wwtpcalculationsbook3.09

8/9/2019 WWTPCalculationsBook3.09

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Calculaons Used in the

Daily Operaons of a

Wastewater Treatment Facility

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1

Te calculations provided in this booklet are tools, much like the equipment utilized, that will enable theoperator to manage and run a wastewater treatment acility as eciently and smoothly as possible.

Operating a treatment acility can be challenging, yet very rewarding. Tese plants are designed usingparameters that take into account various hydraulic and organic loadings, and with equipment that willallow or ecient operation. However, running the equipment alone is not enough to ensure a smoothoperation. Te operator must use the calculations provided to operate the plant in an eective manner.While the operator can choose which calculations to use, it is imperative that the acility is run ollowingoperational guidelines.

We hope you nd this guide helpul.I you have any questions or need urther assistance,

please call Baxter & Woodman at 815-459-1260.

2009 Baxter & Woodman, Inc.

Contents

Areas & Volumes...................................................................... 2

Raw Inuent Calculaons

PlantInuentLoadings....................................................... 2

Clarier Capacity Calculaons

SurfaceLoadingRate-RectangularClarier ...................... 3

SurfaceLoadingRate-CircularClarier ............................. 3

DetenonTime................................................................... 4

WeirOverowRate ............................................................ 4

Acvated Sludge Calculaons

SludgeAge .......................................................................... 5

SolidsRetenonTime(SRT)................................................ 6

F/MRao ............................................................................ 7

MLSSConcentraoninPounds........................................... 7

SolidstobeWasted............................................................ 7

WasteSludgePumpingRate............................................... 8

TypicalWWTPOperaonalParameters .................................... 8

MetalSaltAddionforPhosphorusRemoval........................... 9

Baxter & Woodman Services ................................................. 10


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Calculaons Used in the Daily Operaon

of a Wastewater Treatment Facility

Several basic equations are used in calculations to determine things such as Weir Overfow Rate, Detention

ime, SR, etc. Te ormulas or area and volume appear below, along with examples.

AREA

Area Formula Example

Rectangle (Length) x (Width) (35' L) x (12' W) = 420 sq. ft.

Circle (0.785) x (Dia. sq.) (0.785) x (55') x (55') = 2,375 sq. ft.

VOLUME

Volume Formula Example

Rectangle L x W x H 80'L x 25'W x 10"H = 20,000 cu. ft.

Cylinder (0.785) x (Dia. sq.) x (H) (0.785) x (55') x (55') x (25') = 59,366 cu. ft.

Raw Inuent Calculaons

Plant Inuent LoadingsDetermines the infuent loadings o pounds (BOD, SS, etc.) to a wastewater treatment acility.

Plant Inuent Loadings:

mg/l x mgd x 8.34 = lbs./day

Example (using TSS):

Plant Conditions:

TSSInuent=135mg/l

Inuentow=1.5mgd

Todeterminepoundsintotheplant,usethefollowingcalculation:

mg/l x mgd x 8.34 = lbs/day

Example: 135mg/lx1.5mgdx8.34=1,688.85lbs.

This reects the pounds of TSS into the plant on that particular day.

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Clarier Capacity CalculaonsSurface Loading Rate - RECTANGULAR ClarierGallons o wastewater applied to each square oot o the clarier area. Tis aects the settleable solids andBOD removal eciency in the sedimentation process.

Surface Loading Rate (RECTANGULAR CLARIFIER):

gpd

sq. ft. of clarier

Example:

Clarier:

Length = 75 feet

Width = 12 feet

Inuentow=1.2mgd(1,200,000gpd)

ThesquarefootageoftheclarierisLxW:

75 x 12 = 900 sq. ft.

TodeterminetheSurfaceLoadingRateofarectangularclarier,use

thefollowingcalculation:

gpd

sq. ft. of clarier

Example: 1,200,000gpd=1,333gpd/sq.ft.

900 sq. ft.

Clarier Capacity CalculaonsSurface Loading Rate - CIRCULAR Clarier

Gallons o wastewater applied to each square oot o the clarier area. Tis aects the settleable solids andBOD removal eciency in the sedimentation process.

Surface Loading Rate (CIRCULAR CLARIFIER):

gpd

sq. ft. of clarier

Example:

Clarier:

Diameter=60feet

Inuentow=2,200,000gpd

Thesquarefootageoftheclarieris.785xDia.sq..785 x 60' x 60' = 2,826 sq. ft.

TodeterminetheSurfaceLoadingRateofacircularclarier,usethe

followingcalculation:

gpd

sq. ft. of clarier

Example: 2,200,000gpd=778.48gpd/sq.ft.

2,826 sq. ft.

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Clarier Capacity Calculaons

Detenon TimePeriod o time that a particle remains in a tank.

Detention Time:

tank volume x 24 hours

Inuent ow

Example (rectangularclarier):

Clarier:

Length = 75 feet

Width = 30 feet

Depth=10feet

Inuentow=2,850,000gpd

ThevolumeoftheclarierisLxWxHx7.48

70' x 25' x 10' x 7.48 = 130,900 gals.

TodeterminetheDetentionTimeofa rectangularclarier,usethe

followingcalculation:

tank volume x 24 hours

Inuent ow

Example: 130,900 gals x 24 = 1.10 hours

2,850,000

Weir Overow Rate:

gpd ow

Total feet of weir

Example:

Plant Conditions:

Weir length = 100 feet Flowrate=1,500,000gpd

TodeterminetheWeirOverowRate,usethefollowingcalculation:

gpd ow

Total feet of weir

Example: 1,500,000gpd=15,000gpd/ft.

100feetofweir

Clarier Capacity CalculaonsWeir Overow Rate

Volume o water fowing over oot length o weir per day.

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Acvated Sludge CalculaonsSludge AgeAverage time a particle o suspended solids remains in the activated sludge system. Sludge age is used tomaintain the proper amount o activated sludge in the aeration system.

o determine sludge age, you must calculate both the daily amount o suspended solids and the total amounto solids in the aerator.

Sludge Age:Total lbs. of MLSS in aerator

Daily lbs. of MLSS in aerator

Example:

Suspendedsolidsofprimaryefuent=110mg/l

Inuentow=2.5mgd

Aerationtankvolume=.5mg MLSSconcentration=2,200mg/l

Theplantinuentloading=mg/l x mgd x 8.34

Example:

110x2.5x8.34=2,293.5lbs.dailyofSS(lbsofMLSSinaerator)

2,200x.5x8.34=9,174lbs.total of MLSS in aerator

Withthesecalculations,youcandetermineSludeAge:

Total lbs. of MLSS in aerator = Days Sludge Age


Example:

9,174lbs.total of MLSS in aerator = 4 Days Sludge Age

2,293.5lbs.daily of MLSS in aerator

Example:

Inuentsuspendedsolids=250mg/l

Inuentow=2.5mgd

Aerationtankvolume=.5mg

MLSSconcentration=2,200mg/l

Theplantinuentloading=mg/l x mgd x 8.34

Example:

250x2.5x8.34=5,213lbs.dailyofSS(lbsofMLSSinaerator) 2,200x.5x8.34=9,174lbs.total of MLSS in aerator

Withthesecalculations,youcandetermineSludeAge:

Total lbs. of MLSS in aerator = Days Sludge Age


Example:

9,174lbs.total of MLSS in aerator = 1.76 Days Sludge Age

5,213lbs.daily of MLSS in aerator

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Sludge Age - Plants with Primary Clarier

Sludge Age - Plants without Primary Clarier


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Usingthesegures,calculatetheamount

ofsuspendedsolidsleavingthesystem:

Example:

(7,250mg/lwastesludge)x(.08wastesludgeow)x(8.34lbs.)

+(20mg/lSSnalefuent)x(4.3MGDinuentow)x(8.34lbs.)

=4,837.2lbs.SS+717.2lbs.SS=5,554.4lbs.SSleavingsystem

Forthisexample,thevolumeoftheaerationtankandclarierequals

1.7mg.

Pounds of Aeration Tank MLSS =

Aeration Tank mg/l MLSS x mg x 8.34

Example:

2,500mg/lMLSSx1.7mgvolumex8.34lbs.=35,445lbs.MLSS

Solids Retention Time (SRT):

SRT days = lbs./day of SS in system

lbs./day of SS leaving system

Example:

35,445lbs.MLSS=6.38SRT

5,554.4lbs.SSleavingsystem


Solids Retenon Time (SRT)Average time a given unit o cell mass stays in the activated sludge system. SR is based on solids leaving theActivated Sludge process, and includes solids in the clariers. Also called MCR (Mean Cell Residence ime).

Solids Retention Time (SRT):

SRT days = lbs./day of SS in system

lbs./day of SS leaving system

FactorsindeterminingSRT:

1. Solidsleavingthesystem(wasted)

2. Solidsleavingthesystem(SSinthenalefuent)

3. Solidsinthesystem(aerationbasinsandclariers)

Example:

Tankvolumes: Aerationvolume=1.6mg

FinalClarifervolume=.10mg

SSConcentration: Finalefuent=20mg/l

WastesludgeSS=7,250mg/l

AerationTankMLSS=2,500mg/l

Flows: Inuentow=4.3mgd

Wastesludgeow=0.08mgd(24-hourperiod)

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Solids to be WastedSolids (measured in pounds) to be wasted over a set period o time (typically daily).

Solids to be Wasted:

Current inventory

- Desired inventory to achieve peak performance

= Pounds to be wasted

AftercalculatingtheMLSSConcentration(seeabove),usethe

followingformulatodeterminethepoundsofsolidstobewasted.

Example:

Peakperformance=22,000poundsofMLSSinaerationsystem

Currentinventory=25,000poundsofMLSSinaerationsystem

25,000pounds(currentinventory)

- 22,000pounds(desiredinventory)

= 3,000poundstobewasted

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MLSS Concentraon in PoundsPounds o MLSS in the aeration system.

MLSS Concentration:

MLSS (mg/l) x volume of aeration tank x 8.34

Example:

MLSSinaerationtank=2,500mg/l

Aerationsystemvolume=1.4mg

MLSS (mg/l) x volume of aeration tank x 8.34

2,500mg/lx1.4x8.34=29,190lbs.ofMLSS


F/M Ratio

Ratio o ood (biochemical oxygen demand) entering the aeration tank to microorganisms in the tank.

F/M Ratio:

lbs./BOD

lbs. MLSS

Example:

lbs.ofBODenteringplantdaily=4,340lbs.

lbs.ofMLSSinaerator=8,201lbs.

lbs.BOD or 4,340lbs.ofBODenteringplantdaily=.53F/M

lbs.MLSS 8,201lbs.ofMLSSinaerator


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Waste Sludge Pumping RateRate at which to pump the sludge to be wasted rom the system. Normally expressed in gallons per minute (gpm).

Example:

Plant Conditions:

lbs.ofMLSStobewasted=1,400lbs.

MLSSconcentration=5,900mg/l

lbs. to be wasted = ow rate (mgd)

MLSS concentration x 8.34

Example:

1,400lbs.tobewasted =.0284mgdwastingrate

5,900mg/lx8.34

Convertmilliongallonsperdaytogallonsperday:mgd wasting rate x 1,000,000 = gpd wasting rate

Example: .0284x1,000,000=28,400gpd

Convertgallonsperdaytogallonsperminute(over8hours):

gpd wasting rate

480 minutes (8 hours)

Example: 28,400gpd =59.166gpm

480minutes

Typical WWTP Operaonal Parameters

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Metal Salt Addion for Phosphorus Removal

Using metal salt chemical data, theoretically calculate the amount of chemical salt solution to add in

gallons per day to remove phosphorus.

*Valuesthatneedtobeenteredareshowninthegrayboxes.

Step 1. Determine the amount of influent phosphorus to remove.

InfluentflowinMGD InfluentP(mg/l) lbs/gallon lbsofPtoremove

2 x 8 x 8.34 = 133

Step 2. Determine the pounds of metal salt in a gallon of solution knowing the specific gravity.

Specificgravity lbs/gal lbsmetalsalt/gal

1.4 x 8.34 = 11.7

Chemical SpecificGravity

Alum 1.33Ferric Chloride 1.441

Ferrous Chloride 1.23

Ferrous Sulfate 1.185

Step 3. Determine the pounds of actual metal in a gallon of metal salt solution with certain percentage

metal content (provided by chemical supplier).

lbsmetalsalt/gal %metal lbsmetal/galmetalsaltsolution

11.7 x 12.5 = 1.5

Step 4. Look up removal ratio for the metal salt being used.

Chemical RemovalRatio

Alum 0.87 to1

Ferric Chloride 1.8 to 1

Ferrous Chloride 2.7 to 1

Ferrous Sulfate 2.7 to 1

Step 5. Determine the pounds of metal needed to remove the incoming pounds of phosphorus.

Removalratio InfluentlbsofP lbsofmetaltoadd

1.8 x 133 = 240

Step 6. Determine the gallons of metal salt solution with a certain percentage metal content to thus add.

lbsofmetaltoadd lbsofmetal/gal gal/dayofmetalsaltsolutiontoadd

240 1.5 = 165Thisestimatemaybedifferentthan

thevalueobtainedfromacalculator

due to rounding differences.

ThisspreadsheetwasdevelopedbytheWisconsinDepartmentofNaturalResources

andtheOperatorCertificationPhosphorusRemovalExamWorkgroup(2008)


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Qualied sta is available to meet with you on site.

Call 815-459-1260 for addional informaon

or to schedule an appointment.

10

Baxter & Woodman provides a ull range o services to meet your daily and long-term operational needs,complemented by a sta that provides customized Municipal Engineering Services. Licensed and certiedoperators are available to assist with your water and wasterwater operations needs.

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