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 (S-8). 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 (S-6(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 S-8 formation in the dual-reactor biological desulfurization process.