As urban areas encroach onto formerly remote rural areas, livestock operators are frequently targeted with complaints about manure odors.
A recent demonstration project staged by researchers at the Pennsylvania State University (Penn State) to take a proactive approach to the problems of pig manure odor by trying to reduce it at the source; namely the livestock buildings where the manure originates.
The good news: Based on the results, as published in an online Penn State Extension article entitled, Manure Additive Shows Swine Odor Reduction, it is possible to reduce pig odor levels by using a humic-based additive; one that cuts odors emanating from barn ventilation systems and treated pig manure surface-applied to fields.
The problem
Pig manure is odoriferous for a reason. “Odor generation results from by-products of microbial degradation of molecular components found in the manure,” says Robert Meinen, an assistant research professor at Penn State.
“Some specific classes of compounds are rated as more offensive by most people, including volatile fatty acids, sulfur compounds, and aromatic rings. Put simply, it’s the smell of decomposition. It is hard to measure the offensiveness of manure with a single molecule because the manure is expected to emit a mixture of molecules that most people would find unfavorable. Anaerobic conditions found in liquid manure are considered to create more offensive odors than those found in aerobic conditions.”
To make matters worse, “Swine manure is very low in solid content and fiber, so the formation of a crust on manure storage surfaces is not typical,” continued Meinen. “A thick manure crust can provide a microbial media where odor compounds formed deeper in liquid manure can be captured and degraded to less odorous compounds in aerobic conditions. Lack of a crust in swine manure allows gasses to escape the manure as they are generated.”
The project
The Penn State demonstration project was created with one idea in mind: “The goal is to reduce neighborhood odor complaints from new and expanded large-scale livestock farms, buildings and manure storage structures only,” says Robert (Bob) Mikesell, a teaching professor with the Penn State department of animal science and one of the article’s authors. “We made no attempt to regulate odors from manure application.”
To find out if odor reduction was actually possible, the Penn State team mixed a commercial humic-based additive to liquid swine manure. “Humic additives are extract solutions from partially decomposed stable organic matter,” explained the Penn State article. “This microbially resistant solution of dark brown colloidal organic decomposition products is characterized by large complex molecules with high chemical reactivity. Humic materials are incompletely understood, but are known to act as a biostimulant.”
In line with accepted research practices, two similarly operated, 2,250-pig, tunnel-ventilated finishing barns on one farm were used in the project. They were both occupied by pigs of similar ages, while being separated by 1,800 feet of fields and forests.
During the project, the five-foot-deep underfloor manure storage pit of one barn received monthly doses of humic-based additives, over a period of five months, while the other did not.
“After 20 weeks when hogs were finished for market and barns cleaned for restocking, treatments were switched so the previously untreated barn received the amendment,” the Penn State article said.
The treatment protocol consisted of pouring ‘shock-treatment applications’ of humic-based additives through the center-aisle slotted floor, using seven equally-spaced locations in each of two rooms of the finishing barn. The dose was 3.3 gallons of additive per 1,000 square feet of barn.
To scientifically assess the impact of the humic-based additive on reducing pig manure odors, measurements were taken of the odors coming out of the barn’s ventilation tunnel fan, and from treated pig manure that was surface-applied to nearby fields.
The outdoor manure samples were laid down in a 20-foot wide swath (at a rate of 7,000 gallons per acre) within a 200-foot diameter ring.
For the record, “A four-person odor assessment team was located 30-feet away facing the barn exhaust fan,” said the article.
“Each assessor was equipped with a Nasal Ranger Field Olfactometer (NRO) unit and collected four separate observations each (16 total observations). Whole-air samples were also collected in odor-free Tedlar® bags during NRO observations and transported to campus for laboratory olfactometry. Exhaust fan output for each barn observation set was also measured to enable calculation of odor emission rates for both field and laboratory olfactometry assessment methods.”
Outdoors, “The odor assessment panel, stationed in the middle of the manure ring, gathered D/T [Dilutions-to-Threshold, aka the volume of odor-free air/volume of odorous air ratio] data using field olfactometer units,” the article said. “Surface isolation flux chamber whole-air samples from manure-spread areas were collected in odor-free Tedlar bags and transported to the olfactometry laboratory for evaluation.
The results
According to Penn State’s research data – quoting the article for utmost accuracy – “Barn exhaust fan odor flux rates were reduced by 21 [percent] (OU/min, P < 0.001) for both field & laboratory odor assessment methods. Land application manure-ring odor D/T and DT concentration levels were reduced by 21 percent (P = 0.15) and 60 percent (P < 0.001) for field and laboratory assessment methods, respectively.”
In plain language, “Under the controlled conditions of this demonstration project, the humic manure additive demonstrated a statistically significant ≥21 percent odor reduction for both the barn ventilation exhaust and land-applied manure using field and laboratory odor assessment methods.
“This odor reduction level may not be readily discernible at the source by many people. However, dilution at distance from the source (e.g. at the property line) could make a significant difference when it comes to nuisance odor complaints, especially when combined with other odor mitigation practices, such as land application via shallow disk injection.”
As for the time and money required to achieve this measurable reduction in pig manure odor emissions? “The monthly manure storage shock treatments involved less than eight hours labor over a full 20-week hog finishing-cycle. The total estimated cost for the humic amendment including labor was $0.70/hog. Product farm delivery costs would be in addition to this and vary by location.”
Implications for pig farmers in Pennsylvania and beyond
The research conducted by Penn State shows that pig manure odors can be significantly reduced by 21 percent by adding humic-based additives to liquid manure on a monthly basis.
To put it mildly, this is tremendously good news for pig farmers; particularly in areas where housing developments are getting close to their operations.
This is certainly the case in Pennsylvania, which “has unique odor programming that focuses on proper siting of livestock and poultry farms,” says Meinen.
Specifically, “Pennsylvania has a state-defined category titled Concentrated Animal Operations (CAO), which are farms that have high livestock or poultry density of total farm animal weight per harvested crop or pasture acre,” he notes. “Since 2006, farms in the CAO program that propose new animal housing or manure storages, or plan to expand housing or manure storage capacity must have a certified specialist develop an Odor Management Plan (OMP) for the new facility. The OMP considers many factors and uses a tool called the Odor Site Index (OSI) to assign numeric values that indicate risk of potential odor conflict. Starting with the map location of the new facility, the number of neighbors, distance to the neighbors, and direction the neighboring house is in relation to the facility are plotted.
“Since Pennsylvania’s prevailing winds are fairly predictable, houses to the east of the proposed facility are more heavily weighted than houses the same distance away in another direction.”
Animal factors also play a key role in CAO calculations. “The OSI considers the number of animals, and more animals increase potential odor conflict,” says Meinen. “The species of animal is important and hog farms are in the highest category of potential odor conflict because we know odor from swine farms can be more offensive than odor generated from some other species. Social factors are considered too, such as if the proposed site is in an area zoned for agriculture or if there are other animal farms close to the site.”
Fortunately, “The OSI can be applied to multiple sites on a property before commencement of construction, with the goal of identifying a favorable, low-scoring site with low potential for odors to affect neighbors,” adds Mikesell.
As well, Penn State offers a non-regulatory, voluntary site evaluation service for any proposed animal farm in Pennsylvania. “The site evaluation service considers the risk of odor conflict with neighbors after an animal barn receives inventory,” says Meinen. “The service began in 1999 and has evaluated over 250 locations where swine farms were proposed.
Beyond the OSI measurements cited above, all regulated farms in this state are required to address odor sources through (generally routine) management practices, designated as Level I BMPs (Best Management Practices).
According to Mikesell, these BMPs include reducing dust and feed accumulation in pens, aisles, and on animals; sufficient ventilation to keep animals and facility surfaces clean and dry, and the minimization of damp, exposed manure that contributes to odor generation.
The BMPs also include the daily removal and sanitary disposal of dead animals in the barn, matching feed nutrients to animal nutrient requirements to avoid excess manure production, and management of the manure storage facility to reduce exposed surface area and off-site odor transfer.
Taken as a whole, the 21 percent odor reduction process defined by Penn State’s researchers and Pennsylvania’s sensible BMPs for pig manure management are worth consideration by pig farmers everywhere.
“It is difficult to measure the benefits of reduced odor generation, but it is worth pursuing,” says Meinen. “The social benefits of avoided odor conflict should pay off from increased neighborhood perception of the farm to increased consumer confidence at the local supermarket.” •
