Development and Design of Sludge Freezing Beds

Abstract

A new unit operation called a sludge freezing bed is proposed for dewatering sludges produced by treatment facilities in cold regions. This unit operation uses natural freeze‐thaw to condition the sludge for dewatering. It can dewater all types of aqueous sludges up to a depth of 2.0 m. Basic construction details are identified, and procedures for operating the bed are discussed. Equations for predicting the design depth are presented along with an example of how they can be used. Convection was found to be the controlling heat transfer mechanism during freezing. Solar radiation, ambient air temperature, and the thermal conductivity of the settled sludge layer over the frozen sludge are important parameters controlling the thawing rate. Data from various sludge freezing operations indicate that the design equations are valid.