Fall 1999
Geotextile covers for liquid manure storages
by Jeffery Lorimor, Department of Agricultural and Biosystems Engineering
A new type of manure storage cover is being tested in the upper Midwest. Artificial covers are being used throughout the state on liquid swine storages, and natural ones develop on bovine storages. The two primary types of artificial covers used are biocovers and solid synthetic covers. Covers have been shown to effectively minimize odors and gases emanating from the storages.
Biocovers
are typically composed of 8 to 12 inches of straw, grass, or chopped cornstalks
blown onto the liquid manure surface. Biocovers work well for one season.
They are typically applied in the spring and removed during pumpout in
the fall. Recurring costs for biocovers include the estimated biomass
cost of 5 to 10 cents per square foot of surface area, as well as the
spring application and additional fall agitation costs.
Solid synthetic (plastic) covers also are being used on a few storages in Iowa. They are more expensive initially (typically $1.00 per square foot of surface area), but do not require the recurring costs and management input. One problem with solid covers is their tendency to balloon up as they capture gases. The wind can then catch the covers and damage them.
Geotextile covers have been tested by Minnesota researchers. Geotextile is a tough, porous fabric that feels like felt. Its toughness makes it easy to install; it is light so it floats; and because it is porous, gases do not accumulate under it and cause ballooning. Replicated tests in Minnesota were conducted with 200-gallon tanks of swine manure. The geotextile covers reduced odors 59 percent and hydrogen sulfide emissions 71 percent compared with uncovered tanks, but the reduction was less than for straw covers or solid PVC covers that ranged from 70 to more than 90 percent. Geotextile covers typically cost less than $1.00 per square foot, making them potentially good alternatives for reducing odors from both basins and lagoons.
A geotextile cover has been in place on a swine lagoon in Minnesota for more than a year. It has some straw on top of it to help minimize gaseous emissions (see photo). Currently, it is functioning well.
