The selective removal of H2S over CO2 from biogas in a bubble column using pretreated digester effluent

Raw biogas purification can be achieved using various physicochemical techniques. Unfortunately, techniques for the simultaneous absorption of CO2 and H2S are susceptible to the corrosive nature of H2S. Furthermore, the absorbents utilized are often expensive, thus requiring regeneration. Concurrently, on farm digesters are now moving toward the incorporation of NH3 recovery. One such process, air stripping, requires elevation of pH, which as a result produces an alkaline effluent. Due to this, a physicochemical H2S removal process was investigated in a bubble column reactor using this manure based alkaline absorbent. Selective removal of H2S over CO2 increased nearly 50% by altering the sparger configuration. Additional selectivity was achieved by decreasing the effluent height in the bubble column and increasing the superficial gas velocity. Continuous countercurrent mode of operation was tested and relatively high H2S removal efficiency (84%) was achieved at a biogas-to-effluent ratio (v/v) of 20:1, close to that typically found on dairy digesters.