Sugarcane production causes more intense soil erosion thanany crop produced in Brazil because the total sugarcane biomass is harvested andprocessed in ethanol production.. sugarcane conv
Trang 1364 D Pimentel, T.W Patzekpetroleum used in the U.S was about 1,200 billion liters in 2004–2005 (USCB, 2004–2005) To produce the 18.9 billion liters of ethanol, about 5.0 million ha or 20% ofU.S corn land is used Furthermore, the 18.9 billion liters of ethanol (energy equiva-lent to 12.5 billion liters of vehicle liquid fuel) provides only 1% of the petroleumutilized by U.S each year If corn-ethanol production were expanded to using100% of U.S corn production, this would provide only 7% of the petroleum needs!
14.7 Ethanol Production and Use in Brazil
In contrast, Brazil can fuel most of its automobiles and other vehicles with ethanolbecause Brazilians consume only 9% of the U.S consumption in petroleum (BP,2005) Since 1984 the portion of Brazilian sugarcane used for ethanol decreasedfrom a peak of 70% to about 55% in 2000 (Schmitz et al., 2003) During that timethe percentage of ethanol cars declined from 94% in 1984 to less than 1% in 1996(Rosillo-Calle and Cortez, 1998) The difference included gasoline for the cars Flexcars replaced the ethanol cars and as a result Brazil’s oil consumption has increased42% during the last decade (BP, 2001, 2005)
Proponents of ethanol point to the production of ethanol in Brazil but ignore thefact that the U.S now produces more ethanol (18.9 billion liters ethanol per year)compared with Brazil that produces about 15.1 billion liters per year (Calibre, 2006).Brazil is fortunate to have the land and climate suitable for sugarcane Sugarcane
is a more efficient feedstock for ethanol production than corn grain (Patzek andPimentel, 2005) However, because Brazilian energy balance is only slightly posi-tive (1 kcal:2.28 kcal), the Brazilians need to heavily subsidize their ethanol industry
as does the U.S In the 1980s and 1990s the Brazilian government sold ethanol tothe public for 22
(Pimentel, 2003) Because other priorities emerged in Brazil, the government hassince abandoned directly subsidizing ethanol (Spirits Low, 1999; Coelho et al., 2002).Now the consumer is paying the subsidy directly at the pump (Pimentel, 2003).The total Brazilian subsidy is estimated to be about 50% for ethanol production(CIA, 2005) Earlier it was mentioned that it costs 26
in Brazil that sells for 86
nearly $1.23 per liter or about 43% higher than a liter of ethanol (R.M Boddey,Senior Scientist, Empresa Brasileira de Pesquisa Agropecuaria (Embrapa), Brasil,personal communication, 2007) Thus, higher gasoline prices help subsidize the cost
of ethanol production in Brazil (CIA, 2005)
14.8 Environmental Impacts
Some of the economic and energy contributions of ethanol production both in theU.S and Brazil are negated by the widespread environmental pollution problemsassociated with ethanol production using sugarcane Many of the environmentalimpacts in Brazil associated with sugarcane production also occur in the U.S
Trang 214 Ethanol Production 365sugarcane production Sugarcane production causes more intense soil erosion thanany crop produced in Brazil because the total sugarcane biomass is harvested andprocessed in ethanol production This removal of most of the biomass leaves the soilunprotected and exposed to erosion from rainfall and wind energy For example, soilerosion with sugarcane cultivation is reported to have the highest soil erosion rate
in all Brazilian agriculture, averaging 31 t/ha/yr (Sparovek and Schung, 2001) The
31 t/ha soil loss is 30–60 times greater than sustainability of the soil in agriculture(Troeh et al., 2004; Pimentel, 2006)
In addition, sugarcane production uses larger quantities of herbicides and ticides and nitrogen fertilizer (Tables 14.1 and 14.2) than most other crops produced
insec-in Brazil and these chemicals spread to ground and surface water thereby causinsec-ingsignificant water pollution (NAS, 2003)
Relatively large quantities of water are required to produce sugarcane Because
it takes 12 kg of sugarcane to produce 1 L of ethanol, about 7,000 L of water areneeded to produce the required 12 kg of sugarcane per liter of ethanol
Although the Brazilian government has passed legislation to curtail the burning
of sugarcane before harvest to reduce air pollution problems, most of the sugarcane
in Brazil is still burned and this is resulting in respiratory problems in children andthe elderly (Braunbeck et al., 1999; Cancado et al., 2006) The rules need to beenforced to help protect the people from this serious air pollution problem Addi-tional smoke is released during the removal of forests for sugarcane and other cropproduction Between May 2000 and August 2005, Brazil lost more than 132,000square km of forest, an area larger than Greece (Mongabay, 2006)
The harvesting of sugarcane by laborers is hard and dangerous work, cutting thesugarcane with large knives As Broietti (2003) reported these are dangerous andmiserable conditions under which to work
All these factors confirm that the environmental and agricultural system in whichBrazilian and U.S sugarcane is being produced is experiencing major environmentalproblems Further, it substantiates the conclusion that the sugarcane productionsystem, and indeed the ethanol production system, are not environmentally sus-tainable now or for the future Because sugarcane is the raw material for ethanolproduction in Brazil, it cannot be considered a renewable energy source, consideringthe production and processing aspects
Another pollution problem concerns the large amounts of waste-water produced
by each ethanol plant As noted, for each liter of ethanol produced using sugarcane,about 10 L of wastewater are produced This polluting wastewater has a biologicaloxygen demand (BOD) of 18,000–37,000 mg/liter depending of the type of plant(Kuby et al., 1984) The cost of processing this sewage in terms of energy (4 kWh/kg
of BOD) must be included in the cost of producing ethanol (Tables 14.3 and 14.4)
14.9 Air Pollution
Reports confirm that ethanol use contributes to air pollution problems when burned
in automobiles (Youngquist, 1997; Hodge, 2002, 2003, 2005; Niven, 2005) The use
Trang 3366 D Pimentel, T.W Patzek
of fossil fuels, as well as the use of ethanol in cars, releases significant quantities ofpollutants to the atmosphere Furthermore, carbon dioxide emissions released fromburning these fossil fuels contribute to global warming and are a serious concern(Schneider et al., 2002) Additional carbon dioxide is released during the fermen-tation process Also, when the soil is tilled serious soil erosion takes place and soilorganic matter is oxidized When all the air pollutants associated with the entireethanol production system are considered, the evidence confirms that ethanol pro-duction contributes to the already serious U.S and Brazilian air pollution problem(Youngquist, 1997; Hodge, 2002, 2003, 2005; Pimentel and Patzek, 2005; Patzekand Pimentel, 2005)
14.10 Food Security
At present, world agricultural land supplies more than 99% of all world food ries), while aquatic ecosystems supply less than 1% (FAO, 2002) Worldwide, dur-ing the last decade, per capita available cropland decreased 20% and irrigation land12% (Brown, 1997) Furthermore, per capita grain production has been decreas-ing, in part due to increases in the world population (Worldwatch Institute, 2001).Worldwide, diverse cereal grains, including corn, make up 80% of the food of thehuman food supply (Pimentel and Pimentel, 1996)
(calo-The current food shortages throughout the world call attention to the tance of continuing U.S and Brazilian exports of grains and other food crops forhuman nutrition The expanding world population that now numbers 6.5 billion,further complicates and stresses the food security problem now and for the future(PRB, 2006) Almost a quarter million people are added each day to the worldpopulation, and each of these human beings requires adequate food Today, the mal-nourished people in the world number more than 3.7 billion (WHO, 2006) This isthe largest number of malnourished people and proportion ever reported in history.Malnourished people are highly susceptible to various serious diseases and this isreflected in the rapid rise in the number of seriously infected people in the world,with diseases like tuberculosis, malaria, and AIDS, as reported by the World HealthOrganization (Kim, 2002; Pimentel et al., 2006)
impor-14.11 Food versus the Fuel Issue
Using sugarcane, a human food resource, for ethanol production, raises ethical andmoral issues (Wald, 2006) Expanding ethanol production entails diverting valuablecropland from the production of food crops needed to nourish people The ener-getic and environmental aspects, as well as the moral and ethical issues also deserveserious consideration In spite of oil and natural gas shortages now facing the U.S.,ethanol production is forcing the U.S to import more oil and natural gas to produceethanol and other biofuels (Pimentel and Patzek, 2005)
Trang 414 Ethanol Production 367The expansion of ethanol production in the U.S and Brazil is having negativeimpacts on food production and food exports (Chang, 2006), and is likely to havefurther negative impacts on food production and the environment.
Furthermore, increasing oil and natural gas imports in the U.S and other tries drives up the price of oil and gas This is especially critical for the poor indeveloping countries of the world Even now this is documented by the fact thatworldwide per capita fertilizer use has been declining for the last decade because ofthe increased costs for the poor farmers of the world (Worldwatch Institute, 2001)
coun-14.12 Summary
For a thorough and up-to-date evaluation of all the fossil energy costs of ethanolproduction from sugarcane in both the U.S and Brazil, every energy input in thebiomass production and ultimate conversion process must be included In this study,more than 12 energy inputs in average U.S and Brazilian sugarcane production areevaluated Then in the fermentation/distillation operation, 9 more fossil fuel inputsare identified and included Some energy and economic credits are given for thebagasse to reduce the energy inputs required for steam and electricity
Based on all the fossil energy inputs in U.S sugarcane conversion process, a total
of 1.48 kcal of ethanol is produced per 1 kcal of fossil energy expended In Brazil, atotal of 2.28 kcal of ethanol is produced per 1 kcal of fossil energy expended.Some pro-ethanol investigators have overlooked various energy inputs in U.S.and Brazilian sugarcane production, including farm labor, farm machinery, pro-cessing machinery, and others In other studies, unrealistic low energy costs wereattributed to such energy inputs, as nitrogen fertilizer, insecticides, and herbicides(Corn-Ethanol, 2007)
Both the U.S and Brazil heavily subsidize ethanol production The data suggestthat billions of dollars are invested in subsidies and this significantly increases thecosts to the consumers
The environmental costs associated with producing ethanol in the U.S and Brazilare significant but have been generally overlooked The negative environmentalimpacts on the availability of cropland and freshwater, as well as on air pollutionand public health, have yet to be carefully assessed These environmental costs interms of energy and economics should be calculated and included in future ethanolanalyses so that sound assessments can be made
In addition, the production of ethanol in the U.S and Brazil further confirms thatthe mission of converting biomass into ethanol will not replace oil This mission isimpossible
General concern has been expressed about taking food crops to produce ethanolfor burning in automobiles instead of using these crops as food for the many mal-nourished people in the world The World Health Organization reports that morethan 3.7 billion humans are currently malnourished in the world – the largest number
of malnourished ever in history
Trang 5368 D Pimentel, T.W Patzek
Acknowledgments We would like to thank the following people for their valuable comments
and suggestions on earlier drafts of this manuscript: Andrew B Ferguson, Optimum Population Trust, Oxon, UK; Mario Giampietro, Istituto Nazionale di Ricerca per gli Alimenti e Nutrizione (INRAN), Rome, IT; Matthew Farwell, Alternative Energy, Energy, Nanotechnology, Palo Alto, CA: Marcelo Dias de Oliveira, University of Florida, Gainesville, FL; Odo Primavesi, Empresa Brasileira de Pesquisa Agropecu´aria (Embrapa), Brazil; Thomas Standing, San Francisco Public Utilities Commission, San Francisco, CA; Sergio Ulgiati, Department of Chemistry, University of Siena, Italy; Walter Youngquist, Petroleum Consultant, Eugene, OR.
This research was supported in part from a grant from the Podell Emertii award
at Cornell University
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Trang 9Chapter 15
Ethanol Production Using Corn, Switchgrass and Wood; Biodiesel Production Using SoybeanDavid Pimentel and Tad Patzek
Abstract In this analysis, the most recent scientific data for corn, switchgrass, and
wood, for fermentation/distillation were used All current fossil energy inputs used
in corn production and for the fermentation/distillation were included to determinethe entire energy cost of ethanol production Additional costs to consumers in-clude federal and state subsidies, plus costs associated with environmental pollu-tion and/or degradation that occur during the entire production process In addition,
an investigation was made concerning the conversion of soybeans into biodieselfuel
Keywords Energy· biomass · fuel · natural resources · ethanol · biodiesel
15.1 Introduction
Green plants, such as corn, soybeans, switchgrass and trees, and all other kinds ofbiomass, convert solar energy into plant material but require suitable soil, nutrients,and freshwater In the conversion of the biomass into liquid fuel, water, microor-ganisms, and more energy are required Andrew Ferguson (2006, personal commu-nication, Optimum Population Trust, Manchester, UK) makes an astute observationthat the proportion of sun’s energy that is converted into useful ethanol, even usingvery positive energy data, only amounts to 5 parts per 10,000, or 0.05% of the solarenergy
Some recent papers are claiming returns on ethanol production from corn of where from 1.25 kcal to 1.67 kcal per kcal invested (Shapouri et al., 2004; Farrell
Trang 10374 D Pimentel, T Patzek
et al., 2006; Hill et al., 2006) These excessively high returns are achieved by eitheromitting several energy inputs, reducing other energy inputs, or giving credits thatare too optimistic for the by-products
15.2 Energy Inputs in Corn Production
The conversion of corn into ethanol by fermentation in a large plant is about 1 liter ofethanol from 2.69 kg of corn grain (approximately 9.5 liters pure ethanol per bushel
of corn; see Footnote (a) in Table 15.2) (Pimentel and Patzek, 2005) The production
of corn in the United States requires a significant energy and dollar investment forthe 14 inputs, including labor, farm machinery, fertilizers, irrigation, pesticides, andelectricity (Table 15.1) To produce an average corn yield of 9,400 kg/ha (149 bu/ac)
of corn using up-to-date production technologies requires the expenditure of about8.2 million kcal of energy inputs (mostly natural gas, coal, and oil) listed in Ta-ble 15.1 This is the equivalent of about∼930 liters of oil equivalents (∼25% ofgrain energy) expended per hectare of corn The production costs total about $927/hafor the 9,400 kg/ha or approximately 10
Full irrigation (when there is insufficient or no rainfall) requires about 100 cm/ha
of water per growing season Because only about 15% of U.S corn production rently is irrigated (USDA, 1997a), only 8.1 cm per ha of irrigation was included forthe growing season On average irrigation water is pumped from a depth of 100 m(USDA, 1997a) On this basis, the average energy input associated with irrigation is320,000 kcal per hectare (Table 15.1)
cur-15.2.1 Energy Inputs in Fermentation/Distillation
The average costs in terms of energy and dollars for a large (245 to 285 millionliters/year), modern drygrind ethanol plant are listed in Table 15.2 In the fermen-tation/distillation process, the corn is finely ground and approximately 15 liters ofwater are added per 2.69 kg of ground corn Some of this water is recycled Afterfermentation, to obtain a liter of 95% pure ethanol from the 8–12% ethanol beerand 92–88% water mixture, the 1 liter of ethanol must be extracted from approxi-mately 11 liters of the ethanol/ water mixture Although ethanol boils at about 78degrees C, and water boils at 100 degrees C, the ethanol is not extracted from thewater in the first distillation, which obtains 95% pure ethanol (Maiorella, 1985;Wereko-Brobby and Hagan, 1996; S Lamberson, personal communication, CornellUniversity, 2000) To be mixed with gasoline, the 95% ethanol must be further pro-cessed and more water removed, requiring additional fossil energy inputs to achieve99.5% pure ethanol (Table 15.2) Thus, a total of about 10 liters of wastewater must
be removed per liter of ethanol produced, and this relatively large amount of sewageeffluent has to be disposed of at an energy, economic, and environmental cost
To produce a liter of 99.5% ethanol uses 46% more fossil energy than the energyproduced as ethanol and costs 45
feedstock requires about 32% of the total energy input In this analysis, the totalcost, including the energy inputs for the fermentation/distillation process and the
Trang 1115 Ethanol Production Using Corn, Switchgrass and Wood 375
Table 15.1 Energy inputs and costs of corn production per hectare in the United States
b It is assumed that a person works 2,000 hrs per year and utilizes an average of 8,000 liters of oil equivalents per year.
c It is assumed that labor is paid $13 an hour.
d Pimentel and Pimentel, 1996.
e Prorated per hectare and 10 year life of the machinery Tractors weigh from 6 to 7 tons and harvesters 8–10 tons, plus plows, sprayers, and other equipment.
f Hoffman et al., 1994.
g Wilcke and Chaplin, 2000.
h Input 11, 400 kcal per liter.
u Input 281 kcal per kg.
v Pimentel and Pimentel, 1996.
w Pimentel and Pimentel, 1996.
x USDA, 1997b.
y USDA, 1997a.
z Batty and Keller, 1980.
aa Irrigation for 100 cm of water per hectare costs $1,000 (Larsen et al., 2002).
bb Larson and Cardwell, 1999.
cc USDA, 2002.
dd USDA, 1991.
ee Input 100,000 kcal per kg of herbicide and insecticide.
ff Input 860 kcal per kWh and requires 3 kWh thermal energy to produce 1 kWh electricity.
gg Goods transported include machinery, fuels, and seeds that were shipped an estimated 1,000 km.
hh Input 0.83 kcal per kg per km transported.
ii
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Table 15.2 Inputs per 1000 liters of 99.5% ethanol produced from corna
b Data from Table 15.1.
c Calculated for 144 km roundtrip.
d Pimentel, 2003.
e 15 liters of water mixed with each kg of grain.
f Pimentel et al., 2004.
g Pimentel et al., 2004.
h 4 kWh of energy required to process 1 kg of BOD (Blais et al., 1995).
i Estimated from the industry reported costs of $85 millions per 65 million gallons/yr dry grain plant amortized over 30 years The total amortized cost is $43.6/1000L EtOH, of which an estimated $32 go to steel and cement.
j Illinois Corn, 2004 The current estimate is below the average of 40,000 Btu/gal of denatured ethanol paid to the Public Utilities Commission in South Dakota by ethanol plants in 2005.
k Calculated based on coal fuel Below the 1.95 kWh/gal of denatured EtOH in South Dakota, see j).
l $.07 per kWh (USCB, 2004–2005).
m 95% ethanol converted to 99.5% ethanol for addition to gasoline (T Patzek, personal
communication, University of California, Berkeley, 2004).
n 20 kg of BOD per 1000 liters of ethanol produced (Kuby et al., 1984).
o Newton, 2001.
p DOE, 2002.
apportioned energy costs of the stainless steel tanks and other industrial materials,
is $454.23 per 1000 liters of ethanol produced (Table 15.2)
15.2.2 Net Energy Yield
The largest energy inputs in corn-ethanol production are for producing the cornfeedstock, plus the steam energy, and electricity used in the fermentation/distillationprocess The total energy input to produce a liter of ethanol is 7,474 kcal (Table 15.2)