In multimedia filtration, a bed of media material (e.g. sand, active carbon or a mix of different medias) is used to remove particles from water. Typical use cases are the pre-treatment of raw water before the water softening and membrane treatment stages. Media filtration can also be used for the removal of iron and manganese, for example. Cartridge filters work on basically the same principle; however, instead of loose media, a solid cartridge with the preferred filtration range (particle size) is used to trap particles. Various types of cartridge are available for different use cases (e.g. active carbon, string wound, metallic or folded).
Equipment and system principle
A multimedia filtration system consists of pressure/filtration vessel(s) filled with media, valves and piping. An additional pump is usually not needed as filters are typically operated using the supply network pressure. Filtration media is usually ion-exchange or catalytic (polymer resin or manganese oxide). Depending on the capacity/flow of the system, the valve and control system used can be based either on standard automatic water filtration valves (e.g. Autotrol, Fleck, Clack, etc.), water filtration valves + an external control system or loose valves + an external control system. In cartridge filtration, the system is typically a little simpler, consisting of a filter housing and a replaceable cartridge.
Multimedia filters require regular back-flushing in order to maintain their performance. During back-flushing, trapped particles are flushed into the drain by water fed in the opposite direction to that of normal operation. If the need for filtrated water is continuous (including during back-flushing), the system is equipped with two or more filtration vessels (only one vessel is back-flushed at a time while the others are in normal operation). Cartridge filters are usually not back-flushed but instead replaced or washed manually and placed back into their housing.
Required information for system design
To complete a water treatment system design, a raw water analysis is needed together with information about the required water flow/capacity of system and the required water quality after treatment or information about the use of the water produced. If the equipment is being installed in an existing space, information about available drainage and room dimensions is also good to know.