Using a Shear Test-Based Lab Protocol to Map the Sticky Phase of Activated Sludge

Abstract Drying is widely recognized as an essential step in the management of waste activated sludge. Despite growing economic, industrial, and environmental interest in sludge drying in recent years, only few studies have been devoted to the stickiness of drying sludge. During the course of drying, activated sludge passes through a highly cohesive, plastic-rubbery phase. This transition occurs at some intermediate moisture content range, which is referred to as the sticky phase of sludge. During this phase, the sludge tends to stick to the dryer walls, which alters its hydrodynamics and often results in severe operational problems and in a corresponding significant reduction of the dryer capacity. This work presents a simple and repeatable lab protocol to map the sticky phase of activated sludge based on the Jenike shear test. When sludge begins to exhibit sticky behavior, there is an increase in the level of shear stress required to make the preconsolidated sludge slip over a steel surface. The protoco...