Reduction of pathogenic bacteria in organic compost using gamma irradiation

Organic compost is a useful fertilizer for organic farming. However, it poses a microbiological hazard to the farm products because most of the composts are originated from excremental matters of domestic animals. In this study, the radiation treatment was performed to improve microbiological safety of organic compost and the effectiveness of gamma irradiation for inactivating Salmonella Typhimurium and Escherichia coli was investigated. The total aerobic and coliform bacteria in the 16 commercial composts were ranged from 105 to 107 CFU/ml and 0 to 103 CFU/ml, respectively. All coliform bacteria in the composts were eliminated by irradiation at a dose of 3 kGy, while about 102 CFU/ml of the total aerobic bacteria were survived up to 10 kGy. In the artificial inoculation test, the test organisms (inoculated at 107 CFU/g) were eliminated by irradiation at 3 kGy. Approximate D10 values of Salmonella Typhimurium and E. coli in the compost were 0.40 and 0.25 kGy, respectively. In the cultivation test, the test organisms of the compost had transfer a lettuce leaves. The growth pattern of lettuce was not different between irradiated and non-irradiated composts.