Water multimedia filters, which include multiple layers of media, are by far the most popular kind of water filtration. The size of each layer's layer depth and coarseness increases gradually. The media layers are layered in ascending order, with the heavier, finer media at the top and the densest, coarsest material—typically gravel—at the bottom.
What do multimedia filters remove?
The amount of TSS (Total Suspended Solids) and SDI (Silt Density Index) in the incoming feed water is decreased, using a water multimedia filter. Small particles including silt, clay, grit, organic debris, algae, and other microorganisms make up suspended solids.
High suspended particles in incoming input water might result in a large pressure drop, and impair the efficiency of downstream filtration machinery, like reverse osmosis membranes, electrodeionization (EDI), UV sterilizers, and ion exchange beds.
How should a Multimedia Filter be chosen?
To get optimal filtration results, you must take into account a number of different criteria, while choosing a water media filter.
· The highest flow rate necessary
· Turbidity or the type of suspended solids (colloidal or non-colloidal)
· Feed water is analysed
· Required level of treated water quality
· Ample water supply for the backwashing operation.
Need for a Multimedia Filter
Where there is a lot of pollution, media filters are frequently utilized because they are simple to clean, which reduces the requirement for replacement filter cartridges or bags, and operator effort.
Because, they may be "backwashed," media filters have an advantage over other types of filters. Backwashing restores/extends the performance of the filters, by cleaning out the collected filtered particles and purging the filter.
When the Silt Density Index (SDI) value exceeds 3 or the turbidity is more than 0.2 NTU, a multimedia filter is typically utilized. Although, there is no precise rule, these recommendations should be followed to stop RO or NF membranes, from becoming prematurely fouled. The SDI is required by all major membrane producers.
A Multimedia Filter's Operation: Process of operation in multimedia filters
There are numerous graded layers in a multimedia filter. The layers are graded from heavier to lighter at the bottom and top, respectively. Typically, bigger grains are intended for the lighter layers. In this approach, the water is filtered more effectively per unit of filter media, because larger contaminants are removed from the water before smaller ones.
Sand and anthracite serve as the filtration material in the most typical multimedia filter
The sand weighs more than anthracite and contains smaller granules. The sand layer will settle behind the anthracite and offer finer filtration as a result.
Size of particles removed through multimedia filtration
A properly functioning multimedia filter can filter out particles as small as 20 microns.Particulates as small as 10 microns, can also be removed by a multimedia filter that employs a coagulant addition. It causes minute particles to band together to form particles large enough to be filtered.
What makes up a multimedia filter?
Let’s enlist the components of a multimedia filter.
· Filter Tank
This part, which is stainless steel, FRP, or steel with an epoxy coating, will contain the filtration medium. Tanks made of metal can withstand greater heat and pressure.
This is the filtration media, which consists of several gravel layers, garnet, anthracite, and silica sand. This will depend on the calibre of the required filtered water. It is advised to apply a layer of garnet media to improve water quality.
· Internal upper and bottom distributors
During the service cycle, the top distribution system will disperse the flow harmonically, while, the lower distribution system will keep the media from escaping. Stainless steel or PVC can be used for construction. We advise stainless steel internals, tank, and face piping for applications that use hot water.
Depending on various cycles the valves opens and closes. They could be manual valves for manual filters, or automatic electric or pneumatic valves for automatic water filters.
This element will manage your filter's automation. This might be an electromechanical timer, a digital stager, or a PLC. Typically, this is a preference based on the facility's or the building's primary control.
· Face plumbing
All of the valves that manage the various cycles will be connected via face piping. PVC, stainless steel, or carbon steel with epoxy coating is all possibilities. Whether the application is for indoor or outdoor use, the temperature or operating pressure will determine the piping material.
To control the backwash flow rate and stop the media from escaping into the drain, a flow controller is put on the drain outlet.
FRP Media Tanks' Features and Advantages
· Standard vinyl ester or polyester structure that is resistant to chemicals
· Simple to setup and handle
· No corrosion or painting is required
· Good compatibility with RO
· Superior corrosion resistance to epoxy-lined carbon steel metal in many situations
· Cheaper than stainless steel and steel with epoxy coating
· Lightweight, weighing only 1/4 as much as steel, making it simpler to handle
· More traction (slip resistance) than metal
· Good insulating material with adequate thermal expansion qualities, which is non-conductive, i.e., prevents electrical equipment from shorting out.
Steel or stainless steel media filter tanks have the following features and advantages:
· More work than FRP
· Able to withstand pressure and temperature increases
· May be altered by incorporating hand-holes, manholes, and different exits
· Suitable for outdoor use
· Bolted directly to the skid
· Can handle vacuum
· Better for the pharmaceutical and beverage sectors than FRP tanks
· Shaped head construction according to standards for toughness and security
Provider/service flow in multimedia filters
During service flow operation, influent water to be filtered enters at the top of the filter, percolates through the filter bed, and is taken off through the collector or the distribution system at the bottom. Conventional pressure fast filters function in a down-flow direction.
Typically, the filter medium is 15 to 30 inches deep. Depending on the filter's function, many types of filter media are utilized.
We usually advise to size the media filter appropriately based on accurate calculation, because the majority of filter media perform successfully at a modest filtration velocity flow rate, of 3-5 gpm per sqft of filter area.
What makes backwashing crucial?
The primary reason a filter in use can require a backwash is if contaminated material accumulates, to the point that either the water flow is impeded or the quality of the filtered water is no longer acceptable. A differential pressure gauge or switch can be used to track this condition and signal, when the filter needs to be backwashed. When the difference pressure is more than 10-15 psi, a backwash should be carried out.
How is backwashing carried out?
1: A regeneration cycle might be started by some operators depending on a schedule or volume intervals.
2: Water travels counterclockwise to the typical service down flow during the backwash phase.
3: The media must expand by 40–50% and become de-compacted thanks to a high backwash flow rate. The medium is said to be fluidized at this point and behaves more like a water flow, than a solid filter bed.
4: Contaminants are permitted to escape when the media is fluidized and fall into the filter drain, where they are disposed. The filter drain should be mostly clean and the majority of the pollutants should have been washed away, after around 10-15 minutes.
5: The multimedia filter eventually exhibits a large pressure drop over the bed, and higher turbidity levels coming as the filter eliminates turbidity, from the incoming feed water.
6: Multi-Media Filter in order to clean the bed will eventually need a backwash. In order to elevate the media bed adequately without pushing any media out of the top of the filter, the suggested backwash flow rate is 12–15 gallons per minute per square foot.
7: Most filters have a flow restrictor on the backwash exit to keep this flow rate constant. This is crucial given that water temperature varies seasonally. Colder water is more viscous and lifts the bed higher with less flow, which might cause media to leak out of the top during backwashing.
System Backwash Flow for a Water Multimedia Filter
Backwashing should be done when either the effluent turbidity rises by 10%, or the pressure differential across the bed reaches 10 psi (above clean). Before beginning a backwash, it is important to take into account the pressure drop that typically occurs across a "clean" Multi Media Filter, which ranges from 3 to 7 psi.
A differential pressure switch, timer, PLC, digital controller, or manual initiations, are all options for starting the backwash.It is advised to replace the sand beads and other media after 5-7 years for MMF since over time, their sharp edges might become softened and impair their ability to filter.
1: Adjustment Cycle
The filter closes and no water flows in or out during the settle phase. Allowing the fluidized medium to settle will create the graded filter bed. This stage could last for 15-20 minutes. This step is frequently omitted to save time because it is not always necessary. Additionally, some valves or control systems might not include this feature, in order to be sold for less money.
It does, however, conserve water and perhaps improve filtration effectiveness. Those who live in areas with limited access to water ought to give the settle phase, some serious thought.
2: Repeat Cycle
The rinse phase may start after the settle phase. Water flows normally in the service direction but is routed to the drain during the rinse phase. This provides the media time to compact, so that it may conduct filtration more effectively before the filter is put into use.
The drained water may still include a few tiny particles at this time. The drained water should be noticeably cleaner than the influent water, after around 3–4 minutes. At that point, the filter bed is regarded as compacted and prepared for use.
Applications of multimedia filters
· The decrease of turbidity and suspended solids
· Removing iron and manganese
· Remediation of groundwater
· RO/NF and membrane system preparation
· Before using UV sterilisers
· Grey, river, or surface water filtration
· Wastewater tertiary treatment
· Heat exchanger and a cooling tower
· Process water used in industry
· Water for irrigation and storms
· Water in a swimming pool
· Drinking water
· Food and beverage processing
Manufacturer of water treatment systems
In India, Netsol Water is one of the top manufacturer and supplier of industrial RO systems, commercial RO plants, water softeners, effluent treatment plants, sewage treatment plants, disinfection products, multimedia filters, etc. Our technology is extremely trustworthy and economical to use in a business and industrial setting.