The modeling of gravity driven batch filtration is dicussed in which the slurry is considered to comprise a flocculated suspension. The gravity belt thickener and the sludge drying bed are commonly employed devices to which this model may be applied. In both devices, the slurry is applied to a filter medium through which the filtrate passes under the influence of the hydraulic head of the slurry. The solids are retained on the filter and accumulate in up to 3 distinct zones. A fourth zone of clear liquor may also exist above the solids zones. As the filtration process proceeds, the hydraulic head declines because of the discharge of filtrate. A model of this filtration process is developed together with methods for its solution. The model links the filtration rate to the physical properties of the slurry through constitutive relationships for the permeability and compressive yield stress. (C) 2004 American Institute of Chemical Engineers.