Polysulfide Concentration and Chain Length in the Biological Desulfurization Process: Effect of Biomass Concentration and the Sulfide Loading Rate

Removal of hydrogen sulfide (H₂S) can be achieved using the sustainable biological desulfurization process, where H₂S is converted to elemental sulfur using sulfide-oxidizing bacteria (SOB). A dual-bioreactor process was recently developed where an anaerobic (sulfidic) bioreactor was used between the absorber column and micro-oxic bioreactor. In the absorber column and sulfidic bioreactor, polysulfides (S_x^2-) are formed due to the chemical equilibrium between H₂S and sulfur (S₈). S_x^2- is thought to be the intermediate for SOB to produce sulfur via H₂S oxidation. In this study, we quantify S_x^2-, determine their chain-length distribution under high H₂S loading rates, and elucidate the relationship between biomass and the observed biological removal of sulfides under anaerobic conditions. A linear relationship was observed between S_x^2- concentration and H₂S loading rates at a constant biomass concentration. Increasing biomass concentrations resulted in a lower measured S_x^2- concentration at similar H₂S loading rates in the sulfidic bioreactor. S_x^2- of chain length 6 (S₆^2-) showed a substantial decrease at higher biomass concentrations. Identifying S_x^2- concentrations and their chain lengths as a function of biomass concentration and the sulfide loading rate is key in understanding and controlling sulfide uptake by the SOB. This knowledge will contribute to a better understanding of how to reach and maintain a high selectivity for S₈ formation in the dual-reactor biological desulfurization process.