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UC Davis ITS researchers take a detailed look at water consumption and withdrawal requirements for ethanol

Mishra
Water consumption intensity of ethanol from corn grain and crop residue and the avoided/displaced water use credits assigned to coproducts: DGS and electricity. Credit ACS, Mishra and Yeh. Click to enlarge.

While a number of studies have tired to assess the water consumption required for ethanol production, the results differ by orders of magnitude, with estimates ranging from 1.1 to 335 L/vehicle kilometer traveled (VKT) for Iowa and from 59 to 214 L/VKT for Nebraska.

The major difference between these studies stems from the debate existing in the water life cycle analysis (LCA) literature regarding whether, and how, to include consumption of green water (GW), which comes from precipitation before and during the crop season and is stored as soil moisture, note UC Davis Institute of Transportation Studies (ITS) Gouri Shankar Mishra and Sonia Yeh in a new paper published in the ACS journal Environmental Science & Technology.

In their paper, Mishra and Yeh analyze the lifecycle water requirement consumption and withdrawal requirements of ethanol produced from corn and from crop residue.

To address the controversy regarding GW use, this study explicitly states the sources of water inputs (GW versus BW [blue water, i.e., surface water and groundwater] and surface water versus groundwater). Our water accounting system also considers different types of uses (consumptive, nonconsumptive, and withdrawal) and accounts for application losses, conveyance losses, water use of direct energy inputs throughout the life cycle, and coproduct credits.

—Mishra and Yeh

Comparison with fossil fuels
Water is required for crude oil recovery by water flooding, enhanced oil recovery via steam injection, and steam extraction of bitumen from oil sands and during refining of crude oil to produce gasoline.
BW consumption intensities of gasoline from conventional crude oil and Canadian oil sands range from 0.41 to 0.78 and from 0.29 to 0.62 L/VKT, respectively. A recent GAO report suggests the water intensity of gasoline from large oil shale deposits in the western United States could range from 0.29 to 1.01 L/VKT.
Assessing the differences in water impacts of biofuels and fossil fuels is more complicated than simply comparing the total water intensities, Mishra and Yeh note. The BW consumption of biofuels from rain-fed crops and residue is lower than that of gasoline, but orders of magnitude higher for those from irrigated crops.
Though the water intensity of fossil fuels is on average low compared with that of biofuels, oil sand production and shale oil development could result in substantial streamwater withdrawals and significant alteration of water flows during critical low river flow periods, groundwater depletion and contamination, and wastewater discharges.

Mishra and Yeh’s estimates of corn grain ethanol’s BW and GW consumption are lower than those of previous studies, due to the accounting of coproduct credits for water use, which they estimated to be 5% and 45% of the total BW used to produce ethanol from rain-fed and irrigated corn, respectively, and around 50% of GW in both cases.

They found that corn ethanol consumes 50-146 L/vehicle kilometer traveled (VKT) of BW and 1-60 L/VKT of GW for irrigated corn and 0.6 L/VKT of BW and 70-137 L/VKT of GW for rain-fed corn after coproduct credits. Extending the system boundary to consider application and conveyance losses and the water requirements of embodied energy increases the total BW withdrawal from 23% to 38% and BW + GW consumption from 5% to 16%.

They estimated that, in 2009, 15-19% of irrigation water was used to produce the corn required for ethanol in Kansas and Nebraska without coproduct credits and 8-10% after credits. Harvesting and converting the cob to ethanol reduces both the BW and GW intensities by 13%.

The BW and GW requirements of ethanol from corn grown in different regions provide useful information for local water resource management; for example, water use by ethanol can be compared with a region’s total water budget to identify potential water availability constraints and risks. However, such volumetric estimates do not consider differences in ecosystem or socioeconomic trade-offs as a result of differences in local hydrological conditions—specifically water “scarcity”.

Our method necessarily employs spatial and temporal aggregation. It sums across types of water consumption (BW and GW consumption and avoided water credits) in locations where the relative importance of water-related aspects may differ; thus, some results may carry no clear indication of potential social and/or environmental harm or trade-offs. Similarly, temporal aggregation of water use estimates ignores the interseasonal variability of water use and water scarcity and can therefore yield erroneous conclusions concerning seasonal water use competition.

Recent literature on freshwater LCA has developed regionally differentiated characterization factors that measure water scarcity at a watershed level and also account for temporal variability in water availability. Volumetric estimates of GW and BW may be converted using characterization factors to provide “stress-weighted” or “ecosystem-equivalent” water footprint estimates that can be compared across regions. Work is ongoing to use the explicit water inventory results to undertake impact analysis and accurately assess the effects of biofuel production on water resources.

—Mishra and Yeh

Resources

  • Gouri Shankar Mishra and Sonia Yeh (2011) Life Cycle Water Consumption and Withdrawal Requirements of Ethanol from Corn Grain and Residues. Environmental Science & Technology Article ASAP doi: 10.1021/es104145m

Comments

SJC

Corn is a major water user, the large leaves transpire water at a huge rate. That is why you grow corn grain for food/feed and use the stalks and cobs for fuels.

Nrb

As SJC indicated, the corn is grown for fuel/feed anyway. Also...

Water is one of the most renewable resources on the planet (remember learning about the water cycle in grade school?). Unlike California, the Corn Belt isn't on a desert.

http://www.all-water.org/H2O_Images/Water_cycle.png

HarveyD

Who is currently using corn stalks and cobs to produce fuel?

JMartin

Nrb - You must live in a wet area. In Colorado, if the water evaporates, it becomes renewable in Missouri or the Ohio valley. That does not do us much good. The same is true of water cooled electric production, whether coal or nuclear -- it is a poor use of water.

SJC

The Poet Corporation is beginning to produce ethanol from corn cobs, they estimate that the U.S. can produce 5 billion gallons of cellulose ethanol from cobs each year.

Nrb

JMartin, that's exactly my point. Some places are dry and some places are wet. I can understand being concerned with water usage in dry places (expensive to get), but those rules don't apply to wet places.

My issue is that many people often try to apply the same rules everywhere. I was watching a 'green' show on TV the other day where they'd trained a high schooler to say "Water is a limited resource. Once we use it, it's gone forever" (paraphrased). It drives me crazy that they're teaching kids this kind of stuff.

Let's conserve for the right reasons, not made up crap. Otherwise, we're misdirecting our efforts.

SJC

"Companies such as Iogen, POET Broin, and Abengoa are building refineries that can process biomass and turn it into ethanol, while companies such as Diversa, Novozymes, and Dyadic are producing enzymes which could enable a cellulosic ethanol future."

http://en.wikipedia.org/wiki/Cellulosic_biofuel_commercialization

SJC

“Our business model calls for us to build one corn cob plant, at a nameplate of around 25 mgy, and then building, owning, and operating one switchgrass-to-ethanol plant,”

http://ethanoltoday.com/index.php?option=com_content&task=view&id=5&Itemid=6&fid=66

wintermane2000

Again because fuel is more valuaable then food alot of corn will go into fuel for a very long time. You dont decide that the farmer does.

SJC

We all decide what the farmers do.

wintermane2000

Only if you paid more for your food which is exactly the problem. Food costs alot because it takes alot of fuel to make and we arnt going back there simply is no money in it.

SJC

Farm subsidies, price supports and other measures all affect what the farmers do. If we decided to take away the subsidy for corn grain ethanol but keep it on cellulose ethanol, we might see a shift in behavior.

HarveyD

Let us not accept claims/mandates versus real cellulosic ethanol production. For 2010 the national commercial production was about zero gallon. Estimates for 2011 have been revised down to 3.94 million gallons or to a mere 2% of original claims. Considering that the first cellulosic ethanol was produced over 100 years ago, the progress has been rather slow.

It seems that electrified vehicles (after a similar slow start) may gain ground against cellulosic ethanol production, specially in China and other Asian countries.

SJC

Ethanol is just one fuel, synthetic fuels have a better future. If anyone thinks that EVs are going to do the trick the next 10 years, they are fooling themselves and trying to fool others as well.

HarveyD

We may have a tendency to judge vehicles' future electrification by our own bias resistance to such vehicles. Our love for our ICE monsters is very deep, even if we not longer can produce enough oil to run them and the cost of oil importation is hurting our economy. At $100+ per gas bar visit, resistance to change may weaken.

There are 10+ million electrified units (2, 3 and 4 wheels) in use in China and the number is increasing by a few more millions every year.

By 2020, China may have close to 100 million electrified units in use and we may have at least one million units running on electrons. We may never catch up with China, but thats life.

SJC

I tend to refer to the U.S. and the projected sales of EVs over the next 10 years and how many are estimated to be on the roads in the U.S. by 2020. The projections I have seen do not flatten the demand curve for oil all that much.

wintermane2000

sjc again corn for fuel is more valueable even without any subs at all then it is for food. It has set a price floor that we arnt going to break.

SJC

Again, do not use food for fuel, use grain for food and stalks for fuel.

wintermane2000

As long as fuel is valued this high the grain will be bought for fuel in rather large amounts. Already many farmers are signing multi year agreements and ive heard some signing 5 year agreements. Its solid dependable income.

SJC

Yes, but they can sell the grain for food and the stalks for fuel DOUBLING their income.

wintermane2000

No your not getting it. They can make more money selling the grain for fuel and the stalks for fuel then selling the grain for food and the stalks for fuel.

Now that the system is running as well as it is its basicaly eaten away all the cheaper food crops.

AND after its gone to make fuel it comes back to be cattle feed which in most cases was where bit was going anyway. Just after making fuel it has less energy in it of course...

JRP3

And it's still more efficient to simply burn biomass in generating plants to power EV's than it is to distill it into fuel to power inefficient ICE's. Plus you don't need to use a food crop, any biomass will do.

SJC

Watch and see what develops. It is a world market for corn grain. The farmer does not turn the corn grain into ethanol the producer does, the farmer sells the grain and someone buys it, there is not much vertical integration.

If the farmers did make the ethanol we would not have seen corn grain speculators drive the price up and put the ethanol producers into a bind a few years ago. Farmers would have made all the money from the field to the ethanol wholesaler, but they did not and they do not.

HarveyD

Lets face it. Speculators and Wall Street scams do make more quick profits than farmers. Thats where we are at.

SJC

This is one of those Homer Simpson "DOH!" moments, companies build ethanol plants and have ONE feed stock, corn grain and then watch commodities speculators double the price of corn. One semester in business school will teach you that is not a good way to go.

There are many markets for corn grain, it is in just about all processed foods from corn oil to corn starch to corn syrup in soft drinks, breads and just about everything else on the supermarket shelf.

So basic business says look at the customers and demand, it is easy to speculate on corn grain prices when the demand is huge and growing. NOW look at the market for corn stalks and cobs. Not much of a market there, you can make fuels out of those and the only customers are your competitors.

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