Researchers from Penn State have published a study, cited by PigProgress, in which humic acid was added to manure in order to reduce odors. Dr. Eileen Fabian and her colleagues note that while using digesters and solid separation are effective methods to reduce odors, they can be costly to implement.

Although many commercial additives are available, Fabian points out that only a few have been properly evaluated. Among those that have been studied, "research shows that odor reduction is inconsistent, temporary, or even non-existent."

Humic Acid

Humic acid, vaguely defined as a component capable of biostimulating soil humus through the decomposition of organic materials, has been examined as an odor control agent for over 50 years. For instance, a 1972 paper in the Journal of the Air Pollution Control Association mentions that using humic acid in the feed ration has the potential to eliminate odors from pig and other livestock manure.

Study Details

At a large-scale finishing operation, the team found that a liquid humic acid additive called ManureMax significantly reduced pig odor emissions from barn ventilation and odor concentrations in the field where pig manure was surface-applied.

For the demonstration, two tunnel-ventilated finishing barns on a farm were used, each separated by 1,800 feet (167 m2) of woods and fields, with 2,250 similarly aged pigs in each barn. The manure pit under the floor of one barn received monthly additions ("shock treatments") of the additive, while the other did not receive any. Treatments were switched when the barns were cleaned for repopulation. Additionally, five monthly shock treatments were applied to the outdoor manure pits.

Human subjects were used to quantify odor levels, as this method is considered the most accurate. The subjects' input was aided using portable devices that provided various preset odor dilution reports.

Costly Treatment

Besides measuring odor levels, the team also examined the monthly treatment costs for the manure pits. With less than 8 hours of work per complete 20-week pig finishing cycle, the total estimated cost for the process was $0.70 USD per pig.

Attention to Results

Fabian explains that these "results showing the odor-reducing efficacy of a manure additive cannot be broadly extrapolated to other products or even to other scenarios using the same additive. The production of unpleasant gases from manure is extremely complicated and depends on the nature of the manure, the specific agricultural practice considered, the frequency and rate of treatment, etc."

Other Recent Research

Another recent study from the Institute of General and Inorganic Chemistry in Belarus examined three chemical mixtures: sulfuric acid and sodium hypochlorite, ammonium persulfate and peracetic acid, and sodium nitrite mixed with ammonium molybdate.

These mixtures were examined because adjusting the pH of manure slurry to a certain point can prevent the formation of odor-forming substances.

The study found that all three mixtures removed unpleasant odors, but the latter two also provided significant disinfection effects after 21 days. However, cost analysis was not performed.