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 O₂ rate that achieved a concentration of H₂S of 150 mg/Nm³ 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. O₂ 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/Nm³. An optimal O₂ rate of 6.4 NLO₂/Nm³ of biogas when treating the biogas was found with 0.33% (v/v) of H₂S and 118 NLO₂/Nm³ 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 O₂ supply.