A drum filter is a large, cylindrical machine typically used in industrial applications to filter liquids carrying high concentrations of suspended solids. The rotating drum filter functions by drawing water through its external filter surface into its interior space by means of an internal vacuum. Suspended solids in the water are trapped on the surface of the drum and the filtered water is then pumped away. Drum filters may utilize removable screen type filter panels or have a sieve pattern of holes in their surfaces for use with a filter aid coating. Drum filters feature a minimum of moving parts and are cheap to operate and maintain.
This machine typically consists of a large drum which rotates through a tub or bath filled the contaminated water. The interior of the drum is fitted with a vacuum duct in its center and a system for pumping out the filtered water. Once the system is started, the rotating drum has a powerful vacuum created in its interior which draws the soiled water from the tub through the filter element into its interior. Suspended solids are trapped on the exterior surface of the drum filter to be discarded or used depending on their nature.
Drum filters which make use of fine mesh panels are usually fitted with a spray system which washes the collected solids off the filter elements as the drum rotates. This variant is commonly known as the micro-screen drum filter and is typically used in applications where the solids are to be discarded. The micro-screen drum filter is particularly useful for cleaning water contaminated with coarser solids, such as animal hair or feathers, which would clog conventional filters. Filter panels are also simple to replace once worn.
Perforated drum filters are often used in water treatment plants that remove large amounts of fine sediment from water. They can also be used to remove waste water from suspended slurry products. These filters operate on the same basic principle as removable panel filters but employ a regularly applied layer of filter aid to trap the sediment. The drum is perforated with numerous holes which create a sieve-like external surface through which the water is drawn. The drum is then coated with materials such as diatomaceous earth or perlite which perform the filtering process.
The drum filter rotates against a flexible plate or knife which scrapes the trapped sediment off for later use or disposal. This knife removes a thin layer of filter aid at the same time exposing fresh, uncontaminated material to continue the filtering cycle. This causes gradual depletion of the filter aid layer necessitating regular re-coating of the drum. Both types of drum filters are not only very effective at separating heavy, dense suspensions but can be cost effective due to the simplicity of the systems.