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Feasibility of Large-Scale Biofuel Production

Mario Giampietro; Sergio Ulgiati; David Pimentel

BioScience, Vol. 47, No. 9. (Oct., 1997), pp. 587-600.

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Feasibility of Large-Scale Biofuel Production Does a n enlargement of scale change the picture?

M ari o Giam pietro, Sergio Ulgiati, an d David Pimentel

B iofuels are widely seen as afeasible alternative to oil. In-deed, in 1995 the Clinton Ad-ministration proposed amendmentsto the Clean Air Act that would re-quire gasoline sold in the nine mostpolluted US cities to contain addi-tives from renewable sources, suchas grain alcohol. This move, even ifblocked by a three-judge panel of theUS Court of Appeals in Washington,DC (Southerland 1995), has helpedto focus attention on the question ofwhether research and developmentin biofuel production from agricul-tural crops should be increased (e.g.,Abelson 1995). In Europe, similarfiscal and regulatory provisions havealready been introduced (Chartierand Savanne 1992, Sourie et al.1992). These policies assume thatbiofuels have the potential to reducecurrent dependence of industrializedsocieties on rapidly disappearing fos-sil energy stocks and that biofuelsare desirable from an ecological pointof view. But are these assumptionscorrect?Although abundant scientific lit-erature is available on various biofuelproduction techniques, attempts toMario Giampietro (e-mail : [email protected]) is senior researcher at theIstituto Nazionale della Nutrizione, ViaArdeatina 5 46, 001 78 R ome, I taly. SergioUlgiati (e-mail: [email protected]) is a re-searcher at the D ipar t imento di ChimicaFisica, Universith di Siena, Siena, Italy.David Pimentel (e-mail: dpl8@ corne ll.edu)is a professor in the C ollege of Agricultureand Life Sciences at Cornell University,Ithaca, NY 1 4 8 5 3 . O 199 7 Amer ican In -stitute of Biological Sciences.

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Large-scale biofuelproduction is not analternative to the current

use of oil and is not evenan advisable option to

cover a significantfraction of it

provide a comprehensive evaluationof large-scale biofuel production asan al ternative to fossil energy deple-tion are few and controversial. Thecomplexity of the assessments in-volved and ideological biases in theresearch of both opponents and pro-ponents of biofuel production makeit difficult to weigh the contrastinginformation found in the literature.Moreover, the validity of extrapo-lating results obtained at the level ofthe individual biofuel plant or farmto entire societies or ecosystems hasrarely been explicitly addressed inthe literature. In this article, we at-tempt to provide such a comprehen-sive assessment of the feasibility oflarge-scale biofuel production by criti-cally reviewing the existing biofuelliterature from a broad perspective.W hat are biofuels?A biofuel is any type of liquid orgaseous fuel that can be producedfrom biomass substrates and thatcan be used as a (part ial ) substitute

for fossil fuels. Common examplesare ethanol, methanol, and biodiesel.Ethanol alcohol can be obtained bvyeast- or bacteria-mediated fermen-tation of sugar crops, such as sugar-cane, sugarbeet, and sweet sorghum,or of starchv crom, such as corn and

*cassava. It can also be obtained, al-beit a t lower yields, from cellulose, asugar polymer from woody crops,through acid or enzymatic hydroly-sis followed by fermentation. Metha-nol can be obtained from wood orwoody crops by means of a woodgasification process followed by com-pression and methanol synthesis(Ellington et al. 1993, Wyman et al.1993).Finally, biodiesel fuels can beobtained from oil crops, such as soy-bean, rapeseed, sunflowers, and palms,by extracting the oil with suitable sol-vents or through mechanical pressingand then converting the oil into dieselfuel by a transesterification process(Shay 1993).Ethanol is a good substitute forgasoline in spark-ignition engines(Marrow et al. 1987, Parisi 1983);methanol can also be used as a sub-stitute for gasoline. Of course, exist-ing vehicles cannot run on 100%etLanol or methanol fuel unless en-gines are modified substantially.However. gasoline and biofuel mix-"tures in a proportion of 85% and15 %, respectively, can be used withonly minor adjustments to the en-gine. Performance tests indicate thatbiodiesel can be a good substitute fordiesel oil in compression-ignition en-gines (Shay 199 3).Research is still in Drogress to"improve the chemical and industrial

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Table 1. Typical biofuel ~roductionystems from agricul tural crops. straints because they are invisible atthe small scale of the laboratory, indi-Ethanol inEthanol in ( sub) t ropica lIndicators of performance Biodiesela temperate areas areasGross energy yield (GJ . ha-' . yr-')Net energy yield (G J . ha-' . yr-I)Output-input energy ratioNet to gross ratio (F"lF1)Water requirement ( t . ha-l . yr-')Energy throughput (net MJIh)Best-performing systemLand requirement (halnet GJ)Water requirement ( t lnet GJ)Labor requirement (hlnet G J)

oilseed rape0.1005004

corn-sorghum0.0331 7 01

sugarcane0.020b-0.014L200"200'4h-0.6'^Trans-me thylesterfrom oi l seeds (sunflower, rapeseed, o r soybeans) . Sunflower and soybeansystems have net energies close to or less than zero.hLow- input product ion , as in the Brazi l ian ProAlcohol Project (Giampie t ro e t a l . 1997 a) .LHigh-inputproduct ion, as reported in Pimentel et al . (1988).

aspects of biofuel production pro-cesses in attempts to reduce energyinputs and increase the overall fuelyield. Typical yields and output-in-put ratios have been discussed indetail elsewhere (Giampietro et al.1996a) 'and are summarized in Table1. Other assessments are available(CCPCS1991, CNR-PFE 1979, ERL1990, IEA 1994) ,as are general stud-ies on evaluation procedures for en-ergy from biomass (Herendeen andBrown 1987, Lyons et al. 1985,Pellizzi 1986).Evaluating biofuel productionWe propose that the feasibility ofbiofuel production as an alternativeto oil be analyzed by relating theperformance of the biofuel energy sys-tem to the characteristics of both thesocioeconomicand environmentalsys-tem in which the biofuel productionand consumption take place. Specifi-cally, biofuel can substitute for fossilenergy only if the large-scale pro-duction of biofuel is biophysicallyfeasible (i.e., not constrained by theavailability of land and fresh watersources for energy crop production);environmentally sound (i.e., does notcause significant soil degradation,air and water pollution, or biodi-versity loss); and compatible withthe socioeconomic structure of soci-ety (i.e., requires labor productivitythat is consistent with the existinglabor supply and per capita energy'S. Ulgiat i , unpublished manuscript .

consumption in society). The lattertwo conditions imply that the biofuelsystem must deliver a sufficientlylarge amount of net energy to societyper hour of labor employed in thecycle of biofuel production to makethe process economically convenientfor society while generating a suffi-ciently low environmental loadingper unit of net energy supplied tokeep the process environmentallysound.Data in the literature on modernbiofuel systems can be used to esti-mate the biophysical requirementsper unit of net energy supply to soci-ety. Depending on the productionsystem, these requirements, pergigajoule (1gigajoule = l o 9joules) ofnet energy, are 0.015-0.100 ha ofarable land, 200-400 t of fresh wa-ter, and 0.6-5.5 hours of labor. Acom~a risonof these values with ac-tual iand and fresh water availabilityand existing socioeconomic con-straints-such as the energy con-sumed by society per hour of labor inthe primary sectors of the economy-for several different countries indi-cates whether biofuel ~ ro du ct ionona large scale is feasible. As we showin this article, this approach indi-cates that biofuels are unlikelv toalleviate to any significant extent thecurrent dependence on fossil energy.Moreover, with current technologies,biofuels do not decrease the environ-mental impact per unit of net fueldelivered to society. Available analy-ses of biofuel production tend tooverlook these biophysical con-

vidual farm, or plant that is ;sed inmost assessments.In this article, we analyze the netenergy requirements of the processof biofuel production, as shown inFigure 1. This analysis is based onthe net-energy approach proposedby Odum (1971)and Slesser (19 78) ,and used by Cleveland et al. (1984)and Hall et al. (1986) ,among others.Several aspects of the analysis de-serve special attention:

The ratio between net and grossbiofuel production. Large-scalebiofuel production must fulfill theobvious condition that the energv-,,yield ratio (or output-input ratio) ofthe entire process be higher than unity;otherwise, biofuel will not be a fea-sible alternative to oil. In Figure 1,thiscondition means that F1 > (F2 + F3 +F4),where F1 is the amount of biofueloutput generated in the productionprocess and F2, F3, and F4 are thevarious energy inputs required bythe urocess in the form of fuel en-ergy. In addition, the ratio betweenthe gross output of biofuel (F1)andthe fuel consumed in the process (F2+F3 + F4) must be sufficiently high toprevent'an excessive demand ofvlandand labor per unit of net fuel deliv-ered to societv. What is consideredsufficiently hi ih depends on land andlabor constraints. For example, whenthe output-input energy ratio (F l l[F2 + F3 + F4]) equals 1.5, the ratiobetween net (F") and gross output( F l )of biofuel (F"IF1) is 0.33. Thatis, the net supply of 1L of biofuel tosociety requires a gross productionof 3 L of biofuel. When the output-input energy ratio is only 1.2, theratio between net and gross outputof biofuel (F"IF1)is 0.16, and conse-quently, the net supply (F") of 1L ofbiofuel requires a gross biofuel pro-duction ( F l ) of 6 L. Therefore, areduction of 20% in the output-input energy ratio, from 1 .5 to 1.2,doubles the land, water, and labordemand per unit of fuel deliveredto societv.Difference in quality of energy out-puts. In most biofuel production sys-tems, the residues (e.g., the strawthat is left after harvesting graincrops) andlor byproducts (e.g., thesoybean cakes left after pressing oil )

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of the energy crop can be recoveredand used in some fashion. The erossenergy content of these residues orbyproducts (H in Figure 1) is fre-quently accounted for as an outputin the energy balance of the biofuelproduction process and then simplyadded to the biofuel energy produced(e.g., Da Silva et al. 1978, Stout1990, TRW 1980).This accountingmethod obviously increases the cal-culated overall energy efficiency ofthe process, but it is misleading be-cause ethanol, residues, and byprod-ucts differ in quality.Differences in energy quality offuels relate to one or more of thefollowing characteristics of the fu-els: their thermodynamic properties,such as the characteristics defined byexergy analysis (Ahern 1980, Pilletet al. 1987) ; their technical conve-nience, such as transportability, ho-mogeneity for handling, and avail-able devices for energy conversion;and the types of emission (especiallyof particulates) after combustion. Forexample, the quality of a fuel deliv-ered to society in the form of strawresidues is much lower than that ofliquid biofuel endproducts, such asethanol, because of a lower score onall three characteristics.A similar problem exists with theaccounting of byproducts, such assoybean and sunflower cakes, thathave other. nonfuel uses. such asanimal feed. It is mi s ~e ad i h~o addthe energy content of these byprod-ucts, or the fossil energy tha t wouldhave been required to produce anequivalent amount of animal feed, tothe liquid biofuel energy output be-cause liauid biofuels and animal feedare simply different things.Indeed, in large-scale biofuel pro-duction, byproducts should be con-sidered a seriouswaste disvosal vrob-lem (and, most probably, an energycost) rather than a positive event interms of energy output. For example,to supply 10% of the energy con-sumption of the United States (325GJ per capita per year), large-scaleproduction of ethanol fuel wouldgenerate approximately 3.7 t of dis-tiller's dark grains, the byproduct ofethanol production from corn andsorghum (0.83 kg/L ethanol), percapita per year (TRW 1980). Thisquantity of byproduct is more than37 times the 98.5 kg of commercial

livestock feed that is used per capitaper year in the United States (USDA1992).~ i i a l l ~ ,ertain energy inputs inthe process of biofuel production,such as the energy needed for theconstruction of the machinery andplant (F2 in Figure I ) , require high-quality liquid fuel; low-quality fuels,in the form of residues or byproducts,cannot be used. These energy inputsmust therefore be subtracted fromthe gross flow of liquid fuel (F1)thatis vroduced for societv.t h e energy costs of ;sing byprod-ucts. Although the energy content of

byproducts is readily accounted forin the gains of the biofuel productionprocess, the costs involved in recov-ering and using the byproducts (F3in Figure I ) , such as labor and en-ergy requirements to harvest, dry,bale, transport, store, and prepareagricultural byproducts for theburner (e.g., briquetting), are gener-ally ignored. Similarly, losses in en-ergy value of byproducts due tochanges in moisture content and theirdecay during storage are neglected.These costs and losses deserve moreattention because they can seriouslyaffect the convenience of large-scale,use of biomass in terms of energy,economics, and labor.Accounting for inputs in energycrop production. The assessment ofenergy demand in the agriculturalproduction of the energy crop usedto generate biofuel (F4 in Figure 1)isanother source of controversv. Ni-trogen fertilizer or other inputs withlarge embodied energy costs are

sometimes omitted or underesti-mated in the assessment of agricul-tura l energy consumption in biofuelproduction systems. Clearly, how-ever, overlooking the high energydemand of nitrogen fertilizer inputincreases the apparent efficiency ofbiofuel production. Even when nonitrogen fertilizer is applied, energycrop production depends on croprota tion or leaving land fallow, or itdepletes nutrient stocks in the soil.In these cases, one must either ac-count for the area used in rotation orleft fallow in terms of an increasedland requirement or somehow di-rectly account for the difference be-tween the nitrogen taken out withthe harvested biomass and the natu-rally occurring nitrogen fixation inthe soil during the period of the cropcycle. For example, nitrogen in theamount of approximately 180 kg/hais removed from the soil when har-vesting sugarcane (Helsel 1992),only approximately one-sixth ofthe quantity of nitrogen fixed bynatu ral processes.Yields and conversions used in theassessment. Yields and conversionfactors used to evaluate large-scalebiofuel production should refer toreal research or commercial data andnot, as is often found, t o theoreticalconversions, maximum achievableyields, or exceptional results obtainedin experimental plots. Certainly, as-sumptions and models about pos-sible future improvements in biofuelproduction technology deserve at-tention. However, starting with anoverall assessment of the process in

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real terms helps to place such as-su m~t io nsin a more realistic con-text. For example, the maximumyield in the litera ture for sugar fromsugarcane is 15.7 tlha (Buringh1987). As noted by Buringh, such avalue has little to d o with the averageyield of sugar from sugarcane cur-rentlv obtained worldwide. which isless ihan 6 tlha. ~ o r e o v l r ,large-scale production of energy crops willundoubtedlv result in an ex~ansionof energy crop monocultures, whichcould ultimately reduce yields be-cause of increased pest problems,diseases, and soil degradation. Theapproach followed by many biofuelproponents-that is, starting withmaximum achievable crop yieldsmultivlied bv theoretical conversionsthat b e ass lmed to be achievable inthe near future-is unlikely to pro-vide sound da ta for ~ o l i c vdecisions.

Accounting for labor in the assess-ment. In contrast to most studies, weconsider labor not as an energy inputbut rather as another crucial Daram-eter that is needed to examinewhether the proposed biofuel systemis compatible with the present socio-economic structure of society. Onthe basis of data for the labbr re-quirement in the energy sector perunit of net energy delivered to soci-ety, we assess the aggregate laborrequirement of a hypothetical en-ergv sector based on biofuel and com-2Dare this value to the labor that isavailable for the energy sector, giventhe present socioeconomic charac-teristics of society (Giampietro et al.1993. 1996b) . We assume that theenergy cost of supporting humans insociety is already accounted for bythe requirement of energy consump-tion per capita at the societal level.From small- to large-scale assessmentsThe performances of three of themost ~commontypes of biofuel sys-tems from agricultural crops are sum-marized in Table 1.These three sys-tems are biodiesel production fromoilseed crops, ethanol productionfrom crops grown in temperate ar-eas, and ethanol production fromcrops grown in tropical and sub-tropical areas. The ranges of valueslisted for these systems are based onbiophysical inputs and outputs re-

ported in the literature for variantsof these three biofuel systems. Val-ues found in the literature have beenstandardized by using a single set ofenergy equivalents for the biophysi-cal inputs and outputs instead of theoriginal conversion factors, whichdiffered among the various studies.A critical appraisal of the assessmentsfound in the literature is provided else-where (Giampietro et al. 1997a) .Theperformances in Table 1 do not in-clude energy costs for pollution con-trol nor long-term energy costs to off-set soil erosion because the relevantdata are not available. We addressthese factors in a subsequent section.The performances of the biofuelsystems are evaluated on the basis ofthe ra tio of net to gross energy yield(FS/F1in Figure 1)and the require-ments of arable land, fresh water,and labor per unit of net energydelivered. The assessments are de-rived from data at the individualfarm or biofuel production plantlevel. To extrapolate to a larger scale,we need to consider the impact of theproduction system on the larger eco-system and the compatibility of theproduction system with the socio-economic system in which the biofuelproduction takes place. Both aspectsof the production system can beevaluated on the basis of the demandfor environmental services (environ-mental loading) and labor require-ment per unit of energy delivered.Including the ecosystem. O n a smallscale. it is virtuallv im~ossibletodefine an environmental loading fora biofuel production system per unitof net energy delivered. Environmen-tal loading is, by definition, scaledependent: How many plants areoperating in a particular area? Howbig are the production plants? Whatare the thresholds for economies ofscale and decreasing returns of abiofuel energy system? Moreover,when the scale of biofuel vroductionis enlarged, pollution, soil erosion,and other adverse environmental im-pacts can exhibit nonlinear behav-ior. So far, studies on the environ-mental impacts of biofuel productionhave focused on immediate environ-mental effects, such as the effluentsof ethanol plants as potential sourcesof pollution (e.g., Bevilacqua et al.1981, Hunsaker et al. 1989).

Pollution by effluents. Distillerywaste, the principal component ofeffluent from ethanol plants, has abiological oxygen demand (a stan-dard measure of pollution) after fivedays (BOD,) of 1000-78,000 mg1Land hence poses a serious waste dis-posal problem (de B a z ~ at al. 1991,Frings et al. 1992, Hunsaker et al.1989 ,Mishra 19 93).Approximately10-14 L of stillage waste (distillerywaste) are generated per liter of grossproduction of ethanol ( Fl ). Thisvalue is not affected by the type ofbiomass used in the fermentationbecause it relates to the amount ofliquid removed during the distilla-tion from the fermented broth, andthe level of alcohol cannot be raiseddue to physiological limits: a higherconcentrat ion of alcohol will inhibitthe yeast (Coble et al. 1985).In tropical Brazil, the effluentproblem is already evident. A Brazil-ian distillery producing ethanol fromsugarcane in the amount of 300,000Lld (actually261,000 Lld, given thatF"IF1 = 0.84), which is the equiva-lent of the energy consumed by ap-proximately 40,000 Brazilians (Table2), releases a pollution load that isequivalent to the domestic sewage ofa city of 2 million people (assuminga sewage load of approximately70,000 mg BOD, per person per day;Rosillo-Calle 1987).Things are much worse when etha-nol fuel is produced in temperateareas, where the F"lF1 ra tio is lower(Table 1).For example, if F"IF1 =0.34, the delivery of one net liter ofethanol (F") implies the productionof 2.94 L ethanol at the plant (Fl)and hence a production of approxi-mately approximately 38 L stillage.Under these conditions, the 325 GJof commercial energy used per UScitizen per year (Table 2) , which isequivalent to more than 15,000 Lethanol (Fa),would imply the gen-eration of approximately 1500 kg ofstillage per US citizen per day. In thisway, each American would daily gen-erate the pollution equivalent of thesewage of more than 800 people,assuming the same sewage load of70,000 mg BOD, per capita per day.The energetic cost of treating thispollutant is significant and shouldbe included in the assessment of en-ergy inputs in the biofuel productionprocess. However, none of the stud-

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Table 2. Land a nd water d eman d in large-scale biofuel prod uctio n comp ared to availabili ty (expressed on a per capita basis) .Comm ercial Arable land Fresh water Land demand Water demand To tal arable Biofuel waterenergy consu mption available withdrawal for biofuel for biofuel land dema ndf/ deman dlcurrentCountry (GJ/yr)= (ha )b ( t l ~ r ) ~ (h a) ( t ly r) supply ratio withdrawal ratio

Burundi 1600' 1.8EgyptG h a n a 4200'1200 ' 9. 42. 5Uganda 1600 ' 1 .4Z i m b a b we 6200' 2. 9Argentina 13,200 ' 2.1Brazil 9800' 3.0Cana da 74 ,300d 8 .7Costa Rica 7000' 8 .oMexico 9200d 7 .6United States 55,200d 14.6Bangladesh 600' 1.8China 5000' 7.2India 2400 ' 2 .2J a p a nFrance 22,800d27,700d 1 4 8 . 31 7 . 6Italy 19,2OOd 24.3Ne t h e rl a n ds 3 4 , 3 0 0 d 1 1 2 . 0Spain 14,8OOd 6.5United Kingdom 26,3OOd 43.6Austral ia 43,2OOe 1 .5'Data f rom UN (199 1) .b Da t a f r o m W RI ( 1 9 9 2 ) .cReferr ing to low- input sugarcane system (Table 1 ) .dReferr ing to corn-sweet sorghum system (Table 1) .'Referr ing to high-inpu t sugarcane system (Table 1) .T h e to ta l a rable l and demand equal s the b iofue l l and demand p lus the a rable l and for food securi ty. The demand for a rable l and for b iofue lproduct ion was ob tained by dividing the energy consump tion per capi ta (GJlyr) by the land dem and (ha1GJ) of the biofuel energy system undercons idera tion . For count r i es tha t depend heavi ly on food impor t s (a l l count r i es wi th l ess than 0 .5 ha a rable l and per cap i t a ) , the a rable l anddema nd fo r food prod uct ion is assumed to be equa l to the ent i re arable land in the country. F or net food-exp ort ing countr ies, we est imatedthe demand for arable land for food product ion on the basis of the rat io between food expo rts and internal consum ption: 8 0% of total arableland in France, Uganda, and Zimbabwe, and 50% in Argentina, Austral ia, Brazi l , Canada, and the United States.ies we examined provided data onthis energy cost and it is, therefore,not included in the performanceslisted in Table 1.Nevertheless, someidea of the magnitude of the energycost can be obtained. Assuming aBOD5of approximately 30,000 mg/L (typi-cal of distillery waste), 1kg of BOD5must be removed per liter of netbiofuel produced (30 g/L x 38 L forethanol in temperate areas) . With anapproximate cost of 1k wh per kg ofBOD, removed (Trobish 1992) , thecost of controlling the pollution gen-erated by one net liter of ethanolproduced would be 10.5 MJ (1megajoule = lo6joules) of fuel equiva-lent, or approximately 50% of theenergy supplied per liter of ethanol.Including this cost among the inputsin the biofuel production process sig-nificantly decreases the estimated F*/F1 ratio and dramatically increasesthe demand for land and water thatis reported in Table 1.Because none of the known etha-nol systems can afford to spend 50%of their net output in pollution con-trol, intensive wastewater treatment

is never considered in the literature asa method for dealing with the stillagewaste that is generated by the biofuelproduction process. Instead, environ-mentally friendly alternatives are usu-ally proposed, such as concentratingstillage for use as animal feed, usingstillage as fertilizer, or recoveringmethane from anaerobic fermenta-tion of stillage. However, little or noreliable information exists on thefeasibility of these alternative solu-tions on a large scale (e.g., heir energycosts and labor demand). As notedearlier, the supply of byproducts foruse as animal feed from large-scalebiofuel production would far outweighdemand. As for using stillage as fertil-izer or recovering methane from it,any handling of wastewater fromstillage will increase the demand forboth high-quality energy and humanlabor, ultimately lowering the F"/Flratio. That is, it will increase thedemand for land, fresh water, andlabor per unit of energy delivered bysuch a biofuel system.Energy crop production. Long-term implications for the agroeco-

system cultivated for fuel crops areseldomly addressed in assessmentsof the ~e rf or ma nc e f biofuel svs-terns, e;en though a rough idea'ofthe size of the problem can easily beobtained. The commercial energv,consumed per US citizen is approxi-mately 325 GJ/yr. The best-perform-ing biofuel system for temperate ar-eas, ethanol produced from corn andsorghum (Table 1) would require11.7ha of fuel cropland per capita togenerate sufficient ethanol fuel to,meet annual commercial energy de-mand. This amount is more than 15times the arable land currentlv avail-able per US citizen. Assuming anaverage pesticide consumption of 3.5kglha (for corn) and 2 kg/ha (forsweet s~ rg hu m) ,~uch a biofuel pro-duction system would result in theuse of approximately 31 kg of pesti-ZEs timated on the basis of an insecticide appli-cation rate in the United States for corn of 1 .12kg/ha and a herbicide (predomin antly atrazine)application rate of 3.83 kglha. For sorghum,the average treatment with insecticides is 0.96kglha, and the average herbicide treatment is1.29 kg/ha (Pimentel et al. 1992).

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Figure 2 . Correla- GNP I capita (US$) Labor in agriculture (.h) tm ~ ~ ~ ~ Y ~ ~ ~ E $ $ ~ ~ , " ~ndeed, a correlation analysis (Fig-tions between Bio- I-, - ure 2 ) of the energy throughput con-Economic Pressure sumed by society per hour of labor in(BEP) and several in- ta n the primary sectors of the economydicators of socioeco- and 24 classic indicators of socio-nomic development. 10 - economic development for a sampleBEP is defined as the ,10 jm 10 1,Om ,an tm tm BEP BEP BEPratio between the to- of more than 100 countries has con-

tal energy consumed Infant mortality (per 1000) Phones Ithous. populat. Life expectancy (years) firmed this trend (Pastore et al. 19 96) .by a society in a year m(in megajoules) di-vided by the totalamount of workingtime in the same year(inhours).BEP should w tm tavbe considered a con-straint derived fromthe socioeconomic characteristics of atechniques in the primary sectors.cide per capita per year, or a total ofmore than 8 million metric tons. Thisamount is almost 20 times the currentuse of pesticide in the United States.oreo over. the ex ~a ns io n f mo-nocultures that woulh be required toobtain the high yields necessary foreconomic viabilitv of the biofuel svs-tem is likely to aggravate problemsof soil erosion, pollution from nutri-ent leaching, and overdraft of under--round water-all of which are al-ready threatening current foodsupplies (Ehrlich et al. 1993, Kendalland Pimentel 1994, Pimentel et al.1995).For instance, soil erosion ratesfor corn and sunflower, both rowcrops grown on 2-5 % sloping land,are approximately 20 t ha-I . yr-l,assuming that the corn residues stayon the land. Approximately 4 kg ofnitrogen are lost per ton of fertilesoil eroded, which represents an in-crease in energy demand of approxi -mately 6000 MJIha to produce theequivalent amount of fertilizer. In ad-dition, at least 2 kg of phosphates and410 kg of potassium are lost with thissoil. The removal of croD residues(e.g., straw) from the fields for use asenergy input in the biofuel productionprocess may dramatically increase theerosion rate (La1 1995). Soil erosionassociated with sugarcane productionis among the highest in the world, andincluding its costs in any analysis ofbiofuel production would reduce thefavorable performance of the tropicalethanol system that is considered inTable 1. For instance, Edwards(1993)reports erosion rates of 380 t .ha-l .yr-l on cane fields in Australia,and rates of 150 t . ha-' .yr-' are notuncommon.592

\:.2 ?r:.-..),I * . ,~ m n 0 Im tm ~ m n w tm rav ~ m n

BEP BEP BEP

society on the feasibility of production

Yet another agronomic implica-tion of fuel crop monocultures is anadverse impact on biodiversity.Clearly, hypothesizing a smaller frac-tion of energy coverage by biofuel(e.g., 15% of to tal energy consump-tlon) would reduce this and othereffects on agroecosystems, but thepicture would still be gloomy.Including the socioeconomic system.To analyze the compatibility of abiofuel energy system with the charac-teristics of the society, we examinedenergy consumption at the societallevel per unit of labor in the primarysectors of the economy-in particular,the energy sector. The energy sector isdefined as that part of the economythat ~erfor msll activities involved insupplying energy to society-that is,procuring, processing, and distrib-uting energy (Holdren 1982).Technological development of asociety accelerates energy through-put in the primary sectors of theeconomv because i t increases theaverage per capita consumption ofenergy (from less than 1 GJIyr in de-veloping countries to approximately325 GJIyr in the United States) anddecreases the percentage of totalhuman time that is allocated to workin the primary sectors of the economy(from 10 % in poor developing coun-t r ies to 4% in developed countries;Giampietro et al. 1997b , Pastore etal. 199 6). The latter change resultsfrom an absorption of labor by theexpanding service sector and a re-duction in the labor supply due toprogressive aging of the population,a longer education period, and alighter work load for the labor force.

The western standard of living isbased on a throughput (a t the levelof society) of more than 500 MJ ofcommercial energy per hour of laborin the primary sectors of theeconomy. Given that the work sup-ply in the energy sector of industrial-ized countries is generally less than5 % of the work force in the primaryeconomic sectors, it is evident thatthe energy sector needs to achieve anenergy throughput in the order of10,000 MJ per hour of labor. Forexample, in Italy, with a populationof 57 million, only 7.3% of the totalof 499 billion hours of human timeavailable were spent doing paid workin 1991. Of this yearly labor supply,60% was absorbed by the servicesector, 3 0% by the industrial sector,and 9% by agriculture, fishery, andforestry, leaving a tiny I % , or 360million labor-hours, to run the en-tire energy sector (ISTAT 1992).Total energy consumption in Italythat year was 6,500,000 TJ (1terajoule = 1012 oules), implying thatin 1991 the Italian energy sector de-livered almost 18,000 MJ of energythroughpu t per hour of labor in thatsector. This throughput was achievedwith the almost exclusive use (morethan 9 0% ) of fossil energy sources.Thus, a developed society requiresthat the energy throughput per hourof labor in the energy sector rangefrom 10,000 to 20,000 MJIh. Theselevels are well beyond the range ofvalues achievable with biofuel, thatis, 250-1600 MJIh (Tab le 1).Thismismatch is the primary reason whyprocesses of biofuel generation, sooptimistically assessed in feasibilitystudies, do not pass the economictest in the real world.Large-scale biofuel productionin 21 countriesAn evaluation of large-scale biofuelproduction, including both socioeco-nomic and ecological constraints,requires that the characteristics ofthe biofuel system be checked against

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Table 3. Labor de mand in large-scale biofuel produc t ion com pared to potent ial labor supply.Commercial energy Total Total labor force Potential Biofuel labor Biofuel labor demand

Country consumption( l o 6GJ/yr)" population(106)h (as percentageof population)' labor supply( l o 6h/yr)* demand( l o 6h/yr) (as percentageof supply)BurundiEgyptGhanaUgandaZimbabweArgentinaBrazilCanadaCosta RicaMexicoUnited StatesBangladeshChinaIndiaJapanFranceItalyThe NetherlandsSpainUnited KingdomAustraliaaData from UN (1991 ). eReferring to low-input sugarcane system (Table 1) .hData from W RI (1992). 'Referring to corn-sweet sorghum system (Table 1) .'Data from ILO (1 99 2) . gReferring to high-input sugarcane system (Table 1 ) .*Assuming a common workload of 2000 hlyr.the following data: availability of tries have a per capita consumption sugarcane, can be used in areas wherearable land. fresh water. or other of more than 100 GJIyr, and devel- sugarcane cannot be produced.limiting natural resources (e.g., nu- oping countries have a per capita For biofuel product ion systems intrient supply) as far as they are used in consumption of less than 20 GJIyr. both developed and developing coun-the biofuel production system; aver- ~ e n s e l dDo ~u la te dcountries were tries, we used the technical param-age per capita energy consumption defined as hLving less than 0.1 ha of eters listed in Table 1 for the ethanolin society; and available supply of arable land per capita, and sparsely biofuel system based on corn and sweetlabor time and its distribution over ~ o ~ u l a t e d sor ahu h. These Darameters are basedountries were defined asthe various economic sectors. having more than 0.5 ha of arable on The following optimistic (indeed,

We used readily available data for land per capita. We further distin- unrealistic) assumptions: no soil ero-the national level to assess compat- guished among countries tha t are net sion for the yields of 7500 kglha ofibility with large-scale biofuel pro- exporters of food (i.e., Argentina, corn grain3and 80,000 kglha of sweetduction, although any other level Australia, Brazil, Canada, France, sorghum (wet weight of the total bio-(e.g., regional or global) for which Uganda, United States, and Zimba- mass; 80% of the weight is water) ,data are available could also be used bwe) and those that are net food no major losses of byproducts dur-for such an evaluation. We chose for impdrters (t he other 13 countries). ing storage and transportation, andthe evaluation the best-performing For those developed countries in no energy charge for pollutants gen-biofuel production system, given cli- the sample whose climate is temper- erated by this biofuel system.matic conditions, from those pre- ate and whose energy throughputsented in Table 1. We also made the per hour of labor is high, we consid- Ecological side of the analysis. Theassumption that biofuel will be the ered the highly mechanized ethanol demand and supply of arable landonly energy source in society. The biofuel system based on corn and and fresh water are provided in Tableecological par t of the analysis fo- sweet sorghum (see the upper value 2 for the 21 selected countries. Thecused on arable land and fresh water of the performance range listed for data in this table indicate that noneconstraints. and the socioeconomic ethanol in temperate regions in Table of the biofuel technologies consid-part focused on the labor supply for 1).For developing countries, where ered in our analysis appears eventhe energy sector. tropical or subtropical climatic con- close to being feasible on a largeWe evaluated a total of 21 coun- ditions exist and more labor-inten- scale due to shortages of both arable

L L

utries; these include both developed sive production is common, we con- land and water for fuel crop produc-and developing countries and both sidered ethanol biofuel production tion. This conclusion is true for bothdensely and sparsely populated coun- based on sugarcane, similar t o that developed and developing countries.tries. We defined the level of devel- developed in Brazil in the ProAlcohol 3The cor n grain yield of 750 0 kglha is dryopment of a country based on the project (Pereira 198 3, Rosillo-Calle weight. The corn stover dry weight equalsaGerage per capita consumption of 19 87 ). We assumed that sweet sor- 7500 kglha. Thus, the total biomass of corncommercial energy: Developed coun- ghum, processed in a similar way as is 15,000 kglha dry weight.

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Moreover. the conclusion would beeven gloomier if pollution controlmeasures (which would decrease theoutput-input energy rat io of the pro-duction process) or trends in popu-lation growth and loss of arable land(which would reduce the availablearable land per capita and endangerfood security) were included in theanalysis.In addition, the proposed use ofarable land to farm for fuel is implic-itly based on the hypothesis that suf-ficient arable land can be spared fromfood production. Our analysis showstha t this hypothesis is unrealistic forlarge-scale biofuel production. In-deed, many densely populated coun-tries are unable to supply their inter-nal demand for food without relyingheavily on fossil energy stocks forthe production of fertilizers and pes-ticides.Socioeconomic side. Table 3 com-pares the labor demand of thebiofueled energy sector and the la-bor supply available. We estimatedthe labor supply as the economicallyactive population, as described bythe International Labour Office (ILO1992). but we also included the un-,employed. This assumption takes intoaccount the potential positive effectof biofuel production on employ-ment, although it ignores the poten-tial problem that many unemployedpeople in developed countries maynot want to live in rural areas andwork in the agricultural activity ofproducing feedstock for ethanol dis-tillation. In fact, many Europeancountries are currently experiencingboth high unemployment (more han10%)and, at the same time, a shortageof labor supply in the agricultural sec-tor. To express the labor supply inhours, we applied a common work-load per worker of 2000 hlyr.Socioeconomic constraints onlarge-scale biofuel production are lesssevere in developing countries thanin develoved countries (Table3).Forexample,;f ~ u r u n d i , hana, uganda,Bangladesh, China, and India onlyhad more arable land, then they couldfuel the activities of their societywith biofuel, because up to 10% oftheir labor force could be allocatedto the energy sector without disturb-ing the economic process. However,biofuel is a realistic source of energy

in these poor countries only becausecommercial energy demand is low(less than 15 GJIyr per capi ta) . Giventhe characteristics of biofuel pro-duction (Table 3) , however, thesecountries would have to resort tofossil fuels if they were t o undergorapid economic and technologicaldevelopment. Indeed, a n energy sys-tem that would improve the socio-economic condition of developingcountries would be one that enablesthese societies to decrease the per-centage of total time allocated tolabor (by increasing life expectancyat birth and educa tion), to decreasethe labor force in the primary sectorsin favor of the service sector, and t oincrease per capita energy consump-tion. Conversely, basing the energysector of a developing country onbiofuel means locking that societv"into a low standard of living(Giampietro et al. 1 993, 1997 b).Thelow density of energy flows, both perhectare and ver hour of labor. thatcan be achievkd with biofuel makes a100 % supply of energy by biofuelimvossible even in Australia. a de-veloped country with a large amountof arable land per capita, or in Bra-zil, a sparsely populated country witha relatively low energy consumptionper capita.Nonlinear behavior of biophysicalrequirements. Thus far in this ar-ticle, we have examined the theoret i-cal feasibility of large-scale biofuelproduction by multiplying the crop-land, water, and labor demand perunit of net energy delivered in small-scale biofuel svstems with the totalenergy that is consumed in society.We thus arrived at the total require-ments for land. water. and labor fora biofueled society.

However, in practice, assessmentsof requirements for biofuel produc-tion turn out to be more complex.The fact tha t the biofuel productionprocess is an autocatalytic loop-inthe sense that a fraction of the biofuelgenerated by the system must be usedto run the biofuel production systemitself-implies a nonlinear behaviorof land, water, and labor require-ments in response to changes in tech-nical coefficients of the productionprocess. Land and water require-ments refer to energy consumed inthe production of biofuel rather than

to energy delivered to society; there-fore, these requirements are ampli-fied by an increase of the internalloop of energy use.Indeed, at a fixed level of energyconsumption in society, small fluc-tuations in the overall output-inputenergy ratio of the biofuel productionprocess can generate large fluctua-tions in total biophysical require-ments. Such fluctuations are espe-cially likely when the output-inputrat io is close to 1.0, as is the case forthe vast majority of current biofuelsystems. In this s ituation, any assess-ment of requirements of land, water,and labor for the biofuel system areunreliable. Small fluctuations in theefficiency of the production processmay easily result in the productionsystem running into biophysical con-straints ( that is, requirements sur-pass availability). This situation typi-cally occurs when new activitiesaimed a t pollution control are addedto the biofuel production system,thus lowering the output-input en-ergy ratio of the overall productionprocess.Putting things in perspective. Thecountry analyses presented in Tables2 and 3 are not intended to representan actual scenario of a world tha t ispowered entirely by biofuel, butrather to put the process of large-scale biofuel production in a realisticperspective. Even if we were to adoptdifferent assumptions-for instance,that biofuels will be used to meetonly 1 5% or 30% of the total com-mercial energy requirement-thenature of the problems indicated byour evaluation of biofuel product ionrequirements would remain more orless the same for developed and de-veloping countries, and for denselyand sparsely populated countries.Can technological progresschange the picture?Extensive research has been con-ducted in the last few decades toimprove technological processes toproduce biofuels. Excellent reviewshave been provided by, among oth-ers, the International Energy Agency(IEA 1994 ), ohansson et al. (199 3),Klass ( 199 3), and Wright a ndHohenstein (1994 ). n general, inno-vations appear to aim at two main



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Table 4. Methanol production from wood biomass.oals: improving the efficiency andspeed of the bioconversion process,most notably by direct production ofhydrocarbon fuels from biomass, andenabling the use of biomass. such aswood and herbaceous crops, as rawmaterial for biofuel to overcomeshortages of arable land. As far asthe first goal goes, thermochemicalbiomass liquefaction is still far fromthe commercial stage (Stevens 1992).The second goal mav be closer tohand. Two pGtential ioncrop candi-dates appear to be feasible in themedium term (OTA 1993, Wrightand Hohenstein 1994) : herbaceousenergy crops, which are perennialgrasses such as switchgrass, andshort-rotation woody crovs. which

2 typically consist of a plantation ofclosely spaced (from 2 to 3 m aparton a grid) trees that a re harvested ona cycle of 3-10 years. Both herba-ceous energy crops and short-rota-tion woody crops produce largeauantities of biomass-straw. wood.dark, and leaves-without the needfor intensive human management:The former regrow from the remain-ing stubble, t i e latter from the re-miin ing st;mps. The produced bio-mass is composed principally ofcellulose and lianin. which can beused as feedstocvk (r aw material) togenerate electricity directly or can beconverted to liquid fuels or combus-tible gases (OTA 1993).~ l r h o u ~ haluable information onthe expected performance of thesenew biofuel production technologiesis available (IEA 1994, Johansson etal. 1993),values for the entire set ofparameters required for a compre-hensive assessment. such as we havecarried out for more establishedbiofuels, are not yet available. Ingeneral, published studies do notassess the labor demand and/or all ofthe biophysical inputs required forthe entire production process forthese new biofuels. Our analysis ofthese new technologies is, therefore,limited t o general features.Can woody biomass escape arableland constraints? Methanol produc-tion from wood is a relativelv newbiofuel production system for whichdata are rapidly becoming available.This system is considered to be prom-ising because methanol productionfrom wood may avoid the dilemma

Charac terist ics of the processFertilizer input (as N, P,Oj, K,O)(k g . ha-' . yr-')Pesticide application (kg . ha-' . yr-')Energy input in wood production(MJIt gross methanol produced)Energy input in wood product ion (M JIha)Energy inputs for wood harvesting and handling(MJIt gross methanol produced)Energy inputs at the plant ( F2 )(MJIt gross methanol produced)Wood yield (kg . ha-' . yr-')Heat equivalent of wood (MJIkg)Energy density of wood biomass productionfor fue l (Q ) M J . ha-' . yr-l)Conversion efficiency of wood biomassin to methanol (Fl IQ )Netlgross methanol supply (Fa/F1 )Net methanol supply (F" h (GJIha)"IEA (1 94); equivalent to 22.5 kg N, 4.5 kg P,O,, and 1 3.5 kg K,O per ton of metha nol produced. bTypical value fo r US equivalent to 0.09 kg pest~cide er ton of methanol produced (Hohenstein and Wright 1994 ) . 'Based o n 224 7 kg of woo d per to n of methan ol (Ellington et al. 199 3) and energy conversion factors for fertilizer and pesticide inputs reported in Helsel (1 99 2). dF 3 = F411.2, after IEA (1994). eEllington et al . (1 993 ). 'Estimated after Ellington et al. (19 93 ) considering a smaller F3 tha n in intensive tree farming. gBased on 2 247 kg of wood per ton of methano l produced (Ellington et al. 19 93 ) and listed

Convent iona l wood Shor t - ro ta tionproduct ion wood y cropsnonenone00data not available

assessments of energy in puts.hF" (GJIha) = Q x F l I Q x F"lF1.of whether to grow food or energycrops when arable land is a limitingfactor. The (nonarable) and require-ment for a methanol/wood biofuelsystem depends on the yield of woodbiomass per hectare of land and onthe efficiency of the process by whichwood biomass is converted intomethanol (Fl/Q) .At present, woodbiomass production systems can beclassified into conventional woodproduction, with low yields per hect-are, and short-rotation woody crops,with high yields per hectare.In conventional wood production,a harvest of 2500 kg . ha-' . yr-'(considering the entire area in rota-tion) would be ecologically compat-ible and achievable without externalinputs where water is not a limitingfactor. Based on data for the conver-sion of wood into methanol (Ellingtonet al. 1993) , conventional wood pro-duction delivers a net density ofmethanol to society (F'" in Figure 1)of 12.2 GJ . yr-I . ha-l (Table 4) . Toput this number in perspective, if the325 GJ of energy required per UScitizen per year were to be producedexclusively by this biofuel system,approximately 27 ha of wood-pro-ducing area would be needed per

capita-an area of wood cultivationof almost 7000 million ha, or morethan 20 times the entire area of for-est and woodland present in theUnited States (WRI 1994).Thus, evenif all US forest and woodland wereharvested for biofuel production, noteven 5 % of the current US energydemand would be covered.In biomass production from short-rotation woody crops, yields are re-ported to be much higher than inconventional forestry, ranging fromapproximately 10,000 kg/ha atpresent to a projected 12,500 kg/hain the near future (IEA 199 4).How-ever, these higher yields imply higherenergy costs because of the necessityof using fertilizers. The reportedyields are based on nitrogen inputsof 50-100 kg - ha-' .yr-', along withphosphate and potassium fertilizers(IEA 1994). Moreover, yields of10,000-12,500 kglha on marginalland and without amvle nutrientsand water use are probably unrealis-tic. If these woody crops are culti-vated on marginal land to avoid com-petition with food production onarable land. the estimated nitrogendemand of 100 kglha seems too &wfor the expected yields.

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Never theless , for our assessmentof metha nol p roduct ion f rom shor t -ro ta t ion woody crops we used theopt imis t ic values for biomass pro-duc t ion found in l i t e r a tu re (Table4) . Account ing for th e fer ti lizer an dpes ticide inp uts and us ing the wo oddem and of 22 47 kg per ton of grossmetha nol repo r ted by El l ington et al .( 1 9 9 3 ) ,we f ind tha t 2 .7 L methanolh av e t o be ~ r o d u c e d e r li te r of n e tme than ol dglivered toLsociety an F'.'/F1 rat io of 0 .37) .Therefore , us ing energy inp uts inthe fo rm of ferti lizers an d vesticidesin shor t - ro ta t ion woody crops in -creases the yield pe r hectare b ut de-creases the efficiency of th e process.The F"IF1 rat io is much lower ins h o r t - r o t a t i o n w o o d y c r o p s ( 0 . 3 7 )than in convent iona l wo od produc-t ion (0 .55 : Tab le 4 ) .The idea beh indthe Lul tiGation o'f sho r t - ro ta t io nwood y crop s is the same as for high-input agr icul ture: saving land by us-ing more energy inpu ts , such as fer -ti l izers and pesticides. Indeed, theF" IF1 r a t io fo r methanol p ro duct ionf r o m s h o r t - r o t a t i o n w o o d y c r o p s(0 .37) is c lose to tha t fo r e than olproduct ion f rom corn and sweet sor -g h u m ( 0 . 3 4 ) .As a result . the fourfold increasein wood biomass yield per hectarefor shor t - ro ta t ion wood y crops com-pared w ith convent ion al forest ry re-sults in only a 2.5-fold decrease inland r equ i rement per un i t o f ne tm e t h a n o l b i o f u e l ~ r o d u c e d .T h ehigher r equ i rement fo r inpu t s inshor t - rotat ion woody crops offsetsthe potent ial gain of this biomassproduct ion sys tem by lower ing theF*/F 1 rat io . If co ntrol measures forthe env i ronmenta l p rob lems tha t in -tens ive, large-scale product ion ofshor t - rotat ion w oody crops are l ikelyto cause are included, the resul t ingincrease in the internal energy de-man d would probably t r ans la te in toeven more severe increases in landand l abo r deman d, because the ou t -put- input energy rat io of this pro-cess is al ready 1.58 (determin ed bythe value F'VF1 = 0 .37) .Meth anol v roduct ion f rom shor t -ro ta t ion wood y crops thus does no tappear to r epresen t a major b reak-throu gh in terms of avoiding arab leland cons traints . A net supply of32.8 GJ of methanol per hectarewould imply a l and demand of 1 0 ha

of shor t - ro ta t ion woody crops perUS ci t izen, assuming that methanolis the o nly energy source in the U nitedStates . This land d ema nd is equiva-l en t to mo re than 250 0 mi l lion ha ofs h o r t - r o t a t i o n w o o d y c r o p m o n o -cul ture, o r eight t imes the s ize of al lpresent US fores ts comb ined, and a nan n u a l r e le a s e of ap p r o x i m a t e l y97 0,0 00 t of pesticide, which is mo rethan three t imes the current pes t i -cide appl icat ion in the Uni ted S tates .Even assuming a less impo r tant rolefor me than ol in the US energy sector(e.g. , 30% of the total energy de-m a n d )would not significantly changethe overall picture.Labor demand in methanol b iofue lproduct ion . Data on l abor inpu t int h e p r o d u c t i o n o f s h o r t - r o t a t i o nwo ody crop s are not avai lable in thel i t e r a tu re , so we cannot de te rminew h e t h e r t h e e n er g y t h r o u g h p u tachieved Der hour of labor in thissys tem of methan ol product ion meetsthe expectat ion of an energy sectorof a mo dern society ( i .e . , more tha n1 0 , 0 0 0 M J I h ) . C o m p ar ed w i t h co n -v en t i o n a l f o r e s t r y , s h o r t - r o t a t i o nwoody crops a re more l abor in ten-sive (Betters et al . 1 99 1) .A reductionof labor invu t would reauire intensivemechaniza t ion , bu t mechaniza t ionwould have adver se env i ronmenta li m ~ a c t sand would fu r ther increasethe energy requireme nts for harves t -ing operat ions (caus ing a decrease inthe F"IF1 rat io through higher en-ergy inves tment in the internal loop ) .W h e n c o n s i d e r i n g l a r g e - s c a l emethanol biofuel product ion, pol lu-t ion co ntrol and recycl ing within theproduct ion sys tem are necessary tokeep the process environmental lyfr iendly. As a general t rend, a dding~ o l l u t i o ncont ro l measures t o a Dro-huct ion process increases the laborrequirement per uni t of net energysupply, even in the case of fossilenergy power p lan t s . For example ,i n s ta l l in g a n t i p o l l u t i o n d e v ic e s( scrubber s ) r equ i red an increase inthe num ber of workers of 2 7 unitsou t of a total of 1 94 worke rs in a675-MW coal - f i r ed v lan t in NewYork State.4 Limit ing environm entalimpac ts throu gh recycling of natura l4J . I. Fiala, 1993, personal communlcat lon.New York State Electric & G a s C o r p o r a t ~ o n ,Binghamton, NY .

f lows can also dram at ical ly increasethe labor req uireme nts of an energysys tem. Wh en the energet ic return ofrecycling-that is, th e energy ga inobta ined by recycl ing divided by theextra labo r required- is lower tha nthe min imum labor r equ i rement pernet gigajoule imposed by socioeco-nom ic cons traints , recycling shouldbe considered a service and, there-fore, a cos t (Giamp ietro et al . 199 7b ) .Indeed. i t has been show n repeatedlytha t when economic deve lopmentp r o v i d e s a cce s s t o f o s s i l en e r g ythrough the marke t . t ime-demand-ing act ivi t ies wi th a lo w energy re-tu rn a re abo l i shed . For example ,a ~ ~ r o x i m a t e l va lf o f t h e 7 m i ll io ndfiiesters for biogas (gas prod uce d a tthe home and fa rm level through fer-men tation of organic wastes) in Chinahave reportedly been abandoned ascomm ercial energy has become increas-ingly available in rural areas (Stuckey1 9 8 6 ) .Similar econom ic vroblems dueto the low density of b iiga s are expe-rienced in the United States (Frankand Smith 198 7, Schiefelbein 19 89 ).Obstacles to improv ing biofuel pro-d u c t io n f r o m w o o d y an d h e r b aceo u sbiomass . An energy input made ofwood v an d/or herbaceous b iomass .because of i ts physical nature, is ofmuc h low er qual i ty than a foss i l en-ergy input . Moreover , because bio-mass is generate d by biophysical pro-cesses opera ting at a larg e scale (e.g.,at the ecosystem level) , i t is verydiff icul t to ch ange the o veral l char-acter ist ics of such pro duc t ion.Poor intrinsic reliability o fbio fuelsupply . T o remain viable, any biofuelsystem opera t ing a t a n ou tpu t - inputenergy rat io close to 1.0 must be ableto m aximize energy crop yields andopt imize the use of every s inglebyproduct . Consequent ly , per for -mance of such a biofuel system issuscept ible to natural per turb at ions ,such as c l imat i c f luc tua t ions andoutb reak s of pes ts o r diseases , and tosocioeconomic per turbat ions , suchas pr ice f luctuat ions an d s t r ikes .For ins tance, the mois ture con-tent of herbaceou s energy crops candrama tically affect their caloric valueand the poss ibi l i ty of s tor ing themfor use as an energy source later onin the year (Bel let t i 1987, Bludau1 9 8 9 ) .Comple te d ry ing of s t r aw andother herbaceous c rops consumes



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high-qual i ty fuel , which would fur-ther lower the energet ic perform anceof the system. Therefore , these cropsare normal ly dried natura l ly in thefie ld or e l sewhere in the open a i r(Apfe lbeck e t a l . 198 9) . Th i s ap -proach i s successfu l only when theent i re dry ing period i s free of ra inand low in humid i ty (B ludau 1989 ) .Such c l imat ic condi t ions are rar e int empera t e a reas , mak ing th i s so lu -t ion unrel iable in northern Europe,Canada . and the no r the rn Un i t edStates . In warm t ropical areas , con-versely, intense biological activi tyinduced by h igh temper ature mayreduce the quant i ty and qual i ty ofhe rbaceous c rops t ha t a re l e f t t oolong in the field.I m p r o v i n g e n e r g y e f f i c i e n c ythrough genetic research. Some re-search on t rees and a l ternat ive en-e rgy c rops a ims to improve the den -si ty and rel iabil i ty of the supply ofbiomass by genet ic impro vem ent ofc u l t i v a t e d t r e e s a n d b y s p e c i f i cchanges obta ined through b io tech-nology. We bel ieve that th e potent ia limprovements through th is approachare l im i ted . M ajo r advances i n ag r i -c u l t u r a l ~ r o d u c t i o nwere obta ineddur ing t i e Green Revo lu t ion by re -a l locat ing energy use wi th in p lants(i .e. , by increasing that part of thep l an t s t ruc tu re o r func t ion t ha t i su sefu l t o hum ans) , bu t t he goa l o fincreasing t ree b iomass produ ced perhectare would rea ui re a n increase inthe eff ic iency of xphotosy nthesis a tth e ecosystem level-that is, a rear -rangem ent of the f lows of nut r ientsand -w a te r in en t i re ecosys t ems on alarge scale (G iampiet ro 1994 , Hans en19 91 ) . Th i s ob j ect ive i s ove rambi -t ious g iven the present s ta te-of- the-art in b io technology. T echnologicalimprovemen t s ach i eved in t he GreenRevolut ion th at increased y ie lds perhectare induced. as a side effect . adrama t ic reduct ion in the energy out -put-input rat io of crops (i .e., theydecreased marginal re turn of inputappl icat ion). Such a solution ha s beenaccep ted fo r food c rop p roduc t ionby modern socie ty because increas-ing suppl ies of food was seen aswo rth a n increase in expend i tures off o s s i l e n e r g y . H o w e v e r , s u c h at radeoff would be unacceptable forene rgy c rop cu l t iva t i on .Environmental obstacles to theproduction of wo od y energy crops.October 2997

Lit t le research has been don e on thelong-term envi ronm ental impac ts ofwoody ene rgy c rops , even - thoughthese energy crops are l ikely to gen-e ra t e env i ronmen ta l p rob lems tha ta re s im i l a r t o o r worse t han thoseex ~e r i e nc edwi th conven t iona l foodanh cash crops. T he few studies avail -able have been sho rt term, sm all scale,and of l imi ted scoDe iOT A 1 99 3) .\One possib le long-term problkmis loss of biodiversi ty and the disap-pea rance o f en t i re na tu ra l communi -t ies when energy crop monoc ul turesspread onto adjacent nonarable land.In tensive product ion of t rees andother sources of cellulose Doses thesame r i sks t o b iodivers i ty as cul t iva-t ion of convent ional energy crops.Assessmen ts o f t he ~ o te n t i a l i ofuely ie ld of short -ro ta t ion woody cropsse ldom pay a t t en t ion t o t he po t en t i a llong-term envi ronmental effects ofsuch a s t ra tegy ( Ferm et a l . 198 9,Verma and Mis ra 1 98 9) . ndeed , t hepo ten t i a l l y se r ious env i ronmen ta limp act of intensive harvesting for en-ergy produ ction have, in general, beenoverlooked in the research agenda ofmost countr ies (D yck and Bow 199 2).Ou t look fo r new b io fue l p roduc t ionsystems. In l ight of gen eral trends intechnological development of agri-cul ture , f i sheries , and forest ry , i tapp ears tha t the densi ty of f lows ofnatural resources harvested by hu-mans can be augmen ted , bo th pe rhectare and per hour of labor, onlyby a m ore t han p ropor t i ona l i ncreasein the density of inputs used in theprocess (Ha l l e t a l . 1986)-that i s,t h e h i g h e r t h e i n t e n s i t y o f t h eth roughpu t , t he l ower t he ou tpu t -inpu t ra t io of the process . S imi larly ,t he more t he pa t t e rn o f ma t t e r andenergy f lows in a managed ecosys-tem di ffers from natural pat terns th atoccurred in the ecosvstem that wasreplaced, the h ighe; the expectede n v i r o n m e n t a l i m p a c t o f h u m a nm a n a g e m e n t ( G i a m p i e t r o 1 9 9 7 ,Giampie t ro et a l. 19 92) . Finally, theneed fo r a h igh th roughpu t pe r hou ro f l a b o r in b i o m as s ~ r o d u c t i o n a ll sfor mechanizat ion , which cal l s , intu rn , fo r an expans ion o f monocu l -tures t o svnchronize th e act iv i t ies inthe b iomass p ro duc t ion p rocess .The com bina t ion o f t hese fac to rssuggests that technological improv e-men ts a imed a t in tensi fy ing b iomass

flows to overcome biophysical con-st ra in ts wi l l, so oner or la ter , decreasethe marginal re turn in the use ofenergy inputs , decrease the F" /F lra t io , and increase envi ronmental im-pacts . Because , as we have shown,large-scale biofuel production willbe feasible only if th e energy throu gh-pu t per hectare and per hour of laborof curren t biofuel energy systems in-creases severa lfold, i t is unlikely th ata massive ado pt ion of sho rt -ro ta t ionwoody c rops o r he rbaceous ene rgycrops wi l l represent a v iable so lu t ionfor b iofuel prod uct io n in the fu ture .Biophysical l imits to large-scaleproduct ion of b iofuel , such as l im-i ted suppl ies of lan d and w ater , en-dangered na tu ra l equ i l ib r i a , and un -sustainable rates of deforestat ion an dsoi l erosion , a re d i ff icult to detect a tthe p i lo t p lant scale . Therefore , tech-nological opt imists , by consideringonlv thei r ow n smal l scale of analv-s is , wi l l cont inue to c la im to havedram atica lly increased the efficiencyof the single step of the process th atthey are studying. By contrast , so-c ioeconomic cons t ra in t s t o l a rge -scale produ ction of biofuel are hard erto i gno re : No one can reasonab lvexp ect that biofuels wil l achieve any-th ing l ike the energy throughputs( o n h e o r d e r of 1 0 , 0 0 0 M J ) p e r h o u ro f l abo r t ha t a re cu r ren t lv ob ta inedby mining of fossi l energy stocks . Ashi f t to b iofuel systems wi th muchsmal le r ene rgy th roughpu t s pe r hou ro f l abo r wou ld requ i re a d ramat i csetback in the s ta nda rd of l iv ing , thepop ulat ion s ize , or both . Al l of theseissues must be addressed in discus-sions of future scenarios of large-scale b iofuel prod uct ion .Hu ma ns a l ready app rop r i a t e , di -rectly or indi rect ly , 40 % of the pro-ductivity of the biosphere (Vitouseke t a l. 1 9 8 6 ) .To pu t t he i ssue o f l a rge -scale product ion of b iofuel in per-spective, the following questions needto be answered . Are huma ns a l readyoverdis turbing the envi ronm ent justt o p roduce food and fo res t p roduc t sand to mainta in a certa in l i fes ty le?M any indicators, including deforesta-tion, soil erosion, loss of biodiversity,ozone layer depletion, accumulationof carbon dioxide in the atmosphere,shortages of fresh water, and pollu-t ion , suggest cau t ion in using fur therresources (Brow n 1980-1 994). Is i tconceivab le t o augmen t o u r cu r ren t

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level of a ppro pr iat io n by several foldto produce, via biological conver-s ion, the huge qua nt i ty of fuel that i sc u r r e n tl y b e i ng c o n s u m e d ? W estrongly bel ieve that , f rom an eco-logical perspective, large-scale pro-duct ion of biofuel f rom herbaceousgrass o r shor t - ro ta t ion t rees wouldfur ther des t roy natural habi tats wi th-ou t improving the cur ren t unsus ta in -able solut ion in which fossi l energys tocks a re dep le ted an d greenhousegases are accumulat ing.Biofuel productionin perspectiveDespi te the need for more rel iabledata on large-scale biofuel systemsoperat ing w ithou t foss il energy sub-sidies, we believe that some conclu-s ions a re war ran ted based on cur -r en t da ta on b iofue l p roduct ion :

Large-scale biofuel product ion isno t a n a l t e rna t ive to the cur ren t useof oi l and is not even an advisableopt io n to cover a s ignif icant f ract ionof i t . Biofuel sys tems appear to beunable to match the demand for ne tusefu l energy or the h igh-energythroughp ut per ho ur o f l abor typica lof the energy sector of a developedsociety. First , none of the countriestha t we analvzed has suff icient landor w ater t o rely exclusively on biofuelfor energy secur i ty . The rat io of thedemand for l and to ava i l ab le l andr an g es f r o m 1 . 4 t o 1 4 8 f o r t h e co u n -,t r ies in our sample, and the rat iobe tween f r esh water demand andc u r r e n t f r e s h w a t e r w i t h d r a w a lranges f rom 3 t o 104 . Second , indeveloped countr ies an en ergy sectorbased ent i rely on biofuel would ab-s o r b f r o m 2 0 % t o 4 0 % of t h e w o r k -ing force, including the unem ployed,which is not compat ible wi th thecurrent labor dis t r ibut ion over thevar ious econo mic sectors . Third, theda ta o n which the f i r s t and secondconclus ions are based do not evenaccount for ecological costs . If theenergy requirement for reducing theBOD, of effluents from eth ano l plantsto acceptable levels ( 1 0 MJ per l i terof net ethanol del ivered) were in-c luded , then l and , water , and l ab ordemand would increase dramat ically .In addi t ion, in the long term, theenergy cos t of soi l eros ion wouldfur ther increase land, f resh water ,

and l abor demand per g iga jou le de-l ivered through a reduct ion of biom-ass yields . Meet ing the current de-ma nd f or energy in the Uni ted Stateswi th e thanol f rom crops would ne-cessitate a 20-fold increase in cur-rent pesticide use. And de stroying allexis t ing fores t a nd increas ing pes ti -cide use threefold to produ ce m etha-no l f rom shor t - ro ta t ion woody cropswould no t cover even 1 5 % of cur -rent US energy deman d.Food and env i ronmenta l s ecur ityshould be of greater con cern to soci-ety tha n energy secur i ty for a wor ldpopula t ion tha t is p ro jec ted to r eacha plate au of app roxim ately 8-12 bil-l ion. At present , less than 0.2 7 ha ofarab le land is available per capi ta forfood product ion , an d hum ankind i sal ready us ing foss i l energy t o reduceland dem and fo r food secur i ty . Thus ,us ing arable land for saving foss i lenergy is impractical. Heavy reli-ance of the world econom y on biofuelwould make i t imposs ib le to guaran-tee food secur i ty because of the com -pet i t ion fo r a rab le l and and water .Mo reover , biofuel product ion w ouldresul t in more ser ious environm entalimpact s than a re cur ren t ly exper i -enced with the use of fossil energy.Biomass does have a role to play inthe energy secur i ty of m ode rn soci-ety, both in developed and develop-ing countr ies , in terms of bet ter en-ergy efficiency of agricu lture. Desp itetheir impor tance for soi l conserva-tion and the high direct and indirectcosts involved in their harvest, agri-cultural residues and byproducts cancontribute t o a m ore efficient and sus-tainable agricultural system. Th ey canbe used as energy inputs in all caseswhere their use is compatible withexisting constraints (e.g., the directfir ing of biomass with cogen eration).How ever, the recognition th at there isroom for a more rational a nd efficientuse of biomass at the rural level hasnothing to d o with the idea of farmingo n large scale for fuel per se. Resea rchinto new processes of biofuel produ c-t ion other than ethanol should avoidrepea t ing the m is take w i th e thanol ,in which declared yields and expec-tat ions seem t o have been inverselyre la ted to th e qua n t i ty o f r ea l da taused in the assessment.The e conom ic cos t of biofuel , espe-cially in develop ed countr ies, derivesmos t ly f rom the l abor demand per

uni t of energy through put del ivered.This cos t i s related to the oppor tu-nity cost of lab or in the rest of soci-ety. In developed coun tr ies , this cos tis p ropor t iona l to the ab i l i ty to p ro -duce and consume goods and ser -vices by us ing a large amount ofuseful energy an d a smal l f ract ion ofhuman t ime. Mass ive adopt ion ofbiofuel , wi th i t s much lo wer energythroughput per un i t o f l abor thanfossil energy, would reverse a basict r end confer red by t echnolog ica lprogress-namely, reducing the frac-t ion of hum an t ime tha t can be al lo-cated to the service sector . ret i re-ment , a nd leisure.T h e n o n ~ u b s t i t u t a b i l i t ~f o i l w it hbiofuel is a major cause of concernbecause it does not provide an escapefrom the current unsustainability of acivilization that is based on depletionof fossil fuels. While fossil energystill lasts , alternativ e energy sourcesother than biofuel wi l l need to bedeveloped, along with technologiestha t im prove the ef ficiency of energyuse and l i fes tyles tha t are m ore con-s i s t e n t w i t h s u s t a i n a b l e n a t u r a lcycles.If a major increase in energy effi-ciency, a dra ma tic ch ang e in lifestyle,and implementat ion of energy re-sources other than oi l wi l l enableh u m an k i n d t o s o o n cu r b t h e en er gyrequirement of a wor ld populat iontha t wi l l eventual ly s tabi lize at a s izeof app roxim ately 8-12 bill ion, bio-mass wi l l be essent ial for other p ur-poses. Specifically, the biomass ofnatu ral ecosys tems wil l be needed toprov ide l i f e suppor t to the humanspecies by stabilizing the structurean d funct ions of the biosphere. Thedivers i ty and heal th of natu ral com-munities existing in different typesof ecosystem all over the plan et willb e t h e m o s t i m p o r t an t " cap i t a l "ava i l ab le to humankind to ach ievesus tainabi l i ty , because technologywil l never be ab le to su bs t i tute for i t .AcknowledgmentsWe wou ld l ike to than k the fo l low-ing persons for their helpful com-ments and sugges t ions : David 0 .Hall , of King 's Col lege, London;Ch arles A. S. Ha ll , Will Raven scroft ,and D an R obinson, of State Univer-sity of Ne w Y ork, S yracuse; GiuseppePellizzi, of the University of Milan;



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and tw o ano nym ous rev iewers . Werecognize that our v iews were notshar id by al l of these persons. Thef inal version of the te xt ha s great lybenef i ted f rom the valuable contr i -but ion of Sandra G. F. Bukkens . Wegratefully ackno wledg e f inancial as-s i s tance to M ar io G iampie t ro f romT he Asah i Glass Fou nda t ion , Japan ,and to Sergio Ulgiati f ro m the I ta l ianM inistry of University an d Scientif icResearch.References citedAbelson PH. 199 5. Renewable liquid fuels.Science 268: 955.Ahern JI. 198 0. The energy method of energysystems analysis. New York: John Wiley& Sons.Apfelbeck R, Bludau D, Kramer U. 1989.Technical improvement of systems forharvest, transport, storage and dehydra-tion of wood and straw for energy underconsiderat ion of economical aspects. Pages267-273 in Grassi G, Gosse G, dos SantosG, eds. Biomass for energy and industry,5th E.C. Conference. Vol. 1 . Policy, envi-ronment, production, and harvesting.London: Elsevier Applied Science.Belletti A. 1987. Sweet sorghum: from har-vesting to storag e. Pages 129-135 inFerrero GL, Grassi G, Williams HE, eds.Biomass energy from harvesting to stor-age. London: Elsevier Applied Science.Betters DR, Wright LL, Couto L. 19 91. Shortrotation woody crop plantations in Braziland the United States. Biomass andBioenergy 1: 305-316.Bevilacqua OM, Bernard MJ 111, MaxfieldDP. 1981. The environmental implica-tions of the large scale utilization of alco-hollfuels in the United States. Pages 719-726 in Proceedings of the IV InternationalSymposium on Alcohol Fuels Technol-ogy. Vol. 11, C-1. 5-8 Oct obe r 198 0;Guaruja, Brazil. SBo Paulo (Brazil): stitutode Pesquisas Tecnologicas do Estado deSBo Paulo S.A., Brazil.Bludau DA. 1989. Harvest and storage ofsweet sorghum. Pages 260-266 in GrassiG, Gosse G, dos Santos G, eds. Biomassfor energy and indust ry, 5th E.C. Confer-ence. Vol. 1. Policy, environment, pro-duction a nd harvesting. London: ElsevierApplied Science.Brown L. 1980-1994. The state of the world.Washington (DC):Worldwatch Institute.Buringh P. 1 987 . Bioproductivity and landpoten tial. Pages 27-46 in Hall DO,Overend RP, eds. Biomass. New York:John Wiley & Sons.[CCPCS] Commission Consultative pour laProduction de Carburant de Substitution.1991. Rapport des Travaux du GroupeNumer o 1 . Paris: Commission Consulta-tive pour la Production de Carburant deSubstitution.Chartier PL, Savanne D. 19 92. Medium-termoutlook for biofuels. Comptes Rendus de1'AcadCmie d'Agriculture de France 78:35-50.

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A critical appraisal of energetic assess-ments of biofuel production systems. En-vironmental Biology. Cornell UniversityTechnical Report nr 97-1.Giampietro M, Bukkens SGF, Pimentel D.1997b. Linking technology, natural re-sources and socioeconomic structure ofhuman society: examples and applications.Pages 129-199 in Freese L, ed. Advancesin human ecology. Vol. 6. Greenwich (CT):JAI Press.Hall CAS, Cleveland CJ, Kaufmann R. 19 86.Energy and resource quality. New York:John Wiley & Sons.Hansen EA. 19 91. Poplar woody biomassyields: a look to the future. Biomass andBioenergy 1: 1-7.Helsel Z. 199 2. Energy and alternatives forfertilizer and pesticide use. Pages 177-201 in Fluck RC, ed. Energy in farmproduction. Vol. 6. Amsterdam: Elsevier.Herendeen R, Brown S. 1987 . A comparativeanalysis of net energy from woody biom-ass. Energy 12: 75-84.Hohenstein WG, Wri ght LL. 19 94. Biomassenergy produc tion in the United States: anoverview. Biomass and Bioenergy 6: 161-173.Holdren JP. 19 82. Energy hazards: what tomeasure, what to compare. TechnologyReview 85: 32-38, 74-75.Hunsaker DB, McBrayer JF, Elmore JL. 1 989.Ethanol production and the environment.Energy 14: 451-468.[IEA] International Energy Agency. 1994.Biofuels. Policy Analysis Series: Energyand Environment. International EnergyAgency. Paris: Organization for EconomicCooperation and Development.[ILO] Internationa l Labour Office. 1992.Economically active population, estimatesand projections 1950-2025. Geneva: In-ternational Labour Office.[ISTAT] Istituto Centrale di Statistica. 1 992 .Annuario statistic0 Italiano. Rome:Istituto Centrale di Statistica.Johansson TB, Kelly H, Reddy AKN, Will-iams RH, e d ~ . 993. Renewable energy:sources for fuels and electricity. Washing-ton (DC ): Island Press.Kendall H, Pimentel D. 199 4. Constraints tothe world food supply. Ambio 23: 198-205.Klass DL, ed. 1993. Energy from biomass andwastes XVI. Chicago: Institute of GasTechnology.La1 R . 199 5. The role of residues manage-ment in susta inable agricultura l systems.Journ al of Sustainable Agriculture 5: 51-78 .Lyons GJ, Lunny F, Pollock HP. 1985. A

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Executive DirectorAssociation of Systematics Collections

The Association of Systematics Collections (ASC) invites applica-tions for the position of chief executive officer in Washington, DC.Duties include: establishing and maintaining relationships within thecommunity of natural history collections through direct contact withmembers, organization of national meetings, representing constituencyto Congress, federal agencies, and other organizations; program develop-ment and implementation; and supervising business operations of theASC office (including finances, fund raising for the organization's activi-ties, and administrative support for the organization).

Required skills: Demonstrated abilities relevant to working with pri-vate, public, federal and state institutions and agencies in affectingregulations and legislation; a background in natural history collectionsand/or working in the Washington, DC environment. Prior professionalexperience in a relevant scientific field of organismal, collection-basedresearch (e.g., systematics, conservation, community or species ecology,etc.) will be useful but not required.

Send a letter of application, resume or curriculum vitae, and names,addresses and telephone numbers of at least three references to: Associa-tion ofsystematics Collections; 1725K Street, NW; Suite 601, Washing-ton, DC, 20006-1401. Email may be used for preliminary inquiries:[email protected]. Review of applicants will begin 1 September 1997 andcontinue until a suitable candidate is hired.

Shay EG. 1 993 . Diesel fuel f rom vegetab leo i ls : s ta tus and opportun i t ies . B iomassand Bioenergy 4: 227-242.S lesser M. 1978 . Energy in the economy.New York : S t . Mart in ' s P ress .Sour ie JC , Hau tco las J , B lanchet J . 1992 .W h ich o p p o r tu n i t i e s fo r t h e sh o r t t e rmdevelopment of biofuels as a result of thenew f iscal and regu lato ry p rov is ions inFrance and wi th in EEC. Comptes rendusde I'Acad imie d 'hg r icu l tu re de F rance 78 :19-29 .S o u th e r l an d D . 1 9 9 5 . C l in to n m an d a te o ncleaner gas was re jected . Th e Wash ing tonPost , 29 Apri l 1 995 , sec . C , pp . 1 -2 .Stevens DJ. 19 92.Biomass conversion: an over-view of the IEA bioenergy agreement taskVII. Biomass and Bioenergy 2: 213-227.S tou t BA. 1990 . Ha ndb ook o f energy fo rworld ag r icu l tu re . London : E lsev ier Ap-plied Science.S tuckey DC. 1 986 . Biogas: a g lobal perspec-tive. Page 18 n El-Halwagi MM, ed. Biogast e c h n o l o g y , t r a n s f e r a n d d i f f u s i o n .Amsterdam: Elsevier.T ro b i sh K H . 1 9 9 2 . R ecent d ev e lo p m en t s inthe t reatme n t o f chemical waste water inEurope. Water Science and Techno logy2 6 : 3 1 9 -3 2 2 .[T R W ] T R W E n erg y S y s tem s P l an n ~ n g ivi -s ion . 19 80 . Energy balances in the p ro -duct ion and end-use o f a lcoho ls der ivedfrom b iomass , a fuels-speci f ic compara-t ive analysis o f a l ternate e th ano l p roduc-t ion cycles . Repor t p repared fo r the USNational Alcohol Fuels Commission andthe Office of Advanced Technology R&DAssistant Secretary for Policy and Evalua-t ion . Wash ing ton (D C):US Department ofEnergy. Document nr 976 11-E002-UX-00 .[UN] Uni ted Na t ions . 199 1 . Energy s ta t is t icsyearbook . New York : Un i ted Nat ions .[USDA] US Depar tme n t o f Agricu ltu re . 1 992 .Agricu l tu ral s ta t i s tics . Wa sh ing ton (DC ):US Dep ar tme n t o f Agricu l tu re .

V erm a S C , M is ra P N . 1 9 8 9 . B io m ass an denergy p roduct ion in copp ice s tands o fVitex negundo L. in h igh densi ty p lan ta-t ions on marg inal lands . B iomass 19 : 189-1 9 4 .Vitousek PM , Ehrlich PR, Ehrlich AH, Ma tso nP A . 1 9 8 6 . H u m an a p p ro p r i a t i o n o f t h eprod ucts of photosynthesis. BioScience 36:368-373 .[W R I] W o r ld R eso u rces In s t i tu t e . 1 9 9 2 .World resources 1992-93 . New York :Oxfo rd Univers i ty P ress.1 9 9 4 . o r ld reso u rce s 1994-95 . NewYork : O xford Univers ity P ress.Wrig h t LL, Hohenstein WG , eds . 1994 . Ded i-cated feedstock su pp ly systems: thei r cu r-r en t s t a tu s i n t h e U S A . B io m ass an dBioenergy 6 (special issue): 159- 241.Wyman CE, Bain RL, Hinman ND, S tevensD J . 1 9 9 3 . E th an o

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GIAMPIETRO_biofuel.pdf