Microaeration through a biomembrane for biogas desulfurization: lab-scale and pilot-scale experiences
Microaeration, a biological method to remove H2S from biogas by oxidizing it to elemental sulfur, has been shown to be highly efficient, simple and reliable. However, dosing air directly into an anaerobic fermenter results in the dilution of biogas with nitrogen and oxygen and can cause clogging of biogas pipes by elemental sulfur. These disadvantages can be overcome by the use of a biomembrane, i.e. a membrane covered with a biofilm that separates air and biogas. Experiments with bare, wet and biofilm membranes were conducted with a commercially available PVDF LM-P2 membrane to evaluate the chemical and biological oxidation rates of H2S. Different amounts of air were dosed through the biomembrane to determine the optimum air-to-biogas ratio, to evaluate methane losses and to evaluate biogas contamination with nitrogen and oxygen. The H2S content decreased from 3000 ppm to less than 100 ppm within two days. The loss of methane was 3.7% of the total methane production and the specific H2S removal rate was 32 mg m−2 d−1.