Lecture 5: Filtration - site. 5: Filtration Dr. Fahid Rabah 1. 5. Filtration in water Treatment 5.1 Definition of Sedimentation: Filtration is a solid –liquid separation process in

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  • IslamicUniversityofGazaEnvironmentalEngineeringDepartment

    Water TreatmentWaterTreatmentEENV4331

    Lecture5:Filtration

    Dr.Fahid Rabah

    1

  • 5.FiltrationinwaterTreatment

    5.1 Definition of Sedimentation:Filtration is a solid liquid separation process in which theliquid passes through a porous medium to remove asmuch fine suspended solids as possible

    5.2 Locations of filtration tanks in water treatment:Filtration tanks are used in all types of water treatmentplants except for disinfection treatment plants. SeeFigures 5.1 through 5.4 illustrating the location of filtrationtanks.

    2

  • River

    Screen

    RiverWater

    PreSedimentation

    Screen

    Coagulation FlocculationSedimentation

    DistributionDisinfection StorageFiltration

    Figure5.1:FiltrationTreatmentPlant (RiverWater)

    3

  • Screen

    Surfacewater

    S di t tiCoagulation Flocculation

    Sedimentation

    DistributionDisinfection StorageFiltration

    Figure5.2:FiltrationTreatmentPlant

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  • GroundWaterWater

    RapidMixing Flocculation Sedimentation Recarbonation

    DistributionDisinfection StorageFiltration

    Figure5.3:SofteningTreatmentPlantSinglestagesofteningsoftening

    5

  • GroundWaterwell

    FiltrationAeration

    DistributionDisinfection Storage

    Figure5.4:AerationTreatmentPlant( iron and manganese removal plant)(ironandmanganese removalplant)

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  • 5.FiltrationinwaterTreatment5 3 Need for filtration:

    Settlingisnotsufficienttoremoveallparticlesand

    5.3 Need for filtration:

    flocsfromwater. FiltrationNeededforfineparticlesnotremovedbydi t tisedimentation.

    FilterscanalsocaptureGiardia cysts, viruses,andasbestos fibersasbestosfibersTypicaloverflowqualitiesfromsedimentationtanksrangefrom1to10NTU.Filtration,usuallyrapidsandfiltration,isthenemployedforfurtherpolishing,i.e.togettheturbidity to lower than 0 5 NTU (as required byturbiditytolowerthan0.5NTU(asrequiredbylegislation).Rapid sand filtration after prior sedimentation is the

    7

    Rapidsandfiltrationafterpriorsedimentationisthemostcommonconfigurationworldwide

  • 5.FiltrationinwaterTreatment

    5.4 Types of filters used in water treatment:Granular material filters are the most used types of filtersin water treatment. Usually sand, anthracite, and Garnet.y

    There are three types of granular filters:1. Single medium filters :

    one type of media is used: either sand or anthraciteone type of media is used: either sand or anthracite

    2. Dualmedia filters: two types of media is used usually sandand anthraciteand anthracite

    3. Multimedia filters: three types of media are used usuallysand , anthracite , and Garnet

    Most famous filters in water treatment are Rapid Sand Filters.Most famous filters in water treatment are Rapid Sand Filters.

    8

  • 5.FiltrationinwaterTreatment

    5.5 Geometry and components of Rapid Sand Filter:y p p

    Rapid sand filters are always rectangular tanks.

    Figures 5.5 to 5.10 show typical Rapid sand filters used inwater treatment.

    Main components of Rapid sand filter are: Main components of Rapid sand filter are:1. A concrete tank2. Filter media3 Under drain system3. Under drain system4. Backwash system: pressurized water and air lines

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  • Figure5.5:Rapidsandfiltercomponents

    10

  • Figure5.6a:Rapidsandfiltercomponents: withgraveland

    11

    p p gperforatedpipesunderdrainsystem

  • Fi 5 6b

    12

    Figure5.6b:Rapidsandfiltercomponents: withgravelandperforatedpipesunderdrainsystem

  • Figure5.7:Rapidsandfiltercomponents: withgraveland

    13

    p p gperforatedpipesunderdrainsystem

  • Fi 5 8

    14

    Figure5.8:Rapidsandfiltercomponents:withductsunder drainsystem

  • 15

    Figure5.9:Rapidsandfiltercomponents:withnozzleunder drainsystem

  • 5.FiltrationinwaterTreatment

    Figure 5.10 :Figure5.10:Rapidsandfilterperforatedslabandnozzleunderdrain

    system

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  • 5.FiltrationinwaterTreatment

    Figure5.11:Nozzle used in Rapid sand filterNozzleusedinRapidsandfilterunderdrainsystem

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  • 5.FiltrationinwaterTreatment

    5.6 Operation of Rapid Sand Filter:

    There are two modes of operation of Rapid sand filterThere are two modes of operation of Rapid sand filter

    Filtration mode ( see Figure 5.12 )

    Backwashing mode ( see Figure 5.13 )

    18

  • 5.FiltrationinwaterTreatment

    5 7 Filtration mode:

    Waterflowsdownwardthroughabed5.7Filtrationmode:

    ofsandandgravel Particles are captured on and between Particlesarecapturedonandbetweensandgrains

    Filteredwateriscollectedintheunderdrain, sent to disinfectiondrain,senttodisinfection

    19

  • 5.FiltrationinwaterTreatment

    5 8 Backwash mode:

    Sand is backwashed when

    5.8Backwashmode:

    Sandisbackwashedwhen Itbecomesclogged,or Turbidityoffilteredwatergetstoohigh

    During backwash, water is pumpedDuringbackwash,waterispumpedupwardsthroughthesandbed

    20

  • 5.FiltrationinwaterTreatment

    Sandbecomesfluidized,andparticlesareflushedfromthesand

    Dirtybackwashwaterispumpedintoasettling pond and eithersettlingpond,andeither Recycledbackintoplant,orDi d Disposed

    Backwashingcanconsume1%to5%ofaplantsproduction

    21

  • 22Figure5.12:Rapidsandfilterduring

    filtration

  • 23

    Figure5.13:Rapidsandfilterduringbackwashing

  • 5.FiltrationinwaterTreatment

    5.9Filtermediaproperties

    24

    Figure5.14:filtermediagraindistribution

  • 5.FiltrationinwaterTreatment

    h f l d d h d h lThesefiltersusesandandcrushedanthracitecoalonagradedgravelbase.

    Medialayersarearrangedinacoursetofinegradationinthedirectionofflow,whichallowsgreaterdepthofpenetrationoffloc particles.p

    Multimediafiltersareselectedwithspecificgravitiessothatmoderate intermixing between media layers occurs duringmoderateintermixingbetweenmedialayersoccursduringbackwashing.

    25

  • 5.FiltrationinwaterTreatment5.10FiltermediapropertiesThefiltermediaischaracterizedbytwomainparameters: the effective size and the uniformity

    Effectivesizeofthefiltermedia

    parameters:theeffectivesizeandtheuniformitycoefficient.

    Th ff ti i f th di i th di tTheeffectivesizeofthemediaisthediameterthat10%ofthefiltermediaislessthanitsizeandisdenotedasd10.

    60

    dd

    U

    Uniformitycoefficientofthefiltermedia

    10dU=Uniformitycoefficientd60 =sievesizethatpasses60%byweightd10 =sievesizethatpasses10%byweight

    d60 andd10 arefoundbysieveanalysisofthemediatobeusedinthefilter.

    26

    Anotherimportantsievesizeisd90 thatisusedtocalculatethebackwashrate.

  • 5.FiltrationinwaterTreatment

    27Figure5.15:Rapidsandmedialayers

  • Figure5.16:Rapidsandmedia layersmedialayers

    28

  • 5.FiltrationinwaterTreatmentTable 5.1Table5.1

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  • 5.FiltrationinwaterTreatmentTable 5 2Table5.2

    30

  • 5.FiltrationinwaterTreatmentTable 5.3Table5.3

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  • 5.FiltrationinwaterTreatment

    Figure5.17:Headlossandeffluentturbidityincreasewithtimeduringfiltration

    32

    y g

  • 5.FiltrationinwaterTreatment

    Figure5.14:Headlossinrapidsandfilter during filtration cycle

    33

    filterduringfiltrationcycle

  • Figure5.14:Headlossinrapidsandfilter

    34

    g p

  • Headlossinacleanfilter

    CarmenKozeny equation:

    2 v

    AV

    gk

    Lh 2

    3

    2)1(

    dAV

    6

    sA

    Qv

    Where,k=dimensionlesscoefficient,5forsand,6foranthracite;v filtration rate m3/m2 d or filtration velocity m/d

    s

    v=filtrationratem3/m2.d,orfiltrationvelocitym/d.A=thegrainsurfacearea;As=surfaceareaofthesandfilter;V= the grain volume;V=thegrainvolume;=filterporosity;around0.40forsandfilter=shapefactor;1forsphericalparticles,0.70forsand;=dynamic viscosity; N s/m2

    35

    =dynamicviscosity;N.s/m=waterdensity;kg/m3

    h=headlossincleanfilter,m

  • Example5.1:

    Adualmediafilteriscomposedof0.30manthracite(meanparticlesize0.20mm)thatisplacedovera0.60mlayerofsand(meanparticlesize0.70mm)

    /withafiltrationrateof9.78m/h.Assumethegrainsphericity =0.75andporosity()=0.40forboth.Estimatetheheadlossinthecleanfilterat150C.

    A H d l i th th it lA.Headlossintheanthracitelayer:

    mh 0508.000272.0*0020*750

    6400*1000*819

    )40.01(*00113.0*6*30.02

    3

    2

    B.Headlossinthesandlayer:

    002.0*75.040.0*1000*81.9 3

    2

    mh 6918.000272.0*007.0*75.0

    640.0*1000*81.9

    )40.01(*00113.0*5*60.02

    3

    2

    B.Headlossinthesandlayer:y

    mhtotal 743.06918.00508.0

    36

  • Headlossduringfiltration(None clean filter)(Nonecleanfilter)

    Where

    filterdtl bVavh Where,v=filtrationratem3/m2.d,orfiltrationvelocitym/d.a,b=coefficientsdependingonthefiltermediaproperties;Vfilt d = filtered volume per unit area of filter since last backwash; m3/m2Vfiltered filteredvolumeperunitareaoffiltersincelastbackwash;m /m(hl)t =headlossatanytime(t),m

    37

  • Example5.2:

    Afilterhasaheadlossof0.30mwhenclean(newlywashed),and1.30mafter24hrsoffiltrationatarateof1.5L/s.m2 .Estimatetheheadlossbothimmediatelyafterbackwashand10hrslater,ifthefiltrationrateischangedto2L/s.m2 .

    A.Estimatethevaluesofaandb:

    5.15.1

    0*1000

    5.130.0 ba

    3600*24*

    10005.1*

    10005.130.1 ba

    Bysolvingthe2equationssimultaneously,a=200,b=5.14

    B.Calculateheadlossforthenewflowrate:

    2 mbH 40.00*2001000

    20

    mH 88.13600*10*1000

    2*14.52001000

    2