Optimization of polysulfide in the biological desulfurization process

Summary

Hydrogen sulfide (H2S) gas is a corrosive and toxic component of various gas streams. The biological desulfurization process under haloalkaline conditions is a technology developed to mitigate H2S emissions where sulfide-oxidizing bacteria (SOB) convert H2S into elemental sulfur, which can then be recovered. Recently, a dual-reactor system was developed in which a secondary, highly sulfidic bioreactor was implemented between the initial absorber column and micro-oxic bioreactor. The highly sulfidic environment in the secondary bioreactor increased polysulfide formation, which is formed via chemical equilibrium between bisulfide and elemental sulfur. Polysulfide anions were proposed as the intermediate that the SOB use to produce elemental sulfur. Therefore, to better understand and eventually optimize the dual-reactor biological desulfurization process, this research investigates polysulfide anions and the distribution of the different chain lengths in a dual-reactor pilot-scale system and a dual and single-reactor lab-scale systems. The influence of sulfide concentration, biomass concentrations, pH values, and oxidation-reduction potential (ORP) set points on polysulfide anions was determined. Through various experiments, the results identified that polysulfide concentrations and their chain lengths were influenced the most by sulfide concentration, biomass concentrations, and pH values. Therefore, to enhance the uptake and minimize chemical oxidation, polysulfide formation must be balanced with biological removal and transformation to achieve optimal sulfur selectivity. Overall, the findings in this work highlight the importance of polysulfide in the dual-reactor biological desulfurization process and provide insight into opportunities for optimization.