A pilot scale filter was tested for thickening of alum sludge generated during the production of potable water in a conventional compact water treatment plant (WTP). The alum sludge is produced from coagulation / flocculation / sedimentation processes that are using aluminum sulfate (Alum) (Al2 (SO4)3. 18H2O). The pilot scale was fabricated from scheduled uPVC pipe. The reactor was filled with floatable media (polystyrene) working as filtration media with counter flow concept. The alum sludge was discharged in the pilot scale setup from the sludge holding tank in the WTP using submersible pump. The pilot scale filter was tested at different rate of filtration (ROF) ranged from 25 to 400 m3/m2/d. In addition, different media heights (100 – 800 mm) were investigated to study the efficiency of the sludge thickening. The filter washing rate (ROW) was tested to determine the optimum ROW that will clean the filter. ROW equal to one to four times the ROF were investigated. The efficiency of the sludge thickening was achieved around 30% at the optimum range of ROF that founded in the range of 150 - 200 m3/m2/d and the filtration media height between 400-600 mm. at the optimum operating conditions, the floatable media filter had the ability to thicken the alum sludge and, the turbidity of the water produced after thickening were less than 12 NTU.