Compression-Permeability Characteristics and Effect of Freezing and Thawing Process of Excess Activated Sludge.

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Abstract
The characteristics of compression and solid-liquid separation of excess activated sludge were investigated. Compression-permeability experiments were made under low solid compressive pressure (103–105 Pa), and centrifugal settling experiments under 30–2000 Pa. In these experiments, we used excess activated sludge from a municipal wastewater treatment plant and sludge treated by a freezing and thawing process. An equation for inorganic sludge (1 – ε = E·psβ) is proposed, where ε and ps are the porosity and the solid compressive pressure, and E and β are empirical constants for each sludge. The equation can be applied to both experiments, if the average values of ε and ps which were defined previously by the authors are used in the centrifugal settling experiment. Consequently, the compression characteristics over a wide range of ps can be estimated by a centrifugal settling experiment which is relatively simple. The relationship between local specific filtration resistance α and ps can be represented by a straight line which has a bending point at the pressure where εw is nearly equal to zero. The freezing and thawing treatment of excess activated sludge diminishes the specific filtration resistance of the sludge by more than one order over the whole experimental range of ps. This implies that our treatment improves the solid-liquid separation characteristics of excess activated sludge.

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