Abstract
The floatation of a primary sewage sludge was studied experimentally. Micro gas bubbles in sewage sludge decrease the efficiency of gravity settling. In the present paper, the buoyancy force of these bubbles were utilized for thickening. To promote the gas generation, sludges were continuously heated during the floatation.The results obtained by laboratry experiments are as follows ; (A) at 40°C heat treatment, the floatation process completes for about 20 hours and the value of pH increased during the floatation. (B) in case of 60°C, floatation time is sufficient with 6 hours and pH decreased. (C) In both cases, primary sewage sludge with 95% of intial moisture content was thickened to 90%. (D) In case of 50°C, floatation speed and thickening effect were lower than those of both 40°C and 60°C.Pilot plant experiments also showed the similar results as those of laboratory experiments. In addition, floatation thickened sludges were compressed with a belt press. Without using any additives, the sludge was dewatered to 61% moisture content. Thus. thermally treated primary sludge exhibited so high dewaterbility.
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