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H2S 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 emissions, 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. This aerobic zone should also curtail the formation of reduced sulfur compounds, such as hydrogen sulfide. Reported reductions in hydrogen sulfide emissions have not been found; however, reports of odor reductions of 40 to 50 percent are common when various straw materials are used. An odor reduction efficiency of 85 percent has been noted following the use of a floating mat or corrugated materials. Cover depth is very important for permeable covers. Most recommendations suggest a minimum of 8-inch depth, preferably 10 to12-inch depth of coverage on a manure storage surface. Leka™ rock needs to be at least 3 to 4-inch deep. New covers (except Leka™ rock) need to be applied at least annually, and 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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Costs for biocovers vary widely depending on the
material used and the 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 emission control. Straws and cornstalks cost
approximately $0.10 per square foot, applied annually; peat moss
and foam cost about $0.26 per square foot, applied annually; and
Leka™ rock costs in excess of $2.50 per square foot for a
3-inch layer, but only has to be applied one time. Leka™ rock
is a product of Norway, thereby requiring considerable shipping
costs ($5 to $6 per cubic foot). The cost to cover a 1.5-acre earthen
storage was $6,000 whereas an above ground tank with 0.2 acre was
$500, for the same material.
