Is the biogas dry, or does it contain water vapor as well? If you inject SO2 into humid H2S (or H2S in Methane as would be the case in biogas), elemental sulfur will form and can be filtered out. In a perfect world, you can burn the sulfur formed in air and make SO2, and reinject it into the system.
2H2S + SO2 -(H2O)-> 2S + 2H2O
^ |
| v
SO2 <----- S + O2
This occurs easily, even at room temperatures as long as water is present, although the equipment to keep it running perfectly would be quite sophisticated. You'd have to test how much H2S was present initially.