Industrial water filter design centers around separating contaminants, either solid or liquid, from a process fluid. There are generally two types of industrial water filters designed for this use: surface filters, which consist of a single layer of filter material and rely on physically straining the fluid to extract contaminants, and depth filters, which are designed to use a porous filtration medium to collect contaminants throughout the medium, rather than just on the surface. Depth filters are used predominantly in industrial water treatment because they allow the filter to retain a higher volume of contaminants before becoming clogged. This is due to the substantially higher available collection area (since contaminants are being collected throughout the depth of the medium, rather than merely on the surface layer of the filter).
Depth filters used in industrial water filtration typically use one of two types of filtration systems: filters with a bed of media, or cartridge filters. While both of these systems perform similar activities, they differ in their effectiveness and optimal use. Both types of filtration systems rely on fluid being forced through the filtration medium, either by pumping or using gravity to drain through.
Fluid is driven through the filter medium following constricted, tortuous routes, and the contaminants are caught, either due to direct collision with the filtration medium or precipitated by molecular attractive forces. The selection of the type of filter media to remove contaminants is dependant on removal goals, as well as the type of contaminant.
Deep Bed Filters
Many different types of material are used in filter beds. Sand filters are typically used in municipal treatment plants, walnut shell filters where oil removal is needed, and activated carbon for removal of heavy metals and other contaminants. Over time, once the filter becomes restricted with captured particulates, a backwash of the bed is initiated. Flow is redirected so that the downstream equipment is not contaminated, and the filtering layers are mechanically agitated. Water is circulated through the filter during the agitation process to collect contaminants and, once the process is complete, exits through the backwash screen. This screen allows the waste to pass through while retaining all of the filter media. The wastewater is then sent to either upstream processing equipment or waste handling, and the filter is again ready for use.
Deep bed filters are used to filter drinking water, polish wastewater or cooling water, and as pretreatment for water desalination. They are particularly effective as a means of removing solid particulates while minmizing maintenance. The ability to backwash deep bed filters eliminates the need to replace filter media. If activated carbon is used as a filtration medium, the filtration process will also remove tastes and smells from the filtered water.
Cartridge filters for industrial water treatment systems usually consist of a single piece of filter material wound around a perforated cylinder, which is made of metal or plastic. The unfiltered fluid enters the filter and is forced through the medium. Once the filtration medium has reached its maximum contaminant load, it is discarded. Cartridge filters are a low cost alternative to bed filters, that can achieve very high contaminant removal efficiencies at a fraction of the cost.