Effect of biologically produced sulfur on gas absorption in a biotechnological hydrogen sulfide removal process

Absorption of hydrogen sulfide in aqueous suspensions of biologically produced sulfur particles was studied in a batch stirred cell reactor, and in a continuous set-up, consisting of a lab-scale gas absorber column and a bioreactor. Presence of biosulfur particles was found to enhance the absorption rate of H(2)S gas in the mildly alkaline liquid. The mechanism for this enhancement was however found to depend on the type of particles used. In the gently stirred cell reactor only small hydrophilic particles were present (d(p) < 3 microm) and the enhancement of the H(2)S absorption rate can be explained from the heterogeneous reaction between dissolved H(2)S and solid elemental sulfur to polysulfide ions, S(x) (2-). Conditions favoring enhanced H(2)S absorption for these hydrophilic particles are: low liquid side mass transfer (k(L)), high sulfur content, and presence of polysulfide ions. In the set-up of gas absorber column and bioreactor, both small hydrophilic particles and larger, more hydrophobic particles were continuously produced (d(p) up to 20 microm). Here, observed enhancement could not be explained by the heterogeneous reaction between sulfide and sulfur, due to the relatively low specific particle surface area, high k(L), and low [S(x) (2-)]. A more likely explanation for enhancement here is the more hydrophobic behavior of the larger particles. A local increase of the hydrophobic sulfur particle concentration near the gas/liquid interface and specific adsorption of H(2)S at the particle surface can result in an increase in the H(2)S absorption rate.