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Best Management Practices for Odor Control
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The trend towards larger and larger animal feeding operations, coupled with the influx of nonagricultural people into rural areas, has brought the issue of livestock odors to the forefront, in addition to concerns about water quality and the environment. Although water quality can be directly measured, odor strength and offensiveness can vary through personal perceptions. Perceptions are influenced by personal preference, opinions, experiences and variability in individual olfactory systems.

Total elimination of odor from animal feeding operations probably never will be accomplished. However, management practices and technology are becoming available that are capable of reducing odor. Economic issues control the implementation of new odor technologies. The livestock industry is very competitive, with low profit margins. However, most producers agree that continued productivity, profitability, and sustainability of livestock production depends in part upon cost-effective technologies and management practices to mitigate odor. The following is a quick overview of some available practices and technologies. Most odor technologies work best in very specific situations, and should be thoroughly researched before being implemented.

Odors in Buildings
Odors associated with livestock buildings are often overlooked for the more obvious odor source -- the waste storage structure.

Cleanliness goes a long way to prevent odor from buildings.
Small changes that may have a positive effect include:
Waste Storage Structures:
Lagoons or holding ponds that are designed and managed properly usually have low odor potential. However, if an anaerobic lagoon is undersized or organically overloaded, it may be a significant odor source.
Land Application:
The application of liquid manure onto cropland maybe a significant source of odors and nuisance complaints from surrounding neighbors. The following procedures may help alleviate those concerns.
Open Lots:
Although odor from open lots is highly subject to climate changes. A number of things that can be done. Dust from feedlots is a primary concern because dust can absorb and concentrate odor compounds. Dust can also be carried long distances by wind, and tends to stay closer to the ground than gaseous odor compounds. Other odors can come from decaying organic matter.
Additional Measures:
Additional technologies or management practices exist that may be implemented to reduce odors. Many of these available technologies are new and costly, but have proven effective in certain instances.

Facility Site Selection and Perception:
The primary method of reducing the number of odor complaints begins with the selection of the site for the livestock waste control facility. Sites located near residences, commercial enterprises, recreational areas, or major roads are particularly prone to complaints. When selecting a site, also consider topography and prevailing wind directions.
Research has shown that perception plays a role in how pleasant or offensive an odor is to any individual. Aesthetically pleasing livestock operations have fewer complaints. A clean, well-landscaped and well-maintained operation is perceived to be less odorous. Trees and shrubs can help to reduce odor through air mixing and can add to the overall quality of appearance.

Anaerobic Lagoon:
The most common form of waste treatment for swine producers in Nebraska is an anaerobic lagoon. Lagoons break down organic waste into gases, liquids, and biosolids through microbial action. Many waste control facilities are called lagoons, but actually are earthen storages. Lagoons are built much larger and contain a permanent bacterial and water pool. Most cattle feedlots use earthen storages, while pork producers tend to use anaerobic lagoons.

Improperly designed or managed lagoons can emit odorous gases like H2S (Hydrogen Sulfide) and intermediate VOCs (Volatile Organic Compounds). On the other hand, correctly functioning anaerobic lagoons can treat wastewater with very little odor. As the size of a lagoon increases, the potential for odors, the rate of sludge buildup, and the number of pathogenic organisms decrease, while nitrogen losses increase.

Lagoons operate more efficiently in warmer temperatures. They may produce considerable odor in the spring as bacterial populations are restored. Two main groups of bacteria exist in lagoons -- the acid-producing and methane-producing.

The acid-producing bacteria work at the lower temperatures, breaking down organic matter into VOCs and VFAs (Volatile Fatty Acids), both of which are odorous. The methane- producing bacteria, which flourish at higher temperatures, convert these complex odorous organic by-products into simple, nonodorous compounds like methane and CO2, (Carbon Dioxide). However, the methane-producing bacteria don’t get started as early in the spring as the acid-producing bacteria.

An anaerobic lagoon that is operating properly will have a pH of 7 to 8 (slightly basic). Overloaded lagoons tend to be more acidic (6.5 or less). This problem can be solved temporarily with the addition of hydrated agricultural lime on the surface. Excessive additions of antibiotics or metals, like copper sulfate, to animal feeds may disrupt bacterial populations and cause odor.

Many lagoons exhibit a purple/reddish color on the surface. This color is caused by a phototrophic sulfur oxidizing bacteria that can occur naturally. The color is a good sign that the lagoon is functioning properly and odor, NH4-N (Ammonia-Nitrogen), and soluble phosphorus are reduced. Research is being done at the University of Nebraska to determine how these bacteria reduce odor.

Manure Storage Covers:
Manure storage structures are often the focus of odor control efforts. Therefore, many producers have covered them. In Nebraska, storage structures tend to be very large, like anaerobic lagoons. Covering them isn’t always economically feasible, due to the high costs per square foot of material. However, several types of covers exist that have been successful.
Solids Separation:
Anaerobic Digester:
Product Additives:
An increasing number of companies have been recently claiming to be able to reduce odor and H2S and NH4 emissions, break down organic sludge, control flies, improve animal health, and increase fertilizer value for the manure -- all through the addition of certain additives to manure storages.
These compounds can be chemical, enzymatic, bacterial, odor adsorbents, and masking agents. Numerous compounds have been tested by the ISU and NCSU to determine their effectiveness on odor reduction. A few products tested showed some positive odor-reduction capabilities, but the vast majority had no effect. However, the costs of such products are usually low when compared to other odor-reducing strategies.

Biomass Filters:
Biofilters can be used to treat ventilation air coming out of confined animal production buildings. Biofilters provide a medium for the growth of certain bacteria, which convert odorous compounds like VOCs, VFAs, and NH4 into simple non-odorous compounds. Industrial biofilters can be very expensive, but biomass filters can be constructed and operated for as little as $0.22 per weaned pig produced. Buildings must use only mechanical ventilation, because naturally ventilated air can’t be forced through the bacterial medium.
The University of Minnesota has shown that inexpensive biomass filters can be constructed with wood pallets and wood chips or other fibrous material. They had removed as much as 95% of the odor and 90% of the H2S with little resistance to air flow in the building.

Windbreak walls also are used to reduce odors and dust coming from production buildings. The walls are placed downwind of ventilation fans, settling dust out and forcing odorous air upwards. They have limited success due to wind directions and atmospheric conditions, but are used heavily in Asian poultry operations at low costs. Diet Manipulations:
Research has already shown that altering the diet can greatly reduce excreted nutrients like nitrogen, phosphorus, copper and zinc. This technology is beginning to be applied to odor issues and shows future promise that may revolutionize the way animals are fed. However, at this time, any odor reduction gained through dietary manipulation is lost once the manure undergoes anaerobic degradation. Oil Sprinkling:
Recent research has demonstrated that sprinkling a small amount of oil (2 ounces per 100 sq. ft.) in totally housed confinement operations can reduce gas and dust concentrations substantially. On average, this practice reduced total dust by over 80%, H2S by 27%, and NH4 by 30%. The decrease in dust not only reduced odor, but also improved worker and animal health. It is important that the oil is sprinkled and not sprayed at high pressures because aerosolized oil can be detrimental to human health. Also, when too much oil is used, surfaces become very slick creating a hazardous working environment. The main cost is labor, but automation could solve this problem.

Other Odor-Reducing Technology:
Industrial and municipal systems faced odor issues for a long time and have used a number of odor-reducing technologies very successfully. Some of these technologies have shown to be adaptable to animal production systems. The main drawbacks are very high costs and increased management concerns. If odor issues are very sensitive in a facility site, these options should be researched fully to see if they could mitigate any concerns. Some of this technology includes:
Questions? Contact: Nebraska Department of Environmental Quality, P.O. Box 98922, Lincoln, NE 68509-8922; phone (402)471-2186. Visit our web site at www.


Nebraska Department of Environmental Quality
1200 "N" Street, Suite 400
P.O. Box 98922
Lincoln, Nebraska 68509
(402) 471-2186