Abstract: At present, heavy metal pollution in the leachate of waste disposal site only can be controlled by hydraulic barrier of extremely low permeability. The chemical field of the barrier has never been used for the retardation of heavy metal pollution. A conception of “sewage sludge barrier” is proposed based on the integration of low permeability with plentiful organic matter and anaerobe contained in the sewage sludge. To investigate the feasibility of the sewage sludge barrier, the flexible wall permeameter is used in this study to measure hydraulic conductivity of sewage sludge under different effective stresses; and the chemical properties of the effluent are monitored. Test results show that with the increase in effective stress, the dry density increases and the logarithm of hydraulic conductivity decreases linearly with decrease in void ratio. The formation of biofilm and inorganic precipitates with the anaerobic respiration, and the increase of the thickness of diffuse double layer of the clay particle within sewage sludge specimens are also responsible for the decrease in hydraulic conductivity. Hydraulic conductivity of sewage sludge as low as , combined with strong adsorption and neutral to weak alkaline reducing conditions induced by the anaerobic respiration, makes the heavy metals of Zn and Cd retarded effectively.

Key words: sewage sludge, hydraulic conductivity, effective stress, anaerobic microorganism, heavy metal