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Sep 1, 2007 (Vol. 27, No. 15)

Is Biomass the New Texas Tea?

Solid Waste Demands Consideration as a Cheaper Source of Fuel Ethanol

  • Until the invasion of Iraq, it seemed that the U.S. had little motivation to curb its voracious appetite for oil (aka black gold or Texas tea). The oil crisis during the 1970s was perhaps the last time the country was motivated to look to alternate energy sources. At that time, the U.S. government identified ethanol as having potential as a fuel alternative.

    The primary source for ethanol in the U.S. is corn. Given that 40% of the world’s corn is grown in the U.S., one might think that use of fuel ethanol would have outpaced the use of gasoline by now. However, although 3.9 billion gallons of fuel ethanol were produced from corn in the U.S. in 2005, the country still consumed more than 140 billion gallons of gasoline in that same year.

    The media would lead one to believe that the discrepancy between the use of fuel ethanol and the use of gasoline stems from our addiction to oil. However, the discrepancy has more to do with economics than appetites or addictions. The energy content of ethanol is less than that of gasoline. In practical terms, it takes 50% more ethanol to drive one mile than it does with gasoline. Thus, in 2005, the savings in gasoline associated with ethanol use amounted to a mere 1.9% of total gasoline sales.

    Moreover, it currently costs more to produce ethanol than gasoline. By May 2006, the average wholesale price of ethanol was $2.65 a gallon, as compared with $2.20 a gallon for gasoline. Taking into consideration the government subsidy paid to U.S. corn growers (approximately $.51 per gallon) and the lower energy content of ethanol, the consumer on average would have to pay about $4.00 per gallon to obtain enough ethanol to provide the energy output of one gallon of gasoline.

    So is the promise of fuel ethanol only an illusion? Hardly. Enter biomass and biotechnology.

  • Solid Waste

    Biomass, which constitutes a significant portion of municipal and industrial solid waste, refers to organic plant material that can be used as fuel or, more importantly, to produce fuel. Through photosynthesis, energy from the sun is stored in the chemical bonds of the plant material. It is this energy that is harnessed in biomass.

    Examples of biomass include agricultural residues such as corn husks/stalks, sugar cane fiber, rice chaff, and wood waste including paper trash, yard clippings, saw dust, and wood chips. It is the sugar content of biomass that makes it particularly useful for fuel ethanol production.

    Biotechnological methods such as genetic engineering can be used to transform microorganisms to convert the sugars in biomass into ethanol. It has been estimated that microbial conversion of the sugar residues present in waste paper and yard trash from U.S. landfills could provide over 10 billion gallons of ethanol. Such cellulosic ethanol would require less energy and would be produced from waste material that is otherwise buried or burned. More importantly, corn currently used to produce ethanol could be better used to feed livestock and people.

    Recombinant DNA technology could transform the ethanol industry. But, is the current geopolitical situation the mother of invention? Not necessarily, because this technology has been around for a while.

    For example, U.S patent 5,000,000, granted in 1991, describes ethanol production by E. coli strains engineered to express heterologous pyruvate decarboxylase (pdc) and alcohol dehydrogenase (adh) of Zymomonas mobilis. E. coli, a gram-negative enteric bacterium, is not naturally ethanologenic. That is, it does not produce ethanol as a major metabolic by-product but rather produces organic acids such as lactate, acetate, succinate, and butyrate as major metabolic by-products. E. coli is a robust organism and can break down a variety of organic materials, including cellulose, which is why it is the predominant normal flora found in the human digestive system.

    Z. mobilis, commonly found in plant saps and honey, has unusual metabolic characteristics and is reportedly capable of producing ethanol at rates that are substantially higher than that of yeasts. However, the range of sugars metabolized by this organism is limited and normally consists of glucose, fructose, and sucrose.

    Co-expression of pdc and adh genes of Z. mobilis by recombinant E. coli enables the organism to ferment a wide variety of sugars resulting from breakdown of cellulose into ethanol. By means of genetic engineering, E. coli can produce ethanol as a primary fermentation product.

    However, the sugars present in the majority of the world’s cheap, renewable sources of biomass are not solely simple monomeric sugars such as glucose but include more complex sugars such as xylose, the primary sugar component, as well as arabinose, mannose, and galactose. Thus, the technology has been extended to other gram-negative enteric bacteria such as Klebsiella and Erwinia (see, e.g., U.S. patent 5,424,202, issued in 1995), which co-express not only ethanol production genes but also genes coding for proteins that enable the host to transport and metabolize oligosaccharides and polysaccharase genes coding for proteins that degrade the feedstock into fermentable monosaccharides and oligosaccharides.

    Likewise, the technology has been extended to gram-positive bacteria including Bacillus, Lactobacillus, Streptococcus, Fibribacter, Ruminococcus, Pediococcus, Cytophaga, Cellulomonas, Bacteroides, and Clostridium.

    In the wake of the war in Iraq, the U.S. government has significantly stepped up funding for research in renewable energy sources, including ethanol production from biomass. Similarly, the venture and corporate communities have realized the potential for growth and return on investment in this industry sector and have begun making significant and meaningful investments.

    Future R&D will focus on making ethanol production from biomass cost-competitive with gasoline production through improvements in recombinant microorganisms and refinements in the preparation and handling of feedstocks and the saccharification and fermentation process. Future IP will reside in these improvements and refinements.

    Clearly this biotechnology application has the potential to revolutionize solid-waste management by making biomass the black gold or Texas tea of the 21st century the way that crude oil was in the 20th century. As exciting as the future possibilities are, just imagine if we had the political will to exploit fully this technology back in 1991, when U.S. patent 5,000,000 was granted. Perhaps we would not be involved in a war in Iraq.

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