The elimination of Salmonella typhimurium in sewage sludge by aerobic mesophilic stabilization and lime hydrated stabilization

This study observed the effects of two methods, aerobic mesophilic stabilization and lime hydrated stabilization of sewage sludge upon the survival of Salmonella typhimurium. Raw (primary) sludges from the mechanical biological municipal sewage treatment plant were used. Aerobic stabilization and lime hydrated stabilization were carried out in a laboratory fermentor. Aerobic stabilization was carried out in the mesophilic temperature range (from 25.70 ± 0.40 to 37.82 ± 1.38 °C). Lime hydrated was used at an amount of 10 kg/m3 for the stabilization. Sludge samples were inoculated with a broth culture of S. typhimurium. Quantitative and qualitative examinations of the presence of S. typhimurium were carried out. Aerobic mesophilic stabilization caused elimination S. typhimurium within 48 h. The T90 value of S. typhimurium was 6.66 ± 0.20 h. During the lime hydrated stabilization pH values significantly increased from 5.66 ± 0.07 to 12.12 ± 0.02 (P < 0.01). S. typhimurium was inactivated within 1 h and the T90 value was 0.19 ± 0.01 h. Our study confirmed that the treatment of sewage sludge with lime hydrated was significantly more effective than the aerobic mesophilic stabilization, (P < 0.01).