The steady state continuous thickening of non-ideal suspensions such as sludges from water and wastewater treatment plants was investigated. Suspensions of high grade calcium carbonate, activated sludges, water softening sludges, and suspensions of fine glass beads were used. The suspensions were thickened in a closed, continuous, pilot, thickening system. The solids flux theory was used successfully for predicting performance of the steady state continuous thickener from batch settling velocities of the suspensions. The feed concentration generally did not affect the thickening function. However, the interaction between thickening and clarification functions of the tank was established through the magnitude of feed concentrations. As the feed concentration decreased with fixed solids loading, the overflow velocity increased, and the clarity of overflow generally deteriorated. (Author)