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Reducing Hydrogen Sulfide Emissions in Manure Collection Pits

Entering Confined Space in a Dairy/Swine Facility

Dick Nicolai, associate professor
Sarah Smith, graduate research assistant

Funding Source

High Plains Intermountain Center for Agricultural Health and Safety (HICAHS)


The purpose of the study was to determine the amount of ferrous chloride and hydrogen peroxide are needed to reduce hydrogen sulfide emissions from a manure collection pit and to determine the time required for that reduction to occur. 

Need or Impact

A confined-space hazard that often claims multiple lives before anyone realizes there is a danger in manure gas. Many farm workers appear to be unaware of the immediate danger posed by entry into manure pits. Like other types of confined spaces, manure pits present special problems regarding worker awareness of hazards. Manure pits can be oxygen-deficient, toxic and explosive. Hydrogen Sulfide is one gas in manure pits that is of primary concern. Hydrogen Sulfide is a highly toxic gas that is heavier than the air that sinks to the bottom of the head space in a manure pit. It can cause dizziness, unconsciousness and death. At low concentrations, it may smell like rotten eggs, but at high concentrations, it deadens the sense of smell so that no odor can be detected. 

Project Status 

Completed and final report is Hydrogen Sulfide Reduction of Swine Manure using Potassium Permanganate and Hydrogen Peroxide.

Project Results

Adding a metallic salt to the manure reduces the hydrogen sulfide emissions. The salt impacts the sulfur cycle and therefore reduces hydrogen sulfide production, but not volatile fatty acid production. Ferrous chloride and hydrogen peroxide are several salts that have shown promise to reduce hydrogen sulfide emissions. Two trials of H2O2  and two trials of KMnO4 were performed. In each trial, H2S was reduced by at least 91%. With the second trial of H2O2, H2S concentration in the headspace was reduced from 50 ppm to 0.38 ppm in six minutes. Additional research is needed to prove the amount of chemicals to add to ensure safe entry of the pit.