Summer 2001
Manure treatment for control of odor and odorous gases
by Jeff Lorimor, Department of Ag and Biosystems Engineering
Manure treatment methods for odor control include maintaining aerobic conditions (with free oxygen) during storage, aerobic treatment (aerated lagoons or composting), anaerobic digestion (without free oxygen), or biochemical treatment. For open lot surfaces, rapid drying is the key to odor control. This article discusses minimizing odor from open feedlots.
Wet
manure on a feedlot or dairy lot surface can be responsible for the generation
of substantial odor, in terms of both odor concentration and offensiveness.
Research has determined a 60-fold difference in odor units (measured with
a dynamic forced-choice triangle olfactometer, a device to quantify odor
intensity) between dry and wet feedlot surfaces. Odors were highest at
mid-day. Odor generation peaked at 2–3 days after rainfall and at
a surface moisture content of 60–67% (wet basis). Results showed
that ration had less effect on odor concentration than did moisture content.
Therefore, open feedlots or feedyards with wet, anaerobic manure accumulation
produce odor of greater concentration, offensiveness, and duration than
a well-drained and well-maintained feedlot. It is also beneficial to conduct
frequent, uniform removal of surface manure and have good drainage in
which manure is regularly harvested, leaving a smooth, uniformly sloped
pen surface with the interfacial layer intact to maintain surface-sealing.
Well-drained feedlot surfaces with relatively low quantities of manure dry rapidly after rainfall, restoring odor intensities to original levels. Feedlot maintenance and manure collection strategies should be aimed at 1) avoiding chronic wet spots caused by poor drainage, potholes, or spills; 2) harvesting only the top one-half to two-thirds of the feedlot manure; and 3) preserving an uncomposted manure–soil interfacial layer for surface sealing and denitrification. This strategy helps reduce odor, maintains reasonable manure quality as a fertilizer, and protects groundwater. A feedlot should be designed and managed to shed water. Pen slope of at least 3 to 5 percent away from feedbunks or feeding alleys is needed, with discrete drainage provided for each feed pen into a drainage channel that accelerates runoff away from the feedlot surfaces with minimal solids deposition. Potholes should be backfilled as soon as they develop, and overflows or leaks from cattle-watering facilities onto the feedlot surface should be avoided. Proper stocking density in pens can ensure that moisture excretion by cattle plus rainfall does not exceed average evaporation in the winter as well as the summer.
In short, keeping your feedlot as dry as possible through proper design and management is the best way to minimize feedlot odors.
This article was excerpted from the article Odor Mitigation for Concentrated Animal Feeding Operations by Dr. John Sweeten of Texas A&M University, Amarillo, Texas.
