DOE Awards Novozymes $12.3M to Increase Efficiency of Enzymes for Cellulosic Ethanol Production 2x
China Has 168M Motor Vehicles on the Road

New Life Cycle Study Concludes That Biomass for Ethanol Is Not the Most Advantageous Energy and Emissions Use of the Feedstock

A new life cycle study assessing the benefit of cellulosic ethanol in the context of projected feedstock constraints concludes that in terms of reducing greenhouse emissions and fossil fuel dependency, more is lost than gained when prioritizing biomass or land for bioethanol, rather than for use in technology pathways involving heat and power production and/or biogas, or natural gas and electricity for transport. The study was published online in the journal Environmental Science & Technology on 4 October.

The study by researchers in Denmark begins with the conclusion that toward 2030, the amount of biomass which can become available for bioethanol or other energy uses will be physically and economically constrained, regardless of whether of global or a European perspective is applied. This implies that the use of biomass or land for bioethanol production will most likely happen at the expense of alternative uses.

Specifically, the study compares the use in transportation of cellulosic ethanol produced from whole-crop maize by fermentation in several process configurations to alternative use of the feedstock in heat and power applications fueled by coal or natural gas.

Among the scenarios investigated, the researchers found that using willow in CHP production combined with using electric cars for transport yields the highest GHG mitigation and reduction in oil dependency.

They also found that the optimal biogas scenario is for biogas to substitute for natural gas in heat and power production and to use the displaced natural gas to substitute for oil in the transport sector.

In terms of greenhouse gas emissions, the ethanol baseline scenarios provide by far the lowest net GHG mitigation compared to the alternative utilizations of land for energy purposes. For example, use of the land to produce willow used for combined heat and power in substitution for coal provides GHG mitigation more than twice and high, and even higher if combined with electric cars.

Even when using fodder byproduct as fuels, the ethanol scenarios are still compared to the alternatives. The researchers attributed the low net GHG mitigation in the ethanol scenarios to the considerable amounts of steam and electricity consumed in the process of converting biomass into ethanol, especially for pretreatment, hydrolysis, extract concentration, distillation, and drying processes.

Less energy is required for catalyzing anaerobic digestion in the biogas process, for the thermal gasification of willow, or for wood pellet manufacturing. Other factors contributing to the difference in GHG mitigation across the scenarios include the high CO2 content of coal, which results in large GHG mitigation when biomass is used to displace coal, and the high energy efficiency of electric motors compared to combustion engines.

The ethanol scenarios also provide a low net fossil fuel displacement compared to several of the alternative technology pathways. Up to 2.5 times as high oil savings can be obtained with the alternative energy crop utilization pathways, for example.

Overall, for the case presented, the reductions in GHG emissions and fossil fuel dependency, obtained by producing whole-crop maize for bioethanol production happens at the expense of other land/biomass utilizations, which would provide considerably larger reductions. Thus, for this technology case and perspective, more is lost than gained when prioritizing land/biomass for bioethanol.

This is mainly caused by the significant energy conversion losses in bioethanol production compared to use of biomass in the energy sector. The losses lie in the need for pretreatment (lignocellulosic based production), the relatively low fermentation yield of ethanol, the need to dry and further process the byproduct and residual unconverted matter in order to make use of them, and the need to separate ethanol and water, implying distillation in all known cases. Such losses are not present in alternative technologies, e.g., biomass conversion to electricity and/or heat by incineration or conversion to biogas.

As long as fermentation-based conversion of biomass to ethanol implies these losses, bioethanol will come out disadvantageous to the alternatives studied heres and this is the case for presently known bioethanol technologies including both starch and lignocellulose based production. Thus, the results question the assumed justification for lignocellulosic fermentation based bioethanol: instead of reductions in GHG emissions and fossil fuel dependency, net increases will much more likely be the outcome, when considering the alternative biomass/land utilizations deprived on behalf of bioethanol.

—Hedegaard et al. (2008)


  • Karsten Hedegaard, Kathrine A. Thyø, and Henrik Wenzel (2008) Life Cycle Assessment of an Advanced Bioethanol Technology in the Perspective of Constrained Biomass Availability. ASAP Environ. Sci. Technol., doi: 10.1021/es800358d



Jeff Baker repeats one of the favorite misconceptions of ethanol and especially E85 advocates - that the Saab BioPower gets higher mileage on E85. Verifiably false by looking at information from 1) Saab, and 2) DoE NREL testing. Ethanol is playing and can continue to play an important (but not major) part in reducing fossil fuel consumption, but no one is well served by overstating its benefits. The low energy content of ethanol is just a fact of life that will always limit its potential.

Go to GM / Saab website - (scroll down about 2/3 down the page)

"The overall fuel consumption of the current Saab 9-5 BioPower engine using E85 is about 30% higher than on gasoline and the optimized BioPower 100 engine is expected to yield a near 10% gain against this."
What they mean that is that the 9-5 can improve the mileage penalty by about 10%, so that there is only a 27% penalty instead of 30%. This was also noted in:
Optimizing the Saab BioPower 100 Concept Engine for E100
7 March 2007

DoE is a huge ethanol proponent, but their research shows the same thing, as noted in a recent presentation - "Benchmarking the Ethanol-Optimized Saab 9-5 BioPower" Slide 9 says:
"Saab BioPower Fuel Economy Data Shows that E85
Fuel Economies 23-27% lower than Gasoline"
West, B., et al, Oak Ridge National Laboratory, presentation to the Society of Automotive Engineers,
Government/Industry Meeting, May 1416, 2007



I can understand that for some reason you are a strong Ethanol proponent, after all in US a lot of american men care more about their liquid fuel based SUV or bulky cars than about their own wife, but that deosn't change the pysics of the whole thing, right? This study just confirm what have been observed elsewhere : biogas is more efficient path than ethanol, period. And I think efficiency is critical when it comes to scale biomass for powering 200 millions of cars. And I maintain that an AD biogas digester can be implemented at the farm level even with the CO2 and H2S scrubber when a Ethanol cellulosic processing unit can simply not.

fred schumacher

"Whole crop maize" appears to be the use of grain corn, corn cobs and stover (corn stalk) for conversion to ethanol. This still leaves us with annual grain crop agriculture, which is a high input process.

Cellulosic biomass production from perennial grasses and trees is an animal of quite a different nature. This is low input, low fertility agriculture. Output/input ratio is significantly higher than grain crop agriculture. (See field trials studies done by the University of Illinois Urbana-Champaign.) The concentration of edible resources into a seed head, that is done by annuals, is a very energy intensive process and requires high fertility and soil disturbance. Removing corn cobs and stover from the field will result in soil degradation, reduction in soil organic matter, and increased soil erosion.

We won't be able to make a breakthrough on biomass fuel production if we rely on annual grain crops. That's a dead end.

Although personal transportation can be converted to stored electrical energy "fuel" source, movement of cargo by this method is limited to very short run pickup and delivery. Biomass fuel should be saved for cargo, not general, transport. Hydrogen based transportation is so low, from a total system basis, it really should be discarded as an alternative.

fred schumacher

Oops. I meant to say hydrogen based transportation is so low in efficiency, on a total system basis. See: Proceedings of the IEEE Vol. 94, No. 10, October 2006 "Does a Hydrogen Economy Make Sense?" by Ulf Bossel. It's available online as a pdf.



Maybe we should just agree to disagree, until a test can be performed.

It seems that CO2 is dense enough to pile up and kill someone in just a half hour:

I dunno. This might not fit your definition of a mixed gas, but it certainly doesn't seem likely that a tank kilometers in height would take centuries to settle either, based on this behavior.

Deep pits in factories, buildings, etc. are routinely noted as hazards for collecting CO2, even if the CO2 sources are not located in the pits themselves. Again, this is not indicative of a centuries settling time.

Paul F. Dietz

It seems that CO2 is dense enough to pile up and kill someone in just a half hour:

Yes, if you have large parcels of gas of different compositions, the parcels of the denser gas can sink down below those of the lighter gas. If the parcels are sufficiently big, diffusive/turbulent mixing is not efficient and they remain distinct.

But once those gases are mixed, unmixing them involves separation at the molecular level. The physics of this is well understood; indeed, there's a section on it in Feynman's lectures on physics. The way it works is that in a state of complete thermodynamic equilibrium, the partial pressure of each gas decreases with altitude as an exponential function, decreasing by a factor of e over a 'scale height'. The scale height is inversely proportional to the molecular weight. For methane and CO2 the scale height is measured in kilometers (indeed, for a gas of MW ~29, the average MW of air, the scale height is a bit less than the thickness of the troposphere.)

The *time* for this equilibrium to be established is given by the diffusive mixing time, which is (linear dimenions)^2 / diffusion constant. For typical gases at 1 bar the diffusion constant is on the order of 1 cm^2/sec. So, for a 3 km tower, the time is about 10^11 seconds, or about 3000 years. In the real atmosphere, turbulence remixes the air much faster than this, so air does not separate according to molecular weight except in the very high atmosphere where the diffusion constant is much larger (since molecular mean free paths are longer).

Kit P

@ Treehugger

I am a strong advocate of using AD to treat animal waste in semi-arid regions where the organic fertilizer can be used to reduce soil erosion. I am a strong advocate of pyrolysis or gasifiers to process excess biomas from semi-arid forest because the excess biomass results in intense fires that destroys the forest and causes soil erosion.

Look for the root cause of environmental problems and match technologies to fix the problem,

“This study just confirm what have been observed elsewhere : biogas is more efficient path than ethanol, period.”

That is just not true and Treehugger did not read the LCA. I have read many LCA for EU systems. They are very informative for the EU but Treehugger the EU is not the US.

“I think efficiency is critical when it comes to scale biomass ...”

So Treehugger, Germans should be riding cows to work instead of overprices fast cars.

No, efficiency is not critical. Selecting the correct process for the problem you are trying to solve.

As Fred suggests the 'total system basis' must be evaluated. Again look at the Mead plant. Biogas is produced to heat boilers to make ethanol and the AD returns much of the organics to the soil to grow more corn.



This is perhaps a different form of "public education".


You are probably right about this one. The literature is pretty clear about gas distribution in the atmosphere. Scale heights are higher for lighter gases, which mostly explains why they diffuse out faster. (Because more of them, proportionally, are higher up, they have a better chance of getting knocked out; plus less energy is needed to accelerate them to escape velocity. Which all leads to weird theories by creationists citing helium concentrations as proof the earth is only 7000 years old, but I won't go there.)

I guess I can't reconcile this fact with reality of stable accumulation of dense gases in certain circumstances, such as radon in basements and co2 in deep pits. I appreciate that something with such a small (or large?) Reynolds number can essentially ignore gravity, but obviously it doesn't at the macro level. It's POSSIBLE that gas in a tall narrow tube might act a bit differently (wall strikes ?) than gas in a more typical atmospheric situation.

It just seems odd that tiny leaks of radon (hardly a dense parcel) can nonetheless accumulate in a basement instead of occupying its nominal distribution of its scale height as it should. Somehow the walls of the house contain it. (I'm not trying to defy Feynman, just basically confused.)

Oh well. This thread was about ethanol; and I was just trying to point out that separating CO2 from CH4 is not a big deal. As others have mentioned, absorbants or membranes would probably work fine.

Efficacy of methane for transportion depends on cost and density of storage. The charcoal briquette-like substrate apparently provide good density at low total pressure. Probably promising. Since ethanol can never compete with methane with respect to production costs, this is the only remaining weak point.

The infrastructure argument is a sham as we are already plumbed nationwide for NG, whereas gas stations owned by oil companies have to be dragged kicking and screaming into supplying E85 pumps.


Quoth solar nano:

if you know of an easy and cheap way of removing CO2 from biogas, let me and the rest of the world know.
You fractionally distill the gas under pressure, removing CO2 as a liquid and recovering it as a saleable product; this also removes the H2S and siloxanes.  This is the essence of the CO2 Wash process.

Paul:  Good note on diffusion.  Very valuable.

Kit P


Thanks for the link. That was Kit P. you were quoting. What part of ‘easy and cheap’ do you not understand?

Biogas from a farm anaerobic digesters can be used in an ICE to make electricity or boiler without removing CO2. No compressors, no refrigeration systems.




I don't think it's that simple. Generators and engines runs somewhat poorly on biogas. I think you at least need to scrub the H2S out of it.

Cost is an issue with all biomass related technology because you are forced to have many little plants, as the cost of transporting feedstock becomes onerous pretty quickly. (Another problem the ethanol folk tend to ignore.)

-One who now understand gas diffusion a bit better

Kit P


You are right, there is nothing simple about biomass especially AD. Lot of ICE have been destroyed over the years. Several manufactures have engines designed for biogas. Removing H2S and moisture for farm application is relatively simple. WWTP and LFG require much more complicated systems because of the bad stuff in the gas.

The point is to keep as simple as possible. There are compelling reasons beyond producing a little energy. Every concentrated animal feeding operation has a zero discharge permit under the CWA. Taking the data from a manure handling plan for a 1000 head dairy farm and adding a AD provides the following benefits as a result of reducing air emissions:

- 5.5 ktons of methane captured
- 1.0 ktons of nitrogen compounds (mostly ammonia) captured (1.6 ktons of methane displaced from ammonia production)
- 60 tons phosphate
- 60 tons potassium

CAFOs can not pollute the water directly but blowing away is okay because you can used to your eyes watering.



Agreed. According to Gail the actuary ( peak Phosphorus happened around 1990. But the Nitrogen/ammonia savings are probably more important.

Expensive energy means driving is expensive, which is not good. But it also means Haber-Bosch is more expensive, which is REALLY not good.

Without cheap Haber-Bosch (for fixing Nitrogen) we can only sustain about half the people on earth we have now. So DEFINITELY a problem. This should motivate more AD more than than anything.


If CO2 Wash isn't easy and cheap (requires pressurization and refrigeration, pretty trivial stuff), pray tell... what is?

CO2's triple point is at 5.2 bar, IIRC.  Single-stage centrifugal compressors can hit about 10:1, so there you are.  How this relates to biomass-to-ethanol I don't know, we've gotten a ways from there.



I think it all started with a comment by Kit on Oct. 10.

I didn't start it; I just posted a bunch of stuff that didn't make much sense; which is slightly different.

Kit P

“what is?”

Not separating the biogas and using it directly in a boiler or ICE to make electricity is simpler.

“How this relates to biomass-to-ethanol”

Did you read the whole thread?

Paul F. Dietz

I guess I can't reconcile this fact with reality of stable accumulation of dense gases in certain circumstances, such as radon in basements and co2 in deep pits.

The reason radon is elevated in basements is that the radon is being produced in the soil and rocks under the basement (from the decay chains of uranium). As it diffuses out it goes through the basement before escaping to the atmosphere. Since there is a net flow of radon from the basement out to the atmosphere, the concentration of radon must be higher in the basement than in the outside air. If there is a lot of radon being produced, and the basement is not well ventilated, significant concentrations of radon can be reached.

The density of radon has absolutely nothing to do with this -- the same effect could be observed if (say) helium were diffusing into the basement from the underlying soil and rock.

Similarly, situations where concentrations of CO2 develop are because CO2 is being produced (either volcanically or biologically) and is accumulating, not because CO2 is separating itself from the air. High concentrations of CO2, once developed, can remain stable in low spots because density inhibits macroscopic mixing.



Not (really) doubting you. But check out this fact sheet, which has the seal of the Department of Energy on it. They seem to confuse hydrogen's rapid diffusing with it's lightness. They say some other stuff that you clearly would not agree with.

Paul F. Dietz

I see nothing in that link that I would disagree with. Note that hydrogen, when it leaks, is not initially mixed with air, and so there are macroscopic density differences that can cause the hydrogen to rise.

Once the hydrogen is mixed into the air at the molecular level, it does not then spontaneously separate up near the ceiling, as I suspect you are thinking it could do.


No, I don't think that.

But I think it would diffuse rapidly enough to then be essentially individual molecules. By the time a plume got to a ceiling (depending on the size of the plume) the molecules should be pretty much dispersed. I don't think ceilings have much to do with it (again, depending on the size of the plume) as the safety sheet implies.

In fact, it makes no mention of plumes at all, nor does it specify radically different behavior of the gas based on its concentration.

Most of the safety points imply (or straight out say) that hydrogen is safe because it rises so quickly, when it is actually safe because it diffuses so quickly. (Again, based on the size of the plume.)

Kit P


Small concentrations of gases in air and water is a complex topic. Since I was a certified “gas free engineer' in the navy, let me provide some "public education".

You were not reading a 'safety sheet' but a carefully written propaganda piece. It is called lying.

Hydrogen has unique physical and chemical properties that has not substitutes. However, it is very difficult to handle.
“nor does it specify radically different behavior of the gas based on its concentration”

You mean like explosive range, detonation range, difficulty detecting, difficulty containing, difficulty compressing, difficulty transporting, difficulty containing, and metal embrittlement.

There are many hazards associated with producing and using energy. They must be mitigated to an acceptable level of risk. Assuming that a hydrogen leak will not collect in a roof and result in a detonation of sufficient force to displace the roof to the neighboring roof, would be an incorrect assumption.


Quoth the troll:

Not separating the biogas and using it directly in a boiler or ICE to make electricity is simpler.
Not if your LFG contains silanes, it isn't.  The silanes burn to SiO2, which coats engines and boilers and requires costly rebuilds.  H2S has its own problems.

Since you have to separate the silanes and H2S to run engines anyway, you might as well upgrade the LFG/biogas to pipeline quality.  This lets you use it as compressed fuel gas in vehicles, export via pipelines, or otherwise serve the same markets as natural gas.

Now how come the soi-disant "expert" didn't know this... or wouldn't admit to it?  No prizes for guessing.


I agree with Engineer-Poet.

First, why waste biogas on a boiler? Just burn the biomass instead.

Second, why have special equipment to use the biogas, when if cleaned properly, it can be integrated into our existing NG infrastructure and its myriad applications and technology?

So, the cleaning problem is not an unreasonable one to ponder, in my view. I appreciate Mr. Poet's comments on CO2 Wash, but wonder if something yet cheaper is possible.

Kit P


You drop into middle of a discussion without understand the topic or having the curtsey to read the entire thread. If you note several times I have qualified the source of biogas such as:

“Removing H2S and moisture for farm application is relatively simple. WWTP and LFG require much more complicated systems because of the bad stuff in the gas.”

E-P linked a DOE funded demonstration project for a new method if converting biogas from WWTP and LF to pipeline gas but it has not been commercially proven.

What E-P does not understand, just because you can do something, does not mean you should do it?

Based principles of minimizing environmental impact based on LCA or reducing dependence on foreign fossil fuel; there is no reason to put biogas into pipelines.


At the least, methane has its placce. But storage (both CNG and LNG)has problems. So what about adsorption? Is metal-organic frameworks key?

For example:

Please email me directly at, as well as responding here, if you would be willing to provide an update.


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