Hydrogen sulfide gas treatment by a chemical-biological process: Chemical absorption and biological oxidation steps

In order to remove high concentrations of hydrogen sulfide (H₂S) gas from anaerobic wastewater treatments in livestock farming, a novel process was evaluated for H₂S gas abatement involving the combination of chemical absorption and biological oxidation processes. In this study, the extensive experiments evaluating the removal efficiency, capacity, and removal characteristics of H₂S gas by the chemical absorption reactor were conducted in a continuous operation. In addition, the effects of initial Fe²⁺ concentrations, pH, and glucose concentrations on Fe²⁺ oxidation by Thiobacillus ferrooxidans CP9 were also examined. The results showed that the chemical process exhibited high removal efficiencies with H₂S concentrations up to 300 ppm, and nearly no acclimation time was required. The limitation of mass-transfer was verified as the rate-determining step in the chemical reaction through model validation. The Fe²⁺ production rate was clearly affected by the inlet gas concentration as well as flow rate and a prediction equation of ferrous production was established. The optimal operating conditions for the biological oxidation process were below pH 2.3 and 35°C in which more than 90% Fe³⁺ formation ratio was achieved. Interestingly, the optimal glucose concentration in the medium was 0.1%, which favored Fe²⁺ oxidation and the growth of T. ferrooxidans CP9.