Water treatment contractors in the Philippines & use of Multimedia Filters
These filters, which have more than one medium, may be open gravity filters or pressure filters. In water treatment, they have become more popular in recent years with water treatment contractors in the Philippines. In advanced and tertiary waste treatment, they are the main type of filters that have been used successfully. Dual-media filter beds usually employ anthracite and sand; however, other materials have been used, such as activated carbon and sand. Water treatment contractors in the Philippines uses multimedia filter beds generally use anthracite, sand, and garnet. However, other materials have been used, such as activated carbon, sand, and garnet. Also, dual- and multimedia filters using ion exchange resins as one of the media have been tried. In some of these filters, the media may have additional characteristics other than removing particles. For example, activated carbon removes dissolved organic substances.
Water treatment contractors in the Philippines general practice.
The main advantages of multimedia filters compared to single-medium filters are longer filtration runs, higher filtration rates, and the ability to filter a water with higher turbidity and suspended solids. The advantages of the multimedia filters are due to:
the media particle size,
the different specific gravities of the media, and
the media gradation.
These result in a filter with a larger percent of the pore volume being available for solids storage. In the single-medium filter, the pore volume available for solids storage is in the top portion of the bed, whereas in the multimedia filter, the available pore volume is extended deep within the filter bed. Because of the deep penetration of accumulated floc, these filters are frequently referred to as “deep bed filters.” The single-medium filters are rarely used in wastewater or advanced wastewater treatment because of short filter runs. As a result of the large pore volume available for floc storage, the multimedia filters can be used in advanced or tertiary wastewater treatment and still have a reasonable filter run.
HOW TO CHOOSE A WATER MEDIA FILTER
The choice of a water media filter depends on several different factors which must be considered in order to achieve good filtration results:
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
WHEN IS A MULTIMEDIA FILTER REQUIRED?
Because they can be easily cleaned, media filters are often used where there is a large amount of contamination, reducing the need for replacement filter cartridges or bags and operator effort.
water treatment contractors in the Philippines feels that media filters have the advantage over other types of filters in that they have the ability to be ‘backwashed’. Backwashing purges the filter and clean out the accumulated filtered particles and restores/extends the filters’ performance.
A multimedia filter is practically used when the Silt Density Index (SDI) value is greater than 3 or when the turbidity is greater than 0.2 NTU. There is no exact rule, but these guidelines should be followed to prevent premature fouling of RO or NF membranes. All major membranes’ manufacturers require the SDI to be treated to less than 3, otherwise the warrantee will not valid.
HOW DOES A MULTIMEDIA FILTER WORK?
In a multimedia filter, there are multiple graded layers. The heavier layers become graded at the bottom and the lighter layers become graded at the top. Usually, the lighter layers are designed to have larger grains. This way larger contaminates are filtered out of the water before smaller contaminates, and the filtration efficiency for the volume of filter media is increased.
The most common multimedia filter consists of sand and anthracite as the filtration media. The sand has smaller grains and is heavier than the anthracite. This ensures that the sand layer settles beneath the anthracite and provides finer filtration. A well operated Multimedia Filter can remove particulates down to 20 microns. A Multimedia filter that uses a coagulant addition (which induces tiny particles to join together to form particles large enough to be filtered) can remove particulates down to 10 microns.
COMPONENTS OF MULTIMEDIA FILTER?
Filter Tank: This component will house the filtration media, it is either stainless steel, FRP or epoxy coated steel. Metallic tanks can handle higher temperatures and pressure.
Media: This is the filtration media that includes different layers of gravels, silica sand #20, garnet, and anthracite. This will depend on the quality of the filtered water that is needed. To achieve better water quality, it is recommended to add a layer of the garnet media.
Internal upper and bottom distributors: The bottom distribution system will prevent the media from escaping, while the upper distribution system will water treatment contractors in the Philippines distribute the flow harmonically during the service cycle. The materials of construction can either be schedule 80 PVC or stainless steel. If your application has a high temperature water, we recommend stainless steel internals, tank and face piping.
Valves: The valves open and close according to the different cycles. They could be automatic electric or pneumatic valves for automatic filters, or manual valves for manual filters. For seawater, it is recommended to use nonmetallic valves. Some industries do not allow electric valves.
Controller: This component will control the automation of your filter. This could be a PLC or a digital stager or an electromechanical timer. This is usually a preference based on the main control in the facility or the building.
Face piping: Face piping will connect all valves that control the different cycles. It could be schedule 80 PVC, stainless steel or epoxy coated carbon steel. The material of the piping depends on the temperature or operating pressure, and if it’s an indoor or outdoor application.
Flow controller: This component is installed on the drain outlet to control the backwash flow rate and prevent the media from escaping to the drain.
WHY IS BACKWASHING IMPORTANT?
The main reason that a filter in service may need a backwash is that contaminant material may build up so much that either the water flow is hindered or the filtered water quality is no longer acceptable. This condition may be monitored with a differential water treatment contractors in the Philippines pressure gauge or switch to indicate that the filter needs backwashing. A backwash should be performed when the differential pressure is greater than 10-15 psi.
Some operators may choose to initiate a regeneration cycle based on a time table or volume intervals.
During the backwash phase, water flows in the opposite direction of the normal service down flow. The backwash flow rate must be high enough that the media becomes de-compacted and expands by 40-50%. At this time the media is considered to be fluidized and acts more like the water flow than the solid filter bed.
While the media is fluidized, contaminants are allowed to slip away and escape into the filter drain where they are discarded. After about 10-15 minutes, most of the contaminants should be washed away and the filter drain should be mostly clear.
As the multimedia filter removes turbidity from the incoming feed water, eventually the filter will display a high pressure drop across the bed and/or increased turbidity levels coming from the Multi Media Filter. As a result, the multimedia filter will eventually require a backwash to clean the bed. The recommended backwash flow rate is 12-15 gallons per minute per square foot, which enough to lift the media bed sufficiently without forcing any media out of the top of the filter. Most filters are equipped with a flow restrictor on the water treatment contractors in the Philippines backwash outlet that maintains this flow rate. This is important with seasonal fluctuations in water temperature, as colder water is more viscous and lifts the bed higher with less flow, which can result in losing media out of the top during backwash.
The backwash should be performed when the pressure differential (delta-P) reaches 10 psi (above clean) across the bed or when the effluent turbidity increases by 10%. A normal pressure drop across a ‘clean’ Multi Media Filter ranges from 3-7 psi, so this needs to be taken into consideration before initiating a backwash.
The backwash can be initiated by a differential pressure switch, via timer, PLC, digital controller or manual initiation.
The sharp edges of the sand beads and other media can become rounded over time and therefore reduce their filtration ability after many years of service and should be replaced, recommended after 5-7 years for MMF.
