*water treatment*Presented by :-Prof. Kalpesh SolankiMajor Clean Up Water Treatment Processes:-Coagulation , Flocculation, Filtration

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Course ContentIntroductionWater treatment process or MethodsCoagulation and flocculationFiltration

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IntroductionWhy it is needed?

To kill all pathogenic germs, which are harmful to human health

To remove the unpleasant and objectionable taste and odours from the water

To remove dissolved gases ,colour of water

To make water fit for domestic, industrial, and commercial uses.

To remove micro organism and colloidal matters

To remove hardness of water

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Raw water collection*water treatment*

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Initial Stages Screening - the removal of any floating objects like leaves, branches, fishes , weeds, etc. from the water.

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*water treatment*Sedimentation: Removal of Suspended matters having higher specific gravity than water and also fine suspended matter.

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*water treatment*Aeration Dissolving oxygen into the water to remove smell and taste, promote helpful bacteria to grow, and precipitate nuisance metals like iron and manganese.

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*water treatment*Spray aerators

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Major Clean UpCoagulation and flocculation - causes the agglomeration and sedimentation of suspended solid particles through the addition of a coagulating agent (usually aluminum sulfate and/or iron sulfate) to the raw water along with a polymer to help form a floc.

Filtration- Remove Micro-organism and colloidal matter

Disinfection---Pre-chlorination and dechlorination - mostly to kill algae that would otherwise grow and clog the water filters. Also kills much of the remaining unprotected bacteria.

Softening- To remove hardness

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*water treatment*COAGULATION & FLOCCULATIONRemoval of colloidal substances from water

Potable water requirements:

health, aesthetics, economic

Colloids

Size of colloids - light waves

Brownian motion

Stability of colloids

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*water treatment*Theory of coagulation

Coagulation is the destabilization of colloids by addition of

chemicals that neutralize the negative charges

The chemicals are known as coagulants, usually higher valence

cationic salts (Al3+, Fe3+ etc.)

Coagulation is essentially a chemical process

Ionic layer compression

Adsorption and charge neutralization

Entrapment in a flocculent mass

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*water treatment* Relative coagulating power

Na+ = 1; Mg2+ = 30 Al3+ > 1000; Fe3+ > 1000

Typical coagulants

Aluminum sulfate: Al2(SO4)3.14 H2O Iron salt- Ferric sulfate: Fe2(SO4)3Iron salt- Ferric chloride: Fe2Cl3 Polyaluminum chloride (PAC): Al2(OH)3Cl3

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*water treatment*Aluminum Chemistry

1 mole of alum consumes 6 moles of bicarbonate (HCO3-)

Al2(SO4)3.14 H2O + 6HCO3- 2Al(OH)3+ 6CO2 + 14H2O + 3SO4-2

If alkalinity is not enough, pH will reduce greatly

Lime or sodium carbonate may be needed to neutralize the acid.

(Optimum pH: 5.5 6.5)

With alum addition, what happens to water pH? Al2(SO4)3.14 H2O 2Al(OH)3+ 8H2O + 3H2SO4-2

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*water treatment*Alkalinity calculation

Al2(SO4)3.14 H2O + 6HCO3- 2Al(OH)3+ 6CO2 + 14H2O + 3SO4-2

594 mg 366 mg If 200 mg/L of alum to be added to achieve complete coagulation. How much alkalinity is consumed in mg/L as CaCO3?

594 mg alum consumes = 366 mg HCO3-

200 mg alum will consume = (366/594) x 200 mg HCO3- = 123 mg HCO3-

Alkalinity in mg/L as CaCO3 = 123 x (50/61)

= 101 mg/L as CaCO3

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Al3+ species as a function of pH*water treatment*

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*water treatment*Iron Chemistry

FeCl3+ 3HCO3- Fe(OH)3+ 3CO2 + 3Cl-

With iron salt addition, what happens to water pH? (Wider pH range of: 4 9; Best pH range of 4.5 5.5)

1 mole of FeCl3 consumes 3 moles of bicarbonate (HCO3)

If alkalinity is not enough, pH will reduce greatly due to hydrochloric acid formation. Lime or sodium carbonate may be needed to neutralize the acid. Lime is the cheapest.

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Mixing device*water treatment*1- Mixing basins with baffle walls2- Mixing basin with mechanical devices (Rapid mixing)

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*water treatment* Rapid or Flash mixingis the process by which a coagulant is rapidly and uniformly dispersed through the mass of water. This process usually occurs in a small basin immediately preceding or at the head of the coagulation basin. Generally, the detention period is 30 to 60 seconds and the head loss is 20 to 60 cms of water. Here colloids are destabilized and the nucleus for the floc is formed.

Slow mixingbrings the contacts between the finely divided destabilised matter formed during rapid mixing.

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Coagulation aim*water treatment*

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What is Flocculation?*water treatment* Flocculation is the agglomeration of destabilized particles into a large size particles known as flocs which can be effectively removed by sedimentation or flotation.

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*water treatment*Why coagulation and flocculation? Colloids so small: gravity settling not possibleG r a v I t y s e t t l I n g

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Fe species as a function of pH*water treatment*

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*water treatment*Hydraulic Flocculation Horizontally baffled tank

Plan view (horizontal flow) Vertically baffled tank

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Isometric View (vertical flow)LWHThe water flows horizontally. The baffle walls help to create turbulence and thus facilitate mixingThe water flows vertically. The baffle walls help to create turbulence and thus facilitate mixing

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*water treatment*http://www.environmental-center.com/magazine/iwa/jws/art4.pdfHydraulic Flocculation

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Hydraulic flocculators*water treatment*

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*water treatment*Hydraulic flocculators:

simple technology

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*water treatment*Flocculators integrated with settling

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*water treatment*Flocculators integrated with settling

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*water treatment*Flocculators both sides of settling

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ClarifierAfter Flocculation Water enters the settling tank which is commonly called Clarifier.

Clariflocculator

In modern practice, flocculator and clarifier are provided in one unit called Clariflocculator in which chamber is provided in the center and clarifier compartment is formed by the periferical space.*water treatment*

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Filtration*water treatment*The process of passing the water through the bed of such granular materials is known as filtration.

Types of filter

1- The slow sand gravity filter

2- Rapid sand filter

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Slowsand filtersare used in water purification for treating raw water to produce a potable product. They are typically 1 to 2 metres deep, can be rectangular or cylindrical in cross section and are used primarily to treat surface water.

Filter through a 3 to 5 foot deep bed of unstratified sandflow rate 0.05 gallons per minute per square foot. Biological growth develops in the upper surface of the sand is primarily responsible for particle and microbe removal.Effective without pretreatment of the water by coagulationflocculation.Periodically clean by removing, cleaning and replacing the upper few inches of biologically active sand.

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Microbial Reductions by Slow Sand FiltrationEffective in removing enteric microbes from water. Virus removals >99% in lab models of slow sand filters. Up to 4 log10; no infectious viruses recovered from filter effluents Field studies: naturally occurring enteric viruses removals97 to >99.8 percent; average 98% overall; Comparable removals of E. coli bacteria.Virus removals=9999.9%; high bacteria removals (UK study)Parasite removals: Giardia lamblia cysts effectively removedExpected removals ~ 99%

Rapid sand filters*water treatment*

Rapid sand filtrationis a purely physical drinking water purification method.Rapid sand filters(RSF) providerapidand efficient removal of relatively large suspended particles. Two types of RSF are typically used:

Rapidgravity Rapidpressuresand filters

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*water treatment*The biggest disadvantages of slow sand filter is that it requires large area due to slow filtration rate.

This Requirement make it uneconomical for places where land is very costly in urban area. In order to reduce requirement of space and to increase the rate of filtration , a lot of research conducted which finally led to the developed of rapid sand filter.

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*water treatment*Rapid sand filters have filter rates 40 times those of slow sand filters. The major parts of a rapid sand filter are:

Filter tank or filter box

Filter sand or mixed-media

Gravel support bed

Under drain system

Wash water troughs

Filter bed agitators

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*water treatment*PRESSURE FILTERS Pressure filters fall into two categories: pressure sand and diatomaceous earth filters. Pressure filters are used extensively in iron and manganese removal plants. A pressure sand filter is contained under pressure in a steel tank, which may be vertical or horizontal, depending on the space available. As with gravity filters, the media is usually sand or a combination of media, and filtration rates are similar to gravity filters. Groundwater is first aerated to oxidize the iron or manganese, and then pumped through the filter to remove the suspended material.

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Construction rapid sand filter*water treatment*1- Enclosure tank

2- Filter Media

3- Base material

4- Under Drainage system

5- Other appurtenances

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Enclosure tank*water treatment*Rectangular in plan

Constructed either of masonary or of concrete , coated with water proof material

Depth- 2.5 to 3.5 m

surface area- 10 to 50 m2

length to width ratio 1.25 to 1.35

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Filter media*water treatment* It consist sand layer -60 to 90 cm in depth

Effective size of sand varies from 0.35 to 0.6 mm

finer sand be used

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Base material*water treatment* Graded gravel

total depth varies from 45 to 60 cm

Divided in to 4 to 5 layers

Size (mm)Depth (cm)2 to 55-85 to 125-812 to 208-1320 to 388-1338 to 6513-20

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Under drainage system*water treatment*Purpose:

It collect the filtered water uniformly over the area of gravel bed.

It provides uniform distribution of backwash water without disturbing the gravel bed and filter media.

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Types of under drainage system*water treatment*1- Manifold and lateral System

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*water treatment*Wheeler system

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*water treatment*Leopald system

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*water treatment*THANKYOU

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