A Missouri roadway leading to Six Flags St. Louis is paved with asphalt produced from pig manure. "We're taking a waste product and finding a value-added purpose for it," said Karlton Krause, a hog producer from northern Iowa. Innoventor, an engineering and design firm, scrubs the waste to remove the odor, and then converts the manure to a bio-oil used to bind the asphalt.

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