The seemingly ever-present challenge associated with raising hogs is keeping odors at bay.
The questions commonly associated with odor control are basic:
What are the realistic expectations for odor in the building, at the site of production?
Where does the odor originate?
How difficult will it be to manage the odor?
What is the cost of controlling the odor and where will I get the most bang for my buck?
Jay Harmon, with the agricultural and bioengineering department at Iowa State University, offered 10 steps to managing odor during an environmental seminar at the World Pork Expo in early June.
Step 1: Siting decisions — The proposed siting of hog production facilities is all about location, Harmon emphasizes. The distance to nearby dwellings, the size of the pork production facility and the exposure angles — from the facility to a residence — must be taken into account.
Before siting, study the historical prevailing winds for direction and frequency during various times of the year. Understand the percentage of time (hours) that a dwelling will experience the “downwind” direction of prevailing winds. The exposure angle — the angle when neighbors are directly downwind — should be documented.
The terrain will affect the intensity of the odor. “As winds die down, wind flows down through valleys,” he explains.
“Acceptable distances are not equal in all directions,” reminds Harmon. “In Iowa, predominant summer winds are from the south and south-southeast. A facility to the south of a neighbor at a given distance has a greater odor impact than one to the north at the same distance.”
Selecting the proper site for a new hog production unit is one of the cheapest odor-control options available, he adds.
Step 2: Manure handling — Injecting manure can reduce odor 50-75% compared to broadcasting. The cost is roughly $0.003/gal. Umbilical systems can be less visible than tankers because of the difference in road traffic. “This may make handling manure more ‘invisible,’” he says.
Step 3: Dietary manipulation — Harmon feels this is one of the easiest options to implement for reducing odors. Cutting crude protein levels and bumping crystalline amino acids can reduce odors 20%, he says. More strategies will emerge.
Step 4: Cover manure storage — Whether permeable (straw, cornstalks, geotextiles) or impermeable (high-density polyethylene), covers help prevent gases from escaping.
Permeable covers can reduce odors by 40-50% at a cost of 10-25¢/sq. ft., Harmon explains. Impermeable covers are more costly at $1.00-1.40/sq. ft., but they also improve odor reduction by 70-85%. Snow and rain accumulation on the impermeable covers must be managed, he adds.
Step 5: Visual barriers and eye appeal — “Well-kept sites get fewer complaints,” Harmon relates. “It serves as a reflection on the overall management of the site.”
The fact of the matter is, people complain less when the hog operation is out of sight. “Although it is very difficult to quantify the impact or costs, the adage ‘out-of-sight, out-of-mind’ is real,” he assures.
Step 6: Pit ventilation — The more odorous air comes from the pit, contributing more than half of the total odor during critical periods. Pit ventilation accelerates volatilization and offers limited benefits to indoor air quality. “Inlet management is more critical with pit ventilation, and remember, a full pit essentially eliminates pit ventilation,” reminds Harmon.
Step 7: Biofilters — Drawing exhaust air through a biofilter bed can reduce odor, ammonia, hydrogen sulfide and dust. Like any odor-curbing technology, the biofilters must be managed properly, particularly the moisture content. Odor levels can be reduced 65-80% at an estimated cost of about 42¢/finished pig.
Precautions must be taken to ensure the biofilter design is compatible with the ventilation system. Whole-house ventilation through a biofilter is not practical, he explains.
Step 8: Vegetative environmental buffers — A properly designed vegetative filter helps lift and mix odorous gases. A wedge-shaped design, with shorter shrubs/trees planted in the outside rows and progressively taller trees in the rows closer to the buildings, will help with this lifting and mixing action.
Naturally, these barriers take years to establish, with the cost ranging from 6-10¢/pig over 20 years, he estimates. A side benefit is the vegetation provides a visual barrier, but be aware of the impact these trees and shrubs can have on a naturally ventilated facility.
Step 9: Chimneys — These relatively low-cost design features promote air mixing and reduce the noise of the ventilation system. Height of the chimney is important for effectiveness, as is the cross-sectional area.
Step 10: Other odor deterrents:
Additives — Most effective in dilute systems; effectiveness varies from zero to about 20%.
Aeration — 40 to 80% effective in dilute systems with costs averaging about $4/pig.
Barriers — They force exhaust air up and reduce dust at ground level; Harmon estimates this relatively low-cost option is about 20% effective.
Biocurtains — Remove dust.
Digestion — Requires a large investment, but considered 50-80% effective in reducing odors; nutrient neutral.
Oil sprinkling — Considered 40-50% effective; can create slippery conditions; commonly not automated.
Harmon says focus on the simple solutions first. “Consider management as well as cost. If you are building new facilities, spend time focused on proper siting. Consider covering or protecting outside manure storage. And be careful with manure application. Remember, you are hauling odor to your neighbor's doorstep.”
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