| Summary: | Slurry can be oxidized to eliminate undesirable emissions, including malodorous hydrogen sulfide (H<sub>2</sub>S). However, it is difficult to assess the optimal amount of oxidizing agent required. In this study, one cow and one pig manure, each in three particle size ranges were oxidized with 0–350 mg ozone/L manure. Redox and H<sub>2</sub>S concentration were measured continuously. During ozonation the manures gave equivalent redox potential curves. A relatively rapid rise in redox potential was observed within a range of −275 mV to −10 mV, with all manures changing as a minimum from −200 mV to −80 mV. The gaseous H<sub>2</sub>S emissions were decreased by 99.5% during the redox increase (−200 mV to −80 mV). This is attributed to H<sub>2</sub>S oxidation by ozone and oxygen, and is not due to H<sub>2</sub>S deprotonation or gas flushing. By identifying the initiation of the final redox level following the rise, the amount of ozone required to remove H<sub>2</sub>S from the manure samples was estimated to be in the range of 6–24 mg O<sub>3</sub>/L manure, depending on the type of manure. Hence, continuous monitoring of redox potential (termination of the redox rise) during the oxidation treatment is a simple method of achieving cost-effective minimization of H<sub>2</sub>S emissions from slurry.
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