Elimination of high concentration hydrogen sulfide and biogas purification by chemical–biological process

• We constructed the chemical–biological H2S removal system in lab and pilot scale.
• The pilot system had operated consecutive 311 d for livestock biogas purification.
• Stable cell density and iron ratio contributed to high H2S removal performance.
• The change of microbial populations was analyzed in pilot scale study.
• This process is feasible for high concentration H2S elimination from biogas.

A chemical–biological process was performed to remove a high concentration of H2S in biogas. The high iron concentration tolerance (20 g L−1) of Acidithiobacillus ferrooxidans CP9 provided sufficient ferric iron level for stable and efficient H2S elimination. A laboratory-scale apparatus was setup for a 45 d operation to analyze the optimal conditions. The results reveal that the H2S removal efficiency reached 98% for 1500 ppm H2S. The optimal ferric iron concentration was kept between 9 and 11 g L−1 with a cell density of 108 CFU g−1 granular activated carbon and a loading of 15 g S m−3 h−1. In pilot-scale studies for biogas purification, the average inlet H2S concentration was 1645 ppm with a removal efficiency of up to 97% for a 311 d operation and an inlet loading 40.8 g S m−3 h−1. When 0.1% glucose was added, the cell density increased twofold under the loading of 65.1 g S m−3 h−1 with an H2S removal efficiency still above 96%. The analysis results of the distribution of microorganisms in the biological reactor by DGGE show that microorganism populations of 96.7% and 62.7% were identical to the original strain at day 200 and day 311, respectively. These results clearly demonstrate that ferric iron reduction by H2S and ferrous iron oxidation by A. ferrooxidans CP9 are feasible processes for the removal of H2S from biogas.