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Part 6. Peak Soil: Why biofuels are not sustainable and a threat to America's National SecurityPart 6. The problems with Cellulosic Ethanol could drive you to drink. Many plants want animals to eat their seed and fruit to disperse them. Some seeds only germinate after going through an animal gut and coming out in ready-made fertilizer. Seeds and fruits are easy to digest compared to the rest of the plant, that's why all of the commercial ethanol and biodiesel are made from the yummy parts of plants, the grain, rather than the stalks, leaves, and roots. But plants don’t want to be entirely devoured. They’ve spent hundreds of millions of years perfecting structures that can’t easily be eaten. Be thankful plants figured this out, or everything would be mown down to bedrock. If we ever did figure out how to break down cellulose in our back yard stills, it wouldn't be long before the 6.5 billion people on the planet destroyed the grasslands and forests of the world to power generators and motorbikes (Huber 2006) Don Augenstein and John Benemann, who’ve been researching biofuels for over 30 years, are skeptical as well. According to them, “…severe barriers remain to ethanol from lignocellulose. The barriers look as daunting as they did 30 years ago”. Benemann says the EROEI can be easily determined to be about five times as much energy required to make cellulosic ethanol than the energy contained in the ethanol. The success of cellulosic ethanol depends on finding or engineering organisms that can tolerate extremely high concentrations of ethanol. Augenstein argues that this creature would already exist if it were possible. Organisms have had a billion years of optimization through evolution to develop a tolerance to high ethanol levels (Benemann 2006). Someone making beer, wine, or moonshine would have already discovered this creature if it could exist. The range of chemical and physical properties in biomass, even just corn stover (Ruth 2003, Sluiter 2000), is a challenge. It’s hard to make cellulosic ethanol plants optimally efficient, because processes can’t be tuned to such wide feedstock variation. Where will the Billion Tons of Biomass for Cellulosic Fuels Come From? The government believes there is a billion tons of biomass “waste” to make cellulosic biofuels, chemicals, and generate electricity with. The United States lost 52 million acres of cropland between 1982 and 2002 (NCRS 2004). At that rate, all of the cropland will be gone in 140 years. There isn’t enough biomass to replace 30% of our petroleum use. The potential biomass energy is miniscule compared to the fossil fuel energy we consume every year, about 105 exa joules (EJ) in the USA. If you burned every living plant and its roots, you’d have 94 EJ of energy and we could all pretend we lived on Mars. Most of this 94 EJ of biomass is already being used for food and feed crops, and wood for paper and homes. Sparse vegetation and the 30 EJ in root systems are economically unavailable – leaving only a small amount of biomass unspoken for (Patzek June 2006). Over 25% of the “waste” biomass is expected to come from 280 million tons of corn stover. Stover is what’s left after the corn grain is harvested. Another 120 million tons will come from soy and cereal straw (DOE Feedstock Roadmap, DOE Biomass Plan). There isn’t enough no-till corn stover to harvest. The success of biofuels depends on corn residues. About 80% of farmers disk corn stover into the land after harvest. That renders it useless -- the crop residue is buried in mud and decomposing rapidly. Only the 20 percent of farmers who farm no-till will have stover to sell. The DOE Billion Ton vision assumes all farmers are no-till, 75% of residues will be harvested, and fantasy corn and wheat yields 50% higher than now are reached (DOE Billion Ton Vision 2005). Many tons will never be available because farmers won’t sell any, or much of their residue (certainly not 75%). Many more tons will be lost due to drought, rain, or loss in storage. Sustainable harvesting of plants is only 1/200th at best. Plants can only fix a tiny part of solar energy into plant matter every year -- about one-tenth to one-half of one percent new growth in temperate climates. To prevent erosion, you could only harvest 51 million tons of corn and wheat residues, not 400 million tons (Nelson, 2002). Other factors, like soil structure, soil compression, water depletion, and environmental damage weren’t considered. Fifty one million tons of residue could make about 3.8 billion gallons of ethanol, less than 1% of our energy needs. Using corn stover is a problem, because corn, soy, and other row crops cause 50 times more soil erosion than sod crops (Sullivan 2004) or more (Al-Kaisi 2000), and corn also uses more water, insecticides and fertilizers than most crops (Pimentel 2003). The amount of soy and cereal straw (wheat, oats, etc) is insignificant. It would be best to use cereal grain straw, because grains use far less water and cause far less erosion than row crops like corn and soybeans. But that isn’t going to happen, because the green revolution fed billions more people by shortening grain height so that plant energy went into the edible seed, leaving little straw for biofuels. Often 90% of soybean and cereal straw is grown no-till, but the amount of cereal straw is insignificant and the soybean residues must remain on the field to prevent erosion Energy Crops Poor, erodible land. There aren’t enough acres of land to grow significant amounts of energy crops. Potential energy crop land is usually poor quality or highly erodible land that shouldn’t be harvested. Farmers are often paid not to farm this unproductive land. Many acres in switchgrass are being used for wildlife and recreation. Few suitable bio-factory sites. Biorefineries can’t be built just anywhere – very few sites could be found to build switchgrass plants in all of South Dakota (Wu 1998). Much of the state didn’t have enough water or adequate drainage to build an ethanol factory. The sites had to be on main roads, near railroad and natural gas lines, out of floodplains, on parcels of at least 40 acres to provide storage for the residues, have electric power, and enough biomass nearby to supply the plant year round. No energy crop farmers or investors. Farmers won’t grow switchgrass until there’s a switchgrass plant. Machines to harvest and transport switchgrass efficiently don’t exist yet (Barrionuevo 2006). The capital to build switchgrass plants won’t materialize until there are switchgrass farmers. Since “ethanol production using switchgrass required 50% more fossil energy than the ethanol fuel produced” (Pimentel 2005), investors for these plants will be hard to find. Energy crops are subject to Liebig’s law of the minimum too. Switchgrass may grow on marginal land, but it hasn’t escaped the need for minerals and water. Studies have shown the more rainfall, the more switchgrass you get, and if you remove switchgrass, you’re going to need to fertilize the land to replace the lost biomass, or you’ll get continually lower yields of switchgrass every time you harvest the crop (Vogel 2002). Sugar cane has been touted as an “all you need is sunshine” plant. But according to the FAO, the nitrogen, phosphate, and potassium requirements of sugar cane are roughly similar to maize (FAO 2004). Bioinvasive Potential. These fast-growing disease-resistant plants are potentially bioinvasive, another kudzu. Bioinvasion costs our country billions of dollars a year (Bright, 1998). Johnson grass was introduced as a forage grass and it’s now an invasive weed in many states. Another fast-growing grass, Miscanthus, is now being proposed as a biofuel. It’s been described as “Johnson grass on steroids” (Raghu 2006). Sugar cane: too little to import. Brazil uses oil for 90% of their energy, and 17 times less oil (Jordan 2006). Brazilian ethanol production in 2003 was 3.3 billion gallons, about the same as the USA in 2004, or 1% of our transportation energy. Brazil uses 85% of their cane ethanol, leaving only 15% for export. Sugar Cane: can’t grow it here. Although we grow some sugar cane despite tremendous environmental damage (WWF) in Florida thanks to the sugar lobby, we’re too far north to grow a significant amount of sugar cane or other fast growing C4 plants. Wood ethanol is an energy sink. Ethanol production using wood biomass required 57% more fossil energy than the ethanol fuel produced (Pimentel 2005). Wood is a nonrenewable resource. Old-growth forests had very dense wood, with a high energy content, but wood from fast-growing plantations is so low-density and low calorie it’s not even good to burn in a fireplace. These plantations require energy to plant, fertilize, weed, thin, cut, and deliver. The trees are finally available for use after 20 to 90 years – too long for them to be considered a renewable fuel (Odum 1996). Nor do secondary forests always come back with the vigor of the preceding forest due to soil erosion, soil nutrition depletion, and mycorrhizae destruction (Luoma 1999). There’s not enough wood to fuel a civilization of 300 million people. Over half of North America was deforested by 1900, at a time when there were only 75 million people (Williams 2003). Most of this was from home use. In the 18th century the average Northeastern family used 10 to 20 cords per year. At least one acre of woods is required to sustainably harvest one cord of wood (Whitney 1994). Energy crop limits. Energy crops may not be sustainable due to water, fertilizer, and harvesting impacts on the soil (DOE Biomass Roadmap 2005). Like all other monoculture crops, ultimately yields of energy crops will be reduced due to “pest problems, diseases, and soil degradation” (Giampetro, 1997). Energy crop monoculture. The “physical and chemical characteristics of feedstocks vary by source, by year, and by season, increasing processing costs” (DOE Feedstock Roadmap). That will encourage the development of genetically engineered biomass to minimize variation. Harvesting economies of scale will mean these crops will be grown in monoculture, just as food crops are. That’s the wrong direction – to farm with less energy there’ll need to be a return to rotation of diverse crops, and composted residues for soil nutrition, pest, and disease resistance. A way around this would be to spend more on researching how cellulose digesting microbes tackle different herbaceous and woody biomass. The ideal energy crop would be a perennial, tall-grass prairie / herbivore ecosystem (Tilman 2006). Farmers aren’t Stupid: They won’t sell their residues Farmers are some of the smartest people on earth or they’d soon go out of business. They have to know everything from soil science to commodity futures. Crop production is reduced when residues are removed from the soil. Why would farmers want to sell their residues? Erosion, water, compression, nutrition. Harvesting of stover on the scale needed to fuel a cellulosic industry won’t happen because farmers aren’t stupid, especially the ones who work their own land. Although there is a wide range of opinion about the amount of residue that can be harvested safely without causing erosion, loss of soil nutrition, and soil structure, many farmers will want to be on the safe side, and stick with the studies showing that 20% (Nelson, 2002) to 30% (McAloon et al., 2000; Sheehan, 2003) at most can be harvested, not the 75% agribusiness claims is possible. Farmers also care about water quality (Lal 1998, Mann et al, 2002). And farmers will decide that permanent soil compression is not worth any price (Wilhelm 2004). As prices of fertilizer inexorably rise due to natural gas depletion, it will be cheaper to return residues to the soil than to buy fertilizer. Residues are a headache. The further the farmer is from the biorefinery or railroad, the slimmer the profit, and the less likely a farmer will want the extra headache and cost of hiring and scheduling many different harvesting, collection, baling, and transportation contractors for corn stover. Residues are used by other industries. Farm managers working for distant owners are more likely to sell crop residues since they’re paid to generate profits, not preserve land. But even they will sell to the highest bidder, which might be the livestock or dairy industries, furfural factories, hydromulching companies, biocomposite manufacturers, pulp mills, or city dwellers faced with skyrocketing utility bills, since the high heating value of residue has twice the energy of the converted ethanol. Investors aren’t stupid either. If farmers can’t supply enough crop residues to fuel the large biorefinery in their region, who will put up the capital to build one? Can the biomass be harvested, baled, stored, and transported economically? Harvesting. Sixteen ton tractors harvest corn and spit out stover. Many of these harvesters are contracted and will continue to collect corn in the limited harvest time, not stover. If tractors are still available, the land isn’t wet, snow doesn’t fall, and the stover is dry, three additional tractor runs will mow, rake, and bale the stover (Wilhelm 2004). This will triple the compaction damage to the soil (Troeh 2005), create more erosion-prone tire tracks, increase CO2 emissions, add to labor costs, and put unwanted foreign matter into the bale (soil, rocks, baling wire, etc). So biomass roadmaps call for a new type of tractor or attachment to harvest both corn and stover in one pass. But then the tractor would need to be much larger and heavier, which could cause decades-long or even permanent soil compaction. Farmers worry that mixing corn and stover might harm the quality of the grain. And on the cusp of energy descent, is it a good idea to build an even larger and more complex machine? If the stover is harvested, the soil is now vulnerable to erosion if it rains, because there’s no vegetation to protect the soil from the impact of falling raindrops. Rain also compacts the surface of the soil so that less water can enter, forcing more to run off, increasing erosion. Water landing on dense vegetation soaks into the soil, increasing plant growth and recharging underground aquifers. The more stover left on the land, the better. Baling. The current technology to harvest residues is to put them into bales of hay. Hay is a dangerous commodity -- it can spontaneously combust, and once on fire, can’t be extinguished, leading to fire loss and increased fire insurance costs. Somehow the bales have to be kept from combusting during the several months it takes to dry them from 50 to 15 percent moisture. A large, well drained, covered area is needed to vent fumes and dissipate heat. If the bales get wet they will compost (Atchison 2004). Baling was developed for hay and has been adapted to corn stover with limited success. Biorefineries need at least half a million tons of biomass on hand to smooth supply bumps, much greater than any bale system has been designed for. Pelletization is not an option, it’s too expensive. Other options need to be found. (DOE Feedstock Roadmap) To get around the problems of exploding hay bales, wet stover could be collected. The moisture content needs to be around 60 percent, which means a lot of water will be transported, adding significantly to the delivery cost. Storage. Stover needs to be stored with a moisture content of 15% or less, but it’s typically 35-50%, and rain or snow during harvest will raise these levels even higher (DOE Feedstock Roadmap). If it’s harvested wet anyhow, there’ll be high or complete losses of biomass in storage (Atchison 2004). Residues could be stored wet, as they are in ensilage, but a great deal of R&D are needed and to see if there are disease, pest, emission, runoff, groundwater contamination, dust, mold, or odor control problems. The amount of water required is unknown. The transit time must be short, or aerobic microbial activity will damage it. At the storage site, the wet biomass must be immediately washed, shredded, and transported to a drainage pad under a roof for storage, instead of baled when drier and left at the farm. The wet residues are heavy, making transportation costlier than for dry residues, perhaps uneconomical. It can freeze in the winter making it hard to handle. If the moisture is too low, air gets in, making aerobic fermentation possible, resulting in molds and spoilage. Transportation. Although a 6,000 dry ton per day biorefinery would have 33% lower costs than a 2,000 ton factory, the price of gas and diesel limits the distance the biofuel refinery can be from farms, since the bales are large in volume but low in density, which limits how many bales can be loaded onto a truck and transported economically. So the “economy of scale” achieved by a very large refinery has to be reduced to a 2,000 dry ton per day biorefinery. Even this smaller refinery would require 200 trucks per hour delivering biomass during harvest season (7 x 24), or 100 trucks per day if satellite sites for storage are used. This plant would need 90% of the no-till crop residues from the surrounding 7,000 square miles with half the farmers participating. Yet less than 20% of farmers practice no-till corn and not all of the farmland is planted in corn. When this biomass is delivered to the biorefinery, it will take up at least 100 acres of land stacked 25 feet high. The average stover haul to the biorefinery would be 43 miles one way if these rosy assumptions all came true (Perlack 2002). If less than 30% of the stover is available, the average one-way trip becomes 100 miles and the biorefinery is economically impossible. There is also a shortage of truck drivers, the rail system can’t handle any new capacity, and trains are designed to operate between hubs, not intermodally (truck to train to truck). The existing transportation system has not changed much in 30 years, yet this congested, inadequate infrastructure somehow has to be used to transport huge amounts of ethanol, biomass, and byproducts (Haney 2006). Cellulosic Biorefineries (see Appendix for more barriers) There are over 60 barriers to be overcome in making cellulosic ethanol in Section III of the DOE “Roadmap for Agriculture Biomass Feedstock Supply in the United States” (DOE Feedstock Roadmap 2003). For example: “Enzyme Biochemistry. Enzymes that exhibit high thermostability and substantial resistance to sugar end-product inhibition will be essential to fully realize enzyme-based sugar platform technology. The ability to develop such enzymes and consequently very low cost enzymatic hydrolysis technology requires increasing our understanding of the fundamental mechanisms underlying the biochemistry of enzymatic cellulose hydrolysis, including the impact of biomass structure on enzymatic cellulose decrystallization. Additional efforts aimed at understanding the role of cellulases and their interaction not only with cellulose but also the process environment is needed to affect further reductions in cellulase cost through improved production”. No wonder many of the issues with cellulosic ethanol aren’t discussed – there’s no way to express the problems in a sound bite. It may not be possible to reduce the complex cellulose digesting strategies of bacteria and fungi into microorganisms or enzymes that can convert cellulose into ethanol in giant steel vats, especially given the huge physical and chemical variations in feedstock. The field of metagenomics is trying to create a chimera from snips of genetic material of cellulose-digesting bacteria and fungi. That would be the ultimate Swiss Army-knife microbe, able to convert cellulose to sugar and then sugar to ethanol. There’s also research to replicate termite gut cellulose breakdown. Termites depend on fascinating creatures called protists in their guts to digest wood. The protists in turn outsource the work to multiple kinds of bacteria living inside of them. This is done with energy (ATP) and architecture (membranes) in a system that evolved over millions of years. If the termite could fire the protists and work directly with the bacteria, that probably would have happened 50 million years ago. This process involves many kinds of bacteria, waste products, and other complexities that may not be reducible to an enzyme or a bacteria. Finally, ethanol must be delivered. A motivation to develop cellulosic ethanol is the high delivery cost of corn grain ethanol from the Midwest to the coasts, since ethanol can’t be delivered cheaply through pipelines, but must be transported by truck, rail, or barge (Yacobucci 2003). The whole cellulosic ethanol enterprise falls apart if the energy returned is less than the energy invested or even one of the major stumbling blocks can't be overcome. If there isn’t enough biomass, if the residues can’t be stored without exploding or composting, if the oil to transport low-density residues to biorefineries or deliver the final product is too great, if no cheap enzymes or microbes are found to break down lignocellulose in wildly varying feedstocks, if the energy to clean up toxic byproducts is too expensive, or if organisms capable of tolerating high ethanol concentrations aren’t found, if the barriers in Appendix A can’t be overcome, then cellulosic fuels are not going to happen. If the obstacles can be overcome, but we lose topsoil, deplete aquifers, poison the land, air, and water, what kind of Faustian bargain is that? Scientists have been trying to solve these issues for over thirty years now. Nevertheless, this is worthy of research money, but not public funds for commercial refineries until the issues above have been solved. This is the best hope we have for replacing the half million products made from and with fossil fuels, and for liquid transportation fuels when population falls to pre-coal levels. |
SearchLatest NewsNetroots Nation is going on right now - these links will take you to live blogs of the past two year's presentations: The Energy Smart Communities Act of 2007What people are saying about EA2020Does a new century's government need to approach problems differently the last century's? What's cool about Energize America, if I understand it, is that it decentralizes the solution, rather than just creating another assembly line program, and relies on local markets. Recent blog posts
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