The multimedia filter in water filtration is the most common method of water filtration. These filters contain multiple layers of media through which water flows. Each layer is progressively sized in coarseness and layer depth. The media layers are stacked such that the layer to remove the coarsest and densest media, usually gravel, is at the bottom. The layer to remove lighter, finer media is at the top.
The multimedia filter reduces the level of suspensions in the feed water. Suspended solids in a waste stream usually include small particles such as silt, clay, organic matter, grit, algae, and other microorganisms.
A water media filter depends on several factors which must be considered to achieve the best filtration results. These are:
- The maximum required flow rate
- The nature of the suspended solids or turbidity (colloidal or non-colloidal)
- Water analysis of feed water
- Required quality of treated water
- Availability of adequate supply of water for backwashing process.
Since they can be easily cleaned, media filters are often used for a large amount of contamination, eliminating the need for replacement filter cartridges or bags and operator effort.
Media filters can be “backwashed,” a great advantage over other types of filters. Backwashing cleans the filter and removes the accumulated filtered particles, restoring and extending the filters’ performance.
In a multimedia filter, there are many graded layers. The heavier layers are placed at the bottom and the lighter layers are placed at the top. Usually, the bottom layers are designed with larger grains so that larger contaminants are filtered out before the smaller contaminants. This increases the filtration efficiency of filter media.
The most common multimedia filter uses anthracite and sand as filtration media. The sand has smaller grains and is heavier than anthracite. Thus, the sand layer will settle below the anthracite and improve filtration drastically. A well-operated multimedia filter can remove particulates as small as 20 microns.
- Filter Tank: This component has filtration media. It is either made of stainless steel, FRP, or epoxy-coated steel. Metallic tanks can tolerate higher temperatures and pressure.
- Media: This is filtration media includes different layers of gravel, silica sand #20, garnet, and anthracite. The layers will depend on the required quality of the filtered water. For higher water quality, a layer of garnet media is recommended.
- Internal upper and bottom distributors: The bottom distribution system prevents the media from escaping, while the upper distribution system will harmonically distribute the flow during the service cycle. They can be constructed using either schedule 80 PVC or stainless steel. For higher water temperatures, we recommend stainless steel for internals, tank, and face piping.
- Valves: The valves open and close according to the different cycles. They could be of various types:
- Automatic electric or pneumatic valves for automatic filters or
- Manual valves for manual filters. For seawater, non-metallic valves are strongly recommended.
In fact, some industries do not allow the use of electric valves.
- Controller: This component will control the automation of your filter. This could be a PLC, an electromechanical timer, or a digital stager. Preferences are usually based on the facility’s main control.
- Face piping: Face piping connects all valves controlling the different cycles. It could be made of schedule 80 PVC, epoxy-coated carbon steel, or stainless steel. The piping material depends on the temperature or operating pressure and varies for indoor and outdoor applications.
- Flow controller: This component is the part of the drain outlet that controls the backwash flow rate. It stops the media from flowing into the drain.
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