As part of a National Pork Board study, Purdue University scientists evaluated 35 odor-control products for use with manure-storage pits.

They tested each product in an enclosed 15-inch diameter by 48-inch tall cylinder. These cylinders were stored in an environmentally controlled room, maintaining a temperature of 20°C. They continuously ventilated each cylinder with clean air, and periodically added manure and products throughout the 42-day trial. Manure added to the cylinders came from a commercial swine grow/finish operation with a shallow-pit manure system.

Researchers collected air samples four times during each of the three trials and evaluated odor concentration using olfactometry. They also analyzed initial and final manure characteristics during the test
period. Effectiveness of each product was determined by comparing odor, hydrogen sulfide and ammonia in the treated cylinders vs. the untreated ones.

Results were reported at levels of 95 percent and 75 percent certainty. At 95 percent certainty, none of the products reduced odor, while seven products reduced hydrogen sulfide up to 47 percent and eight reduced ammonia up to 15 percent.

At 75 percent certainty, four products reduced odor up to 32 percent, three reduced hydrogen sulfide up to 19 percent and four reduced ammonia up to 3 percent. Overall, 20 products had a positive effect on reducing one of the three air-emission measurements.