Enhancement of Biogas Production from Sewage Sludge with the Addition of Geobacillus sp. Strain AT1 Culture

Abstract

We investigated the enhancement of biogas production from anaerobic digestion of sewage sludge with the addition of an aerobic thermophilic bacterial culture of Geobacillus sp. strain AT1. Biogas production was significantly enhanced by the 2 ml addition of stationary-growth-phase culture (24h) of strain AT1 to 38 ml methanogenic sludge. Strain AT1 grew aerobically in F-JX synthetic medium, and optimum growth ocurred at pH 7.0 and 65ºC with shaking at 140 rpm. The optimum temperature for protease activity in the strain AT1 culture was around 65ºC in the presence of 2mM CaCl2, where relative protease activity reached 210% compared with that at 35ºC without CaCl2. Protease activity was stable from 35ºC to 65ºC, but rapidly decreased within 30 min incubation at 85ºC. A protease inhibitor mixture (AEBSF, bestatin, E-64, EDTA, and pepsatin) inhibited the biogas enhancement by the strain AT1 culture. Methane production was enhanced by 2.1 times with the addition of the strain AT1 culture compared with the addition of F-JX medium, and was enhanced by 2.8 times with the additions of authentic protease and serine protease S. These results suggest that the enhancement of biogas production from anaerobic digestion of sewage sludge was caused by the protease activity of aerobic thermophilic Geobacillus sp. strain AT1