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.
[ILLUSTRATION OMITTED]
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
COPYRIGHT 2007 American Mushroom
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NOTE: All illustrations and photos have been removed from this article.