PHYSICO CHEMICAL

CLARIFICATION

Clarification is the process to remove suspended solids from water. The clarifiers operate on the principle of gravity-separation. The separated solids would flow downward and settle on tapered floor.

Flocculants and pH correction chemicals are dosed to increase the efficiency of settling.

* [Flocculants: A substance which promotes the clumping of particles, especially one used in treating waste water.]

It forms an essential part of pre-treatment of Raw Water Treatment Plants and post treatment of Effluent Treatment Plants.

Types of clarifiers :
High Rate Solid Contact Clarifiers ( HRSCC ) :
It works on coagulation and flocculation followed by hydraulic separation. The principal of separation is based on mixing existing floc with incoming water, to create a dense floc that can be easily settled done. It can take care of wide variation in inlet load.

HRSCC is mainly employed to remove colloidal silica from influent water.
Tube Settlers :
Tube settlers are structure consisting of multiple tubular channels that are sloped/ tilted at an angle, adjacent to each other, which combine to form an increased effective settling area. The settling velocity of the suspended solids is hugely enhanced by incorporating tube settling media.
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DEPTH FILTRATION

Depth filtration is a process in which water is passed through various media which retains the suspended particles in water throughout the mass.

Depth filtration works by collecting particulates within filter media & passing a clean outlet flow of the liquid.

The white spaces in between the media particles provide a narrow passage for the water to pass through.
Dual Media Filters (DMF) :
In Dual Media Filters, graded sand and anthracite are used as filtration media. While anthracite filters the coarse solids suspended in water, sand restricts the finer solids. The filtration velocity in Dual Media Filters is substantially higher than conventional pressure sand filters.

The dirt loading capacities in DMF is also higher than conventional sand filters.
Activated Carbon Filter (ACF) :
ACF is a method of filtering that uses a bed of activated carbon to remove traces of organic contaminants, chlorine etc. using chemical adsorption process. Thereby ACF improves the colour and odour of the treated water.

Adsorption is a process whereby pollutant molecules in the water to be treated are trapped inside the pore structure of the carbon substrate.
Oxidation Chambers :
Oxidation Chambers are used to oxidise the soluble ferrous iron salts present in water to insoluble Ferric iron salts. Manganese dioxide (MnO2) is used as a catalyst to the process.

Once oxidised, the ferric salts comes into a suspended form which subsequently is removed by Filtration.
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ION EXCHANGE

Ion Exchange is one of the most practical and flexible methods of treating water in which special resins are used which releases certain ions in exchange of certain undesirable ones.

There are two fundamental types of ion exchange resin :
Softeners :
Softeners are used for removal of calcium, magnesium salts, which causes hard scales when heated, and replacing the same by sodium ions. The resulting soft water is more compatible and extends the lifetime of pipelines, heat exchangers etc.

Softeners do not reduce TDS in water.
Dealkalisers :
Utilise weak cation resin to change the bicarbonates (alkalinity) in the water to carbonic acid. To remove the carbonic acid, the water is passed through a degasser tower. When exhausted, the resin is regenerated by acid. The total dissolved solids (TDS) content of the water is reduced by an amount equivalent to the alkalinity present in the raw water and therefore partially demineralised water is produced.

This is very useful as the capital and operating costs of the treatment are very low.
Demineralisers :
In Demineralisers or DM plants resins are used to replace both the cation and anions by hydrogen (H+) and hydroxyl (OH-) ions respectively and in the process reduces the mineral content or TDS in water.
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