FILTER MEDIA CHOICES AND FILTER OPTIMIZATION

11

FILTER MEDIA CHOICES FILTER MEDIA CHOICES

AND FILTER OPTIMIZATIONAND FILTER OPTIMIZATION

Marvin Gnagy, P.E.Marvin Gnagy, P.E.

Water Resources ManagerWater Resources Manager

URS Corporation URS Corporation -- ToledoToledo

22

AgendaAgenda

•• Importance of filter optimizationImportance of filter optimization

•• Filter coring techniquesFilter coring techniques

•• Floc retention profilesFloc retention profiles

•• Bed depth evaluations Bed depth evaluations

•• Backwash duration testsBackwash duration tests

33

AgendaAgenda

•• Bed expansion evaluationsBed expansion evaluations

•• Sieve analysesSieve analyses

•• Water temperature effects on wash rateWater temperature effects on wash rate

•• FilterFilter--toto--waste simulationswaste simulations

•• Media growth / acid solubilityMedia growth / acid solubility

•• Media design parametersMedia design parameters

44

Importance of Filter Importance of Filter

OptimizationOptimization

•• Optimize filtration and backwashOptimize filtration and backwash

•• Improve filter effluent qualityImprove filter effluent quality

•• Reduce filter ripening timeReduce filter ripening time

•• Reduce turbidity / particle count spikesReduce turbidity / particle count spikes

•• Meet lower turbidity standardsMeet lower turbidity standards

•• Prevent exceptions reportingPrevent exceptions reporting

55

Importance of Filter Importance of Filter

OptimizationOptimization

•• Identify filter operating problemsIdentify filter operating problems

•• Identify current media conditionsIdentify current media conditions

•• Define proper bed depthDefine proper bed depth

•• Establish operating adjustmentsEstablish operating adjustments

•• Predict media replacement needsPredict media replacement needs

•• Optimize particle/microbial removalsOptimize particle/microbial removals

66

Filter Exceptions ReportingFilter Exceptions Reporting

• Exceed filter effluent turbidity limits in 2

consecutive samples taken 15 minutes

apart…

•• Filter profileFilter profile

•• Filter self assessmentFilter self assessment

•• ThirdThird--party Comprehensive Performance party Comprehensive Performance

Evaluation (CPE)Evaluation (CPE)

77

Turbidity MonitoringTurbidity Monitoring

•• Continuous turbidity monitoring of Continuous turbidity monitoring of

individual filter effluents individual filter effluents

•• 0.3 NTU in 95% samples taken0.3 NTU in 95% samples taken

•• Maximum 1 NTU at any timeMaximum 1 NTU at any time

88

Filter Coring TechniquesFilter Coring Techniques

1 2 43

6 5 7 8

99


1010


1111


1212


1313


1414


1515


•• Electrical conduit makes good coring Electrical conduit makes good coring

devicedevice

•• Core in same spot each depthCore in same spot each depth

•• Samples in individual marked bagsSamples in individual marked bags

•• Samples washed and turbidity Samples washed and turbidity

measuredmeasured

1616

Floc Retention ProfilesFloc Retention Profiles

0

3

6

9

12

15

18

21

24

27

30

33

36

39

42

45

0 100 200 300 400 500 600 700 800 900 1,000 1,100 1,200

NTU/100 grams

Bed Depth, inches

Less than 3,500 NTU/100

grams

Less than 150 NTU/100

grams at midpoint

No apparent potential for

breakthrough

1717


0

3

6

9

12

15

18

21

24

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000

NTU/100 grams

Bed Depth, inches

More than 3,500

NTU/100 grams

No apparent potential for breakthrough

Less than 150 NTU/100

grams at midpoint

1818


0

3

6

9

12

15

18

21

24

0 200 400 600 800 1,000 1,200 1,400

NTU/100 grams

Bed Depth, inches

Less than 3,500

NTU/100 grams

More than 150 NTU/100

grams at midpoint

Apparent breakthrough due

to excessive run time

1919

Backwash ProfilesBackwash Profiles

0

3

6

9

12

15

18

21

24

0 10 20 30 40 50 60 70 80

NTU/100 grams

Bed Depth, inches

Clean Range

Increased

surface wash

time needed

2020

Backwash ProfilesBackwash Profiles

0

3

6

9

12

15

18

21

24

0 10 20 30 40 50 60 70 80 90 100 110 120

NTU/100 grams

Bed Depth, inches

Clean Range

Poor bed expansion (16%)

lead to incomplete wash

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Backwash ProfilesBackwash ProfilesFLOC RETENTION GUIDELINES FOLLOWING BACKWASH

NTU/100 GRAMS MEDIA CONDITION ACTIONS NEEDED

Less than 30 Very clean Bed is too clean – examinethe wash rate and duration-

this bed will not ripen quickly.

30 to 60 Clean A well cleaned and ripenedbed – no action needed.

60 to 120 Slightly dirty Slightly dirty bed – reschedule

a backwash retention analysissoon.

Greater than 120 Dirty Dirty bed – re-evaluate the

backwash system andoperating procedures.

Greater than 300 Mud ball problems Mud balls are most likely

present – consider filterrehabilitation or rebuilding.

Greater than 2,000 Extreme mud ball

problems

Bed must be taken off line and

rebuilt to new specifications.

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Bed Depth EvaluationsBed Depth Evaluations

2323


2424


2525


•• Minimum bed depthMinimum bed depth

• Mono/dual media L/D10 Ratio 1,000

• Multimedia L/D10 Ratio 1,250

• Provides 15% excess - media loss

•• Based on L/DBased on L/D1010 for each media layerfor each media layer

• 12-inches * 25.4 mm / inch = 304.8 mm

• 304.8 mm ÷ 0.45 mm (ES) = 677.3

2626


Original Original

Media Media

DepthDepth

Depth Depth

with with

Media Media

LossLoss

Particle travelParticle travel

2727

Backwash Duration TestsBackwash Duration Tests

0

50

100

150

200

250

300

350

400

450

500

550

600

650

700

750

0 1 2 3 4 5 6 7

Backwash Duration, minutes

Turbidity, NTU

10 NTU reached at 4.5 minutes

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Backwash Duration TestsBackwash Duration Tests

020406080100120140160180200220240260280300320340360380400420440

0 1 2 3 4 5 6 7 8 9 10

Backwash Duration, minutes

Turbidity, NTU

Too many rate changes in wash cycle

10 NTU reached at 8.5

minutes

2929

Bed Expansion EvaluationsBed Expansion Evaluations

•• Determine actual bed expansionDetermine actual bed expansion

•• 30% expansion accepted as standard30% expansion accepted as standard

•• Simple device used to check expansionSimple device used to check expansion

•• Expansion observed on clean filterExpansion observed on clean filter

•• Rate adjustments should be obviousRate adjustments should be obvious

3030


3131


9.5-inches

3232


Gravel displacementGravel displacement60%60%

Excessive media lossExcessive media loss50%50%

Ineffective cleaningIneffective cleaning40%40%

Normal rangeNormal range30% to 35%30% to 35%

3333

Sieve AnalysesSieve Analyses

•• Indicates current condition of filter Indicates current condition of filter

mediamedia

•• Defines effective size and uniformity Defines effective size and uniformity

coefficientcoefficient

•• Perform every two years on each layer Perform every two years on each layer

of representative filter bedof representative filter bed

•• Helps define interfacial mixingHelps define interfacial mixing

3434


Grain Size Distribution Curve

0

10

20

30

40

50

60

70

80

90

100

0.1001.00010.000

Diameter, mm

Percent Passing Sieve

3535



0

10

20

30

40

50

60

70

80

90

100

0.1001.00010.000

Diameter, mm


0.62 mm

3636



0

10

20

30

40

50

60

70

80

90

100

0.1001.00010.000

Diameter, mm


0.62 mm1.44 mm

3737


•• DD1010 0.62 mm0.62 mm

•• DD6060 1.44 mm1.44 mm

•• ES = DES = D1010 0.62 mm0.62 mm

•• UC = DUC = D6060 ÷÷ DD1010

• 1.44mm ÷ 0.62mm = 2.32

3838

Temperature Effects on Temperature Effects on

Washwater RateWashwater Rate•• Decrease in temperature decreases the Decrease in temperature decreases the

effective backwash rateeffective backwash rate

•• Change wash rate 2% for each 1Change wash rate 2% for each 1ooC C

changechange

•• Lower rate in winterLower rate in winter

•• Higher rate in summerHigher rate in summer

•• UC also affects backwash rateUC also affects backwash rate

3939


Washwater RateWashwater Rate

ABC WATER TREATMENT PLANT

ANTHRACITE SAND

D10, effective size, mm 0.85 0.45

D60/D10, uniformity coefficient 1.40 1.50

D90 calculated, cm 0.15 0.09

Media specific gravity 1.6 2.6

Water temp, 0C 2.0 2.0

Water viscosity, g/(cm-s) 0.01676 0.01676

Galileo Number 6,949 3,881

Fluidization Velocity, Vmf 0.45 0.43

Desired Bed Expansion, % 30% 30%

Backwash Velocity, Vmf 0.58 0.56

Backwash rate, gpm/ft2 * 8.6 8.2

Backwash rate, in/min 13.7 13.2

BACKWASH MODEL FOR RAPID RATE FILTRATION

RECOMMENDED MEDIA DESIGN BASED ON MEDIA AVAILABILITY

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Washwater RateWashwater Rate

ABC WATER TREATMENT PLANT

ANTHRACITE SAND

D10, effective size, mm 0.85 0.45

D60/D10, uniformity coefficient 1.40 1.50

D90 calculated, cm 0.15 0.09

Media specific gravity 1.6 2.6

Water temp, 0C 28.0 28.0

Water viscosity, g/(cm-s) 0.00835 0.00835

Galileo Number 28,051 15,618

Fluidization Velocity, Vmf 0.79 0.80

Desired Bed Expansion, % 30% 30%

Backwash Velocity, Vmf 1.03 1.03

Backwash rate, gpm/ft2 * 15.1 15.2

Backwash rate, in/min 24.2 24.4

BACKWASH MODEL FOR RAPID RATE FILTRATION

RECOMMENDED MEDIA DESIGN BASED ON MEDIA AVAILABILITY

4141

Filter Efficiency EvaluationsFilter Efficiency Evaluations

•• Filter efficiency calculationFilter efficiency calculation

•• Gross Water Production (GWP)Gross Water Production (GWP)

%100=−

x

filteredGallons

backwashgallonsfilteredGallons

runftgalftgpmtimerunFilter //60*/*22

=

4242


•• Filter efficiency greater than 95%Filter efficiency greater than 95%

•• GWPGWP

• Monomedia 5,000 gal/ft2/run

• Dual media 10,000 gal/ft2/run

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•• Filter run timesFilter run times

• 48 hrs. monomedia

• 72 hrs. dual media or multimedia

• Marvin’s maximum - 150 hours

•• Washwater usageWashwater usage

• 2% to 4% raw water pumpage

• 100 gal / ft2 to 150 gal / ft2

4444

FilterFilter--toto--Waste SimulationsWaste Simulations

0.060

0.080

0.100

0.120

0.140

0.160

0.180

0 10 20 30 40 50 60 70 80 90

RUN TIME, minutes

NTU

4545


0.060

0.080

0.100

0.120

0.140

0.160

0.180

0 10 20 30 40 50 60 70 80 90

RUN TIME, minutes

NTU

4646


0.060

0.080

0.100

0.120

0.140

0.160

0.180

0 10 20 30 40 50 60 70 80 90

RUN TIME, minutes

NTU

6363--minute ripening timeminute ripening time

4747

Filter ProfilingFilter Profiling

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0 10 20 30 40 50 60 70 80 90 100

Filter run time, hours

Turbidity, NTU

Increased flow due to

filter wash

Terminal head loss,

terminate filter run

4848

Media Growth / Acid SolubilityMedia Growth / Acid Solubility

•• Check growth rate every yearCheck growth rate every year

• Media above ES range• Consider replacement / acid cleaning

• Growth increases ES and UC

•• Keep COKeep CO33 deposition to a minimumdeposition to a minimum

• CO3 alkalinity ≤35 mg/L applied

• Perform acid solubility every year

• Solubility less than 2% per year

4949

Media Design ParametersMedia Design Parameters

•• ES ranges ES ranges

• 0.40 mm to 0.55 mm sand

• 0.80 mm to 1.20 mm anthracite

• 0.45 mm to 2.0 mm GAC (cap vs. monomedia)

•• UC less than 1.65 UC less than 1.65

• Consider low UC for anthracite to reduce

backwash rate

•• Minimum 12Minimum 12--inches filter sand (24inches filter sand (24--inches inches

monomedia)monomedia)

5050


•• Typical bed depth 24Typical bed depth 24--inches to inches to

6060--inchesinches

•• Match ES and UC for each layer to Match ES and UC for each layer to

obtain similar backwash rateobtain similar backwash rate

•• L/DL/D1010 ratio defines minimum bed depthratio defines minimum bed depth

•• Critical bed depth at lower L/DCritical bed depth at lower L/D1010 rangerange

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•• DD9090/D/D1010 ratios for dual media filtersratios for dual media filters

• 3 for anthracite / sand media

• 5 for GAC / sand media

•• Low DLow D9090/D/D1010 ratio ratio -- media layeringmedia layering

•• High DHigh D9090/D/D1010 ratio ratio -- mixed mediamixed media

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MEDIA DEPTH TO EFFECTIVE SIZE RATIO (L/D10 Ratio)

COARSE TO FINE MEDIA RATIO (D90/D10 RATIO)

ANTHRACITE SAND GAC

Media depth, inches 12 18 12

Media depth, mm 304.8 457.2 304.8

L/D10 Ratio 358.6 1016.0

D90 anthracite, mm 1.49

D90/D10 Ratio (3:1 or 4:1) 3.31

Total L/D10 Ratio >=1,000 1,375

5353

Mud BallsMud Balls

•• Ineffective backwash/surface washIneffective backwash/surface wash

•• Accumulated floc material in mediaAccumulated floc material in media

•• 1/81/8”” to basket ball size mud balls have to basket ball size mud balls have

been observedbeen observed

•• Deteriorate filter bed quicklyDeteriorate filter bed quickly

• Washing wand can break up mud balls

• Raking can break up mud balls

5454

Mud BallsMud Balls

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Mud BallsMud Balls

Effect of mud balls on filter mediaEffect of mud balls on filter media

FILTER MEDIA CHOICES AND FILTER OPTIMIZATION

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