Abstract
Biological removal of hydrogen sulfide in biogas, which was produced from an anaerobic digester treating cattle manure with a HRT of 25 days, was carried out by adding a low amount of air to the headspace of the digester (approximately 1% of oxygen concentration in the digester). The concentration of hydrogen sulfide was successfully reduced from 3,500 ppm to a low level of 1,100 ppm after air adding. A microbial mat with an elemental sulfur content of 90% per g-TS was developed in the headspace of the digester as a result of the sulfide oxidation. Cloning analysis revealed that close-relatives of Halothiobacillus neapolitanus and Sulfurimonas sp., both known as sulfide oxidizer, were predominant in the mat and might be responsible for the sulfide oxidation and for the elemental sulfur accumulation under microaerophilic environment. A microbial sulfide oxidation activity test demonstrated that the wetness of the mat is important to the microbial sulfide oxidation activity. These results suggest that an appropriate design for microbial habitat in a digester is one of the important factors for the biological hydrogen sulfide removal.
