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U of M team continues to study foam on manure pits

By Heather Thorstensen

Date Modified: 02/02/2012 9:12 AM

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MINNEAPOLIS— A University of Minnesota team is on their second round of funding to find ways to mitigate, and ultimately prevent, dangerous foaming in hog manure pits.

Larry Jacobson, an Extension engineer, gave an update on the project Jan. 18 at Minnesota Pork Congress, held at the Minneapolis Convention Center.

A layer of surface foam that forms on some manure pits becomes toxic as it acts like a sponge to capture gases, particularly methane. Agitation can break the foam and release the gas. Just a small amount of methane trapped in the foam has the potential to cause a flash fire or explosion if it comes in contact with a spark from a motor or pilot light.

The most recent victim was a hog unit in northern Iowa, where an explosion in mid-September 2011 injured a worker and killed approximately 1,500 pigs, Jacobson said.

Foaming is also a problem because it takes up manure storage volume and gets pigs dirty.

The U of M team is working under the assumption that the foam is caused by a change in the manure pit's microbial population. The change could be due to diet, water source or other factors.

With the first round of funding, a survey of approximately 200 pork producers found that approximately 25 percent of farms had foaming. At those farms, foaming occurred in 25 percent of rooms.

A second round of funding, from the Minnesota Pork Board and the U of M-administered Rapid Agricultural Response Fund, has been studying effects of adding Rumensin 90 and Bloat Guard to reduce foam. It's also being used to analyze microbes in the pit.

The trials with Bloat Guard didn't show effectiveness so it's no longer being investigated.

Rumensin is fed to beef cattle and works in the rumen to reduce methane gases while increasing meat production, said Jacobson. Different amounts were added directly into the manure at test sites through pump-out pits.

Five pounds of Rumensin 90, a concentrated form, per 100,000 gallons of manure seemed to have the most impact.The product was mixed into the manure pit in four locations. A mechanical agitator wasn't used.It's unknown whether the product stays in the pit after one application.

However, using Rumensin 90 off label is a concern both for human safety and for the swine. If swine eat it, they could get sick and die. The research team is discussing the issue with the Minnesota Pollution Control Agency, since the manure containing the product may be applied to fields.

If acceptable, Rumensin 90 could be a short-term solution.

For a long-term answer, Bo Hu, an assistant professor in the U of M's Department of Bioproducts and Biosystems Engineering, is handling the microbial analysis. Hu's job is to identify which bacteria cause foaming, figure out why they have become dominate and stimulate the scenario in a lab to verify his conclusion.

Hu feels that filamentous bacteria has something to do with foaming, but the question remains why the microbial community has changed, Jacobson said.

In the meantime, it's critical that enough ventilation is provided at farms with foam during pumping to reduce the buildup of methane gas.

The team recommends up to 20 to 30 cubic feet of air per minute per pig, created only by wall fans, not pit fans.

For the best ventilation, keep curtains closed if it's not windy so the fans can properly circulate the air, keep ceiling inlets open and seal the pump-out ports.

Other best management practices for pit pumping with foam are to remove pigs from the barn, keep people out of the building and avoid excessive mixing.