Chiang Mai Journal of Science

 Hydrogen sulfide (H2S), a gas commonly occurring in biogas systems, is harmful to health and causes problems in biogas utilization. Removal of H2S will improve the quality of biogas. This study was aimed to establish an efficient biological process for H2S removal using immobilized sulfur oxidizing bacteria (SOB) in a biofilter. Bacteria were isolated from H2S treatment systems, using modified Thiosulfate medium. Among the eighteen isolates obtained, one isolate, CM1, was selected for further optimization of the H2S removal process based on its rapid growth and metabolic rate observed within 72 hours of culturing. The optimum conditions to achieve the highest cell numbers of CM1 were determined to be at the temperature of 37°C, pH 7 and under strictly aerobic or microaerobic condition. Six supporting materials (porous glass, granular activated carbon, charcoal, polyurethane foam, alginate and alginate mixed with bacterial cellulose) were used to immobilize cells of CM1 for removal of H2S. The immobilized cell numbers were found in the range of approximately 8-11 log CFU/g, with the highest number (10.70 log CFU/g) obtained when polyurethane foam was used as the supporting material. Complete (100%) removal of H2S in the laboratory-scale system was achieved when using porous glass, granular activated carbon, charcoal, polyurethane foam, and alginate as biofilters; while the alginate mixed with bacterial cellulose had a maximum removal efficiency of 77%. CM1 was identified as Paracoccus versutus, using 16S rRNA gene sequencing, and analysis of soxB gene sequence also revealed an identical translated amino acid sequence to the thiosulfohydrolase SoxB sequence of a Paracoccus species.