Ethanol from Biomass: A Sustainable Option?
The Promise of Cellulosic Ethanol
I have mentioned a couple of times the research I was involved in during graduate school. I have provided a couple of links (under “Links”) that describe this research in detail. Briefly, we were trying to turn biomass (switchgrass, corn stover, wheat straw, and municipal solid waste) into ethanol and various organic acids and ketones. Biomass consists of many organic components, but it is primarily the cellulose component that gets turned into ethanol, hence the term cellulosic ethanol.
Cellulosic ethanol has two major advantages, and one major disadvantage over ethanol from grain. The first major advantage is that large fossil fuel inputs in the form of fertilizer are not required to produce the biomass. Therefore, cellulosic ethanol has a much better energy return on energy invested (EROI) than grain ethanol. The second advantage is that the feed stock will be cheap, or even free (in the case of municipal solid waste, you can earn money by just accepting the waste). The disadvantage, however, is the reason cellulosic ethanol has yet to make a major impact. The enzymes required to free the fermentable sugars from the cellulose are very expensive. Historically, these enzymes have added as much as $5.00 a gallon to the cost of producing cellulosic ethanol. (1) However, substantial R&D efforts by a number of companies have brought the costs of these enzymes down to around $0.30 per gallon of ethanol.
One idea that I had in graduate school was the use of termites to do the conversion in our bioreactors. To my knowledge, I was the first person to ever try this. I got some butanol by doing this, but with a very low yield. The reactor probably also made methane, but we only looked at the liquid products. Perhaps if I could have very accurately replicated the termite gut chemistry I could have gotten yields up. It still makes sense to me that since termites are so efficient at converting cellulose, that would be a good place to look for a template organism for a bit of genetic engineering. It was my opinion then, and it is my opinion now, that the future of cellulosic ethanol hinges on genetically engineered microorganisms.
It is safe to say that while the gap has narrowed, cellulosic ethanol is still more expensive to produce than grain-ethanol. However, barring the kind of quantum leap I discussed in my previous essay, grain-ethanol has little upside potential. In addition, even if we turned the entire U.S. corn crop into ethanol, it would supply no more than 10% of the current fuel demand in the United States. (2) Given the facts that 1). The energy balance for grain ethanol is not that great; 2). We don’t grow enough grain to significantly lower our fossil fuel usage by turning it into ethanol; 3). Soil is eroded and fertilizer and pesticide runoffs contribute to water pollution as a result of large-scale corn farming; one wonders why this is even a topic worthy of discussion. Forget grain ethanol. If the government is going to force ethanol into the fuel system, make it cellulosic ethanol. I for one don’t mind paying $0.30 more a gallon for something that actually has a chance to be sustainable. However, many projections indicate that cellulosic ethanol will cost substantially less than grain ethanol in the not-too-distant future. A story in Business Week last year (3) reported:
Last December the bipartisan National Commission on Energy Policy released a report, Ending the Energy Stalemate, that analyzed the potentials of various alternative fuels, including both types of ethanol (which is just an industrial grade of alcohol). Only cellulosic ethanol got a decisive thumbs-up. By 2020, the commission predicts, its production cost could be less than 80 cents a gallon. In stark contrast, after 20 years producing grain ethanol, it still costs $1.40 a gallon to produce — roughly twice as much as gasoline.
Is This Enough to Ensure Sustainability?
Let’s not kid ourselves. It is going to take more than all the ethanol we can possibly produce to replace our current usage of fossil fuels. I watched a CNN special a week ago on the topic of peak oil. Frank Sesno visited Brazil, where they make ethanol from sugar cane. When it was explained that Brazil is supplying much of their own fuel from homegrown ethanol, Sesno asked “Why isn’t the U.S. doing this?” There are a couple of things that Sesno apparently missed. First, sugar cane is the optimum crop for producing ethanol, because the ethanol yield per acre is about twice what you can get from corn. Unfortunately, there are few areas in the U.S. that are ideal for sugar cane production. Brazil is currently exporting ethanol to the U.S. and Europe, and they can ship it to the U.S. for cheaper than we can make it here. (So, we slap a tariff on it to make sure they can’t undercut our corn-ethanol producers). The 2nd thing Sesno apparently didn’t notice was all of the compact cars on Brazil’s roads. They showed a clip of him on the highway, and every car on the road was a compact. Therefore, their per capita fuel demand is far lower than ours.
To put the U.S. situation in perspective, consider a recent article on sustainability in Sweden. (4) The Swedish government has set a goal of being totally independent from oil by 2020. The article reports that today, Sweden only relies on petroleum for 34% of their energy needs, and renewable energy supplies 25% of their energy. However, Sweden relies heavily on Brazil for their ethanol:
Today the most effective source of ethanol is sugar cane. Brazil produces ethanol from it and Sweden obtains most of its ethanol from Brazil. But the country also already produces a fourth of its ethanol from Swedish wheat. Neither system is fully satisfactory in terms of energy output and the effects on the environment involved.
Sweden’s highways, like the rest of Europe’s (and Brazil’s), are dominated by small, fuel-efficient cars. Given that 1). Sweden is far ahead of the U.S. in their march toward energy independence; 2). Their government has made a serious commitment toward energy independence; 3). Petroleum is already a minor contributor toward their energy needs; 4). Renewable energy already supplies 25% of their energy needs; 5). Their per capita energy usage is much lower than ours; and 6). They think it will still be 2020 before they achieve energy independence; it should be clear just what a pipe dream energy independence is for the U.S. at the moment. Barring a concerted effort at conservation in the U.S., we don’t have a prayer of energy independence. We simply won’t be able to make enough ethanol to meet our demands. A combination of renewable sources might be able to meet our current needs, but it is going to require a huge effort on our part. Even then, at some point we are going to have to come to grips with sustainability. That will be the topic of an upcoming essay.
If ethanol is going to be mandated into our fuel supply, we will be far better off utilizing waste biomass instead of grain. The energy balance is more favorable for cellulosic ethanol, and it is projected to have the potential to compete with gasoline without the need for subsidies. However, due to our very high per capita energy usage, we are kidding ourselves to think that we can meet our needs with renewable energy unless we reduce our consumption.