Investigating the ability of sulfur oxidizing strains in biodesulfurisation of sulfide-containing streams, screening the most capable strain and determining the optimum condition for elemental sulfur recovery from sulfide using response surface method

Abstract

Beside numerous chemical methods, biological methods were developed to remove sulfide from streams using Sulfur Oxidizing Bacteria (SOB). Because of the wide variety of such bacteria and deep difference in their capability, the ability of seven well-known SOBs were investigated. According to the results T. versutus and T. aerophilum were selected as capable bacteria for further experiments. The valuable product of sulfide oxidation is elemental sulfur, the production of sulfur in the culture medium was considered as the basis for selecting the appropriate bacteria. Evaluations of bacteria showed that T. aerophilum was not able to produce elemental sulfur and only produced sulfate as its final product. However, by creating oxygen restriction conditions, sulfur production is observed for T. versutus. Therefore, the continuation of experiments on the optimization of sulfur production in the culture medium of T. versutus was investigated. Due to the fact that the amount of dissolved oxygen in bioreactor can be controlled by changing the stirrer speed, the stirrer speed was considered as one of the parameters. In these experiments, sulfide ion concentration and initial agitator speed were considered as variables and sulfur production as a response. Experiments were designed using Design Expert software and RSM method. The results of optimization experiments showed that the concentration of 10000 mg/L of sulfide and the stirrer speed of 130 rpm led to the production of elemental sulfur of 1600 mg/L. Therefore, 40% of the incoming sulfide is converted to sulfur.