Apart from selecting appropriate packing materials, it is also important to screen an effective species to optimize
hydrogen sulfide treatment. Autotrophic and heterotrophic microorganisms have both been used, and there
are inherent differences in their nutritional requirements and abilities to catalyze specific reactions. Some chemolithoautotrophic bacteria, such as members of the Thiobacillus species, have been seeded into different packing
materials and used to metabolize H2S. The products of H2S oxidation are dependent on the strain of Thiobacillus
sp. employed. Some chemolithoheterotrophic bacteria, such as the Thiothrix, Beggiatoa, and Hyphomicrobium genera, can oxidize hydrogen sulfide into elemental sulfur and store it in their cells. This elemental sulfur will be further oxidized to sulfate, and the resulting acidity has adverse effects on microbial activity when the concentration of hydrogen sulfide is low