Enhancing the removal of H2S from biogas through refluxing of outlet gas in biological bubble-column.

Biological bubble-column (BBC) is beneficial for elemental sulfur recycle from H2S, but it's difficult to remove high concentration of H2S in biogas efficiently due to the mass transfer limitation of H2S from gas to liquid. In this study, a novel method with refluxing outlet gas in BBC was investigated. The results showed that gas reflux greatly enhanced the removal of high concentration of H2S (about 5000 ppmv) from biogas. The removal efficiency of H2S was 88.0 ± 4.1% with the reflux ratio at 1.0, which was higher than those without gas reflux (58.4 ± 1.0%), when the inlet H2S loading was 143.1 ± 4.5 g/(m3·h). Moreover, the removal capacity of H2S improved significantly with the increase of the reflux ratios from 1.0 to 4.0 and achieved the maximum at 271.8 ± 2.4 g/(m3·h). This might mainly be attributed to longer residence time and enhanced the mass transfer of O2 and H2S from gas to liquid through gas reflux.