Iron oxide to mitigate hydrogen sulfide gas release from gypsum-bedded dairy manure storages

To mitigate noxious hydrogen sulfide (H2S) gas release that has been observed from gypsum-laden dairy manure, three additives were studied in sequential investigations. Three trials with specific aims were conducted using experimental vessels containing 15 kg of dairy manure each. Trial 1 investigated two additives: iron oxide (specifically, iron oxide-hydroxide, FeOOH) and a proprietary gypsum-lime based product (DriMatt). Trial 2 investigated effective ratios of gypsum to iron oxide and a modified DriMatt additive, and trial 3 evaluated iron oxide at the most effective ratio. Manure agitation events were monitored in the first two trials, while gas releases were continuously monitored in trial 3 during and between agitations. Hydrogen sulfide concentrations were captured using electrochemical sensors or a Fourier transfer infrared (FTIR) gas analyzer assembly over an incubation period of two months for the first two trials and over 40 days for the third trial. Additionally, nutrient analyses were performed for each trial. Extremely high concentrations of H₂S were observed during most manure agitation events (500 to 8000 ppm), while minimum releases (<10 ppm) were found when samples were static. Means of maximum concentrations of H₂S were compared among treatments in each trial. Statistical tests showed that adding iron oxide to gypsum-laden manure reduced H₂S production by an average of 94% compared to treatments without iron oxide. With a 1:1 molar ratio of iron oxide to gypsum, the level of H₂S released was diminished to as low as the control manure (without gypsum). Therefore, iron oxide is a promising additive to mitigate H₂S production in gypsum-laden dairy manure during agitation events.