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Mitigation Technologies

Summary of odor control technologies for swine facilities

During the last two decades, various mitigation technologies have been evaluated to reduce odor emissions from swine production facilities. Approaches to control odor and air pollution can be classified into three categories: ration/diet modification, manure treatment, capture/treatment of emitted gases and enhanced dispersion. Each of these mitigation approaches includes several specific technologies. Table 1 presents a summary of these technologies with an evaluation of overall cost and brief comments on advantages or limitations of each technology. 

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Table 1. Summary of technologies for odor control in swine production facilities.

 

Technology

Effectiveness

Cost

Comments

Installation 

($ per pig space)

Operation

($ per pig produced)

Overall

Ration/diet modification

Low CP content

diets and/or feed additives

Moderate

-

<$0.5[a]

Low

Use of synthetic amino acids to reduce diet CP and cost is well established, and is a common industry practice; should be considered as a BMP.

Manure handling and treatment

Solid-liquid separation

Moderate

$22~$27[b]

$2~$3[b]

Moderate to

high

More research is needed to develop practical techniques for immediate separation of solids from freshly excreted manure.

Storage additives

Uncertain

$1.2[c]

$0.5[c]

Moderate

Only works for a short period or specific odorants; need further research to improve reliability.

Impermeable storage covers

High

$6~$32[d]

-

Moderate

A venting system and a support structure may be needed.

Permeable storage covers

Moderate

$0.6~$5[d]

-

Low to

moderate

Effectiveness highly dependent on how the cover is managed.

Anaerobic

digestion

High

$22~$150[e],[f]

-

High[g]

Not economically feasible for small operations; has problem of NH3 inhibition; has more potentials through co-digestion.

Air treatment

Oil spraying

Low to moderate

~$6[e]

~$0.7[e]

Moderate

Create slick flooring for pigs and people; health concern on oil misting.

Biofilters

High

$4~$11[e]

$0.05~$0.1[e]

Low to

moderate

A promising technology; need careful maintenance.

Wet scrubbers

Moderate

~$40[e]

~$2[e]

Moderate to

high

Need treatment for wastewater; effectiveness on odor depends on solubility of odorants.

Vegetative environmental buffers

Low to moderate

~$1[h]

$0.05~$0.20[h]

Low

Decreases direct visual viewing of facilities; may decrease natural ventilation in summer; requires planning and time.

Note: CP = crude protein; BMP = best management practices.

[a]   Depends on price of synthetic amino acids; the cost of low CP diets sometimes can be lower than regular diets.

[b]   Based on a gravity screen system or a gravity belt thickener system, Walker and Wade, 2009.

[c]   Based on addition of a commercial manure additive (Alliance®), Heber et al., 2000a.

[d]   Calculation was based on assumption of 2.1 m2 lagoon area per pig space; adapted from Stenglein et al., 2011.

[e]   Data were adapted from resources of eXtension. Available online at http://www.extension.org/pages/23980/technologies-for-mitigating-air-emi...

[f]   Calculation was based on installation of an anaerobic digestion system for a capacity of 4,000 pigs.

[g]   Cost effectiveness depends on the value of energy recovery from biogas.

[h]   Data were adapted from Iowa demonstration cooperators and Tyndall, 2008.

Diet and Feed Management to Reduce Gaseous Emissions 

Animals emit gases to the atmosphere from feed digestion and manure decomposition. The production of gases begins in the digestive system of animals and continues after manure excretion and decomposition. Methane (CH4) is produced by ruminants as a result of microbial breakdown of carbohydrates in the rumen. Enteric, or intestinal, CH4 emission from feed digestion is affected by the quality and quantity of the feed consumed and physical conditions in the digestive tract. Animals usually retain less than half the nitrogen in the diet, with the remaining nitrogen excreted in the feces or urine. The feces and urine contain unretained nutrients and undigested diet components, including nitrogen and sulfur (S) compounds. The amount of ammonia (NH3), hydrogen sulfide (H2S), odor, and other gases emitted from manure decomposition largely depends on the nutrient levels and physical properties of manure. These gaseous emissions can be reduced through proper diet and feed management. 

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Design and Management of Biofilters for Odor Reduction 

Biofiltration is an odor reducing technology that can be used to treat the exhaust air from mechanically ventilated livestock barns or covered manure storage facilities. Biofilters contain moist and porous media with a large surface area where microorganisms can grow. The biofilter media treats contaminated air both physically and biologically. When the exhaust air is directed to pass through the biofilter media, the contaminants in air are adsorbed and broken down by microorganisms in addition to physical filtration. Fans are usually required to push the exhaust air through the biofilter media. Generally, biofilters cost less than most other odor treatment technologies and do not involve chemical handling, but they need regular maintenance to perform effectively. A well designed and maintained biofilter can reduce more than 80 percent of odor, hydrogen sulfide (H2S), and ammonia (NH3) in the contaminated air.

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Composting Animal Manure 

Managing manure is a reality for animal agriculture. Manure can be stored with minimum effort in a passive system or a managed composting system. Composting manure changes the quality of manure, but composting may involve more management and costs than a passive storage system. The decision to compost can be a solution to other management problems, and the benefits of composting may compensate livestock producers for the additional costs and efforts. The benefits of composting include less odor, flies, weed seeds, and pathogens in waste, and less amount of waste. In addition, finished compost makes excellent fertilizers and soil amendments, which can improve soil health, fertility, and water-holding capacity. Reasons for a livestock producer to consider composting are summarized in Table 1. 

Table 1. Reasons for composting

Management problems

Benefits of composting manure

Manure has fly, insect, and pathogen problems.

The heat from composting will kill insect eggs, larvae, and pathogens. Flies can’t breed in compost.

Neighbors complain about smells from the manure storage.

Composting reduces odor.

 

Manure needs to be transported for long distance; or manure is too heavy and wet to spread easily.

Composting reduces the volume and density of manure. Finished compost is drier, and thus is easier to transport and spread.

Weed seeds in the manure become a problem for raw manure land application.

The heat from composting will kill most weed seeds.

Neighbors complain about smells from land applied raw manure.

Land applied compost will have little to no odor.

There is not enough cropland to spread all the manure,and there is a local value-added market such as garden centers, landscaping companies, or golf courses.

Compost can be sold or used on other farms. It is generally more “consumer friendly” and preferred by commercial horticulture.

There is a need to meet environmental goals or permit requirements for nutrient balance.

Composting can reduce pollution and could be a useful tool in nutrient management plan.

The cost of rendering becomes prohibitive.

Composting can assist in carcass disposal.

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