Rapid gravity sand filters are normally employed in large raw water treatment plants wherein utilization of pressure sand filters become uneconomical from the point of view of the requirement of large plot areas due to limitation posed by sizes of sand filter vessels.

Rapid gravity sand filters are predominantly RCC constructions having multiple filter beds complete with internal piping, filter water collection channel, under drainage system, gravel media to support the sand media. Isolation of each filter bay is possible and a manual isolation gate is provided for this purpose.

The water flows from top to bottom through the filter and through the sand media with filtered water exiting from the bottom of the bed and collected in filtered box through a pipe. Filtered water (treated water) from filtered box flows to the filtered water reservoir by gravity.

Backwash water tank is normally provided above the filter house. The required quantity of filtered water will be taken for backwashing the filter bed unit from the backwash tank. The backwash storage tank is periodically filled using backwash water pumps. The operation of backwash water pumps is automated with the level in the back wash water tank.

Dirty Backwash water from the filter is routed by gravity to the Effluent collection sump. Dirty backwash water from the effluent collection sump is normally pumped back to the Stilling chamber/ Raw water reservoir by Effluent Disposal pumps for re-treatment.

Rapid gravity sand filters are provided with spare filter cell to facilitate back washing operations.

Air scouring blowers are provided to improve the cleaning of the filter bed during the filter back wash sequence.

Pressure sand filters / Multi Media Filter are used to filters the water to remove the turbidity & suspended solids in water.

Pressure sand filters / Multi Media Filter have commonly employed filtration units and largely found in the following sectors.

Pressure sand filters / Multi Media Filter are of steel construction with the system operating on the feed water pumping pressure. Filters are designed based on specific volumetric flow rate per unit cross sectional filtration area. Multiple sand filter vessels are installed to augment the treatment to the required capacity from a logistic point of view. The filter is complete with inlet distributors, bottom collector/ outlet pipe, vent arrangement, water inlet and outlet nozzles, drain and a pressure safety valve for vessel safety. The filter bed is made of selected layers of sand of various grain sizes.

The sand / multi media filter bed can either be supported by a bed plate with nozzle arrangement or simply filled over a support gravel media. Both models are provided and the selection is done on client’s requirement. Ergonomically designed nozzles of poly propylene nozzles are selected and arranged in a specific fashion for equal distribution and at low pressure drops across the filter nozzles for sand filters having bed plate support arrangement.

Multi layered gravel with different sizes are used as support media where the sand filters are designed with header–lateral arrangement. The water flow from the top inlet distributor, downwards through the filter bed & goes out from the bottom outlet .The filter pump is sized to have adequate head to discharge filtered water to the filtered water tank or further process units.

During the service cycle, the filter bed gets clogged with the inlet turbidity & suspended solids which increase the pressure drop across the filter bed. The sand bed also gets compacted during the continuous service cycle. Hence, it is necessary to periodically backwash the filter bed to remove the accumulated turbidity & suspended solids & also to loosen the filter bed. The frequency of backwash is dependent upon the inlet conditions.

The single media filters have the limitations to accept larger turbidity & suspended solids & clogs faster necessitating frequent backwash.

In such a situation dual media filters with sand at the bottom & layer of anthracite will extend the service cycle.

The backwashing of filters is done with the inlet water or with the filtered water. If it is to be done with the filtered water separate storage & backwash pumps of suitable capacity & head will be required.

To help effective backwashing air scouring is also used. The air scouring is done with low pressure air of 0.35 to 0.4 kg/cm²g & generally with 50 cum/m² flow rate.

Various air scouring methods are adopted. For example air scouring first & followed by water backwash, simultaneous air & water wash. In the case of simultaneous backwash with air separate air grid is provided at the bottom. The selection of media depends on outlet quality required. The filters can be designed for manual or auto operation. In the case of auto operation, PLC can be programmed for full automation with the provision of necessary instruments & control.

Multi Media Filters

Pressure sand filters are also referred as "Dual Media / Multimedia filters". They are used to filters the water to remove the turbidity & suspended solids in water. They have commonly employed filtration units and largely found in the following sectors.

1. Secondary filtration treatment in Raw water treatment unit
2. Post biological treatment and/ or secondary clarifier in Effluent treatment units
3. Pre-treatment of water in a De-mineralization water plant
4. Pre-treatment step to tertiary treatment of water like Ultra filtration or Reverse Osmosis unit

Dual Media sand filters are of steel construction with the system operating on the feed water pumping pressure.Filters are designed based on specific volumetric flow rate per unit cross sectional filtration area. Multiple sand filter vessels are installed to augment the treatment to the required capacity from a logistic point of view.The filter is complete with inlet distributors, bottom collector / outlet pipe, vent arrangement, water inlet and outlet nozzles, drain and a pressure safety valve for vessel safety.

The filter bed is made of selected layers of sand of various grain sizes. The sand filter bed can either be supported by a bed plate with nozzle arrangement or simply filled over a support gravel media. Both models are provided and the selection is done on client’s requirement. Ergonomically designed nozzles of poly propylene nozzles are selected and arranged in a specific fashion for equal distribution and at low pressure drops across the filter nozzles for sand filters having bed plate support arrangement.

Multi layered gravel with different sizes are used as support media where the sand filters are designed with header–lateral arrangement.The water flow from the top inlet distributor, downwards through the filter bed & goes out from the bottom outlet .The filter pump is sized to have adequate head to discharge filtered water to the filtered water tank or further process units.

During the service cycle, the filter bed gets clogged with the inlet turbidity & suspended solids which increase the pressure drop across the filter bed. The sand bed also gets compacted during the continuous service cycle. Hence, it is necessary to periodically backwash the filter bed to remove the accumulated turbidity & suspended solids & also to loosen the filter bed. The frequency of backwash is dependent upon the inlet conditions.

Activated carbon filters are used for different purposes as pre-treatment to various process needs.

The high adsorptive capacity of activated carbon enables it to remove the test, odour causing compounds & other traces of organics from the water. However, not all organic compounds are removed with the same degree of efficiency.

Granular Activated Carbon filters are very effective as a de-chlorination agent. Hence, it is adopted as a pre-treatment filter before the resin based / RO based treatment plants. GAC filters employed for organic removal are similar to pressure sand filters with generally similar design, filtration rates & backwashing arrangements, with the flow rate adjusted to suit the lower density of GAC. The GAC is placed in the filter over the support gravel. Media depth is a function of the empty bed contact time (EBCT). GAC characteristics will very according to the material from which it is made whether wood, coconut shell or peat.

The carbon has to be replaced when the break through occurs. Activated carbon filters are of steel construction with the system operating on the feed water pumping pressure.The water flow from the top to the bottom across the filter bed with the filtered water discharged from the bottom. The filter pump is sized to have adequate head to discharge filtered water to the filtered water tank or further process units.

The filter bed is periodically back washed to loosen the bed to expose the compacted area. Back wash water is sourced from the filtered water tank and pumped counter current to the filtration mode operation. Dirty Backwash water from the filter is routed for further treatment before recycling back to the system. Hot water backwash is adopted in some cases where the volatile are removed for extending the life of the carbon. Air scouring blowers are provided to improve the cleaning of the filter bed during the filter back wash sequence. Special care is taken for sizing of the filter internals and frontal piping to facilitate filtration and back washing.

Rotary Vacuum Drum filters are used as filtration of liquid/ effluent/ mother liquor of the solids. The vacuum created by Vaccum pumps are the driving force utilized in the filtration operation.

Rotary Vacuum drum filters are available in the following models.

1 Rotary Vacuum drum filters – Standard model (RVDF)
2 Rotary Vacuum drum Filters – Belt type (RVBF)

Our Standard Range / Capacity / Size: 3 ft to 12 ft diameter and with length varying from 3 ft to 20 ft on both models.

Salient features of Rotary Vacuum Drum Filters – Standard model (RVDF):

1 The rotary drum is divided into a number of self contained air tight cells, which are connected to ports in a trunnion that rotates against a static valve head.
2 The valve head is usually divided into three sections enabling the operation sequence of cake formation, cake drying, and cake discharge.
3 The outer surface of the drum is covered with natural or synthetic fiber filter cloths, gauze or other media dependant upon the material to be filtered.
4 The rotary drum supported at either end on lubricated trunnion bearings is driven by an electric motor through a variable speed worm reduction gear system. The speed of the drum rotation can thus be varied to suit optimum operating conditions. The drum is dipped in a slurry trough.
5 The trough is installed with an oscillating type agitator supported by self-aligning bearings and driven by an electric motor via a reduction gear to prevent settlement of the suspended slurry solids.
6 The filter cake is dislodged through a blade arrangement into the solid trough/ conveyor.

Salient features of Rotary Vacuum Drum Filters - Belt Type (RVBF):

1 The rotary drum is divided into a number of self contained air tight cells, which are connected to ports in a trunnion that rotates against a static valve head.
2 The valve head is usually divided into three sections enabling the operation sequence of cake formation, cake drying, and cake discharge.
3 The outer surface of the drum is covered with natural or synthetic fiber filter cloths, gauze or other media dependant upon the material to be filtered.
4 The rotary drum supported at either end on lubricated trunnion bearings is driven by an electric motor through a variable speed worm reduction gear system. The speed of the drum rotation can thus be varied to suit optimum operating conditions. The drum is dipped in a slurry trough.
5 The trough is installed with an oscillating type agitator supported by self-aligning bearings and driven by an electric motor via a reduction gear to prevent settlement of the suspended slurry solids.
6 The cake discharge is assisted by a sharper radius of curvature of cloth compared to that of the cake. At the discharge point, the flexing of the cloth tends to extrude cake lodged in the interstices of the cloth weave.
7. Air Purging also can be provided on request or as per process requirement.
8 Jet sprays are provided to scour off any particles of cake that may still adhere to the cloth.

Side Stream filtration is a term used generally for cooling tower filtration systems. where, a percentage of water is withdrawn from the cooling tower sump / circulating water pipe, filtered and put back into the sump. Generally, the side stream filters are designed to filter 3% to 5% volume of circulating water per hour on a continuous basis. or to provide a system volume turnover of 12 to 16 hour.

The circulating water picks up airborne debris & other solid contaminants in the process of recirculation, due to process leakages internal system corrosion etc. which are mainly suspended solids. In a closed loop system, the concentration increases necessitating frequent blowdown.

With the introduction of a side stream filters the frequency of blow down can be reduced.

The side stream filters can be designed as Auto Valve less Gravity Filters (AVGF) or as Pressure Sand Filters (PSF).

Typically in a power station cooling tower the suspended solids are reduced from 50 to 60 ppm to 5 ppm.

Paramount Limited supplies side stream filters of any capacity, tailor made, to the customer requirement on a turnkey basis with design supply erection & commissioning.

The side stream filters are designed in vertical or horizontal construction depending upon the capacity, for the convenience of transportation.

The largest filters we have so far done is for 400 cum/hr capacity each, horizontal filters with a diameter of 3.0 m & length of 11.2 m & the total system flow of 1600 cum/hr with four filters, with outlet solid concentration of 5 ppm.

Paramount designs, manufactures, deliver Walnut filter for removal of oil and grease in water. Paramount can deliver these in various capacities and sizes tailor made on a turnkey basis, or as package units depending on the size & logistics for any flow capacity. Paramount designs these plants in manual or semiautomatic made based on PLC or DCS operations.

Walnut filter shell filtration was developed as a higher performance method of filtering free oil and suspended solids in applications where sand and multi-media filter were traditionally used.

Today, Walnut shell filter is widely accepted for polishing of oily water in the upstream oil field, downstream refineries. After the filtration cycle for a period of time, the bed becomes loaded with dirt and contaminants and begins to lose its effectiveness as a filter. It will begin to clog preventing fluid from passing thorough the bed. Hence, the bed is periodically backwashed to remove the dirt and contaminations from the filter media.

Back washing of the media is done by simultaneously air scouring and water wash at high rates when most of the accumulated contaminants are carried out to the drain.Thorough agitation and good backwash is the key requirement for better performance and life the Walnut shell filter.

The filter can be operated manually or automated. These filters are useful in all fields of water injection or in other places where contaminated water need to be treated and reused / recycled or as a pretreatment to RO plants.

Paramount offers  high solid holding capacities and are used in particulate filtration and pre-filtration water to Reverse Osmosis, deionization & EDI system.

Cartridge filters have larger surface areas compared to other conventional filters like sand filter etc. This enables cartridge filters to operate for longer periods, as obstructions occur less with bigger filter surfaces. Cartridge filter systems also permit better water flow with minimum installation area. The filters are mainly made up of polyester , ceramic and carbon or some other material that can provide a superfine filtering surface.

SAND FILTER

Sand filters are used for water purification. There are two main types:

1. Gravity Sand Filters
2. Pressure Sand Filters

Both the methods are used extensively in the water treatment plants throughout the world. The both the type require the use of flocculant to work effectively.

They can be operated either with upward flowing fluids or downward flowing fluids the latter being much more usual. For downward flowing devices the fluid can flow under pressure or by gravity alone. Pressure sand bed filters tend to be used in industrial applications. Gravity sand filters are used in water purification especially drinking water.

PRESSURE SAND FILTER

The Gravity sand filters are known as Rapid sand filters. Smaller sand grains provide more surface area and therefore a higher decontamination of the inlet water, but it also requires more pumping energy to drive the fluid through the bed. The depth of the sand bed is recommended to be around 0.6-1.8 m. Normally these filters are designed at a maximum flow rate of 10-20 m3/m2/hr. Using the required throughput and the maximum flow rate, the required area of the bed can be calculated.

The main important point for design is to keep in mind is the distribution of fluid across the bed. Pressure sand filters are typically operated with a feed pressure of 2 to 5 bar. The build-up of particulate solids causes an increase in the pressure drop across the bed for a given flow rate. For a gravity bed when the pressure drop or flow is unacceptable the bed is back washed to remove the accumulated particles. For back wash water is pumped backward through the bed until it is fluidized and has expanded by up to about 28 to 30%. The range of back wash water flow is typically 3 to 10 m3/m2/hr and duration is 5-15minutes.

Paramount offers Pressure sand filters for both municipal and industrial water treatment for the removal of suspended solids. Pressure filters are installed after settling/clarification equipment. These filters are used in the pretreatment of ACF/DM/UF/RO systems to increase the life and efficiency of down the line installed systems.

Paramount design horizontal and vertical pressure vessels to meet various constraints of a customer such as water quality, footprint, back wash requirements and flow requirements. Vessels are designed for various pressure capacities.

Media options and arrangements are several and depend on the application and internal piping arrangement but often consist of a dual-media sand-and-anthracite arrangement (to minimize backwash frequency) above a gravel support bed.

Activated Carbon Filters :

Paramount offers activated carbon filters for removal of organic impurities, odor, colour  and free chlorine from water. ACF are also used in effluent treatment plants as polishing filters before disposal of the treated water to take care of left over COD.

These filters are used as pretreatment equipment to increase the life and efficiency of DM, UF and reverse osmosis plants.

These filters are mainly designed based on the contact time required for contaminant removal and media replacement frequency. These filters can be backwash based on the pressure drop across the bed.