In this study, biological methyl mercaptide removal is investigated using the bacterium Thiobacillus thioparus in a fed batch bioreactor. In this process, methyl mercaptide is converted into elemental sulfur particles as an intermediate in the oxidation of methyl mercaptide to sulfate. The main product is sulfur at either low dissolved oxygen or high methyl mercaptide concentrations, and also more sulfates are produced at high dissolved oxygen. According to the reactions performed, a mathematical model is developed. The model parameters are estimated and the model is validated by comparison to experimental data. The results show that the proposed model is in a good agreement with experimental data. According to the experimental results and mathematical model, sulfate and sulfur selectivity are sensitive to the concentration of dissolved oxygen. For concentrations of methyl mercaptide 0.2 mmol L⁻¹ in the bioreactor and dissolved oxygen of 0.5 ppm, only 14% of sulfide load is converted to sulfate while the figure is 60% at the same methyl mercaptide concentration and dissolved oxygen of 4.5 ppm. At high sulfide load to the bioreactor, the concentration of noneliminated methyl mercaptide increases, leading to higher sulfur particle selectivity and consequently lower sulfate selectivity.