Thirty-five manure additive products were measured for their ability to reduce odor levels in simulated manure pits in a laboratory at Purdue University.

Two years in the making, an exhaustive industry test of 35 hog manure pit additives has found that 20 of the products were effective some of the time. They reduced at least one of the three air emissions studied.

The National Pork Producers Council's (NPPC) Odor Solutions Initiative recently concluded testing the 35 commercial products for overall odor levels, hydrogen sulfide and ammonia levels.

More than 50 vendors were invited to have their products tested. Of these, 35 manufacturers were willing to have open evaluations of their products, points out Rodney Goodwin, NPPC director of research.

The products were tested in treated reactors against untreated manure. The reactors are 15-in.-diameter PVC columns, 4-ft. deep to simulate a manure pit, he explains.

The tests followed company instructions as to exactly how their products should be used, says NPPC Research Manager Carrie Tengman.

Table 1. Pit Additive Products
Decreases Odor (ODT) Decreases Hydrogen Sulfide (H2S) Decreases Ammonia (NH3)
Product Name Decrease % Certainty Decrease % Certainty Decrease % Certainty
Agricycle 3% 75%
AgriKlenz Plus 6% 95%
Alken-Murray Clear-Flo® 27% 75% 47% 95%
AWL-80 10% 95%
Biocharge Dry 37% 95% 7% 95%
Biological Manure Treatment 25% 75% 5% 95%
BIO-MAX Biosystem
Digest 54 Plus 2% 75%
EM Waste Treatment 15% 95%
GT-10000OC & BC-2000AF 34% 95%
INHIBODOR® 36% 95%
Krystal Air 7% 95%
Lagoon Aid
Manure Management Plus 6% 95%
MBA-S 19% 75% 3% 75%
M2 Acid Buffer
Nature's Key Pit & Lagoon
N-P 50 3% 75%
Peroxy Odor Control 3% 95%
Pit Remedy
PS1 14% 75%
Roebic Manure Liquefier
Roebic Odor Eliminator 23% 95%
Solmar AW-509
Super Microbial Odor Control 32% 75% 37% 95%
UC-40 Microbe Formula 15% 75%
Zymplex 28% 75% 27% 95%

Odor levels were measured using olfactometry. A machine called an olfactometer continuously dilutes and delivers a mixture of odorous and odor-free air until an odor detection threshold is reached by an experienced odor-sniffing panel. That threshold is the number of dilutions required for the odor to be detected by 50% of the panel members.

Testing Results

The products were screened in three, 42-day test replications at the Purdue University Agricultural Air Quality Laboratory. The project was designed by an Odor Solutions Initiative committee of producers, scientists and vendors who reviewed and accepted all the testing protocols. Al Heber, Purdue University, served as project director for the pork checkoff-funded work.

“Some of the products did produce significant ammonia or hydrogen sulfide reductions. But only a few of the products would reduce odors from stored slurry,” says Goodwin.

None of the products significantly reduced odor emissions at a 95% confidence level by olfactometry, says Tengman. Seven of the 35 products reduced ammonia levels by 3-15%. Seven others reduced hydrogen sulfide levels by 23-47%. Several of the products listed in Table 1 didn't produce any results different than untreated manure. Some, in fact, increased odor levels to some extent, notes Goodwin.

The manure source was a northern Indiana commercial hog farm that was managed under the same conditions for each of the three test periods, stresses Goodwin. Manure was collected from 90- to 200-lb. pigs. Even though farm conditions were standardized, the composition of the manure varied.

Manure was added to the test reactors once a week. The temperature in the test reactor was held constant throughout the slurry, Heber explains.

Controlling the variables is an advantage of the lab testing protocol over field conditions. That means conditions were more conducive for the pit additives to work in the lab than in the field, and why the lab test can be viewed as a valid screening test.

The other advantage the products had in this study was that they were given three replications to succeed whereas all other industry trials of manure pit additives have only used a single test replication, says Goodwin.


Goodwin concludes: “A manure pit is a dynamic environment. Pigs, temperatures, bacterial populations and pumping out and refilling change the composition of manure pits. Accordingly, there may be times when these pit additive products work well, and other times when they don't work as well. And the research here supports that conclusion.”

Moreover, the manure pit additive products tested aren't guaranteed to work. “That depends as much on the interactions of factors in the manure pit as it does with the product itself,” he says.

NPPC will publish a full rundown of product results soon and will post them on their Web site ( in the area called “Especially for Producers” under the “Odor Solutions Initiative.”