Determination of the optimal rate for the microaerobic treatment of several H2S concentrations in biogas from sludge digesters

The treatment of H2S in the biogas produced during anaerobic digestion has to be carried out to ensure the efficient long-lasting use of its energetic potential. The microaerobic removal of H2S was studied to determine the treatment capacity at low and high H2S concentrations in the biogas (0.33 and 3.38% v/v) and to determine the optimal O-2 rate that achieved a concentration of H2S of 150 mg/Nm(3) or lower. Research was performed in pilot-plant scale digesters of sewage sludge, with 200 L of working volume, in mesophilic conditions with a hydraulic retention time of 20 d. O-2 was supplied at different rates to the headspace of the digester to create the microaerobic conditions. The treatment successfully removed H2S from the biogas with efficacies of 97% for the low concentration and 99% for the highest, in both cases achieving a concentration below 150 mg/Nm(3). An optimal O-2 rate of 6.4 NLO2/Nm(3) of biogas when treating the biogas was found with 0.33% (v/v) of H2S and 118 NLO2/Nm(3) of biogas for the 3.38% (v/v) concentration. This relation may be employed to control the H2S content in the biogas while optimising the O-2 supply.