energy lifecycle assessment and environmental impacts of ethanol biofuel

INTERNATIONAL JOURNAL OF ENERGY RESEARCHInt. J. Energy Res. 2009; 33:186–193Published online 2 June 2008 in Wiley InterScience(www.interscience.wiley.com). DOI: 10.1002/er.1435

Energy lifecycle assessment and environmental impacts ofethanol biofuel

Rynosuke Kikuchi�,y, Romeu Gerardo and Sandra M. Santos

ESAC, Departamento de Ciencias Exactas e do Ambiente; Instituto Politecnico de Coimbra, Bencanta, 3040-316 Coimbra, Portugal

SUMMARY

As demand for oil increases, production from large oil fields is declining at 4–5% annually, and the world productionof oil is expected to peak around 2010. In the meantime, there is one liquid fuel that is renewable and can beused in vehicles without major modification of the engine—it is biofuel (biomass fuel). Ethanol is an alcohol-based fuelproduced by fermenting and distilling crops such as corn, barley, wheat, and the like. There are a few issues to bediscussed regarding the use of ethanol biofuel: (i) there is a possibility that more energy is used to grow and process theraw material (e.g. corn) into ethanol than is contained in the ethanol itself; (ii) it is unclear whether the adoption ofethanol fuel will increase greenhouse gas; and (iii) a common objection to biofuel production is that it could divertagricultural production away from food crops (i.e. subsidized food burning). After analysis of these issues, biofuelproduction from wood (forest) residues is considered a sustainable approach to a renewable energy-based society.Copyright r 2008 John Wiley & Sons, Ltd.

KEY WORDS: biofuel (biomass fuel); cellulose; crops; lifecycle; wood (forest) residues

1. INTRODUCTION

Global energy demand is likely to grow froman estimated 8.4 billion tons of oil equivalent(btoe) in 1995 to about 12.6 btoe by 2020,an average annual increase of 1.6% [1]. Owingto the recent sharp increase in the demandfor energy and rapid economic growth, thepetroleum supply is expected to become tightaround 2010 [2]. Effort has therefore beenmade to promote the use of renewable energy

(wind power, solar power, etc.). However, thistype of energy accounts for only 5% of energyuse in Europe and its share is expected to riseto only around 10% by 2020 [1]. The remaining90% of required energy will have to comefrom conventional energy sources. Especially thesupply of oil should be discussed because atpresent automobile engines use mainly gasolineand diesel oil. The historical record and theprospect of global oil production are shown inFigure 1 as an estimate of the current reserves of

*Correspondence to: Rynosuke Kikuchi, ESAC, Departamento de Ciencias Exactas e do Ambiente; Instituto Politecnico de Coimbra,Bencanta, 3040-316 Coimbra, Portugal.yE-mail: [email protected]

Received 27 August 2007

Accepted 25 February 2008Copyright r 2008 John Wiley & Sons, Ltd.

conventional oil and the amount still left to bediscovered [2].

According to Figure 1, it is concluded that adecline in global oil production will begin before2010. The noteworthy points are summarized asfollows [2]: North American and Canadian oilproduction peaked in 1972; production in Russiahas fallen 45% since 1987; a downturn in thevolume of oil produced outside the Persian Gulfregion appears imminent. Policies governing theuse of vehicles are important and need to beaddressed with urgency.

As demand for oil increases, production fromlarge oil fields is declining at 4–5% annually [3],and the world production of oil is expected to peakaround 2010 (see Figure 1). In the meantime, thereis one liquid fuel that is renewable and can be usedin vehicles without major modification of theengine—it is biofuel (biomass fuel) [3]; ethanol isan alcohol-based fuel produced by fermenting anddistilling crops such as corn, barley, wheat, and thelike [3].

A lot of attention has gone to ethanol and itsuse to extend the supply of gasoline as an additiveand eventually its use as a fuel by itself. It isconsidered that another biofuel (so-calledbiodiesel) may turn out to have more potentialthan ethanol as an alternative and renewablesource of fuel [3]. Biodiesel can be made from avariety of sources including vegetable oils, animalfats, waste, and microalgae oils; it is producedthrough a process in which organically derived oilsare combined with alcohol (ethanol or methanol)

in the presence of a catalyst to form ethyl ormethyl ester [3]. There are a few issues to bediscussed regarding the use of ethanol biofuel: (i)there is a possibility that more energy is used togrow and process the raw material (e.g. corn) intoethanol than is contained in the ethanol itself; (ii) itis unclear whether the adoption of ethanol fuel willincrease greenhouse gas (GHG); and (iii) acommon objection to biofuel production is thatit could divert agricultural production away fromfood crops (i.e. subsidized food burning) [4]. Itseems necessary to evaluate and clarify the above-mentioned points in order to support a balancedapproach to propagating ethanol biofuel.

2. ENERGY BALANCE BETWEEN INPUTAND OUTPUT

One of the most controversial issues relating toethanol is what is called the ‘net energy’ of ethanolproduction: there is doubt as to whether moreenergy is used to grow and process the rawmaterial into ethanol than is contained in theethanol itself. There are many net energy studies ofbiofuel, particularly ethanol, which give a widerange of values [5–7]. It is cited that corn ethanolhas a negative energy value [5]; that is, the liquidfuel and other energy sources required to grow andconvert corn into ethanol are greater than theenergy value present in the ethanol fuel. Thisimplies that corn ethanol is not an energysubstitute and that increasing its production doeslittle to displace oil imports and increase energysecurity.

Table I shows the wide variation in theestimates of the net energy value (NEV). Sincesome studies use low heating values (LHV) andothers use high heating values (HHV), the energy

Figure 1. Annual transition of global oil production(redrawn from [2]).

Table I. Energy input assumption of ethanol.

StudyTotal energy use

(Btu gal�1)Net energy value

(Btu gal�1)

Reference [5] 131 017 �33 517Reference [6] 91 127 �8431Reference [7] 73 934 118 324Reference [8] 90 000 �4000

ENERGY LIFECYCLE ASSESSMENT AND ENVIRONMENTAL IMPACTS 187

Copyright r 2008 John Wiley & Sons, Ltd. Int. J. Energy Res. 2009; 33:186–193

DOI: 10.1002/er

estimates for ethanol conversion are not alwaysdirectly comparable due to scale differences. TheHHV, also called gross heating value, is thestandard heat of combustion referenced to waterof combustion as liquid water. The LHV, alsocalled net heat of combustion, is the standard heatof combustion referenced to water of combustionas water vapor. Energy balance calculations maybe made using either basis as long as the basis isconsistently applied. Moreover, NEV estimates arecomparable regardless of the heating value used.

Pimentel reports the highest NEV for cornethanol among the studies: based on an LHVscale, he calculated that the total energy input toproduce 1 gallon of ethanol is 131 017 Britishthermal units (Btu) [5]. Compared with the LHVof ethanol, 76 000Btu, this is a net energy loss of55 017Btu per gallon (Btu gal�1) Even whencoproducts were considered, Pimentel stillestimated a net energy loss of around33 517Btu gal�1. Keeney and DeLuca alsoreported a negative NEV for an average farm [6],but the energy deficit was only 8431Btu gal�1.Keeney and DeLuca do not consider corn-processing byproducts, but they show that apositive energy balance can be attained with low-input corn production [6]. Marland and Turhollowreported that it requires 73 934Btu (HHV basis) toproduce a gallon of ethanol assuming thatconversion takes place in the best ethanolfacilities available today [7]. When energy use isallocated to the coproducts made during theethanol conversion process, such as gluten meal,gluten feed, and corn oil, they conclude that theNEV of corn ethanol is 18 324Btu gal�1 [7].

Figure 2 illustrates the energy inputs used toproduce and deliver ethanol to a refueling station.It follows from Figure 2 that input of fossil energyis required at each step. Some confusion arisesbecause a portion of the total (not fossil orpetroleum) energy input in the ethanol cycle isthe ‘free’ solar energy that ends up in the corn.Since the solar energy is free, renewable, andenvironmentally benign, it should not be takeninto account in the energy balance calculations.While the total (includes solar) energy needed toproduce a unit of ethanol is more than the totalenergy needed to produce a unit of gasoline,

ethanol is superior when calculating either theamount of fossil energy needed or the amount ofpetroleum energy needed [9].

It is important that the most current data beused to estimate the NEV of ethanol because theefficiency of growing corn and converting it toethanol has improved significantly over the past 10years. Higher corn yields, lower energy use perunit of output in the fertilizer industry, andadvances in fuel conversion technologies havegreatly enhanced the economic and technicalfeasibility of producing ethanol. Data trends inyields, fertilizer efficiency, and conversion facilityare summarized in Figure 3.

While energy use has been declining, there hasbeen a rising trend in corn yields. With theexception of a few bad years, annual corn yieldshave been increasing since 1975. The largedownward spikes in 1983, 1988, and 1993 werecaused by adverse weather. Droughts causedunusually low yields in 1983 and 1988, and in1993 the Midwest experienced a devastating flood.Higher yields without corresponding increases inenergy use indicate that resources are being usedmore efficiently. The farm energy use index, anefficiency measurement for fuel and electricity usedon U.S. farms, has improved significantly in recentyears: it fell from a high of 125 in 1978 to 93 in1989. Fertilizer use in grain production rose formany years but lately has appeared to be indecline. Nitrogen use per planted acre of corndeclined from 140 pounds per acre in 1985 to 123pounds per acre in 1993. Phosphate use declined

Figure 2. Energy lifecycle of ethanol (EtOH) production.

R. KIKUCHI, R. GERARDO AND S. M. SANTOS188


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from 60 to 56 pounds per acre, and potash usedeclined from 84 pounds per acre to 79 pounds peracre during the same period.

Making ethanol from corn has also becomemore energy efficient. Hohmann and Rendlemanreported that a shift in production to larger plantsand the adoption of energy-saving innovationsreduced the processing energy required to producea gallon of ethanol from 120 000Btu in 1981 to43 000Btu in 1991. Efforts by the industry toconserve electricity have resulted in substantialenergy savings. In 1980, for example, ethanol

plants used 2.5–4.0 kWh of electricity per gallon ofethanol versus 0.5 kWh used by today’s modernfacilities. Modern facilities conserve energy byutilizing cogeneration facilities that produce steamand electricity simultaneously.

According to a recent study [11], the fossilenergy input per unit of ethanol is lower �0.74million Btu of fossil energy consumed for each 1million Btu of ethanol delivered—compared with1.23 million Btu of fossil energy consumed foreach 1 million Btu of gasoline delivered. Theenergy outputs from the produced ethanol are30–50% less than the fossil energy inputs (i.e.energy ratio of 0.5 to 0.7) [9]. However, the energyratio of ethanol is 1.2 to 1.3 when solar energy istaken into account [9].

3. ETHANOL BIOFUEL AND GHG

One environmental benefit of replacing fossil fuelswith biomass-based fuels is that the energyobtained from biomass does not add to globalwarming. All fuel combustion, including fuelsproduced from biomass, releases CO2 into theatmosphere. However, because plants use CO2

from the atmosphere to grow (photosynthesis), theCO2 formed during combustion is balanced bythat absorbed during the annual growth of theplants used as the biomass feedstock—unlikeburning fossil fuels that release CO2 capturedbillions of years ago. Current corn-ethanol tech-nologies are much less petroleum-intensive thangasoline, but they have (GHG) emissions similarto those of gasoline [12]. However, emissionintensity of GHG depends on the primary materialof ethanol and its use (see Figure 4 based on [9]). Itfollows from Figure 4 that ethanol is beneficial inreducing GHG emissions. Corn ethanol reducesGHG emissions by 20–30%, while cellulosicethanol has an even greater benefit with an 85%reduction in GHG emissions.

4. ENERGY-CROP COMPETITION

As stated in Section 1, a common objection tobiomass energy production is that it could divertagricultural production away from food crops (e.g.

Figure 3. Data trends in corn yield, corn output, andenergy intensity in the U.S.A. (redrawn from [10]): (a) yieldof corn with time; (b) corn output per pound of fertilizer

used; and (c) energy use intensity of ethanol plants.



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corn) in a hungry world [4]. The basic argument isthat energy-crop programs compete with foodcrops (e.g. corn) in a number of ways and thuscause a food shortage and price increase. Burninga human-food resource (e.g. corn) for fuel, ashappened when ethanol is produced, raises im-portant ethical and moral issues [4,13,14]. Agri-cultural land supplies more than 99% of all worldfood, while the oceans supply less than 1% [13].World data confirm that per capita food supplieshave been declining for the past 12 years [13].Expanding ethanol production could entail divert-ing essential cropland from producing corn neededto sustain human life to producing corn forethanol factories. This will create serious practicalas well as ethical problems. It has been calculatedthat powering the average U.S. automobile for 1year on ethanol (blended with gasoline) derivedfrom corn would require 11 acres of farmland, thesame space needed to grow a year’s supply of foodfor seven people [14]. It is suggested that anincrease in the use of corn for alcohol productionwould lead to reduced use of corn for animal feed,thus leading to higher meat, dairy, and poultryprices, eventually resulting in the reduced con-sumption of these products [4]. Alternative foodcrops such as wheat and grain sorghum would beused leading to further price increases [4]; there-

fore, many relationships and uncertainties areinvolved [4].

According to a report of the World FoodProgram [15], there are 830 millionundernourished people in the world today and791 million live in developing countries. In theAsia and Pacific region, 525 million, or 17% of thetotal population of 3 billion, suffer fromundernourishment and the worst hit countriesare North Korea, Mongolia, Cambodia, andBangladesh. In addition, there are millions ofdrought-affected people in Tajikistan, Pakistan,Iran, Armenia, and Georgia. The worst conditionscontinue to be, largely, in Africa. One out of everythree people in Sub-Sahara Africa isundernourished. In Sub-Sahara Africa, 180million, or 33% of the total population of 539million, suffer from undernourishment and theworst hit countries include Angola, Burundi,Sierra Leone, Guinea, Somalia, Sudan, Ethiopia,and Eritrea. In the Near East and North Africa, 33million, or 9% of the total population of 360million, suffer from undernourishment and theworst hit country is Afghanistan. In the LatinAmerica and Caribbean region, 53 million, or 11%of the total population of 481 million, suffer fromundernourishment and the worst hit countries areHaiti, Nicaragua, Bolivia, and Honduras. To putit differently, about 24 000 people die from theeffects of hunger in developing countries each day.That is about one person every 3.5 s.

5. CELLULOSIC ETHANOL AND WOODWASTE

As seen in Figure 4, cellulosic ethanol is morebeneficial than corn ethanol in GHG reduction; itis therefore environmentally friendly to makeethanol from a wide variety of cellulosicsources such as sawdust, small-diameter trees,etc. A major criticism often leveled againstbiomass, particularly against large-scale fuelproduction, is that it could divert agriculturalproduction away from food crops (e.g. corn,wheat, etc.), especially in developing countries.However, cellulosic sources (e.g. trees) have norelation with food crops.

Figure 4. Ethanol and emission of greenhouse gas invehicle [9]: ethanol in E10 and E85 blends (per gallonbasis). GHG, greenhouse gas; EtOH, ethanol; E10, ablend of 10% EtOH and 90% gasoline; E85, a blend of85% EtOH and 15% gasoline; GV, gasoline vehicle;FFV, flexible fuel vehicle, which can run on regulargasoline, E10 or E85; DM, dry mill process ethanol;WM, wet mill process ethanol; and Cell, cellulosic.



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5.1. Wood waste

It is reported that corn-ethanol production isuneconomic between growers and processors [16];it seems to be a worthwhile subject to discuss woodwaste, which is one of the cellulosic sources forethanol production. Wood residues (forest slash,sawdust, etc.) have not been fully utilized or havebeen left on the land, and the amount of theseresidues is huge throughout the world.

The USA—it is estimated that 100 million tonsof wood residues are generated by timber-processing facilities in the U.S., and theseresidues are the excesses of production that havenot been utilized [17]. The apparent value of woodresidues is less than the cost of collection,transportation, and processing for beneficial use.As a result, the waste discharged can causeenvironmental problems and the loss of a naturalresource [17].

European Union—it is likely that the waste ordumping of wood residues will becomeincreasingly unacceptable and/or expensive in allcountries, and that consuming industries willcontinue to seek this raw material source and toset up even more efficient circuits to collect it. Thepercentage of wood residues, which is used as rawmaterial, is expected to rise from 61% in 1990 toabout 75% in 2020 [18]; that is, the volume ofwood waste will rise from �50 million m3 in 1990to �80 million m3 in 2020 (see Figure 5).

Russia—about 80 million m3 of woodproduction was recorded during January toAugust in 2006, and this production discharged�30 million m3 of wood residues. Of this, 20million m3 of waste was left to decay in forestsbecause its recycling was considered unprofitable.

Forest managers have to pay huge forfeits forwood waste [19].

Canada—bark is a huge by-product ofwood processing: some 12 million tons of barkresidues are produced by the forest industry inCanada each year [20]. Recognizing that no oneindustrial application can realistically absorb thehuge volumes of bark produced by the forestindustry, other uses for this by-product are beinginvestigated [20].

5.2. Production of cellulosic ethanol

Unlike grain, the sugars in cellulose are locked incomplex polysaccharides, so it is essential toseparate these complex structures into fermentablesugars [21]. If this separation is possible, cellulosemight be suitable for making eco-friendly fuel—cellulosic ethanol. Cellulose (a fibre found in allplant material) is the most abundant biomass inthe world, but its resistance against chemical andenzymatic hydrolysis and its insolubility in mostsolvents has so far limited its use as a source ofbiofuel [22]. It has been reported that cellulose canform a gel, just like starch, which is commonlyused in biofuel production and the celluloseundergoes a transformation from a crystallineform to an amorphous gel-like one, in water athigh temperature and pressure [23] (see Figure 6).

Starch forms a gel when heated in water toaround 701C. This process is illustrated by thechanges seen when cooking starchy foods likepasta. Gelatinization is a key step for convertingstarch into glucose, which can then be fermentedto make bioethanol. It had been considered thatcellulose could not gelatinize because its crystallinestructure is more stable than starch [23]; however,the above-mentioned transformation suggests thatit is technically feasible to use cellulose as a carbonsource for fermentation.

According to a report by the PortugueseEnvironment Agency (Direcc- ao Geral doAmbiente) [24], renewable sources contributingto energy balance are hydropower, wood andvegetable residues, and urban and industrial waste,but food crops (e.g. corn) are not included.Ethanol production from wood waste conformsto the above-mentioned category.Figure 5. Amount of domestic wood waste in Europe [18].



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6. CONCLUSIONS

Net energy is one of the most controversial issuesin the corn-ethanol scheme. Wood residues aredischarged to the surroundings as timber by-product. These residues have not been fullyutilized, and their amount is huge. The conversionof wood waste into ethanol can contribute notonly to a reduction of solid waste but also toproduction of alternative fuel for the followingreasons: (i) cellulosic ethanol emits less GHG thancorn ethanol in its utilization; (ii) wood waste isnot related to food crops, so there are fewobjections to converting this waste to biofuel;and (iii) the conversion of cellulosic materials toethanol is technically feasible.

It may be necessary to reconsider the currentcorn-ethanol scheme. Considering the energyissue, food ethics, and the solid waste problem,the application of wood waste to ethanolproduction is an approach to establishing asustainable energy society. Future studyworldwide seems to be focused on inducing thecellulose transformation under milder conditionsbefore the commencement of industrial productionof cellulosic ethanol.

ACKNOWLEDGEMENTS

This is reported as part of the pre-feasibility study of abioethanol project by Centro de Estudos de RecursosNaturais, Ambiente e Sociedade (CERNAS). The

authors are grateful to Ms C. Lentfer for the Englishreview.

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Figure 6. A cellulose fiber undergoes a crystalline toamorphous transformation as the temperatureincreases at a pressure of 25Mpa [23] (courtesy of theExtremobiosphere Research Center). Each image is

100� 200mm.



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energy lifecycle assessment and environmental impacts of ethanol biofuel

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