Abstract

Research Subject: Sulfide removal from sour water is essential, before reuse or release of sour water into the environment. Regarding the high costs of traditional methods, biological removal can be used as a reliable alternative.
Research Approach: Biological sulfide removal from sour water was investigated in a batch reactor using Thiobacillus sp. as a dominant species of a mixed culture. A conceptual model was developed to describe the process of H₂S removal from sour water in the batch reactor. The model considers H₂S and O₂ transfer between liquid and gas phases, biological oxidation of H₂S to sulfate and elemental sulfur, and chemical oxidation of H₂S to thiosulfate in the liquid phase. The governing equations were derived using the principles of mass conservation and biochemical reactions. Several batch runs were performed to obtain experimental data on the variation of sulfide, sulfate, thiosulfate, and oxygen concentrations in the system as a function of time, and an algorithm was devised to use the method of Particle Swarm Optimization together with the numerical solution of the model equations to estimate biokinetic parameters. Additional batch runs under different conditions were performed to verify the accuracy of the model. These results indicated reasonable accuracy of the model to predict the performance of a batch reactor for the removal of H₂S from sour water. The novelty of this model is considering different pathways for sulfide oxidation which includes product selectivity.
Main Results: The maxim specific oxygen uptake rate (SOUR=OUR/X) is one of the most important parameters in the evaluation of the biological activity of the microorganisms. The calculated value for this parameter was almost constant (16 mg DO g^-1 VSS min^-1) during all sulfide oxidation tests indicating that the maximum specific oxidation capacity of the biomass is independent of substrate and biomass concentration. Results exhibited bacteria prefer to partially oxidized sulfide to elemental sulfur, however this preference is a function of dissolved oxygen and substrate availability.