Mitigating hydrogen sulfide safety risk and odor for dairy farms using gypsum bedding

Recycled gypsum (calcium sulfate dihydrate; i.e., construction drywall material) provides a bedding alternative for dairy farmers that can be cost effective while benefiting soil properties and animal welfare. On-farm spot-measurements showed dangerous levels of hydrogen sulfide (H2S) gas may be present when manure storages containing gypsum products were agitated. Anecdotal evidence suggests gypsum-laden manure can have an intense malodor, likely due to the sulfur-based compounds produced during decomposition. Project objectives included documenting gas concentration and conditions (on-farm) and odor characteristics of manure storages that contained gypsum bedding via commercially-available products (on-farm and laboratory). Ten dairy farms were monitored during manure storage agitation events, which demonstrated highly elevated levels of H2S at farms using gypsum bedding. One manure additive significantly reduced H2S release during the on-farm trial. During laboratory bench-scale trials three molar ratios of iron oxide and a proprietary yeast-limestone-additive were added to 15 kg dairy manure then evaluated for H2S release and odor at agitation events during storage. Results indicated that a 1:1 molar ratio of gypsum to iron oxide successfully reduced H2S concentrations to below that observed from manure containing no gypsum (control). Odor concentration and intensity were reduced with iron oxide (1:1 molar ratio) manure treatment. Improved awareness of risk and adoption of proven practices can enhance safety during any manure agitation event but are particularly important when gypsum bedding is used.