Emission of gaseous and odorous compounds from livestock operations can be a major impediment to the expansion of these facilities, especially in locations close to the populated areas. O’Neill and Phillips have shown that more than 168 compounds produced either by chemical reactions or by microbial activities are responsible for the odorous emissions from livestock operations. Some of the major odour contributors identified included ammonia (NH3), hydrogen sulphide (H2S), volatile fatty acids, p-cresol, indole, skatole, and diacetyl . Hydrogen sulphide is produced as a result of bacterial reduction of sulphate and decomposition of sulphur-containing organic constituents of the manure under anaerobic conditions. Hazardous H2S levels can be generated in swine confinement buildings during the pulling of manure pit plugs, manure agitation and pump out, operation and maintenance of manure handling equipment and drainage lines, and power washing. In a previous study conducted in Saskatchewan, Chénard et al. demonstrated that such activities could cause short-term spikes of H2S to levels above 500 μLLˉ¹ within the building airspace. Considering the odorous, toxic and corrosive nature of H2S, and severe health problems associated with the presence of H2S, a variety of approaches aimed to control the production and emission of H2S in livestock facilities have been investigated. These include application of various pit additives and chemicals, as well as the treatment of emitted air in biofilters. The oil industry is also concerned with the biogenic production of hydrogen sulphide (H2S). Previous studies have shown that H2S in oil reserves can be controlled effectively using nitrite and molybdate salts. Therefore, in this study the effects of the addition of nitrite and molybdate on reducing the emission of H2S from swine manure slurry was investigated in the laboratory and semi-pilot scale systems. Addition of 80mM nitrite or 2mM molybdate (final concentration in the manure slurry) to fresh manure in the laboratory scale closed systems (125mL and 4 L) reduced the concentration of H2S in the headspace gas from 1500 μLLˉ¹ to 10 μLLˉ¹ which maintained during the remaining period of trials (40–60 days). With aged manure, similar results were achieved with a lower level of nitrite (10 mM). Simultaneous or sequential additions of nitrite and molybdate to fresh manure had similar effects. Contrary to the systems simulating biological conditions in oil reservoirs in which simultaneous addition of nitrite and molybdate has been reported to have a synergistic effect, no synergism was observed when nitrite and molybdate were added to the manure simultaneously. Experiments with fresh manure slurry in the semi-pilot scale systems (200 L) confirmed the effectiveness of this approach in which addition of 80mM nitrite or 2mM molybdate or a combination of 80mMnitrite and 2mM molybdate decreased the concentration of the H2S in the headspace gas from an initial value of 500μLLˉ¹ to a low level in the range 2–25μLLˉ¹ and maintained these low levels during the remaining period of trials (16 days). The concentration of ammonia (NH3) in the headspace gas of the treated systems was similar to that observed in the control system (untreated), indicating that the treatment did not have an effect on the level of present NH3. Although the addition of nitrite or molybdate reduced emissions of H2S from swine manure and the associated health and safety concerns, it had little impact on the intensity of odour in the headspace gas samples from the semi-pilot scale system.

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