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

We studied a biotechnological desulfurization process for removal of toxic hydrogen sulfide (HS) from sour gas. The process consists of two steps: i) Selective absorption of HS 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 HS 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 HS absorption efficiencies at different temperatures and biomass concentrations. The absorption efficiency improved at increasing temperatures, i.e. HS 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 HS absorption is solely determined by physico-chemical factors. Furthermore, increasing biomass concentrations to the absorber also resulted in decreased HS 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 HS absorption and leads to increased HS removal efficiencies in biotechnological gas desulfurization.