Reduction of microbial density level in sewage sludge through pH adjustment and ultrasonic treatment

This work investigated the effects of using ultrasound and pH-value adjustm ent on the microbial density levels in sewage sludge, with total coliform a nd heterotrophic-plate-count (HPC) bacteria as the microbial indices. Appli cation of ultrasound at a high intensity level could sufficiently disinfect both the total coliform and HPC bacteria. Adjustment of pH value could als o disinfect the micro-organisms in the sewage sludge, but at a less efficie nt rate. For the present sewage sludge, the application of ultrasound of 0. 33 W/mL level for 1-2 hours could make ita Class B sludge.