Livestock Odor Prevention
and Control Strategies

John W. Baumgartner
Baumgartner Environics, Inc.

Baumgartner Environics, Inc. employs proprietary modeling software to estimate the emission of odorous gasses from the surface of an outdoor manure storage facility, to predict odorous gas transport off site and, finally, to map the concentration of a gas at a given distance downwind against the odor threshold of a human population for that gas. This information is then used to evaluate which method of odor control will best provide needed odor control. General methods of odor control are aeration, bioaugmentation, chemical additives, covers or a combination of these methods.

Understanding the nature and sources of odors emitted from swine facilities is key to developing a sound strategy to prevent or control odor. HogOdor and PigPit Odor proprietary modeling software (Gantzer Environmental Software and Services, Inc.) are used by Baumgartner Environics, Inc. to predict downwind, ground-level gas phase concentrations of the compounds in swine manure that have the greatest potential to cause offensive odors. The software uses manure sample wet chemistry analytical data, manure temperature and pH as variables in emissions algorithms to project what malodorous gasses and how much of each will be emitted under anaerobic conditions in the manure storage area. The compounds examined using wet chemistry analyses are hydrogen sulfide, ammonia, acetic acid, propanoic acid, butyric acid, vateric acid, phenol and para-cresol.

Once a malodorous gas is emitted, the software uses transport algorithms to model the dispersion and dilution of each malodorous gas over distance. The concentration of a given malodorous gas at a given distance (such as the nearest receptor) is then divided into the known odor threshold for that compound to create an odor number. An odor number of one means that about half of a given population will detect the presence of that specific gas. The odor numbers for each gas from each manure storage area on site can then be compared to the other gas concentrations at a given distance and ranked for severity, which helps to determine where efforts to prevent or control odor should be directed for maximum impact per dollar invested.

A manure supernatant sample from each unique manure storage area on site needs to be collected. In explanation, if there are four identical deep pit barns housing similarly aged animals, only one manure storage pit need be sampled. If the same four barns exist, but one barn is used as a nursery, sample the nursery pit separately from the finishing pits. As another example, if shallow pull plug pits drain to a concrete storage area with overflow going to an earthen basin, each unique shallow pit area, concrete storage area and earthen basin need to be sampled. Samples should be collected a few inches below the liquid surface of the manure supernatant in storage. (This means below a crust if one exists on the surface of the supernatant.)

Use a coliwasa sampler or sample jar clamped on the end of a suitable length of handle to collect the samples. If using a coliwasa sampler, combine several volumes of manure sampled in a container to obtain at least 500 ml, do not stir (dissolved gas is released if mixed), and then carefully pour the commingled sample collected into a 500 ml glass or plastic sample jar. Fill each sample jar completely so there is no airspace when the cover is applied. (If total solids, BOD, COD or other parameters are to be analyzed in addition to the parameters required for odor projection analyses, collect a larger sample volume according to the volume needed by the laboratory doing the analyses.) Identify the sample using day/date/year/military time as a unique numbering system. List the site and manure storage area from which the sample originated.

Place the samples in a cooler with ice packs to cool the samples below 50'F quickly. Samples should be delivered promptly to the laboratory or chilled overnight in a refrigerator and then repacked in a cooler with an ice pack the next day for overnight shipment to the laboratory.

At the time samples are collected, measure and record the temperature and pH of each manure source sampled. Take field notes of the dimensions of each manure storage area sampled (length x width x depth or diameter x depth). Determine the distance from the manure storage area to the nearest property boundary and to the nearest odor receptor (i.e. neighboring residence). For deep pit structures, record the building height to the roof line, count the number of pit exhaust fans, record their spacing, determine the diameter of the fans and obtain information regarding the cubic feet per minute of airflow per fan at maximum flow. This information is necessary to project the transport of malodorous gas emissions downwind.

The odor projection analysis usually reveals one manure storage area as the primary source of malodor and, usually, one malodorous gas predominates. As such, an odor control strategy developed to address that manure storage area and the predominant malodorous gas has the greatest probability of reducing malodor emitted from the site. If, for example, the largest malodorous gas emitted is hydrogen sulfide and it is emitted from an earthen basin, options to control or reduce odor may include:

• Covering with a synthetic cover to limit the release of malodorous gasses from the surface of the basin,
• Covering with straw or a material to create an aerobic zone which will destroy malodorous gasses diffusing through the aerobic zone,
• Aerating the total slurry,
• Air-capping (creating a facultative lagoon),
• Using a chemical treatment such as an oxidant (i.e. potassium permanganate or hydrogen peroxide) as a source of oxygen to promote aerobic microbial activity,
• Using a chemical treatment such as metallic salts (i.e. ferrous chloride) to reduce odor by reducing sulfide concentration,
• Using a bio-cide such as copper sulfate to stop or reduce microbial activity,
• Using a buffer to raise the pH to reduce the potential for hydrogen sulfide to emit from the aqueous phase,
• Using an enzyme to encourage a chemical reaction or, conversely,
• Using an enzyme to inhibit a chemical reaction from occurring that results in reducing the emission of hydrogen sulfide,
• Using bio-augmentation to supplement sulfur reducing bacteria which will reduce the sulfide available for conversion to hydrogen sulfide, or
• Combinations of these options such as bio-augmentation with limited aeration or synthetic covering with gas collection and use/destruction of the gas collected.

• The type of manure storage area (i.e. deep pit, open concrete tank, earthen basin, two stage anaerobic lagoon),
• Whether an emergency odor control strategy needs to be employed,
• Whether long term or short term odor control is desired,
• Whether total odor control is desired or only selected gaseous emissions need to be controlled,
• Whether there are other concerns, such as solids build-up or salt deposits in recycle lines that may be addressed with an odor control strategy,
• Whether adding more organic matter to the manure storage system is of concern (i.e. adding a straw cover to a lagoon may reduce capacity or increase the loading rate),
• Degree of odor control required (i.e. minimal reduction of total odor, or complete elimination of all odor is desired), and, finally,
• Cost considerations.

Aeration: It is generally accepted that fully aerating a manure slurry will provide acceptable odor control because organic matter decomposed aerobically does not create malodorous compounds as a byproduct of microbial activity. Unfortunately, the energy required to satisfy the biochemical oxygen demand of a high strength manure slurry enough to control odorous emissions is generally considered to be more costly than can be afforded by a commercial producer ($2 to $6 per finished pig - depending on reference cited). Creating a facultative lagoon (aerobic layer on top of anaerobic layer) shows promise for effective odor control, but a technical breakthrough is needed to improve the efficiency of oxygen dissolution equipment to reduce energy inputs and cost. Bio-covers (i.e. barley straw) also create an aerobic layer and are effective in the aerobic destruction of the malodorous gas emissions of anaerobic decomposition.

Bio-augmentation: The use of bacterial supplements to influence or control the anaerobic decomposition process so as to convert or metabolize the volatile fatty acids produced has the added potential to reduce solids build-up through increased liquefaction of solids. This added benefit may influence producers to select bio-augmentation over other odor control strategies. It is best to include a sulfur metabolizing bacteria in the bacterial supplement program in order to reduce the production of hydrogen sulfide and to improve the survival rate of less vigorous, but beneficial bacteria.

Chemical Additives: Bio-cides (i.e. copper sulfate), oxidants (i.e. potassium permanganate, hydrogen peroxide), metallic salts (i.e. ferrous chloride) and pH adjusters all have different modes of action to impact the malodorous gas produced as a result of anaerobic decomposition. Bio-cides attempt to stop organic decomposition by killing the bacteria, oxidants convert to aerobic decomposition as long as enough oxygen is provided by the oxidant (usually too costly), and metallic salts have a narrow range of activity (i.e. impacts the sulfur cycle and therefore reduces hydrogen sulfide production, but not volatile fatty acid production, for example), and pH adjustment upward will reduce the volatility of volatile fatty acids and hydrogen sulfide while rapid pH adjustment downward will assist in breaking up accumulated and hardened solids. Some undesirable by products, such as heavy metals, may result from the use of chemical additives.

Covers: Synthetic, floating covers increase the vapor pressure of the air space between the supernatant and the cover, keeping much of the malodorous gas dissolved in the supernatant. Malodorous gas that does volatilize needs to be removed from under the cover to avoid inflation of the cover and the resulting stress. The collected odorous gas can be destroyed by flaring, or through the use of a bio-filter. Biocovers are effective in the destruction of malodorous gasses produced during anaerobic decomposition, but are somewhat difficult to place in service and maintain. Generally, a small surface area is preferred for ease of placement and to avoid destruction of the cover by wave action during periods of high wind. Over time, the bio-cover will sink into the manure storage area and add additional organic matter to the manure slurry. This organic matter may possibly upset the loading rate of the storage area as well as increase the cost of manure removal.

Combinations: (Some examples)

• Limited aeration in conjunction with bio-augmentation increases the effectiveness of the biological treatment due to circulation of the slurry and also due to increased performance of facultative bacteria.
• The use of a bio-filter with a synthetic cover or the flaring of collected gas increases total odor control.
• Collection of gas under a cover for use as an energy source is another example of a combined odor control strategy, but methane production is easier to induce in a warm climate versus that experienced in the Upper Midwest.

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