BIOTRICKLING FILTERS Biotrickling filters (BTF) are irrigated reactors with a packed bed colonized by sulfur-oxidizing bacteria (SOB). As raw biogas is blown through the media, hydrogen sulfide (H2S) is removed from the biogas and metabolized by the SOB. Air and recycled nutrient water support the activity of the SOB. The liquid-phase also aids pollutant capture and removal of the sulfate waste generated by SOB.