Alfa Laval ALDRUM Drum Thickeners are ideal for mechanical thickening of sludge prior to digestion or dewatering, and for reducing sludge volume prior to storage or transportation. The ALDRUM Drum Thickener comes in two sizes, Mini and Midi, for capacities from 4- 22 m3/h (18-97 GPM on the basis of 1% dry solids waste activated sludge). They are available as separate components or as complete sludge thickening modules.