Bacterial removal of pyrite from concentrated coal slurries

To be economically feasible, bacterial coal desulfurization must be done at a high rate in concentrated coal slurries. The rate may be restricted by gas transfer limitation (O(2) or CO(2)), inhibition of the Thiobacilli, or ceil death by mechanical abrasion. Experiments designed to differentiate between these limitations show that CO(2) transport is limiting in shake flasks for slurries of more than 20% (wt/wt) of a coal containing 1% pyritic sulfur. Air sparging removed this limitation in slurries of up to 50%, leaving inhibition as the main limitation. Heterotrophic bacteria that establish themselves in a recycled cell culture increase process rates not only by removing organic inhibitors but also by increasing the O(2)-CO(2) ration required by the biomass to the value that is supplied naturally from air.