The outer road along Interstate 44 near Six Flags St. Louis is freshly paved — with asphalt made from recycled swine manure.

It is believed to be the first time asphalt has been created from swine manure. Two St. Louis County companies, road contractor Pace Construction Co. and the engineering firm Innoventor, joined up on the project.

Innoventor perfected the process of converting the animal waste into a bio-oil used in asphalt binder, the St. Louis Post-Dispatch reported Thursday.

"If this works out, it's a win-win situation for everyone," said Karlton Krause, a hog producer from northern Iowa. "For farmers, it produces revenue. And at the same time, it helps clean the environment. We're taking a waste product and finding a value-added purpose for it."

The smell can still be an issue, at least when the new asphalt is first applied.

"Whew!" gasped a Park worker on Wednesday when a dump truck deposited a 15-ton load of the designer asphalt into a road paver at the Eureka site.

The idea began a decade ago with — what else? — complaints about the smell. In this case, neighbors complained about the odors at the hog farm operated by Kent Schien's in-laws in Barry, Ill., near Hannibal, Mo.

Schien, Innoventor's founder and chief executive, is a former engineer at McDonnell Douglas, which later merged with Boeing. He left the aerospace firm to start his own company, and asked his engineers to figure out a way to address the smell problem for hog farmers. They developed a technique to "scrub" animal odor as it moved outdoors through fans installed on the outer walls of swine sheds.

Another hog producer soon suggested the need for an invention capable of turning swine waste into a moneymaker.

Schien returned to his alma mater, the University of Illinois, where an agricultural engineering professor named Yuanhui Zhang was developing a process to transform pig manure into bio-oil. Schien's Innoventor team utilized Zhang's research. Rick Lux, an engineer with a background in biofuels, was put in charge of the project.

The team developed a multiple-stage system that ultimately moved the manure into a reactor, which applies heat and pressure to the waste material. Innoventor got a big boost this winter when tests conducted on the paving material received a passing grade as a "lower-grade asphalt binder" from a Missouri Department of Transportation research engineer.

On Wednesday, a chute beneath a Pace silo dropped a batch of pig asphalt into the dump truck operated by Mike Cain.

He sniffed the air. "Smells nasty," Cain said. "But I live in the country; I'm used to it."

In the coming weeks and months, MoDOT and Innoventor intend to keep a close eye on the 500-foot stretch where the asphalt was laid. The state will monitor wear and tear on a road subjected to a lot of traffic in the seasons when the amusement park is open for business.

"We'll keep going ahead," Lux said. "We've shown this stuff can be processed at the farm, processed at an asphalt plant and put down on a road."

Schien is making plans to manufacture the prototype for use at hog production facilities across the nation. The plant will be in the place where it all began: Barry, Ill.

Copyright 2010 The Associated Press.