INFRASTRUCTURE - Sewage Removal System - Handout

8/7/2019 INFRASTRUCTURE - Sewage Removal System - Handout

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CIVILENGINEERINGII

INFRASTRUCTURE:

SEWAGEREMOVALSYSTEM

Wastewater

Usedwater(liquid)andsolidsthatflowtoand

t roug t ewastewaterco ect onsystem.

Awastewatercollectionsystemconsistsofall

facilitiesforthecollection,transportation,

,

,

wastewater.

Wastewater

Thetypicalwastewatertreatmentplantis

1. Protectpublichealth.

2. Protectpublicwatersupplies.

3. Protecta uaticlife.

4. Preservethebestusesofthewaters.

5. Protectadjacentlands.

Wastewater

Theprincipalsourcesofdomesticwastewater

nacommun tyaret eres ent a areasan

commercialdistricts.

Otherimportantsourcesinclude:

stormwater(runoff)

Groundwater(infiltration).


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Wastewater:Sources

Wastewaterisgeneratedbyfivemajorsources:

1. Humanandanimalwastes

2. Householdwastes

3. Industrialwastes

4. Stormwaterrunoff

5. Groundwaterinfiltration

Wastewater:Classification

Wastewatercanbeclassifiedaccordingtothesourcesofflows:

. ,householdwastes,smallamountsofgroundwaterinfiltrationandsmallamountsofindustrial wastes.

2. Sanitarywastewater Consistsofdomesticwastesandsignificantamountsofindustrialwastes.

3. Industrialwastewater Consistsofindustrialwastesonly.

. om ne was ewa er ons s so acom na ono san arywas ewa eran stormwaterrunoff.Allthewastewaterandstormwaterofthecommunityistransportedthroughonesystemtothetreatmentplant.

5. Stormwater Containsaseparatecollectionsystem(nosanitarywaste)thatcarriesstormwaterrunoffincludingstreetdebris,roadsalt,andgrit.

Wastewater:Classification

Compositionof DomesticSewage

TypeofWastewater SourceofWastewater

GrayWater

Washingwaterfromthe

kitchen ,bathroom,laundry

(withoutfecesandurine).

BlackWater Waterfromflushtoilet(feces

andurinewithflushedwater).

YellowWater Urinefromseparatedtoilets

andurinals.

Wastewater:Characteristics Physical

1. Color

2. Odor

3. Temperature4. Flow


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Wastewater:Characteristics Biological

Bacteria,viruses,andparasitesmakeupthebiologicalcharacteristicsofwastewater.

Thefeedingactivitiesoftheseorganismsassistindecomposingwastewater.

Aerobicbacteriadecomposeorganicmatterinthepresenceoffreeoxygen.

Anaerobicbacteriadecomposeorganicmatterthatisshutofffromfreeoxygen,suchasintheinteriorofamassoffecesoradeadbody.

Theproductsofanaerobicdecompositionhaveanextremelyunpleasantodor.Matterinwhichthisconditionexistsissaidtobeseptic.

Alargenumberofthebacteriainwastewaterarecoliform bacteria thosefoundinthedigestivetractofnormalhumans.

Wastewater:CollectionSystems

Wastewatercollectionsystemscollectandconveywastewatertothetreatmentplant.

The com lexit of the s stem de ends on the size of the communit and the t eofsystemselected.

SeparateSystem SanitarySewer:Carriesdomestic andindustrialwasteinadditiontoinflowandinfiltration.

StormSewer:Carriesstormwater,replacesnaturaldrainage

Thesizeofthepipesaremuchsmallerthanacombinedsewersystem.

Minimizesthetotalquantityofsewagewhichleadstothefollowingadvantages: Smallerpumpingstations

Usedforbothstormwaterandwastewater.

Preferredforareaswithlongrainyseasons.

Wastewater:CollectionSystems Wastewater:CollectionSystems


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GravityCollectionSystem

Mostsewersaredesignedtoflowbygravity

nc u essewerp pe rom ome osep c an or oamunicipalcollectorpipe

Gravitysewersmustfollowthetopographyoftheland

thecollectionlinesareslopedtopermittheflowtomovethroughthesystemwithaslittlepumpingaspossible.

Wheregravityflowisnotpossible,pumpsareused

Largemunicipallift(pump)station

Theslopeofthelinesmustkeepthewastewatermovingat

avelocity(speed)of2to4ft/sec.


ForceMainCollectionSystem wastewateriscollectedtocentralpointsandpumpedunderpressureto

thetreatmentplant.

.

Theuseoftheforcemainsystemallowsthewastewatertoflowtothetreatmentplantatthedesiredvelocitywithoutusingslopedlines.

VacuumSystem

wastewatersarecollectedtocentralpointsandthendrawntowardthetreatmentplantundervacuum.

Thesystemconsistsofalargeamountofmechanicalequipmentandrequiresalargeamountofmaintenancetoperformproperly.

Generally,thevacuumtypecollectionsystemsarenoteconomicallyfeasible

PumpingStations

providethemotiveforce(energy)tokeepthewastewatermovingatthedesiredvelocity.

Theyareusedinboththeforcemainandgravitysystems.

SewerHydraulics


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SewerHydraulics SewerHydraulics

Findthediameterofthepiperequiredtocarry3

. partially;d/D=0.67,slope=0.4%,n=0.013.

1. Findtheflowangle

2. FindQp/Qf

3. Ca cu ateQf4. Findthediameterofthepipe(D)

5. Findthepartialflowvelocity(Vp)

ManningsRoughnessCoefficientnforVariousTypesofPipe

Example SewerHydraulics

Assumethesewerlinegradegivesasewer

ve oc tyo . m sw t a a u sewer ow.

Theslopeofthelineis0.0081.Whatisthe

diameteroftheuncoatedcastironsewerline?


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DesignCriteria

Wastewaterflow Flowvariesaccordingto:

1. Theseason

2 . We at he rcondidtions

3. Weekofthemonth,dayoftheweekandtimeoftheday.

Estimatepeakflowisused

Estimationofthedesignflow,Qdes: Percapitawastewaterflowdependsuponrateofwatersupplytothecommunityandrateof

groundwaterinfiltration.

Averagedailywaterconsumptionpercapitafordomesticareas,Qavg Averagedailywaterconsumptionpercapitaforinstitution,Qavg Averagedailywaterconsumptionforcommercialandindustrialareas.

Infiltration/Inflow:

Qinfl Qinfil Qdes =Qmax+QVI QvI =Qinfl +Qinfil Qmax=0.8xQavg xPf (0.8=80%returnfromwatersupply)

DesignCriteria


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DesignCriteria Example

Agravitypipeservesacommunityof50,000

n a tants. e engt o t ep pe s m

andtheaveragewaterconsumptionis120

L/c/d.Useaninfiltrationrateof30m3/day.km,

andawastewaterproductionrateof80%.

Neglecttheinflowrate.CalculateQdes and

Qmin.

DesignCriteria Example

SewerAppurtenancesStreetGutter

Atriangleopenchannelalongthecurbstoneofstreetswhichcarrythestormwateralongstreetstotheinlets.

FlowinastreetguttercanbecalculatedbytheManningformula,modified for a trian ular utter crosssection

Thewaterdepthatthecurvecanbecalculatedfromtheflowandthestreetcrosssectionandslope.

The

width

over

which

the

water

will

spread

is

equal

to

yz.


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SewerAppurtenances

SewerAppurtenances SewerAppurtenances


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SewerAppurtenances SewerAppurtenances

Manholes


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PipesMaterialsandLoadsPipesMaterialsandLoads

Loadsonsewerlinesareaffectedbyconditionsofflow roundwater ad acent earth andsuperimposedsituation.

Commontrenchcutsforsewerpipes

PipesMaterialsandLoadsLoadsduetobackfill

Dependson: Trenchwidth

Depthofexcavation

Unitweightofthefillmaterial

Frictionalcharacteristicsofthebackfill

W=verticalloadonpipeasaresultofbackfill,(lb/ftorN/m)

C=dimensionlessloadcoefficientbasedonthebackfillandratiooftrenchdepthtowidth.

C= wor =unitweightofbackfill,(lb/ft3 orkg/m3)

B=widthoftrenchattopofsewer,(ftorm)

k=ratiobetweenactiveinternalpressureandexternalverticalpressure

F=frictioncoefficientbetweenthebackfillmaterialsandthetrenchverticalsides.

PipesMaterialsandLoads


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WastewaterTreatment

Thebasicstepsinwastewatertreatmentare:

Preliminarytreatmenttoprotectplantoperation

Settling

toremovesolids

Biologicaltreatmenttoremoveorganicmatter

Disinfectiontoremovepathogens

Solidsprocessingtoprovidesafefinaldisposal.

WastewaterTreatment


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Wastewater:SecondaryTreatment

Themainpurposeofsecondarytreatmentsometimes referred to as biolo ical treatment is

toprovideBODremovalbeyondwhatisachievablebyprimarytreatment.

RemovesBODanddissolvedandcolloidalsuspendedorganicmatterbybiologicalaction.

,

dioxideandmoreorganisms

Secondarytreatmentproducesaneffluentwithnormorethan30mg/LBODand30mg/LTSS.


ActivatedSludge Secondaryorbiologicaltreatmentisperformedina

tankcontaininga"soup"ofstarvedmicrobescalledactivatedsludge.Likeus,thesemicrobesrequireairtolive(theyareaerobicorganisms)andthusairispumpedintothetank.

Microorganisms inthisaerationtankusethedissolvedandparticulateorganicmatterasfood,producingmore

.

Thusthewastematerialsthatlefttheprimaryclarifierarechangedintomicroorganisms whichcanbecollectedandseparatedfromthewater.


Clarifier

Separateoutthemicroorganisms(activatedslud e so that ust clean water is left.

Some

of

the

solids

collected

in

the

secondary

clarifier(returnactivatedsludge)aresentbacktotheaerationtanktotreatmorewastewaterandtheexcess(wasteactivatedsludge)ispumpedto

treatment.

Thecleanwaterthatflowsoutthetopoftheclarifierissentalongfordisinfection.

Wastewater:Disinfection

Wastewatereffluentisdisinfectedtoprotectublic health in eneral.

Can

be

accomplished

by

adding

chlorine

or

by

exposingthewastewatertoultravioletlight(UV).

Disinfectionwithchlorinecanproducechemicalswhicharedangeroustopublichealth,soalternativessuchasultravioletlightarebecomingmorepopular.


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Wastewater:TertiaryTreatment

Themethodsandprocessesthatremovemore

substances)fromwastewaterthanaretakenoutbyconventionalbiologicaltreatment.

Inotherwords,advancedwastewatertreatment

followssecondarytreatmentorthatincludesphosphorusremovalornitrificationinconventionalsecondarytreatment.

MeasuringPlantPerformance

Toevaluatehowwellaplantortreatmentunitprocessisoperating,performanceefficiencyorpercent

.

PlantPerformanceandEfficiency

%Removal=[InfluentConcentration EffluentConcentration]x100

InfluentConcentration

UnitProcessPerformanceandEfficiency

Theconcentrationenteringtheunitandtheconcentrationleavingtheunit(i.e.,primary,secondary,etc.)areusedtodeterminetheunitperformance.

MeasuringPlantPerformance

PercentVolatileMatterReductioninSludge

MeasuringPlantPerformance:

HydraulicDetentionTime Thetermdetentiontime(DT)orhydraulicdetentiontime(HDT)

referstotheaveragelengthoftime(theoreticaltime)adropof, ,

channel.

Itiscalculatedbydividingthewaterorwastewaterinthetankby

the

flow

rate

through

the

tank.

Theunitsofflowrateusedinthecalculationaredependentonwhetherthedetentiontimeistobecalculatedinseconds,minutes,hoursordays.

Detentiontimeisusedinconjunctionwithvarioustreatmentprocesses,inc u ingse imentationan coagu ationan flocculation.

Detentiontimeisassociatedwiththeamountoftimerequiredforatanktoempty.


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HYDRAULICDETENTIONTIME

DetentionTimeinDays

DetentionTimeinHours

DetentionTimeinMinutes

INFRASTRUCTURE - Sewage Removal System - Handout

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