Settling velocity model of activated sludge

Abstract

The determination of an appropriate settling velocity model is indispensable to calculate secondary settlers of an activated sludge system by using the solid flux theory. Starting from the Carman-Kozeny equation, new settling models were developed by adding the slurry viscosity term. To correlate the settling velocities with the corresponding solid concentrations, Talmage and Fitch's method was utilized. The initial settling period was corrected by Hultman and Hultgren's method. Sedimentation experiments were carried out with a glass column (1 m height, 0.1 m diameter). To observe the variability of the settling characteristics of a flocculated slurry such as activated sludge caused by repetitions of sedimentation and homogenization, clay slurries flocculated with polyacrylamide were used. To verify the settling models, activated sludge slurries from a wastewater treatment plant were used. Six models with two parameters were compared. A newly deduced model v = k exp(- nx)/ x fitted the experimental data best, and another new model v = k(1 - nx) 4/ x gave a better fit than v = k(1 - nx) 3/ x.