Feasibility study of all types of Water Treatment Systems. Identify customer need in different areas of water supply and provide right solution through a total management of water.  

   

Pressure Sand Filters
Iron Removal Filters
Activated Carbon Filters
Softener
Dealkaliser
Demenariliser
Mixed Bed
Reverse Osmosis System
 

Types of Products:

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Pressure Sand Filters:

These are the most conventional filters and are in extensive use. The filtering media in these filters is fine sand (16/32 mesh). The sand is normally supported on a bed of graded pebbles. Under bed can be replaced by strainers also. In case strainers are provided. 100 mm layer of crushed fine silex is provided so that the fine sand does not clog the strainer buttons.

Design parameters

Max service velocity 10 m/h
Back wash velocity with air scoring 24 m/hr
Back wash velocity without air scoring 36 m/hr
Air flow velocity 36 m/hr @ 0.25 kg/cm2

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Iron Removal Filters: ..................................................................................................TOP

Dissolved iron in the water precipitates as ferric hydroxide when the carbon dioxide from the raw water is released and water comes in contact with oxygen from the air

Therefore to facilitate iron removal normally following steps are taken

  1. Aeration
  2. pH Correction
  3. Contacting with catalyst like manganese dioxide
  4. Filteration

The pH of the water is increased by dosing alkali like NaOH. Alkali helps in formation of ferric hydroxide which precipitates out.

The water is contacted with a layer of manganese dioxide as it acts as catalyst in conversion of ferrous to ferric form.

Design parameters

Max service velocity 10 m/hr
Back wash velocity 24 m/hr with air scoring
Without air scoring 36 m/hr
Air scoring 36 m/hr


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Activated Carbon Filter:...............................................................................................TOP

Activated carbon filter is one of the most widely used media for absorption of impurities. In water treatment the activated carbon is employed for:

  1. Dechlorination
  2. Removal of Organics
  3. Removal of Odour

The specific velocity to be employed depends upon the use as well as the treated water quality desired. It also depends upon the nature of Activated Carbon in terms of its pore size, degree of activation, particle size and bed depth. However, typically we use following design parameters:

  1. Max. service velocity for dechlorination 15 m/hr
  2. Max. service velocity for organic removal 10 m/hr
  3. Max. service velocity for odour removal 10 m/hr
  4. Back wash velocity 5-6 m/hr

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Softener: .....................................................................................................................TOP

Most commonly used method for removal of hardness is use of softeners. The softeners contain strong acidic action exchange resin in sodium form (Tulsion T-40). When hard water pass through the resin the calcium and magnesium ions are removed by the resin and equal number of sodium ions are imparted to the water. The resin has finit capacity for removal of calcium and magnesium ions and after this capacity is exhausted, the resin will have to be regenerated to bring it back in sodium form.

The resin is regenerated by passing 10 to 15% of NaCl solution through the resin. After the brine has been injected, the excess salt and regeneration products are washed out of the resin bed by first giving a slow rinse at the flow rate equal to the brine injection flow rate and then by giving first rinse at the flow rate equal to the service flow rate.

Softeners are basically of 2 types:

  1. Down flow softeners
  2. Up Flow Softene
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Dealkaliser:..................................................................................................................TOP

There are basically two major methods that are followed to reduce alkalinity of the water:

  1. Weak acid cation + Degasser
  2. Split Stream + Degasser

Weak Acid Cation + Degasser:

Weakly acidic cation exchange resin can remove all the cations which are associated with alkalinity. The alkalinity gets converted to carbonic acid which splits in the carbon dioxide + water. The carbon dioxide is removed by degassifier.

Split Stream + Degasser:

This type of dealkalisation system is used for reduction in alkalinity when the raw water contains permanent hardness. The system comprises of splitting the water treated in 2 streams. One stream is passed through the softner while the second stream is passed through the SAC exchanger. Two streams are again mixed and passed through the degasser. The alkalinity of water coming out of the softner is neutralized by acidity of water coming out of the strong acid cation exchanger. The carbon dioxide liberated in the neutralized process is removed by degasification.


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Demineraliser:.............................................................................................................TOP

When the dissolved solids in the water are to be almost completely removed a demineraliser is used. A demineraliser essentially consists of a cation exchanger and anion exchanger. The cation exchanger contains strongly acidic cation exchanger resins H' form. When filtered water is passed through this resin cations like calcium, magnesium and sodium are retained by the resin and equal number of hydrogen ions is given to the water.


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Mixed Bed:....................................................................................................................TOP

When water with very high purity is required a mixed bed polisher is used. The mixed bed polisher unit contains strongly acidic cation resin and strongly basic anion exchanger resin in a mixed form. The water passing through the mixed bed exchanger comes successfully in contact with cation and resin. The corresponds to an infinite stage demineralising process and ensures high purity treated water.

The resins are separated prior to regeneration. The cation resin is regenerated with acid while anion resin is regenerated with alkali. After rinsing the resins are again-mixed with air.

When the raw water has very low IDS (less than 50 ppm) the mixed bed is sometimes used directly for demineralization of water.

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Reverse Osmosis System: ..........................................................................................TOP

Reverse Osmosis system separates dissolved solutes from water via a semipermenable membrane that passes water in preference to the solute. An RO membrane is very hydrophilic, meaning that water is attracted to its chemical structure. Water can bond with the ends of the polymer segments making up the membrane. This gives water the ability to readily diffuse into and out of the polymer structure of the membrane.

The basic process of reverse osmosis uses a pump and semipermeable membrane. The pump provides the driving force. The semipermeable membrane passes water in preference to the solute that is dissolved in water; thus the majority of solute is left behind to form a more concentrated stream.

The process of reverse osmosis is not the same as filtration. Filtration is the removal of particulates by size exclusion. Particulates are removed by filtration because they are too large to fit through physical pores in the filter media, where as water molecules can readily fit through the pores.

Reverse osmosis is also a process of separation. The feed water stream is separated into a stream of purified water and a stream of concentrated solutes and particulates. This is as compared to standard filtration where the entire feed stream passes through the membrane pores, leaving the particulates embedded in the filter media.

Recent improvements in the semipermeable membranes used have caused dramatic improvements in the economics of reverse osmosis.

The improvements will result in the continued growth of RO technology into new applications. This acceptance and growth of RO industry will require the availability of more personnel educated in the various aspects and subtleties of reverse osmosis.