Biofuels: ethanol produced from cellulose biomass, neither sustainable nor environmentally benign

Biofuels: ethanol produced from cellulose biomass, neither sustainable nor environmentally benign

By Mae-Wan Ho

Cellulose ethanol can be produced from a wide variety of agricultural residues (corn, cereal, sugar cane, etc.), plant residues from industrial processes (paper pulp, sawdust) and from energy crops such as switchgrass '.

Cellulose ethanol the "Green Gold"

The main limitation of obtaining ethanol from plant material is that most sugars, with the exception of starch from the cob, are not viable for fermentation with bacteria or other microbes. The sugars are enclosed in cellulose, the fibrous material that represents 75 or 85% of the plant, the rest is lignin, the material of wood.

However, a cocktail of enzymes called cellulases can break down cellulose into its sugar units, which can be fermented by microbes, converting sugars into ethanol (see box). That means grass, straw, and other residues from agricultural crops can be turned into ethanol. This has been termed as the 'green gold' that could replace the imported crude 'black gold' and is seen as a potential to sustainably reduce the consumption of fossil fuels.

"It is at least as feasible as using hydrogen as an energy source for the sustainable transportation sector," said the National Resources Defense Council (NRDC) and the Union of Concerned Scientists (UCC). ).

Shell Oil predicted that the global market for biofuels such as 'cellulose ethanol' would grow to over $ 10 trillion by 2012.

A study funded by the Energy Foundation and the National Commission for Energy Policies concluded that "biofuels together with more efficient vehicles and smart growth could reduce the dependence of the transportation sector on oil by two-thirds by 2050 in a sustainable way." 'Smart growth' is a planning term that means growth that maximizes the sustainable development of cities in relation to transportation and other ways of reducing energy use.

Cellulose ethanol can be produced from a wide variety of agricultural residues (corn, cereal, sugar cane, etc.), plant residues from industrial processes (paper pulp, sawdust) and from energy crops such as switchgrass '.

Dartmouth Professor of Engineering Lee Lynd has been working with the Gorham Paper Mill to convert paper pulp into ethanol. Lynd says "this is really a negative cost product, and the fact that it's pretreated eliminates a step in the process."

The Masada Oxynol company is planning to build a plant in Middletown, New York, to process municipal waste and convert it into ethanol. After recovering the recyclables, an acid hydrolysis will be used to convert the plant material into sugars. "The plant will have both economic and environmental benefits," said David Webster, Vice President of Masada. The process reduces or eliminates the need for fillers. Waste from the process includes lignin and ash. The lignin will be recovered through burning to make the plant energy self-sufficient and the ash can be used as fertilizer.

Reducing the cost of production

The cellulases that are needed to break down cellulose so far are obtained from fungi, in particular from Trichoderma reesei. NREL scientists have investigated other sources such as bacteria Acdiothermus cellulolyticus, found in the hot springs of Yellowstone National Park. But exogluconase bacteria are normally not as good as fungus, although they tolerate high temperatures. The next step is to combine high temperature tolerance with the efficiency of the fungus enzyme. NREL and DOE have contracted with the largest enzyme companies, Genecor International and Novozymes to reduce cellulase production costs to an average of $ 0.10-0.20 per gallon of ethanol and they have succeeded (1).

Another improvement is in relation to the simultaneous action of the enzyme and the fermenting microbes, so that while the sugars are produced by the cellulases, the microbes ferment the glucose, converting it into ethanol (3). The Logen Corporation in Ottawa, Canada (4) was the first to develop the process for obtaining ethanol from cellulose. It has built the first and only demonstration plant to convert cellulose biomass into ethanol. The plant processes 40 tons of wheat straw per day, Logen became the first company to commercialize ethanol from plant material in April 2004. The main consumer so far is the Canadian government, which together with the US government. (particularly DOE's NREL) has invested millions of dollars to help market cellulose ethanol.

How cellulases convert cellulose into reserves for ethanol production

The crystalline unit of cellulose is composed of hundreds of strips, each strip contains hundreds of glucose units attached. The cellulose is wrapped in a hemicellulose and lignin sheath, which protects the cellulose from decomposition. Hemicellulose is easier to break down than cellulose itself (2). A combination of mild heat, pressure, and acid breaks down hemicellulose into its mixed sugar components, primarily silose.

Scientists at the Department of Energy's (DOE) National Laboratory for Renewable Energy (NREL) used sulfuric acid to decompose the hemicellulose-lignin sheath by reacting with water, exposing the cellulose.

To hydrolyze cellulose chemically requires high temperatures and pressure and strong acids, this implies quite expensive equipment; which is why cellulase enzymes have been sought to do the job.
Unlike humans who cannot digest cellulose, cows, termites, and fungi can. Some bacteria, fungi, and insects produce cellulase, other animals use cellulase-producing bacteria in their digestive systems.

Most cellulases are made up of three enzyme complexes that work together to hydrolyze cellulose. First the endolucanase breaks down one of the chains within the cellulose crystal structure, then the exoglucanase attracts one of the loose ends and stretches the cellulose chain destroying the structure, cutting the cellulose units into two glucose units. Finally beta-glucosidase splits the two units into two glucose molecules, which can be fermented in ethanol.

Is cellulose ethanol sustainable?

A preliminary study of the life cycle of cellulose ethanol showed that greenhouse gas emissions are reduced by 89% on the use of oil. In contrast, ethanol fermented from sugar reduces greenhouse gases by an average of 13%. (5).

Energy production appears to be the best of all, with a 1.98 investment / profit ratio, which means that each unit of energy invested produces almost 2 units of energy profit from the production of cellulose ethanol; but possibly this is an exaggeration due to flaws in the accounting processes.

Can US agriculture sustain a large-scale cellulose ethanol production system? Is there enough land? Can enough biomass be produced without impacting the cost of agricultural land, competing with food production, and without damaging the environment?

The answer to this question varies from no to definite yes, depending on research efforts, innovative technology, and government policies (1).

One proposal estimates that to produce 50 billion gallons of ethanol per year from cellulose biomass, the waste stream would only provide 40 or 50% of the raw material, the rest would have to come from energy crops such as corn and switch grass, which would cause great impacts to the agricultural system.

Levels higher than this would have impacts on the cost of agricultural land and competition with food production.

The United States has set the goal for gasoline consumption for cars and trucks by 2050 at 290 trillion gallons.

Increasing vehicle efficiency to 50 mpg. or more and including smart growth policies, consumption could be reduced to 108 trillion gallons by 2050.

A report from NRDC , Growing Energy (6) says that the number of gallons of ethanol currently produced for each dry ton of biomass in the United States is 50 gallons, or 208.93 liters (a poor comparison in relation to 371.75 liters per ton of corn (7 ).

If the predictions made for switch grass of 12.4 dry tons per acre (27.77 tons per hectare) - which is more than double the current average of 5 dry tons per acre - so it is estimated that 114 Ha. dedicated to the cultivation of switch grass they could provide enough biomass to produce 165 billion gallons of ethanol (equivalent to 108 billion gallons of gasoline).

This would consume 26.4% of the total production of the United States, or 12.2% of the total agricultural land, and would surely impact food production.

One idea to produce biofuels economically and efficiently is to develop bio-refineries, analogous to oil refineries, where crude is converted into fuels and secondary products such as fertilizers and plastics. In the case of bio-refineries, the plant's biomass would produce a variety of products such as animal feed, fuels, chemicals, polymers, lubricants, glues, fertilizers, and energy.

NREL's John Sheehan has been using a software drill to see the bio-refinery layout. Sheehan thinks the issue of scale is an important issue. He has found that bio-refineries would need to process 5,000 to 10,000 tons of biomass per day to be economically viable. Below 2,000 per day, the cost of capital is high.

A DOE and USDA study published in April 2005 concludes that forests and agricultural lands have the potential to provide a 7-fold increase in biomass than is currently used for biomass energy and products - in excess of 1.3 billion tons. dry - which is enough to satisfy more than a third of the current demand for the use of transportation fuels.

More than 25% would come from the extensive use of forest management and 75% from the intensive management of agricultural lands. Most of the primary resources would be residues from logging and fuel treatment (to reduce fire hazards) from forests, and residues from agricultural products from agricultural land.

These figures are based, among other things, on (optimistic) projections of increased crop production, especially by 50 percent in the largest products for bioenergy, planted on unused land including 8m acres previously used for cultivation. soy.

It is clear that unless consumption is reduced from current levels, biofuels from energy crops will not be able to replace fossil fuels without impacting food production.

Future Developments

Another difficulty is that 27% of the biomass of the plant is composed of sugars other than glucose, such as hemicellulose (for example xylose). These sugars are not fermented by the usual microorganisms.

Cellulose constitutes 40-50 percent of the dry weight, and hemicellulose 20-35%.

Lonnie Ingram, a professor of microbiology at the University of Florida in the Institute of Food and Agriculture, made the headlines (9) because his research team has genetically created a type of bacteria E. coli to produce ethanol from xylose (10). It has been commercialized with the help of the US DOE. The company, BC International Corp., located in Dedham, Mass., Has exclusive rights to the use and license of this genetically modified bacteria.

This transgenic bacteria from Escherichia coli was created by transferring the genes necessary for the fermentation of sugars - decarboxylase pyruvate and dehydrogen alcohol - from the bacteria Zymomanas mobilis, and fermented xylose produces ethanol at 95% of the theoretical level (11).

Greg Luli, vice president of BC International's research team, said the company has plans to build a plant to convert 30 million gallons of biomass into ethanol in Jennings, Louisiana, which is expected to be operational by the end of 2006. Waste of the sugarcane industry in Louisiana will be the main raw material for the plant.

Parallel initiatives are taking place in Europe. The Swiss company Etek Etholtekhnik AB announced that it will open a pilot plant to produce 400-500 liters of ethanol per day from 2 tons of dry biomass (12). The plant is designed to perform two steps, dilute acid hydrolysis and a combination with enzymes.

Although the raw material is light wood, other types of biomass such as hardwoods and annual crops such as straw will also be tested.

The pilot plant will be located in Ornskildsvik in northern Switzerland, close to a pulp sulfate ethanol plant. Three Universities in the region - Umea University, Mid Sweden University and Lulea Technical University - have their own plant.

Not yet economically viable or sustainable

One of the problems with the technology of fermentation of xylose with bacteria, as summarized by the group of professors from the Massachusetts Institute of Technology (MIT) in a document submitted to the MIT Energy Committee (13), is that the ethanol produced is quite diluted, 5-6% maximum, compared to 12% yeast fermented corn starch.

Lonnie Ingram's bacteria produce 4.5% ethanol solution (14). The reason is because some compounds accumulate during the fermentation of the mixture of sugars in the biomass, inhibiting bacterial growth.

In other words, the bacteria produce beer and not wine; and the extra water needed and the extra energy to distill the ethanol would render the process economically unviable or sustainable.

The MIT professors also question whether the idea of ​​making a biorefinery for other products generated from fermentation is economically viable. They propose using biotechnology to create microorganisms that can overcome their growth inhibition and thus improve the production of ethanol from biomass.

If they do this, they will have to ensure that the bacteria do not escape to the environment, and this applies to any other bacteria that are generated to produce cellulose ethanol.

A few years ago, soil scientist Elaine Ingham and her student Michael Holmes tested a genetically modified bacteria, Planeticola Klebsiella which produced ethanol from wood waste (15) and found that it killed all wheat plants regardless of conditions (16).

Environmental impacts of ethanol production

Is Ethanol Really Cleaner And More Environmentally Friendly Than Gasoline? In a session of the US Senate on the National Sustainable Fuels and Chemicals Act of 1999, the NRDC presented evidence (17) that the products generated from the combustion of ethanol include formaldehyde and acetyl, both being carcinogenic; and that increasing the use of ethanol could increase the environmental levels of peroxyacetinitrate (PAN).

Acetaldehyde is listed as a Toxic Air Pollutant in California based on evidence of its carcinogenic properties and PAN says that this chemical is "genotoxic (causes genetic damage) and causes respiratory problems and irritates to the eyes, it can also cause lung damage."

The NRDC noted that increasing the use of ethanol in fuel could lead to increased exposure to ethanol via inhalation, which could result in a variety of toxins associated with ingesting ethanol. They also warned about the emissions of nitrate oxides and flammable organic compounds that produce ozone.

Recently, Cal Hodge of Second Opinion Inc. reported that atmospheric ozone levels have increased in California since 2003 associated with the change from ethanol use by 10% to gasoline compounds one year ago (19).

The excess ozone on the Southern California Coast is twice as high as in the last three years, while the maximum concentration of ozone rose to 22%. This increase in ozone was correlated with an increase in emissions of nitrogen oxide and volatile organic compounds, which were not recorded by the US Environmental Protection Agency (EPA).

The EPA approved ethanol in gasoline using the wrong model for its testing, which does not take into account the fact that ethanol tends to produce more nitrogen oxides, which often leaks from the sealed tubes of the vehicle's fuel system and reduces efficiency, therefore, increases gas emissions. A call is needed for the “no expansion of the use” of ethanol in US gasoline to be allowed.

Biodiesel has greater environmental impacts than diesel

Inorganic primary resources are increased to produce fertilizers by 100%

  • Non-radioactive waste, mainly gypsium, a product generated by the production of phosphate fertilizers, is increased by 98%
  • Radioactive waste is increased by the supply of electricity generated from nuclear plants by 90%
  • It increases photochemical oxidants, especially hexane in solutions based on oil extraction, by almost 70%
  • Water use increased by 30%
  • The acidification of nitrogen oxides and sulfate and ammonium expelled during the growth of colzo crops and also during the combustion of biodiesel is increased by 15%.


1.- This article is part of the recent publication: "Which Energy?" 2006 Energy Report of the Institute of Science in Society, and whose authors are Mae-Wan Ho, Peter Bunyard, Peter Saunders, Elizabeth Bravo and Rhea Gala.
To see the full text on Energy, all the notes, references and learn more about biofuels you can download the complete document (in English) from the site:

2.- The version published in was extracted from the one published in the Resistance bulletin of the Oilwatch Network

3.-What are biofuels?

Biofuels are derived from plant crops, and include biomass that is directly burned, biodiesel from oilseeds, and ethanol (or methanol) that is the product of fermentation of grains, grass, straw, or wood.

Biofuels have gained fame among environmental groups as renewable energies that are "carbon free", so they would not produce greenhouse gases; simply by burning them, the carbon dioxide that the plants took in when they were growing in the field, returns to the atmosphere.

However, there are several aspects that are not taken into account in this analysis. For example, biofuel crops occupy valuable land that could be used to grow food, especially in impoverished countries. There are realistic estimates showing that generating energy from crops requires more fossil energy than the energy they produce, and that they do not substantially reduce greenhouse gas emissions, when all factors are included in the calculations.

Furthermore, they cause irreparable damage to soils and the environment.

Biofuels can also be produced from wood chips, crop residues and other agricultural and industrial wastes, which do not compete for land, but whose environmental impacts are still substantial.

Source: ISIS. 2006

Video: Biodiesel from microalgae (June 2021).