Biofuels and compostable plastics: The future or just a bunch of cornstalks?
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As oil prices rise, the search for petroleum alternatives intensifies. Some companies are betting big on biomass. Think ethanol made from corn stalks or prairie grass. Or the corn-based plastic known as “PLA.”
But David Fridley, staff scientist at the Lawrence Berkeley Lab and Post Carbon Institute fellow, is a skeptic. Here’s an excerpt from my recent interview with Fridley for a story on oil alternatives in laundry detergent:
Gardner: What’s the biggest challenge in moving away from petroleum-based fuels and chemicals to bio-based alternatives?
Fridley: Let’s start with the issue of scale. The size of the world plastics market today, and this is just plastics, not all the other products we make with petrochemicals, is about 220 million tons.
For bioplastics, we now have a global capacity to produce about 300,000 tons so to even make a substantial dent in our current use of petroleum and natural gas for plastics production, we’d have to enormously increase our investment in manufacturing facilities. But more important, we’d have to enormously increase the availability of biomass raw materials to use as the feedstock. And that is a true limiting factor on the scalability for alternatives to petrochemicals.
Gardner: Why is that a limiting factor? We don’t have enough land?
Fridley: That’s part of it. There are trade-offs involved in everything. Let’s take an example for existing crops in the U.S. The most widely planted crop in the United States is corn. It takes up about 25 percent of all the planted acres in the United States. After you harvest corn what you have left over is the residual stalks and leaves. This is what is called corn stover. And that corn stover is the largest volume agricultural residue available in the country. But if we removed, let’s say, half of that corn stover from the fields and we used it as a feed stock in the production of cellulosic ethanol, the output would only replace about a quarter of California’s gasoline consumption. At the same time you’d be removing nutrients from the soil, so you’d have to increase the production of chemical fertilizers to replace the nutrients. You’d also increase soil erosion. You’d reduce the capacity of the soil to hold moisture. So you’d have environmental consequences, yet with very little ability to supplant the scale of the petroleum we’re using today.
In a bio-based economy there are three fundamental inputs. Land, water and nutrients. All of these are in limited supply. The U.S. has no more arable land in 2011 than we did in 1911. So as a bioeconomy grows, the farmers who are in charge of this land, water and nutrients are going to have to make a decision. Are we going to grow bio-energy crops for bio-products and bio-energy or are we going to plant food? And the answer is going to be whichever market bids higher for that resultant product. And as we know given our voracious appetite for energy, the energy market is going to then be setting the price for food because the food market will have to be priced at the level of energy to bid away the land, water and nutrients for food supply. For me, this is extremely poor public policy.
Gardner: What about using algae instead of food crops and crop waste? Might that be a better alternative, environmentally?
Fridley: Algae’s very interesting. The main problem is that you can’t let algae be. You can’t just toss some algae in a pond and come back later and harvest the scum off and make it into fuel. If you’re serious about making fuel out of algae, you have to manage it. And if you’re going it in scale, you have to have open ponds. And if you’re going to have open ponds, you’re going to have to control their temperatures. And if you want them to grow optimally for big production you’re going to have to provide them food and concentrated CO2 and you have to keep the water moving and you have to strain that algae out of the water. And moving water is extremely energy-intensive. So once you’ve gone through this entire process of growing, processing, harvesting and straining algae, you’re actually consuming more energy than you are actually getting out of the algae itself.
Gardner: So where do you see this bio-based movement going?
Fridley: All of these products, such as biomass ethanol or biodegradable plastics or algae-based diesel, likely have niche applications in our future and we’re going to have to use them. For example, I think farm machinery will very likely need to look at biomass produced on the farms themselves as their fuel source. But to suggest that biomass alone, or any combination of biomass products could supplant the scale of usage of petroleum that we have today I think is extremely naïve.
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