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Odor Control for Liquid Manure Storage Practices - Permeable Covers
Permeable covers, or biocovers, act as biofilters on the top of manure storage areas. Materials often used as covers include straws, cornstalks, peat moss, foam, geotextile fabric, and Leka rock. Permeable biocovers reduce odor, in part by reducing both the radiation onto the manure storage surface and the wind velocity over the surface of the storage area. Covers act as a barrier to these forces. At the solution/air interface, humidity is relatively high, which creates a stabilized boundary that slows the emission rate of odorous volatiles. The aerobic zone within the biocover allows the growth of aerobic microorganisms that utilize carbon, nitrogen, and sulfur for growth. Bu further degrading and making use of these compounds prior to exiting the biocover, odors emitted above the biocover are altered and reduced. Reports of odor reductions of 40 to 50 percent are common when various straw materials are used. An 85 percent odor reduction efficiency was noted following the use of a floating mat or corrugated materials.  Costs for biocovers vary widely depending on material used and method
of application. In Minnesota , an operation employed a 1/8-inch thick
geotextile material that cost $0.25 per square foot plus installation.
Straw was added on top of the geotextile cover for additional odor
control. Straws and cornstalks cost approximately $0.10 per square
foot, applied; peat moss and foam cost about $0.26 per square foot,
and Leka rock is approximately $2.50 per square foot for a 3-inch
layer. Leka rock is a product of Norway , thereby requiring considerable
shipping costs ($5 to $6/cubic foot). The cost to cover a 1.5-acre
earthen storage was $6,000 while an above ground takn over 0.2 acres
was $500, for the same material. Most recommendations suggest a minimum
of 8-inch depth, preferably 10-to 12-inch depth of coverage on manure
storage surfaces. New covers (except Leka rock which may be a single
application) need to be applied a least annually, as one study showed
that only 50 percent of the straw cover remained four months after
installation. Therefore, management and re-investment costs need
to be considered. Removal of large, fibrous material during storage
cleanout must also be considered before selecting this option. Extension Publications
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