Abstract
Abstract
Solubilization of sewage sludge by thermophilic bacteria isolated from a hot spring was investigated as a pretreatment for the methane fermentation process. The bacterial strain, designated strain MU3, was grown at an optimum pH of 7.5–8.0 and optimum temperature of 60°C. A phylogenetic analysis based on 16S rRNA gene sequences indicated that strain MU3 formed a distinct clade within the genus Anoxybacillus. Levels of sequence similarity of strain MU3 were the closest to Anoxybacillus rupiensis DSM 17127T. Among the strains of genus Anoxybacillus, only MU3 had an ability to hydrolyze casein. Casein hydrolysis activity of thermophilic extracellular protease produced by the strain MU3 showed an optimum temperature of 70°C. We attempted the application of strain MU3 culture into the sewage sludge, which was treated at 80°C for solubilization. Unfortunately, the isolate showed a decrease in the colony formation unit into the heat-treated sewage sludge. In batch experiments, solubilization of sewage sludge was enhanced by addition of the culture. Solubilization rates of sewage sludge supplemented with and without the culture were 32.0% and 18.8% after 67 h of incubation, respectively. The effect of the number of doses (one or two) of the culture on solubilization of the sewage sludge was investigated. Solubilization of a twofold dose was significantly enhanced as compared to a single dose after 45 h. Therefore, the solubilization of sewage sludge may be enhanced by thermophilic protease secreted by stain MU3.
Get full access to this article
View all access options for this article.