Biologically enhanced hydrogen sulfide absorption from sour gas under haloalkaline conditions.

We studied a biotechnological desulfurization process for removal of toxic hydrogen sulfide (H2S) from sour gas. The process consists of two steps: i) Selective absorption of H2S into a (bi)carbonate solution in the absorber column and ii) conversion of sulfide to sulfur by sulfide oxidizing bacteria (SOB) in the aerated bioreactor. In previous studies, several physico-chemical factors were assessed to explain the observed enhancement of H2S absorption in the absorber, but a full explanation was not provided. We investigated the relation between the metabolic activity of SOB and the enhancement factor. Two continuous experiments on pilot-scale were performed to determine H2S absorption efficiencies at different temperatures and biomass concentrations. The absorption efficiency improved at increasing temperatures, i.e. H2S concentration in the treated gas decreased from 715 ± 265 ppmv at 25.4 °C to 69 ± 25 ppmv at 39.4 °C. The opposite trend is expected when H2S absorption is solely determined by physico-chemical factors. Furthermore, increasing biomass concentrations to the absorber also resulted in decreased H2S concentrations in the treated gas, from approximately 6000 ppmv without biomass to 1664 ± 126 ppmv at 44 mg N/L. From our studies it can be concluded that SOB activity enhances H2S absorption and leads to increased H2S removal efficiencies in biotechnological gas desulfurization.