Conclusions
H2S removal is necessary to enable different ways of biogas utilization. Compared to the traditional air-mix to the biogas, dissolved oxygen supply did not cause dilution of CH4 in treated biogas. Our extremely low pH operation at 4.0–0.5 was able to lower H2S below 200 ppm while achieving the highest H2S removal of 97.3% while CH4 content was raised by 4.7%. Our biofilter was predominated by the acid tolerant Acidithiobacillus sp. with the absence of methane oxidizing bacteria. Biofiltration with O2 supply by the recirculating liquid has a potential for high H2S removal with excellent methane preservation.