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FILTRATION. It is a process for separating suspended & colloidal impurities from water by passage through a porous medium. Filtration with or without pre-treatment effectively removes Turbidity (silt & clay) Color Micro-organisms

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FILTRATION

  • It is a process for separating suspended & colloidal impurities from water by passage through a porous medium.

  • Filtration with or without pre-treatment effectively removes

  • Turbidity (silt & clay)

  • Color

  • Micro-organisms

  • Precipitated hardness from chemically softened water .

  • Precipitated iron & Mn from aerated waters.


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Classification of filters

  • I) According to direction of flow

    1.up flow

    2.down flow

    3.radial flow

    4.horizontal flow

    II) Types of filter media

    1.granular media filters

    single media

    dual media

    multi media

    2.fabric & mat filters


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  • III) Driving force

    (gravity filters/pr.filters)

  • IV) Mtd . Of flow rate control

    (constant rate /declining or variable rate filters)

  • V) Filtration rate

    (SSF / RSF)

  • SSF & RSF are down flow /granular-mediam gravity filters.

  • RSF operate @constant rate of filtration.





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Example 14.1

Design a slow sand filter for a town with population of 20,000. Per capita water supply rate is 90 Lpcd. The expected maximum raw water turbidity is 25 NTU.

Design criteria :

No under drain should be provided within 600mm of the sidewall.


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Solution:

Total daily water demand=20,000X90=1,80,0000 litres

Add 10% extra for operational and other losses

Total water demand including losses=1,980,000 litres or 1.90MLD

Since the raw water turbidity is less than 30NTU the water can be directly fed to the filters.

Assume average hours of operation per day as 16 hours


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Rapid sand filter design

Problem :design the rapid sand filter to treat 10 million liters of raw water per day allowing 0.5% of filtered water for back washing. Half hour per day is used for back washing . Assume necessary data.

Solution :





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Filter hydraulics

  • Actual filtration process by which water is cleaned.

  • Back washing operation by which filter is cleaned.

  • Flow through packed bed can be analyzed by classic filtration theory.

  • Carmen modified Darcy - Weisbach eqns for head loss in a pipe to reflect conditions in a bed of porous of uniforms size.

  • Carmen –Kozeny eqn .is


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f' isthe friction factor related to coefft. of drag around the particles.

For laminar flow,

Clean water @ 20°C is passed through a bed of uniform sand at a filtration velocity of 5m/h. The sand grains are 0.4mm dia. with a shape factor of 0.85 & a specific gravity of 2.65. the depth of bed is 0.67 & porosity is 0.4. Determine the head loss through the bed.



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Backwashing manifold and laterals

Backwashing preceded by air-wash


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Design of Rapid sand filter manifold and laterals

step-1: Estimation of design flow (MLD/Lph):


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Step-2: Determination of surface area of filter: manifold and laterals

Step-3: Dimension of each filter unit:


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Step-4: Depth of filter unit: manifold and laterals

Step-5: Filter sand:



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Design a SSF for a town with population of 20,000.Percapita water supply rate is 90 lpcd. The expected raw water turbidity is 25 NTU.

step-1: Estimation of design flow:


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Step-2: Determination of SA of filter: water supply rate is 90 lpcd. The expected raw water turbidity is 25 NTU.

Step-3: Dimension of each unit


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Step-4: Depth of filter unit: water supply rate is 90 lpcd. The expected raw water turbidity is 25 NTU.

Step-5: Filter sand:


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Step-6:Design of under drainage system: water supply rate is 90 lpcd. The expected raw water turbidity is 25 NTU.


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Back washing water supply rate is 90 lpcd. The expected raw water turbidity is 25 NTU.:


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Wash water Gutter: water supply rate is 90 lpcd. The expected raw water turbidity is 25 NTU.


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SERVICE RESERVOIR water supply rate is 90 lpcd. The expected raw water turbidity is 25 NTU.Find out capacity of SR for the following situations viz.,Power is available throughout 24 hrs.A)16h of pumping during 4am to 12noon & 1am to 9pm. B)8h of pumping during 4am to 8pm & 2pm to 6pm.

Data given are:


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Capacity of SR water supply rate is 90 lpcd. The expected raw water turbidity is 25 NTU.


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Disinfection water supply rate is 90 lpcd. The expected raw water turbidity is 25 NTU.

  • Water has long served as a mode of transmission of diseases.

  • The most important water- borne diseases are

    • Intestinal tract

    • Typhoid

    • Paratyphoid

    • Dysentery

    • Injections hepatitis

    • Cholera

    • Some parasitic worm diseases

  • Major group of microorganisms include

    • Bacteria

    • Viruses

    • Fungi & Mold

    • Algae

    • Protozoa

    • Helminthes

    • Parasitic worms


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    Bacteria water supply rate is 90 lpcd. The expected raw water turbidity is 25 NTU.

    • May cause disease, taste & odors, pipe corrosion, pipe blockages.

    • Shape as spherical (cocci), rod shaped (bacilli), curved rod-shaped (vibrios), spiral (spirilla), or filamentous.

    • Most bacteria are harmless & beneficial.

    • Some form spores & resist chlorination.

    • Actinomycetes (i.e filamentous bacteria )cause musty & earthy tastes & odors in water supply.

    • H2S producing bacteria cause rotten egg smell.

    • Iron & Mn bacteria cause severe clogging or corrosion of pipes. (producing red water) associated with taste, color & staining.

    Viruses

    • More resistant to disinfection than bacteria


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    Fungi & Molds water supply rate is 90 lpcd. The expected raw water turbidity is 25 NTU.

    • Most are saprophytes (obtain food from dead organic matter)

    • From diverse, slimy mats that clog filters & other water treatment units

    • Grow on walls & weirs @ WTP

    • Produce musty taste & odors as well as color & turbidity

    Algae

    • Produce their own food from sunlight & nutrients

    • They have different pigments & colors

    • Some algae produce slime that interface with treatment process

    • Algae blooms in reservoir cause turbidity & color & interface with coagulation & sedimentation & cause filter clogging

    • They cause different tastes & odor problem


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    Protozoa water supply rate is 90 lpcd. The expected raw water turbidity is 25 NTU.

    • Several protozoa cause disease .

      • Giardia lamblia

      • Entamoeba histolytica

      • Cryptosporidum

  • Nagleria fowleri may enter by nasal initialization exposure from swimming & cause amoebic meninpoecephalitis

  • Outbreak of

    • Giardiasis

    • Amoebic dysentery

    • crytosporidiosis


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    Helminthes (Parasitic worms) water supply rate is 90 lpcd. The expected raw water turbidity is 25 NTU.

    • It may cause many disease

    • Transmission of worm & eggs is due to contaminated drinking water

    Nuisance – Causing organisms

    • Many organisms, snails & slime growth cause serious problems in raw water conveyance.

    • Snails & Slime growth on walls of raw water lines result in reduce pipe capasity

    • Prechlo


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    Indicator Organisms water supply rate is 90 lpcd. The expected raw water turbidity is 25 NTU.

    • Analytical procedures for detection of pathogenic organisms are not

    • clear – ad

    • Characteristics of an Ideal Real Indicator Organism:

      • Detection should be quick, simple, & reproducible

      • Result should be applicable to all water

      • It should have greater or equal survival time & be present in large no than pathogen

      • It should not be grow in nature

      • It should be harmless to man

  • Coli form organisms are used as indicator organisms

  • They have non pathogenic bacteria whose origin is in fecal matter

  • The presence of these bacteria in water is an indication of fecal contamination & thus usage water

  • Coli form bacteria are members of Entrobacteriace Family & include genera Escherichia, Kelbsiella, Citrobacter,& Entrobacter


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    • Escheria coli (E.Coli) species appear to be most representative of fecal contamination

    • Fecal stretococci & Enterococci are also used as indicator organisms

    • Std techniques used to ennumerate coli form organisms

      • Multiple – tube Fermentation

      • Membrane filter

  • Multiple -tube Fermentation technique uses a lactose broth medium that is fermented by coli form group

  • Gas hobbles collected inside an inverted inner vial are an indication of gas formation


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    Disinfection representative of fecal contamination

    • Destruction of disease – causing microorganisms, to provide safe potable water supply

    • Factors affecting of disinfection

      • Type & con of microorganisms to be destroyed

      • Type & con of disinfectant

      • Contact time provided

      • Chemical character & temp of water being treated.

        Table 12.1(pa no 469)



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    Disinfection By - products Water at 25

    • Oxidation of natural organic material (i.e humic substances) produce aldehydes, ketones, alcohols & carboxylic acid during disinfection

    • THMs are produced in presence of froc chlomne

    • Organic halides (TOX) are produced

    • Chlormines are formed by reaction of Cl2 with N2 containing organic compounds (amino, acids, proteins)

    • Many halegenated DBPs have been identified in chlorinated drinking water

    • Formation of DBPs depends upon a no of factors

      • Con & type of orgaanic matter present

      • Cl2 dose

      • Temp & PH of water

      • Bromide con

      • Reaction time

  • Control of DBPs include

    • Precursor removal by enhanced cogulation, Adsorption, RO

    • Alternative oxidants

    • Removal of hy products by stripping, Adsorption, RO



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    • Cl Chlorination2 + H2O => HOCl+ H+ + Cl-(12.3)

    • HOCl  H++ OCl-(12.4)

    • Ca(ocl)2 + 2 H2O  2 HOCl +Ca2+ + 2 OH- (12.5)

    • NaOCl +H2O  HOCl + Na+ + OH- (12.6)

    • HOCl +Precursors => CHCl3 + other chlorinated DBPs (12.7)

    • HOCL + Br => HOBr + Cl- (12.8)

    • HOBr + Precursors => CHBr3 + other brominated DBPs (12.9)

    • HOCl + Br +Precursors => CHCl3 + CHBr2 Cl+ CHBr3 + other halogenated DBPs (12.10)

    • NH3 + HOCl => NH2CL (monochloramine) + H2O (12.11)

    • NH2 Cl + HOCl => NHCl2 (dichloramine) +H2O (12.12)

    • NH2Cl + HOCl => NCl3 (trichloramine) + H2O (12.13)


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    CL Chlorination2 as Disinfection

    • H is greenish yellow in color & 2.5 times heavier than air

    • Liquid CL2 is amber colored & about 1.44 times heavier than water

    • When CL2 is added to water, it first react with iron, manganese or H2S that may be present in water

    • Then CL2 will react with organic substances (including bacteria)

    • CL2 will react with organic compounds in water & foom trihalomethanes (THM)

    • It will also react with reducing agents ( eg H2s, ferrous iron, manganous iorn, nitrite irons)

    • CL2 may be added to water in the from of CL2 gas chlorine dioxide or hypoclorite

    • All types of CL2 will kill bacteria & some viruses but chlorine dioxide, will electively kill Cryptoporidium, Giardia, Protozoans, & some viruses

    • CL2 gas is compressed into a liquid & stored in rental cylinder

    • The total ant of CL2 which is used up in reactions with compounds & destroying pathogens in water is known as CL2 demand

    • A sufficient quantity of CL2 must be added to the water so that after CL2 demand is ret, still there is some CL2 left as free residual CL2 to take care of any further contamination.


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    Reaction of CL Chlorination2 with water

    • CL2 reacts with water & breaks down into hypochlorous acid & HCL

    • Chlorine + Water => Hypochlorous acid + Hydrochloric acid

    • CL2 + H2O => HOCL + HCL

    • Hypochlorous acid may further break down, depending on pH

    • HOCL  H+ + OCL- (hypochlorte iorn)

    Advantages of CL2

    • Easily stored for long time without deterioration

    • Highly soluble in water

    • Inexpensive

    • Very powerful disinfectant, may remain in water as free residual

    • No sludge formation

    Disadvantages of CL2

    • Storage & handling need careful practise

    • It forms a very explosive mixture, when mixed with CO gas

    • Larger CL2 residual may cause bad taste


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    Other types of Disinfections Chlorination

    • Hypoclorite

    • Chloaemines

    • Chlorine dioxide

    Hypochlorites

    • Instead of using CL2 gas, some plants use hypochlorite (i.e bleaching powder)

    • They are less pure than CL2 gas * are less than dangerous

    • Temp, light, physical energy could break down hypoclorites

    • They react with water & form hypochlorous acid (disinfection)

    • There are 3 types of hypochlorites viz.,

      • Sodium hypochlorite

      • Calcium hypochlorite

      • Commercial hypochlorite


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    Sodium hypochlorite: (NaOCL) Chlorination

    • H is in liquid from, contains upto 12% C2

    • The reaction of sodium hypochlorite with water is shown below

    • sodium hypochlorite + water => Hypochlorite acid + NaOLI\

    • NaOLI + H2O => HOCL + NaOH

    • It may be prepared by absorbing CL2 gas in cold NaOH soln

    • 2 NaOH + CL2 => NaCL + NaOCL + H2O

    • A soln of NaOCL is frequently used as a disinfectant & as a bleaching agent

    • A 12% soln is widely used in waterworks for chlorination of water

    Advantages

    • Easily stored & transported

    • Dosage is simple

    • Transport & storage are safe

    • It is as elective as CL2 gas for disinfection & produces residual disinfected


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    Disadvantages Chlorination

    • It is a dangerous & corrosives substance

    • Safely reserve have to be taken to protect works

    • Expansion

    Calcium hypochlorite : Ca(OCL)2

    • Also known as bleaching powder or chlorinated time is a white amorphous powder with pen gent smell of CL2

    • When fresh, it contains 30 – 50 % of available CL2

    • It is an unstable compound, on exposure to air, light, moisture, it rapidly loses its CL2 content

    • Ca(OCL)2 + 2 H2O => 2 HOCL +Ca(OH)2


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    • There is a heavy sediment of lime, when bleaching powder is mixed with water, this sediment must be disposed of

    • WHO recommends making up 1% soln comprising 40g bleaching powder to 1 litre of water (~15 % available CL2)

    • 3 drops of this soln should be added to 1L of water for drinking

    • Storing solns of CL2 are very unstable & will lose their CL2 content if explosed to air or sunlight

    Disadvantages

    • They raise pHof water due to line content

    • They contain very low ant of CL2

    • They decompose in strength over time when stored

    • They are expansion & laborious in operation


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    Commercial bleach mixed with water, this sediment must be disposed of

    • Available in market

    Chloramines

    • Some TPs use chloramines

    • First CL2 gas or hypochlorite is added to water to produce hypochlorous acid

    • NH3 is added to water to react with HOCL to produce chloramine

    • 3 types of chloramines can be formed in water viz.,

      • Monochloramine

      • Dichloramine

      • Trichloramine

  • Monochloramine is formed from reaction hypochlorous acid with ammonia

    • NH3 + HOCL => NH2CL + H2O

  • Monochloramine may then react with HOCL to form dichloramine

    • NH2CL + HOCL => NHCL2 + H2 O

  • Dichloramine may react with HOCL to from trichloramine

    • NHCL2 + HOCL => NCL3 + H2O


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    • No .of these reactions depend on p mixed with water, this sediment must be disposed of H of water

    • Monochloramines & dichloramines can be used as a disinfecting agent & are called ‘Combined Residual Chlorine Resudual’, because CL2 is combined with N2

    • Chloramine are weaker than CL2, but are mole stable

    • Chloramines are effective @ killing bactera & some protozoans, but they are very in elective @ killing viruses.


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    Chlorine Dioxide (CLo mixed with water, this sediment must be disposed of 2)

    • CLO2 , a very effective from of CL2, since it will kill protozoans, cryptoridium, Giardia & viruses that other systems may not kill.

    • CLO2 oxideses all metals & organic matter

    • It removes sulphide componds & pherolic tastes & odors

    • THMs are not formed

    • Effective @ high pH

    • It must be generated onside, a costly process

    • It is highly combustible

    Disinfection

    • Nature of disinfectant

    • Dose of disinfectant

    • Length of disinfectant

    • Temp

    • Type & con of organisms to be desinfected

    • pH of water.


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    Dose of disinfectant mixed with water, this sediment must be disposed of

    • CL2 residuals depends on CL2 dose & CL2 demand

    • CL2 residual should be at least 0.5 mgIL

    • When reaching consumer, CL2 residual should be0.2 mgIL

    • CL2 dose = cL2 demand +CL2 residual

    Contact time

    • A min contact time of 30 min is required for adequate disinfection

    Temp of water

    • At lower temp, bacteria kill tends to be & lower & higher doses are needed

    • The con of chemical substances is exerting demand on CL2

    • CL2 must be well disposed & homogeneously mixed assume that contact time for disinfection is applied throughout water supply


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    Types & con of organisms mixed with water, this sediment must be disposed of

    • No & types of microorganisms in water will influence chlorinates

    PH

    • An important factor that influences of disinfection

    • Con of hypochlorous acid & hypochlorite irons in chlorinated water will depend on pH of water

    • A higher pH facilitates formation of mole hypochlorite ions & less hypochlorous acid in water

    • A lower pH facilitates formation of less hypochlorite ions & mole hypochlorous acid in water

    • HOCL is the most elective from of free residual CL2

    • Disinfection is mole efficient @ low pH (with large quantities of hypochlorous acid in water ) than @ high pH (with large quantities of hypochlorous ions in water )

    • At high pH, hypochlorous acid become dissociated into elective hypochlorite ion.


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    Break- point chlorite mixed with water, this sediment must be disposed of

    • When CL2 is added to water, no of reactions take place in water & residual CL2 in water is also changing

    • A typical break-point chlorination crone showing chemical reactions & residual CL2 level @ various stages are shown

    • CL2 added to water first reacts with any iron, manganese or H2S that may be present in water

    • Entire CL2 added will be utilized in reactingwith organic substances (including bacteria)

    • Hence there will not be any residual CL2 (line AB) as initial CL2 demand

    • When CL2 is further added to water, it reacts with Ammonia to produce combined residual chlorine (chloramines)


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    SERVICE RESERVOIRS mixed with water, this sediment must be disposed of

    • Water distribution system

    • Storage reservoirs

    • Purpose is to equalizer rate of flow, to maintain pressure & for emergencies

    • In large cities, SRs are provided @ more locations

    • SRs may be located above, on or below GL

    • Overhead Tank, GL reservoir/Sump.

    Capacity of SR

    • Graphical mtd or mass balance analyse mtd

    • Volume of storage required = (Max +ve defict)+ (max –ve defict)

    • No.of SRs – min . One for each area

    • Shapes – circular, rectangular, square, conical, spherical.


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    Volume of storage required mixed with water, this sediment must be disposed of


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    Depth of SR mixed with water, this sediment must be disposed of


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    Disinfection mixed with water, this sediment must be disposed of

    • Primary Disinfection Techlories:

      • Chlorine & Chloramines

      • Ozone

      • Chlorine dioxide

      • Potassium per maganate

      • UV radiation

  • Chlorination

    • Ist application in 1830s

      • disinfectant

      • taste & odoi control

      • algae control

      • iron & Mn removal

      • H2s removal

      • color removal


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    Cl mixed with water, this sediment must be disposed of 2 gas

    • When Cl2 gas is dissolved in water, it hydrolyses to form hypochlorous acid (HOCl)

    • In this form Cl2 exits as free Chlorine Residual

    • Cl2 + H2o => HOCl + H+ + Cl-

    • HOCl is a weak acid & under goes partial dissociation

    • HOCl  H+ + OCl-

    • HOCl is many times stronger an oxidant than OCl-

    • The perdominant concentrations of HOCl & OCl- are below pH 6.0 & above 7.5 respectively

    • Disinfecting power of Cl2 decreases with increase in pH.

    Calcium & Sodium hypochlorites:

    • Ca(OCl)2 + 2H2O  2HOCl + Ca2+ + 2OH-

    • NaOCl + H2O  HOCl + Na+ + OH-

    • Cl2 gas lowers pH, whereas hypochlorite in soln. raises pH


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    Combined Chlorine Residual mixed with water, this sediment must be disposed of

    • Chlorine reacts with NH3 to from chloramines & exerts combined Cl2 residual. This is a weak disinfectant & does not produce THMs & provides a stable residual in the distribution system.

    • NH3 + HOCl => NH2Cl (Monochloramine) + H2O

    • NH2Cl + HOCl => NH Cl2 ( Dichloramine) + H2O

    • NHCl + HOC => NCl3 (Trichloramine) +H2O

    Break- point chlorination

    • When CL2 is added to water, it is consumed to oxidise various organic compounds in water & that represents initial Cl2 demand

    • Then Cl2 reacts with NH3 to from combined chlorine residual

    • With addition of Cl2, combined Cl2 residual reaches a max. value & further addition of Cl2 causes a decrease in combined residual

    • This is called Break-point Chlorination

    • At this point, Chlorination are oxidised to N2 gas

    • After break point chlorination is reached, free chlorine residual develops @ the same rate as that of applied dose.


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    Representative Cl mixed with water, this sediment must be disposed of 2 dosage Required For Disinfection


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    Cl mixed with water, this sediment must be disposed of 2 dosage & Residuals

    • Cl2 dosage may vary with water quality (Typical 2.0 – 4 mg/L)

    • Combined chlorine residual should be 0.5 – 1 mg/L @ distant points in the distribution system.

    Comparison of Disinfection


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    Chlorine Dioxide mixed with water, this sediment must be disposed of

    • Used for many tears to bleach papers, textiles

    • Since 1970s,used for disintection

    • 5 times mole costly than Chlorine

    • No reaction with organics to from THMs

    • Must be generated onsite

    • It is generated from solns of sodium chlorine (NaClO2) with Cl2 gas or hypochlorous acid

    • 2 NaClO2 + Cl2 (gas) => 2 ClO2(g) + 2NaCl

    • 2 NaClO2 +HOCl =>NaCl + NaOH + 2ClO2 (g)

    Ozonatioin

    • Extensively used in Europe for disinfection & taste & odor control

    • O3 is an unstable gas, to be generated on-site.


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    Advantages mixed with water, this sediment must be disposed of

    • Effective disinfectant (300 – 3000 times faster than chlorine)

    • Effective over a wide pH range

    • Effective in Color, Taste & Odor control problems

    • THM formation lowers

    Disadvantages

    • High capital & O & M costs (about 10 – 15 times higher than Cl2)

    • Residual does not last long

    O3 Formation Reactions

    • O2 + 2e- => 2O-

    • O- + O2 => O3

    • 3O2 + 2e- => 2O3

    • Once O3 is formed it decomposes into O2.This is rapid above 35°C.the energy input per kg O3 generated is 0.82 KWh


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    • O mixed with water, this sediment must be disposed of 3 is a strong oxidising agent

    • With UV/H2O2, it decomposes in water to produce mole active hydroxyl free radicals.

    • O3 + H2O => 2HO2

    • O3 + H2O => 2O2 + HO

    • The hydroxyl free radicals can be a powerful xidising agent

    • free-radical species are mole effective oxidising agents than O3, but short- lived.

    • O3 produces little or no THM

    • O3 reacts with inorganic compounds i.e nitrites, ferrous, managanous, sulphides & ammonium iron

    • O3 destroys many organic compounds that produces color, taste & odor

    • O3 mainly used in Color, Iron, & Mn removal, Taste & odor control

    • O3 is a jointly blue, pungent-smelling & unstable gas

    • It is detectable even @ low con co. 0.1 – 0.02 ppm by vol.)

    • Max permissible con is 0.1 ppm in ambient air

    • An effective off-gas O3 destruction system is to be provided

    • Solubility of O3 is governed by Henryi law

    • Half- life of O3 in water ranges from 8 min to 14 h

    • A solubility of 4.7 mg O3/L @ 20°C has been reported

    • Typical O3 feed rate is 1 – 1.5 mg/L & typical residual con is 0.3 – 0.9 mg/L


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    Potassium permanganate mixed with water, this sediment must be disposed of

    • A strong oxidant, widely used for taste & odor control & mangaese removal

    • A weak disinfectant

    • A purple, crystalline salt of permanganic acid

    UV Ir Radiation

    • Germicidal effect of UV known since 19th century

    • Sunlight was used to purify water, even in ancient times

    • 1901,water treatment

    • Primary mechanism for in activation of microorganisms, by UV light is direct damage to cellular nucleic acids

    • When UV energy is absorbed by DNA of microorganisms, structural changes are included

    • Peak absorption is bt. 250 – 265nm


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    Advantages mixed with water, this sediment must be disposed of

    • No chemical is introduced, no taste, odor or color formation

    • Exposure time is short

    Disadvantages

    • Spores, cysts & viruses are less susceptible than bacteria

    • No residual, so a secondary disinfectant is needed

    • Expensive, high energy cost.

    Secondary Disinfection Technologies

    • It provides an essential residual that prevents re growth in the distribution system

    • Cl2, Chloramines & ClO2 are typical secondary disinfectants

    • Chloramine is the most commonly used.


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    1. Calculate average Cl mixed with water, this sediment must be disposed of 2 required per day to tread 20MLD of weaker. Also calculate the storage required for 60 days. Assume an average Cl2 dosage of 3 mg/L.


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    2. Chlorine used in a WTP for treating 15,000 m mixed with water, this sediment must be disposed of 3per day is 18 kg/day. The residual Cl2 observed after 30 min. contact is 0.2 mg/L. Determine Cl2 dosage & Cl2 demand in mg/L.


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    3. Cl mixed with water, this sediment must be disposed of 2 residuals measured when various dosages of Cl2 were added to water are given below. Determine

    • Break point dosage

    • The design dosage to obtain a residual of about 0.75 mg/L of free residual Cl2i what is the Cl2 demand @ this dosage?


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    It is required ti supply water to a town with a population of 15,000 @ a percapita water rate 70 lpcd. The water is disinfected with 0.5 mg/L of Cl2 using bleaching powder as disinfectant. Determine how much bleaching powder is required for 3 months assume the Cl2 content in bleaching powder as 30%


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    Methods of Defluoridation of 15,000 @ a percapita water rate 70 lpcd. The water is disinfected with 0.5 mg/L of Cl

    • Activated Alumina or Bone char

    • Ro

    • Nalgonda Technique

    • Nalgonda Technique:

    • It uses Al. salt for removing fluoride

    • Raw water is mixed with lime

    • Alum soln. is then added & water is stirred slowly for 10 min & allowed to settle for 1 h

    • Activated Alumina or Bone char:

    • Water is percolated through insoluble granular media

    • Regeneration of bone char consists of backwashing with 1 % soln of caustic soda & then rinsing the bed

    • Regeneration of alumina involves backwashing with caustic soln


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    Defluoridation of 15,000 @ a percapita water rate 70 lpcd. The water is disinfected with 0.5 mg/L of Cl

    • Both lime softening & alum coagulation are effective

    • The only acceptable method of defluoridation is Adsorption onto Activated Alumina or Bauxite

    • The water is filtered through a bed of Activated Alumina

    • The regeneration of alumina bed involves backwashing, regeneration by NaOH soln, Rinising with water neutralisation

    • The major equipment include

      • An activated Alumina bed

      • Acid & base feed

      • pH adjustment & control system

      • 5raw water filtration & backwash system

      • Alumina – bed regeneration &

      • Neutralisation systems


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    Iron of 15,000 @ a percapita water rate 70 lpcd. The water is disinfected with 0.5 mg/L of Cl

    • GWs containing soluble iron (ferrow) are clear & colorless when it is first drown

    • Upon contact with air, a yellowish to reddish brown precipitate of ferric hydroxide is formed

    • Stain the porcelain fixtures & laundry

    • Iron bacteria utilise ferrous iron as energy source & precipitate ferric hydroxide, that may cause pipe clogging


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    Manganese of 15,000 @ a percapita water rate 70 lpcd. The water is disinfected with 0.5 mg/L of Cl

    • Rocks & soil

    • Causes Stain, bad taste & growth of microorganisms

    Iron & Mn Removal

    • Oxidation & Ppn

    • Aeration at high pH by lime addition coagulation & ppn

    • Selective Iron exchange Resins


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    Iron & Mn of 15,000 @ a percapita water rate 70 lpcd. The water is disinfected with 0.5 mg/L of Cl

    • Ferrous iron (fe2+) & Mn2+ are soluble, invisible & reduced froms

    • When exposed to air, insoluble, visible, oxidised Fe3+ & Mn4 in formed

    • Brown colored oxides of Iron & Mn. create unaesthetic conditions

    • Reduced iron in water promote growth of autotrophic bacteria (Iron bacteria ) in distribution system

    Iron & Mn Removal

    • Aeration, Sedimentation& Filtration

    • Tray type aerators, frequently contain coke/Stone contain beds to speed up oxidation reactions.


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    • 2) Aeration, Chemical Oxidation, Sedimentation & Filtration: of 15,000 @ a percapita water rate 70 lpcd. The water is disinfected with 0.5 mg/L of Cl

    • Aeration Strips out chemically oxidised gases &adds o2

    • Iron & Mn are chemically oxidised by Cl2 /KMno4

    • 1 mg/L of KMno4 oxidises 1.06 mg/L of iron & 0.52 mg/L of Mn

    • (Fe2+ + M22+) (soluble Irons) + O2 Cl2/KMno4 (FeOx↓ + MnO2↓) (Insoluble oxids)

    • Filtration is needed to remove Flocculent metal oxides

    • 3)Mn Zeolite Process:

    • It is a natural green sand coated with manganese dioxide that removes soluble iron &Mn from soln

    • Zeolite bed is regenerated with kMno4

    • A pressure filter with media i.e Anthracite & Manganese Zeolite bed


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    4-stage Reverse Osmosis Unit with Tank and Faucet of 15,000 @ a percapita water rate 70 lpcd. The water is disinfected with 0.5 mg/L of Cl


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