USDA APPROACHES ICY ROADS
WITH A CORNY SOLUTION

Each winter, local and state highway departments dump millions of tons of salt on the nation's roads. This may provide motorists with June driving in January, but salt annually causes more than $5 billion in corrosion and other damages.

If a U.S. Department of Agriculture chemical engineer has his way, salt trucks will someday switch to spreading a deicer made from corn.

William L. Bryan at the Agricultural Research Service is beginning work to develop a new process for recovering acetic acid from corn sugar fermentation. Besides being the main ingredient in ordinary vinegar, acetic acid is the expensive part of a compound, calcium magnesium acetate or CMA, that the Federal Highway Administration says is an excellent alternative to road salt.

"More economical acetic acid could clear the way for wider use of CMA as an alternative to deicing salts," Bryan says. He's optimistic about developing a process to reduce the cost of making CMA and will pursue any patentable ideas from the research.

Commercial CMA, tested by several states, is made by reacting petroleum-based acetic acid with lime products. This acetic acid accounts for 85 percent of CMA's 34-cents-a-pound price tag, he says.

Salt costs only a penny per pound, but the Environmental Protection Agency estimates that it annually causes more than $5 billion in damage, including corrosion of reinforced concrete roads, cars, bridges and underground utilities. Salt also kills roadside vegetation and pollutes drinking water supplies, says Bryan at the ARS Northern Regional Research Center in Peoria, Ill.

CMA is effective at lower temperatures than salt, and CMA is noncorrosive and nonpolluting. Bryan also says that runoff from CMA could help reduce harmful effect of acid rain by neutralizing the acids that kill fish and vegetation.

CMA has been made from corn-based acetic acid only on a limited experimental scale. With large-scale production, Bryan estimates cost will be in the range of 10 to 15 cents per pound by the new process. "Partly, of course, it would depend on the price of corn. But the advantage of corn is that it's a renewable resource, unlike petrochemicals. And there's more often a corn surplus than a shortage."

Acetic acid for food-type vinegars is made through yeast and bacterial fermentations of sugar from corn or other plants. But Bryan will use a different bacterium, Clostridium thermoaceticum.

"This bacterium is promising because it yields about 45 percent more acetic acid than the typical vinegar fermentation process," says Bryan. "The higher yield should help reduce CMA's cost."

Highway departments in Alaska, California, Iowa, Massachusetts, Michigan, Minnesota, Washington, Wisconsin and the Canadian province of Ontario have field-tested the petrochemical-based, synthetic CMA. Laboratory tests have also been done in Illinois, Maine and Michigan.

Massachusetts is interested in CMA as an alternative to salt for environmental and health reasons.

"This is the third year we've tried (synthetic) CMA and, except for the cost, 'we're pleased with its effectiveness and optimistic about decreasing sodium levels in our water supplies," says Mark Cain, a snow and ice control engineer with the Massachusetts Department of Public Works.

Besides fermenting corn sugar to acetic acid, the bacterium to be tested can ferment xylose, another type of sugar in many plants, to produce acetic acid. Bryan says this means the possibility of yet another low-cost source of CMA from plants, agricultural residues and logging and other wood wastes. •

March 1989 / Illinois Municipal Review / Page 19