Straw filter for ammonia reduction.

In Europe, a bed of straw is used for at least two mushroom substrate facilities for the purpose of reducing ammonia emissions. The fresh straw is dropped loosely on top of a nozzle floor. After several weeks, the straw is removed and added as an ingredient to the substrate mix. In Pennsylvania, funding was provided to test the function of a straw filter for an existing substrate facility, so a shipping container (40 feet long) was adapted to serve as an experimental straw filter unit. The shipping container had a removable top so that after the straw was dropped in, a fabric cover sealed the container to force the out flow of air across an ammonia sensor.

The source of ammonia emissions for the straw filter was a bunker for Phase I substrate preparation. This bunker was filled and emptied according to the normal routine of preparing mushroom substrate. The first tests with the straw filter were based on drawing air from the bunker continuously--the blower supplying the straw filter was turned on and remained on, independent of what was happening in the bunker. Therefore at times, fresh air was added to the straw, and other times high concentrations of ammonia were added. The measurements for this test showed that occasionally there was measurable ammonia released from the straw as the clean air (zero ammonia) was pushed through.

For subsequent tests, the filter supply blower was controlled to run only at the same time as the bunker blower. thus there was less fresh air pushed through the straw. These tests provided useful measurements of ammonia accumulation in the straw, based on the change in ammonia concentration from in-flow to out-flow. One ammonia sensor was used for this project. This same type of sensor is being used around the country for poultry house ammonia measurements.

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The straw filter reduced ammonia concentrations about 75 percent. During several test intervals, straw captured ammonia at a rate of about 0.0015 pounds of ammonia per hour per cubic foot of straw.

Ken Lomax, Ph.D., University of Delaware