Permeability of High Ash Papermill Sludge

Most deposits of high ash papermill clarifier sludges contain very high water contents, show little drainage over the years, are unstable, and are subject to large settlements under surface loads. Poor drainability is a major part of the problem. Permeability data presented show the influence of gas bubbles trapped in the sludge mass, solids content, organic content of the solids, and admixtures of lime or flyash on the sludge drainage characteristics. Hydraulic pressures required to eliminate the influence of bubbles on drainage were approximated by an expression which considered Boyle's law and Henry's law of solubility. A threshold gradient, required to initiate flow at low pressures, approached zero when the gas bubbles were eliminated. For a constant solids content, data show that permeability increases with an increase in organic content. Lime or flyash admixtures, used as an aid in sludge dewatering methods, increase the sludge permeability.