"Carbonating" Cow Manure Kills Dangerous Microbes

Two people died and 700 became ill last September when drinking water at a county fair in upstate New York became contaminated with a dangerous strain of bacteria. The microbes, a strain of E. coli known as O157:H7, are thought to have come from dairy cattle manure. Now researchers have found a cheap and easy way to kill dangerous microbes in cow manure. They just add carbonate — the same stuff that makes the bubbles in soft drinks.

The new research is reported in the April 1 print edition of the journal Environmental Science & Technology by researchers from Cornell University and the Agricultural Research Service of the U.S. Department of Agriculture, both in Ithaca, N.Y. The peer-reviewed journal is published by the American Chemical Society, the world's largest scientific society. The article was initially published on the journal’s Web site on Feb. 8.

“Farm-scale testing will be needed before the procedure is recommended to the cattle industry,” says USDA/Cornell microbiologist James Russell, “but laboratory tests indicate that carbonate is a highly effective antibacterial agent.” He estimates that the treatment would cost less than $10 per year per cow.

Adding chlorine to water makes it safe to drink. By the same token, chlorinating cow manure would kill microbes. But it's not practical, says Dr. Russell. Composting works, too, but only if the temperature of the compost pile gets hot enough to kill bacteria — and it often doesn't in small-scale operations.

By contrast, sodium carbonate can be added directly to tanks or ponds of manure, which is often how manure is stored before it's spread on fields to enrich the soil.

The researchers made this discovery when they mixed cattle urine with manure and found that microbes were killed. “When the ratio of feces to urine was one to one,” Dr. Russell said, “the E. coli were eventually killed, and we identified carbonate as the antibacterial agent.” Carbonate is produced when an enzyme in the manure (fecal urease) acts on a substance in the urine (urea), producing carbon dioxide, some of which is “trapped” as carbonate.

Cattle ordinarily produce more than twice as much manure as urine, and at that concentration, there's not enough carbonate to kill microbes, Dr. Russell said.

Adding sodium carbonate, however, along with enough sodium hydroxide to keep the pH alkaline, killed the vast majority of E. coli found in the manure within five days.

The research team included Cornell University postdoctoral fellows Francisco Diez-Gonzales and Graeme Jarvis, and undergraduate David Adamovich, in Cornell's Department of Microbiology.