostly dominated by Asian and Europeans countries (Table 3.2) Plus, upon further investigation, it was found that, in the case of wheat production, the average yield is only about 3.4 metric tons/ha (Table 3.3), which is almost half of that of corn, which is about 5.7 metric tons/ha (Table 3.2) This means global wheat productivity (i.e., yield per hectare) is comparatively much lower than that of corn This is probably the reason why, between the two agriculturally produced starchy feedstocks, corn is preferred over wheat as the feedstock of choice for fuel ethanol production in the United States and other parts of the world Also, in many parts of the world, wheat is traditionally cultivated as a staple food primarily for human consumption and to a lesser extent as animal feed I, and its utilization as a preferred feedstock for fuel ethanol production has not gained enough momentum the way it has happened in case of corn, particularly in last few decades (RFA, 2017) 3.2.2 Global Wheat Production and Usage Unlike corn, global production of wheat, which is estimated to be about 737.83 million metric tons in the year 2017, has almost remained stagnant over the past 3–4 years without much fluctuation (Table 3.3) The European Union tops the global list in wheat production with an average of about 150 million metric tons of wheat per year, but if we look at individual countries, China tops the list followed by India and Russia TABLE 3.3 Global Wheat Production and Yield From 2015 to 2017 (in Million Metric Tons) Production (million metric tons) Yield (metric tons per hectare) Country/region 2015/16 2016/17 2017/18 projected 2015/16 2016/17 2017/18 projected World 736.97 755.00 737.83 3.27 3.39 3.34 European Union 160.48 145.70 150.00 5.98 5.33 5.63 China 130.19 128.85 130.00 5.39 5.33 5.37 India 86.53 87.00 96.00 2.75 2.88 3.13 Russia 61.04 72.53 72.00 2.39 2.69 2.64 USA 56.12 62.86 47.89 2.93 3.54 3.10 Canada 27.59 31.70 28.35 2.88 3.57 3.15 Australia 24.17 35.11 23.50 1.89 2.73 1.87 Rest of the world 190.85 191.25 190.09 – – – Source: Data taken from Foreign Agricultural Services/USDA Office of Global Analysis For a more detailed table of data see https://apps.fas.usda.gov/ psdonline/circulars/production.pdf 50 3. Bioethanol Production From Corn and Wheat: Food, Fuel, and Future 3.3 USA—THE GLOBAL LEADER IN FUEL ETHANOL PRODUCTION PREFERS CORN To counteract global warming, the USA’s Renewable Fuels Standards (RFS) program is planning to replace at least 20% its transportation fuel with renewable biofuels by 2022 (Schnempf and Yacobucci, 2013) Towards this goal, in 2016, the United States alone produced a record highest of 15.25 billion gal of renewable fuel ethanol by cumulative effort of 200 ethanol biorefineries operating in 28 different states This corresponds to 58% of total amount of fuel ethanol produced globally (Fig. 3.2) The leading state among the 28 states in the United States is Iowa with 43 operating biorefineries, which produces about 4 billion gal of fuel ethanol per year, which is equal to 25.8% of total fuel ethanol produced in the United States in 2016, followed by Nebraska: 26 biorefineries with production of 2.13 billion gal (13.7%), and Illinois: 15 biorefineries with 1.75 billion gal (11.2%) (RFA, 2017) However, it is interesting to note that these states are also the major producers of corn in the United States This indicates that US ethanol industry, which produces about 60% of global fuel ethanol, is directly dependent on agricultural production of corn (Fig. 3.1), which is about one third of total corn produced in the world (Table 3.2) Choice of corn as the feedstock for ethanol production has worked in advantage of US in becoming the global leader in fuel ethanol production the current state of art of this well-established process is so efficient that when the best ethanolproducing yeast is used, it can turn almost all the sugar (>95%) fed to them directly into ethanol (Gulati et al., 1996) However, it is important to note that the final ethanol yield is not only dependent on the process parameters and its constraints but also on the quality and the variety of the corn or wheat grain (Singh, 2012) For example, a study by Sosulki and Sosulki (1994) suggest that the ethanol yield can vary somewhere between 3% and 23% depending on the variations in corn grain quality in terms of its kernel composition, endosperm hardness, planting location, and the presence of mycotoxins They also found that if corn kernels contain high free sugar then it decreases enzyme consumption during saccharification thereby resulting in higher ethanol yield 3.4.1 Corn Processing for Ethanol Production: From Farm to Fermentation 3.4 TECHNOLOGICAL ASPECTS OF ETHANOL PRODUCTION FROM CORN Corn undergoes many preprocessing steps before it can be considered ready for fermentation for ethanol production However, as a basic first step postharvest, corn is shelled to remove kernels from the cob, followed by separation from impurities, such as stones and sticks by screeners or scalpers before getting stored in silos Subsequently, a commercially well-established large-scale biotechnological process is employed (Sharma et al., 2016) via three broad steps: (1) conversion of starchy feedstocks into fermentable sugars via three major sequential unit operations namely milling, liquefaction, and enzyme-based saccharification, followed by (2) fermentation, where yeast metabolically converts these sugars into ethanol, and ultimately (3) purification, where the ethanol, thus generated, is separated out from other byproducts and impurities by distillation before it gets stored or transported to market (Fig. 3.3) Fuel ethanol is most commonly produced by fermenting cornstarch by yeast, which converts sugars from corn kernels into ethanol In fact, 3.4 Technological aspects of ethanol production from corn 51 FIGURE 3.3 A schematic diagram showing the fuel ethanol production process flow with various unit operations starting from grain storage, milling, cooking, liquefaction, saccharification, fermentation, and distillation to fuel ethanol separation and supply to market and generation of animal feed (DDGs) production 3.4.2 Corn Grain Milling, Liquefaction and Saccharification, and Animal Feed Generation Milling is the very first unit operation in the biotechnological process described earlier Based on how the grain is milled for ethanol production, this step is categorized into two methods; namely, wet milling and dry milling Broadly defined, if the grain is first soaked in water to fractionate it into its individual components, such as starch, fiber, and germ, which are then processed separately, then it is called the wetmilling process, whereas if the whole grain and the residual components are separated at the end instead of the beginning of the process then it is called as the dry-milling process (Fig. 3.4) Thus, it is important to note that although both milling processes involve breaking down the starch present in the corn kernel into simple sugars for further processing, such as fermentation for ethanol production and distillation, the primary difference between the two milling processes is whether the entire kernel is processed as a whole (dry milling) or the corn kernel is first broken down into its individual components (i.e., germ, fiber, gluten, and starch) and then sent for processing (wet milling) (Saville et al., 2016) Both the milling processes have their respective advantages and disadvantages (Saville et al., 2016) While the wet-milling process results in production of a number of coproducts, such as gluten feed/gluten meal, food-grade corn oil, and distillers' grains with solubles (DGS), it could separate individual components of corn grain prior to processing as described earlier, the dry-milling processes usually produce only one primary coproduct; that is, DGS, which is then used as animal feed either wet (WDGS) or dry (DDGS) (Sharma et al., 2016) However, surprisingly, in the United States, wet-milling– based ethanol production plants are far fewer in number compared to that of dry-milling– based ethanol production plants For example, 52 3. Bioethanol Production From Corn and Wheat: Food, Fuel, and Future FIGURE 3.4 A flow chart showing various steps of the dry-milling and the wet-milling process using ethanol production from corn and its coproduct (animal feed) generation Source: Data taken from Saville, B.A., Griffin, W.M., MacLean, H.L., 2016 Ethanol production technologies in the US: status and future developments In: Salles-Filho, S.L.M., Cortez, L.A.B., da Silveira, J.M.F.J., Trindade, S., da Graỗa Derengowski Fonseca, M (Eds.), Global Bioethanol Evolution, Risks, and Uncertainties Academic Press, pp 163–180 Chapter 7; Sharma, A., Sharma, S., Verma, S., Bhargava, R., 2016 Production of biofuel (ethanol) from corn and co product evolution: a review Int Res J Eng Technol 3, 745–749 as per the data published by US Department of Agriculture in 2009, out of 180 corn-based ethanol production plants, only 11 were operating as wet-milling–based ethanol-producing plants and the rest of them, which is around 173, were operating as dry-milling–based ethanol-producing plants (RFA, 2017) In other words, about 90% of the total fuel ethanol produced from corn grain is generated via dry-milling process while the rest 10% is generated via wet-milling process (RFA, 2017) In a typical dry-milling process, enzymatic hydrolysis of cornstarch to simple fermentable sugars is accomplished via two-steps: (1) liquefaction/cooking and (2) saccharification (Mojovic et al., 2006) Liquefaction is basically a high-temperature cooking step where with time the tightly bound grain starch becomes soft and spongy and becomes amenable to efficient enzymatic digestion For example, a typical industrial scale liquefaction step would be cooking the ground corn mash either at 165°C for 3–5 min (very high temperature cooking), or 90–105°C for 1–3 h (Robertson et al., 2006) This step is followed by the saccharification step where enzymatic digestion of starch is initially performed at higher 3.4 Technological aspects of ethanol production from corn temperatures by incubating with thermostable alpha-amylase resulting in production of dextrins, subsequently followed by a lower temperature incubation, which is typically at about 55–60°C (Lamsal et al., 2011) or even as low as 32°C (Mojovic et al., 2006) with an enzyme called glucoamylase to further convert the dextrins into glucose The sugary syrup, thus produced (also known as corn hydrolysate), then proceeds to the fermentation step where yeast Saccharomyces cerevisiae converts sugars into ethanol (Azhar et al., 2017) The ethanol is then recovered via evaporation in a distiller for ethanol separation, purification, and rectification by an well established process called distillation Recently, modern pretreatment methods that use techniques such as ultrasound and microwave have been developed and employed in corn grain processing to improve the glucose concentration in the sugary syrup which is obtained after liquefaction and saccharification steps (Nikolic et al., 2011) A higher glucose concentration of 6.82% and 8.48% was obtained when ultrasonic and microwaves were employed, respectively Consequently, higher ethanol concentration of 11.15% and 13.40%, with respect to the control (untreated) samples, were also obtained from application of ultrasonic and microwaves, respectively Thus, microwave pretreatment seems to have worked better than ultrasound Ultimately, using this new microwave pretreatment technique, a simultaneous saccharification and fermentation (SSF) method was developed for ethanol production from corn in batch mode that resulted in a maximum ethanol concentration of 9.91% (w/w) and percentage of theoretical ethanol yield of 92.27% (Nikolic et al., 2011) 53 ethanol generation (Azhar et al., 2017) Yet, S cerevisiae (also widely known as brewers’ yeast) is still the preferred and is one of the most widely used for commercial fuel ethanol production from sugar and starchy feedstocks (Behera et al., 2010a,b) Starting from ancient wine making to current modern day high-tech commercial-scale ethanol fermentation processes, S cerevisiae has dominated this sector as the biocatalyst of choice, mainly because of the advantageous attributes it has acquired during natural evolution process over other ethanol producing microorganisms (Azhar et al., 2017; Behera et al., 2010a,b) These attributes are: • Extremely high ethanol tolerance (Azhar et al., 2017) • Can grow under stringent anaerobic conditions (Visser et al., 1995) • Is least affected in the presence of oxygen (Lagunas, 1979) 3.4.3 Microorganisms Used in Fermentation Processes for Corn-Based Ethanol Production The best-known strains of S cerevisiae isolated so far and used industrially can convert almost ∼95% of the sugar directly into ethanol (Gulati et al., 1996) S cerevisiae is naturally adapted to ethanol fermentation with a very high tolerance to ethanol (150 g/L) (Claassen et al., 1999) and chemical inhibitors compared to other well-known natural ethanol producing organisms, such as Zymomonas mobilis (Table 3.4) On the other hand, both S cerevisiae and Z mobilis have a very limited spectrum of sugarutilizing capability for ethanol production (Table 3.4) Interestingly, neither of these naturally occurring organisms can use xylose, which is a widely available sugar from plant biomass Fortunately, both these organisms are well studied both genetically and metabolically and so, both are complaisant to genetic modifications and consequently, engineering of their metabolic capabilities are possible Thus, attempts have been made to overcome these above mentioned limitations of S cerevisiae and Z mobilis via metabolic engineering techniques (Ha et al., 2011) A myriad of microorganisms are known to date that are capable of utilizing sugars for 54 3. Bioethanol Production From Corn and Wheat: Food, Fuel, and Future TABLE 3.4 Comparative Analysis of Saccharomyces Cerevisiae Versus Zymomonas mobilis Microorganism Sugars utilized Fermentation conditions Ethanol tolerance Saccharomyces cerevisiae Glucose, fructose, maltose, and sucrose Anaerobic, 30–37°C Zymomonas mobilis Glucose, fructose, and sucrose Anaerobic, 30°C Similarly, at process engineering level, options are available to either use immobilized yeast for ethanol production (Behera et al., 2010b) or use novel fermetation techniques, such as solid-state fermentation (Mohanty et al., 2009), which has shown promising results with other feedstocks Unfortunately, they have their intrinsic drawbacks, both in terms of process economics and yeast biology, that prevents them from getting readily acceptable in industrial corn-ethanol production process (Bai et al., 2008) Furthermore, a comparison between these two naturally ethanol producing strains (S cerevisiae and Z mobilis) reveals that bioprocesses with Z mobilis results in higher ethanol yield and productivity (as high as 97% for theoretical yield) compared to S cerevisiae (Bai et al., 2008) where it is at best 90%–95% of theoretical yield (Table 3.4) However, it is interesting to note that S cerevisiae is still the preferred whole-cell biocatalyst of choice for ethanol production from corn and other starchy feedstocks (and not Z mobilis) because of these two important advantages it has over Z mobilis: (1) wide spectrum of sugar substrate utilizing capability (Table 3.4) and (2) the undesirability of Z mobilis biomass to be used as animal feed (Bai et al., 2008) Other attributes References 150 g/L Up to 95% of theoretical yield Claassen et al (1999) 100 g/L Up to 97% of theoretical yield Claassen et al (1999) 3.4.4 Animal Feeds, an Economically Beneficial By-Product of Corn-Based Ethanol Production biorefineries operating in 28 different states (RFA, 2017), which is then fed to animals in meat and poultry (cattle, swine, and chicken), dairy, and fish industries across the globe It is estimated that about one half of the total corn produced in the United States (46%) is used as animal feed (Fig. 3.1) In fact, it is estimated that about 30% of each bushel of corn that gets utilized in ethanol production comes back to market as animal feed in the form of DDGS, WDG, DGS, corn gluten feed, corn gluten meal, and so on (Wood et al., 2014) This puts in perspective the significance of this high-value by-product of corn-based ethanol industry and the enormous contribution it makes to the economics of this ethanol production technology, but unfortunately often overlooked or not fully appreciated in public debates, discussions, and mainstream media reports In fact, in the past decade, 2006– 16, while ethanol production in the United States has almost tripled (Table 3.1), it is also estimated that the animal feed production has also grown by a factor of eight (RFA, 2017) Furthermore, animal feed is not the only byproduct of corn-ethanol industry that has poised itself as an economically addendum, but many other by-products have also gained popularity in the market lately (Sharma et al., 2016) For example, corn distillers oil, a by-product of corn-ethanol industry has proven itself as a high value coproduct by its application in the biodiesel industry as a feedstock with an estimated market value of US$900 million Thus, without any confusion we can easily understand the multifold economic advantages the corn-based fuel ethanol production technology has, and In 2016, the United States, along with production of 15.2 billion gal of fuel ethanol, also produced about 42 million metric tons of highprotein animal feed from its 200-plus ethanol 3.5 Technological aspects of ethanol production from wheat thus, it is not only emerging as a promising technology to meet the renewable fuel demands and mandates successfully in the years ahead, but also well-poised to address the growing global demand for food and feed 55 3.5 TECHNOLOGICAL ASPECTS OF ETHANOL PRODUCTION FROM WHEAT fermentation and distillation (Fig. 3.3) As this is described elaborately in an earlier section, it will not be described here again to avoid redundancy Concisely describing, wheat grains undergo five basic unit operations (1) milling (mechanical grinding to release starch components), (2) cooking and saccharification (heat, water, and enzymes alpha-amylase and glycoamylase added), (3) fermentation (by yeast where sugars are converted to ethanol), (4) distillation and rectification (ethanol separation from fermentation broth), and finally (5) drying/dehydration (Patni et al., 2013) Plus, just like in the case of corn, dry milling is also the most popular mode of operation in the case of wheat because it helps in barn separation from grain and increased starch content in the wheat flour, which ultimately results in higher ethanol titer at the end of the process For example, Sosulki and Sosulki (1994) reported that a maximum concentration of 344–367 L ethanol per ton of wheat flour can be obtained with a maximum ethanol concentration of 15%–15.89% (v/v) when wheat flour from dry milling is used for ethanol production In another such study, under very high gravity conditions, a maximum ethanol titer of 23.8% (v/v) was obtained, which is much higher than that obtained under normal process conditions (Thomas et al., 1993) A typical small-scale ethanol production process is described by Patni and co-workers (2013), in which the wheat grain is cleaned and grounded to make wheat flour, which is then mixed with 250 mL of water and 0.416 gm of amylase at 70°C for 45 min followed by addition of 0.1 mL of glucoamylase at 55–60°C and incubation for 30 min This constituted the first two steps, milling and saccharification where wheat starch is extracted and separated from barn and converted into fermentable sugars Next about 5 g of S cerevisiae (yeast) is added to the sugary syrup and left for up to 75 h in well stirred and ambient temperature condition for ethanol production which is then transferred to distillation column system to separate ethanol from fermentation mash at 80°C Apart from corn, wheat is the second most widely used starchy feedstock of choice for fuel ethanol production (Patni et al., 2013) and preferred over barley as the cereal feedstock of choice by grain distilleries for ethanol production Recently, Terra Grains has opened North America’s largest wheat-based ethanol producing facility in Belle Plaine, Saskatchewan, Canada with a production capability of 40 million gal (or say, 150 million L) of fuel ethanol and approximately 164,000 tons of DDGs annually This facility procures about 15 million bushels of wheat annually to meet this ethanol production capacity (http://www.terragrainfuels.com/) This implies that, as per the current best-known wheat-based ethanol production technology employed commercially at industrial scale, one bushel of wheat can provide about 2.6 gal of fuel ethanol and 22 pounds of DDGs via dry-milling process as its best operating conditions (as compared to 2.8 gal of ethanol and 17.5 pounds of DDGs in case of corn; see Section 3.2.1) This means that the ethanol yield from wheat is slightly lower than that of corn while the DDGs production is comparatively higher and it also justifies why corn is preferred over wheat as the feedstock of choice for bioethanol production 3.5.1 Grain Processing and Ethanol Production: Recent Advances As wheat is also a starchy feedstock just like corn, the process employed to produce ethanol from wheat is almost the same as in the case of corn, starting from grain processing (milling) to 56 3. Bioethanol Production From Corn and Wheat: Food, Fuel, and Future Subsequently, rectification and dehydration process virtually removes all the water from the purified alcohol resulting in up to 99.7% purity (Patni et al., 2013) However, at industrial scale more sophisticated methods are incorporated into this basic ethanol production process as described later Recently, various technological improvements are developed in this traditional wheat-grain to ethanol process by various wheat-based ethanol producing industries which has ultimately resulted in better process economics, which in turn makes this process more commercially viable and at par with the corn-based technology For example, one of the largest agricultural feedstockbased ethanol producing companies, POET, LLC in South Dakota, USA, has developed and commercialized a new method called the cold-cook (BPX) technology (Saville et al., 2016) to replace the high temperature jet cooking process that is typically used during the liquefaction and saccharification step (Fig. 3.3) This novel improvement not only helps in saving thermal energy, but also helps in avoiding enzyme inactivation that typically occurs in a high-temperature jet cook operation (Saville et al., 2016) However, to compensate for the loss in efficiency that might have incurred due to this reduced temperature operation in the cold-cook technology, a more aggressive milling process is employed along with addition of various types of amylases that break down the starch more efficiently Ultimately, the benefit of this technology is not only thermal energy saving, but also saving the activity of the enzymes added to the slurry tank, because of which the second enzyme addition to the liquefaction system is no more required (Saville et al., 2016) 3.6 SOCIOECONOMICAL ADVANTAGES AND FOOD VERSUS FUEL DEBATE the carbon footprint via carbon recycling As per the estimations of the US Department of Energy, when one gallon of gasoline is replaced with an energy-equivalent amount of bioethanol the greenhouse gas emissions reduces only by ∼20% (Ethanol Myths and Facts, 2013) Furthermore, a recent study by Belboom et al (2015) reported that as high as 42.5%–61.2% of reduction in greenhouse gas emissions is possibly achieved when 1 MJ bioethanol produced from wheat is consumed instead of 1 MJ gasoline However, despite the efficiency of cornbased ethanol production, the entire process is intrinsically limited by how much energy must be put into producing the corn in the first place When corn is grown for producing ethanol, several cultural and agronomic practices are to be followed, such as tilling the land, sowing, and applying fertilizers, harvesting and transporting the corns to ethanol plants (Feng et al., 2010) The more energy used in these processes, the less energy and greenhouse gas emissions are saved from replacing gasoline with fuel ethanol For example, as per USDA estimates, corn-based fuel ethanol yield only ∼2.3 times the amount of energy that goes into producing it (Shapouri et al., 2010) In other words, total energy stored in corn-based fuel ethanol and its coproducts is only 2.3 times of the total energy used up during agricultural production of required feedstock (e.g., production of fertilizers, running farm equipment) as well as during the ethanol production and transportation of the final products Nevertheless, it has also been demonstrated that significant social and economic benefits can be achieved by incorporating renewable fuel into our economic system, primarily via generation of revenue and jobs For example: with the United States as a case study, it is estimated that, in 2016 alone, with production of 15.25 billion gal of ethanol (Fig. 3.2) and 42 million metric tons of coproducts, 74,420 direct jobs and 264,756 indirect jobs are created, which cumulatively made US$42 billion contribution to the nation’s GDP with US$23 billion in household income and US$9 billion in tax revenue Renewable fuel (bioethanol) production from agricultural feedstocks has resulted in a positive environmental effect by significantly reducing 3.7 Conclusion and future perspectives (RFA, 2017) This is an excellent example of showing how the renewable fuel industry can not only help in environment protection and climate control, but also contribute to a nation’s socioeconomic welfare and development, least to mention the added advantages of energy security and energy independency that a nation gains Due to all these advantages, many other developing/developed economics around the globe are now increasingly adopting renewable biofuel production as a replacement to traditional petrochemical-based fuel production 57 3.6.1 Food Versus Fuel Debate: Food Price and Security Thus, increased use of corn for biofuel production may result in further increase in corn and food prices (Schnempf and Yacobucci, 2013) Similarly, some reports have suggested that producing ethanol from feedstocks other than corn, such as sugarcane, might require much less energy and further reduce greenhouse gas emissions (Machado et al., 2017) For instance, ethanol produced from sugarcane in Brazil yields ∼8 times the energy required to produce it and lowers greenhouse gas emissions by >50% when used to replace gasoline (Chum et al., 2014) However, unlike in Brazil, the United States climate is not suitable for growing sugarcane farming, and hence, corn is likely to continue as the major feedstock in the United States in coming decades Moreover, land acquisition for biomass/feedstock sourcing has not only been reported of people’s rights and livelihoods, but also has resulted in the change of natural habitats and loss of biodiversity (Pilgrim and Harvey, 2010) Particularly, in developing countries, monitoring land acquisition is often an issue and often unreliable given the major disparities that are observed between large companies and local people (Van Derhorst and Vermeylen, 2011) Upon that, land usage also depends on different communal or cultural value sets in different geographical locations (Thornley and Gilbert, 2013), as well as the uneven distribution of climate change impacts and its local/ global effects also needs to be considered in all parts of the world Although energy security concerns have pushed developed economies toward adopting sustainable green technologies, it has also raised a long-standing debate of whether corn is better used as food or as a fuel source (Tenenbaum, 2008) Recent reports have shown that utilization of food crops for renewable fuel production can come with hidden economic and environmental costs that are either not considered fully yet or aren't understood in great detail (Wise, 2012) In a recent study, these issues have been quantified and compared in terms of economics of the entire production system to determine if the beneficial effects of corn-biofuel production outweigh the costs (Richardson and Kumar, 2017) Interestingly, it was found that, utilization of corn for production of biofuel is possibly having a much higher negative environmental impact than when the same is grown and utilized for food Similarly, bioethanol production from food crops has also been associated with negative impacts on food security, which is one of the biggest concerns raised about using food crops for producing fuel (Tenenbaum, 2008) Furthermore, reports suggest that there isn’t much land left in the United States to increase its corn production and using previously unused lands could increase greenhouse gas emissions by releasing carbon stored in them (Wise, 2012) 3.7 CONCLUSION AND FUTURE PERSPECTIVES Bioethanol from corn and wheat is generally derived from starch and sugars It is considered as the simplest source for bioethanol compare to other sources In industrial scale, corn is considered as the primary source of the world’s fuel ethanol and mostly comes from the United States Bioethanol from wheat is not popular compared to corn as it is 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