Fluidization of dried wastewater sludge

Experimental measurements were conducted of the minimum fluidization velocities and the entrainment (terminal) velocities for beds of dry, digested wastewater sludge particles. With the use of air, experiments were performed in an 80 mm i.d. glass column with carefully sieved, very narrow fractions of particles in a wide range of 0.65–5.3 mm. Physical examinations of the dried sludge particles revealed their irregular, mostly isometric shapes, their porous character, and their fibrous nature. New correlations, which cover the transitional flow region, have been developed to estimate the conditions of incipient fluidization and those of entrainment for such peculiar materials. Their explicit forms also enable the direct computation of the particle size corresponding to a chosen terminal velocity and the straightforward calculation of the terminal velocity of a given, irregularly shaped particle.