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Researchers Assess Life-Cycle Impact of Soy Biodiesel and Corn Ethanol

An analysis by University of Minnesota researchers of the full life cycles of soybean biodiesel and corn grain ethanol concludes that biodiesel has much less of an impact on the environment and a much higher net energy benefit than corn ethanol, but that neither can do much to meet US energy demand.

The study, funded in part by the University of Minnesota’s Initiative for Renewable Energy and the Environment, was conducted by researchers in the university’s College of Biological Sciences and College of Food, Agricultural and Natural Resource Sciences. The study will be published in the 11 July Proceedings of the National Academy of Sciences.

The researchers tracked all the energy used for growing corn and soybeans and converting the crops into biofuels. They also looked at how much fertilizer and pesticide corn and soybeans required and how much greenhouse gases and nitrogen, phosphorus, and pesticide pollutants each released into the environment.

“Quantifying the benefits and costs of biofuels throughout their life cycles allows us not only to make sound choices today but also to identify better biofuels for the future.

—Jason Hill, lead author of the study

The study showed that both corn grain ethanol and soybean biodiesel produce more energy than is needed to grow the crops and convert them into biofuels. This finding refutes other studies claiming that these biofuels require more energy to produce than they provide. The amount of energy each returns differs greatly, however. Soybean biodiesel returns 93% more energy than is used to produce it, while corn grain ethanol currently provides only 25% more energy.

Still, the researchers caution that neither biofuel can come close to meeting the growing demand for alternatives to petroleum. Dedicating all current US corn and soybean production to biofuels would meet only 12% of gasoline demand and 6% of diesel demand. Meanwhile, global population growth and increasingly affluent societies will increase demand for corn and soybeans for food.

The authors showed that the environmental impacts of the two biofuels also differ. Soybean biodiesel produces 41% less greenhouse gas emissions than diesel fuel whereas corn grain ethanol produces 12% less greenhouse gas emissions than gasoline.

Soybeans have another environmental advantage over corn because they require much less nitrogen fertilizer and pesticides, which get into groundwater, streams, rivers and oceans. These agricultural chemicals pollute drinking water, and nitrogen decreases biodiversity in global ecosystems. Nitrogen fertilizer, mainly from corn, causes the dead zone in the Gulf of Mexico.

We did this study to learn from ethanol and biodiesel. Producing biofuel for transportation is a fledgling industry. Corn ethanol and soybean biodiesel are successful first generation biofuels. The next step is a biofuel crop that requires low chemical and energy inputs and can give us much greater energy and environmental returns. Prairie grasses have great potential.

—David Tilman, Regents Professor of Ecology and a co-author of the study

Biofuels from feedstocks such as switchgrass, mixed prairie grasses and woody plants produced on marginally productive agricultural land or biofuels produced from agricultural or forestry waste have the potential to provide much larger biofuel supplies with greater environmental benefits than corn ethanol and soybean biodiesel.

According to Douglas Tiffany, research fellow, department of applied economics and another co-author of the study, ethanol and biodiesel plants are early biorefineries that in the future will be capable of using different kinds of biomass and conversion technologies to produce a variety of biofuels and other products, depending upon market demands.

There is plenty of demand for ethanol as an additive. he ethanol industry was built on using ethanol as an additive rather than a fuel. Using it as a biofuel such as E85 is a recent and currently unsustainable development. As is, there is barely enough corn grown to meet demand for ethanol as a 10 percent additive.

—Jason Hill


Adam Galas

Well, I have always believed Bio-Diesel was better, and now it is officially scientific fact. Less imputs, lower emissions, higher energy density and larger net energy density.

And as for not being able to replace all petrol in the US? Haven't we been threw this a dozen times now? Algea could easily satiate demand for only 1% of arable land.

Trouble is only 1 company is currently making BD with algea, but I am sure it will catch on once the benefits become clear.

Now if only Toyota and Honda would come out with that Plug in Diesel Hybrid we all know is the future of transportation we could all get to the business of screwing over the Saudis.


The difference between biodiesel and ethanol is that biodiesel is straightforward diesel fuel supplement, while ethanol is valuable additive to conventional gasoline to improve octane rating (and hence potentially improve thermal efficiency of IC engine) and promote cleaner combustion.

Rafael Seidl

Adam -

(a) in GHG terms, biodiesel is more attractive well-to-wheels than almost anything else out there right now. Unfortunately for US consumers, it's still diesel, which means it still generates a lot of NOx. You'll be hard pressed to find a MY 2007 vehicle to put it in (Mercedes E320 CDi is the ONLY one to limbo under the newly-lowered emissions bar, at a price tag few can afford).

Even the larger trucks and buses will have to meet Tier 2 Bin 8 or better by MY 2009, with fleet average emissions at Tier 2 Bin 5. This is already the case with LDVs today. No company wants to be in a position in which government regs limit its ability to meet market demand for any one technology. That is why VW and Honda have said they will not introduce new diesel models until they have a drivetrain that can meet Tier 2 Bin 5. Wrt NOx, which has proven hardest to deal with, that limit implies an improvement of over 87.5% over state-of-the-art turbodiesel technology (without expensive aftertreatment or HCCI). Since even the US cannot afford to run all of its trucks and buses on gasoline, that probably means SCR and area additive is coming to the US, even if EPA and CARB don't much like it.

(b) There are algae species which produce lipids, which may be used as a biodiesel feedstock. However, there are many more that produce starches instead, which can be converted into simple sugars and various alcohols far more easily than cellulose can. Ergo, it may be more useful to talk about algal fuels than about algal oil.

However, youre assertion regarding algal productivity is correct only if the pools they are grown in are artificially enriched with CO2, e.g. by bubbling scrubbed and cooled flue gases from coal-fired power plants over them. That means intensively farmed algae ponds will not be carbon-neutral.

(c) If PHEVs are a good idea (debatable on asset depreciaton, range etc.) and diesels are a good idea (debatable on emissions), the the combination must be the ultimate Good Idea(tm), right? Perhaps for in-town buses, garbage trucks etc. Not necessarily for LDVs, though: the bulk, weight and cost of the drivetrain would turn them into instant Edsels.

For countries other than the US, diesel microhybrids (e.g. Citroen C2) are useful for eliminating emissions due to idling. Lower compression ratios (14-15) would be permit lower engine weight and cost, as well as better weight distribution for subcompact diesel applications. The fuel economy gains from replacing the gasoline engine would vastly overcompensate the slight reduction in thermodynamic efficiency. The main reason compression ratios remain so stubbornly high (17-21) is the difficulty in igniting the fuel in very cold weather.

Biofuels are a fledgling industry whose future gets brighter everyday. Corn and soybeans however, presently are among the least desirable feedstocks. Genetics and production technology advances will no doubt increase outputs, decrease incidental costs.


I agree, especially concerning soybeans. It is a terrible food source and would serve much better as a fuel source. Unless fermented, soy beans and soy products should never be consumed by humans (even fermented there is still a propensity for the chemicals in soy to moderately inhibit mineral and protein absorption).


The crusade against NOx, even when draconian reductions are empiricly proven to not reduce smog further (See: Weekend Effect), will force us into ethanol and butanol rather than biodiesel. More than that, the costs associated with meeting the new regulations will likely keep the older, more polluting semi trucks on the road longer.


Rafael-- since we're burning coal by the megaton anyway, and will continue doing so for the forseeable future, why not bubble that CO2 through an algal pond instead of just blowing it up the smokestack? Ok, so it's not carbon-neutral, but if it can reduce (or eliminate? someday?) the use of fossil petroleum in our vehicle fleet, it's gotta be better than what we're doing now! Doesn't it?

Robert Schwartz

CIA Factbook:

US Land Area 9.2*10^8 ha

Arable Land in US 18% or 1.7*10^8 ha

Table 822 Cropland:

In Crops 1.4*10^8 ha

Census Bureau:

Land in Farms 2002 3.8*10^8 ha (1953 4.9 10^8 ha)

Annual fuel consumption 6.7*10^11 liters

Hippy Dippy Web site:

Crop liters oil/ha
corn (maize) 172
oats 217
cotton 325
hemp 363
soybean 446
pumpkin seed 534
rice 828
sunflowers 952
peanuts 1059
rapeseed (canola) 1190
olives 1212
jatropha 1892
avocado 2638
coconut 2689
oil palm 5950


If we could increase the land in crops by about 20%, we could devote about 3*10^7 ha to oil crops. If we could average 1,000 l/ha*, we would have 3*10^10 of oil. That is about 5% of our current use. In order to run our transportation system on bio-diesel, we must bridge a gap of at least 4 doublings.

Could we bridge the gap? Pushing as hard as we can on automotive technology, we could certainly double fleet efficiency. We might even be able to quadruple it.

1,000 l/ha* is not a stretch. But, of the crops with good oil yields, the only ones on the list above that have any promise and which are not tropical or
sub-tropical, are rapeseed and sunflower. However, we have increased corn yields by over 8 times in the modern era. So we might be able to close the gap that way.

*1l of raw oil=~800ml of bio-diesel

Clearly, the algae approach, if it does not interfere with agriculture would be preferable to plowing up that much additional land.


Sewage treatment plants produce sizeable amount of biogas, 50% of which (by mass, by volume it is about 35%) is carbon dioxide. Biogas could be combusted directly on lean burn high compression gaseous fuel diesel generators (due to CO2 dilution with very low NOx emissions), and after stripping from sulfur components, used to heat up anaerobic digesters, and exhaust, incredible rich in CO2, could be used to enhance algae growth. Additional advantages could be direct use of fertilizers from secondary wastewater treatment, and usually STP are surrounded by wide strips of unpopulated land due to odor nuisance, which could be used for algae ponds.
Just a thought…

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