Treatment of high H₂S concentrations by chemical absorption and biological oxidation process

The feasibility of a chemical absorption and a biological oxidation process to remove high H₂S concentrations (500-1500 ppm) was evaluated. The experiment included the effects of gas retention time (GRT) and H₂S concentration on H₂S removal efficiency, Fe³⁺ oxidation rate, and Fe²⁺ production rate in the chemical absorption reactor. The effects of carbon source and liquid flow rate on pH value, Fe²⁺ oxidation rate, Fe³⁺ production rate, total iron concentration, and growth of Thiobacillus ferrooxidans CP9 in the biological oxidation reactor were also examined. The optimal operating conditions for the individual process and design guidelines for the serial processes were established. The results of this study indicated that a long GRT could elevate H₂S removal efficiency under all operating conditions. However, a high H₂S concentration (e.g., 1,500 ppm) resulted in a significant difference. H₂S removal efficiency stayed above 99.5% for the first 10 h of reaction, but it then decreased because of the decreasing ferric iron concentration in the liquid. The presence of 0.1% glucose favored T. ferrooxidans CP9 growth as well as the Fe²⁺ oxidation rate and prevented the occurrence of jarosite precipitates in the biological oxidation process. In addition, the presence of glucose brought about different Fe²⁺ oxidation patterns (linear or curved type) and recovery percentages of total iron (95 and 74%). The results suggest that the liquid flow rate in the biological oxidation reactor was controlled at 3 mL/min, the volume ratio of biological reactor to chemical reactor was 13.5:1 when 150 g-S/m³/h of inlet H₂S loading was introduced to the system.