The aim of this study was to determine the influence of gypsum (calcium sulphate) on bacterial populations in slurry systems and, as a consequence, its potential to enhance hydrogen sulphide (H2S) generation. The study focused on three slurry / bedding types: slurry from dairy farms that use either a non-slatted collection system or a slatted system, and dry, soiled bedding recovered from sheds used to house beef cattle over winter.
There is clear evidence that the presence of gypsum in slurry will enhance the potential for generation of toxic H2S gas. The levels of the gas produced, even from the small, contained systems, would be toxic to anyone exposed to equivalent concentrations on a larger scale. Therefore, if gypsum residues enter slurry this could increase the risk of H2S gas accumulation in confined spaces in the close vicinity of slurry systems. It is important therefore that this is taken into account in managing risk. Importantly, the levels of H2S gas produced from unamended slurry and bedding (no gypsum added) would still be sufficient to constitute a hazard to anyone exposed to it, though the addition of gypsum further increased the level of H2S gas production.
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Article source: http://www.hse.gov.uk/research/rrhtm/rr1041.htm