"Pac Man" enzymes turn biomass waste into replacement for gasoline

provided by Cornell University

orried by rising gas prices? Top off the tank with paper pulp. Fill 'er up with maple chips. Drive down the freeway using cheese whey. As average US gasoline prices soar beyond $1.80 a gallon, proponents of using bio-based fuels and chemicals are gaining momentum.

Gasoline-replacement research in the past has focused on ethanol derived from corn. But now agricultural engineers are beginning to understand how biomass waste also can be used as a substitute for petroleum. Larry Walker, Cornell professor of agricultural and biological engineering, and his students are using enzymes to break down solid biomass waste into a renewable energy form.

In a talk at the American Chemical Society national meeting in March 29 at the Moscone Convention Center, San Francisco, Walker said there is sufficient biomass waste available to supply all of the organic chemicals that are consumed annually in the United States and still have enough waste left over to convert to auto fuel. "We need renewable resources, and energy flow. How do we develop alternatives to petroleum-based products? We do this through plant materials," said Walker. "Bio-based fuels are recyclable. Fossil-based fuels are not."

Although waste biomass is a cheaper raw material than oil, there is a catch. The cost of converting this raw material to energy is the major constraint to commercialization, according to Walker. The plant biomass is chemically diverse, and it must be separated then converted into desired products. The challenge, he explained, is to develop industries proficient in using this raw material and to develop more cost-effective enzymatic and microbial processes that convert these materials into industrial chemicals and energy.

Walker explained the principles behind biomass fuel: Carbon dioxide is taken in by the plant through metabolism, and carbon enters plant cells where it is converted into cell walls. About 279 million metric tons of plant waste is generated in the United States annually from industrial, commercial and agricultural production. The key to using this resource lies in employing enzymes to break down the woody, fibrous part of the material into fermentable sugars.

Caroline Corner, Tina Jeoh and Hyungil Jung, graduate students in agricultural engineering in Walker's Cornell laboratory, are studying the use of enzymes from thermophilic (heat-loving) bacteria to break down the cellulose in plant waste. The bacteria produce six enzymes, called cellulase, that attack the biomass through a process called hydrolysis. This allows the enzymes to process the cellulose into fermentable sugars, permitting scientists to produce fuel or industrial chemicals. Walker likens the action of the cellulase enzymes in breaking down the fibrous lignins (the binding in plants) to a "tag-team Pac Man moving along the cellulose fiber."

"In essence we would use plants to make organic compounds - carbon compounds once made from petroleum, actively taking the carbon dioxide out of the atmosphere through plant tissue," said Walker.

Not only do plants represent a renewable source of organic compounds, but there also is considerable organic waste produced that could be a carbon source for bio-industries. For example, corn stover (much of it used as fodder) accounts for 100 million metric tons of biomass waste produced annually in the United States, and newsprint biomass waste accounts for 11.2 million metric tons. Urban tree residue - leaves, Christmas trees and broken branches accounts for 38 million metric tons.

The research was funded by the US Department of Agriculture.

Contact: Blaine P. Friedlander Jr., (607) 255-3290, bpf2cornell.edu