This work investigated the effects of using ultrasound and pH-value adjustment on the microbial density levels in sewage sludge, with total coliform and heterotrophic-plate-count (HPC) bacteria as the microbial indices. Application of ultrasound at a high intensity level could sufficiently disinfect both the total coliform and HPC bacteria. Adjustment of pH value could also disinfect the micro-organisms in the sewage sludge, but at a less efficient rate. For the present sewage sludge, the application of ultrasound of 0.33 W/mL level for 1-2 hours could make it a Class B sludge.

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