how are my filters doing? filter profiling · after backwash •rinse using awwa protocol • rinse...

2/18/2014

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How are My Filters Doing? Filter Profiling Reveals All

Laurel Passantino and Jacqueline

Rhoades

Water Treatment Seminar

AZ Water

February 18, 2014

Statements of fact and opinion expressed are those of the author(s) and presenter(s). AZ Water Association, AZAWWA, and AZWEA assume no responsibility for the content, nor do they represent official policy of the Association.

Motivation

• Why profile filters?

Monitoring and Evaluation

• What should be watched?

• What tools and techniques are available?

Solution Implementation

• What are some common fixes?

Long-Term Operation

• What ongoing activities are needed?

Case Studies

Assess

Effectiveness

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Motivation: Why Profile Your Filters?

Sometimes, you can just tell…

Reasons to Profile Filters

• Diagnose obvious failure (Filter Forensics)

• Plan for process changes

• Create baseline for routine operations

• Optimize performance and cost

• Evaluate end-of-life conditions

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Motivation







Long-Term Operation


Case Studies

Assess

Effectiveness

What Data Should be Captured?

• Water quality parameters

• Individual filter effluent turbidity

• Combined filter effluent turbidity

• Operational parameters

• Filter runtime

• Headloss development profile

• Ripening time

• Backwash parameters

• Backwash duration

• Backwash volume

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Understanding Long-term Trends is Critical!

0

0.5

1

1.5

2

2.53/1

4

3/2

1

3/2

8

4/4

4/1

1

4/1

8

Tu

rbid

ity (

NT

U)

Turbidity Limit for

Unfiltered Supply

Qualitative Observations Also Important

Normal Backwash

Backwash with Hot-Spots

Even Surface after Draining

vs. vs. Surface Potholes

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Visual Inspection Can Be the First Line of Defense

• Boiling during wash

• Uneven wash distribution

• Uneven overflow into troughs

• Cratering

• Mudballs

• Cracking at surface

• Separation at walls

• Filter media in troughs

• Uniform surface

• Washwater troughs level

Cratering suggests possible damage to

underdrain.

Filter Inspection has Two Components

• Physical Characteristics

• Media depth

• Grain size distribution

• L/D

• Media support (underdrain, gravel)

• Operational Parameters

• Media Expansion

• Solids retention analysis

• Backwash Profile

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Be Prepared!

• Have a health and safety plan

• Confined Space

• Fall prevention

• Lockout-tagout

• Drain the filter

• Work in teams

• Review available resources

• AWWA B100

• Filter Maintenance and Operations Guidance

Manual (AWWARF 90908)

J

Know Your Tools!

• Maneuvering - Ladder to enter/exit, ¾ inch

plywood to stand on, carabiners, and rope for

transferring samples and equipment to the filter

deck

• Measurement - Shovel, level, 3/8 inch steel rod,

tape measure

• Documentation - camera, clipboard, datasheets,

object for scale in pictures

• Filter Coring - 1.5 inch electrical conduit, 5 foot

length, baggies

• Bed Expansion - One-inch interval tubes or

cups

• Analytical - Turbidimeter, glassware, balance,

sample bottles, baggies

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Steps to Performing a Filter Inspection

• Observe surface or air wash effectiveness

• View surface for boils or “hot spots”

• Look for uneven wash areas or uneven troughs

Visual Observation

• Quantify media loss by measuring the depth to gravel.

• Understand stratification by knowing the depth of layer of filter media, including the mixed zone.

Media Depth

• Take samples at 0-2 inches, 2-6, 6-12, 12-18, 18-24…

• Sample before and after backwash

• Collect multiple cores for a representative matrix

Core Sampling

• Send composite sample to lab. Compare size distribution, effective size, uniformity coefficient to design specs.

• Calculate L/D

Sieve Analysis/ Media

Assessment • Used to evaluate effectiveness of backwash

• Can show too little or too much backwash

• Keep historical records

Solids Retention Analysis

• Collect samples every minute of backwash

• Analyze turbidity and plot over time

• Helps prevent excessive washing

Backwash Turbidity Profile

Determine Media Depth Using Probing and Core Sampling

• Check to see if troughs are level,

then measure distance from trough

to bed

and check for mounding

• Use steel rod to probe media, or dig

into it to determine depth to gravel

• Use core sampling tool and baggies

to obtain samples at various depths

• If filter is dual or mixed bed, note

depth of each strata, and depth of

mixed interface

• Collect multiple cores to develop a

representative matrix of the filter bed

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Send Core Samples for Sieve Analysis

• Know the original specifications

• Understand the key parameters

• Effective size - particle size opening that will just pass 10%

(by dry weight) of a representative sample of filter material

(D10)

• Uniformity Coefficient - calculated ratio of the particle size

opening that will just pass 60% (by dry weight) of a

representative sample of filter material divided by the size

opening that will just pass 10% (by dry weight) of the same

sample (D60/D10)

• Media Depth - measured by probing or coring the filter bed

• L/D ratio - divide media depth (L) by the nominal media

diameter (D) to understand the particle barrier (>1100 for low

NTU production)

Interpret Sieve Analysis Results

• Effective Size is smaller than specified

• Larger grains may have broken down due to abrasion during

backwashing over time

• Effective Size is larger than specified

• Smaller grain size media has been lost over time

• Uniformity Coefficient is a measure of the grain size

distribution

• The closer to one, the narrower the grain size distribution

• If larger than specified, a wider grain size distribution is present.

This could lead to more intermixing between the sand and the

anthracite, resulting in too large of a mixed zone, and decreased

filter performance

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Calculate L/D

• Original specification for

a dual media filter

• 36 inches of 1 mm anthracite

• 6 inches of 0.5 mm sand

• 42 total inches

• Filter inspection revealed

• 32 inches of anthracite

• 6 inches of mixed layer

• 3 inches of sand

• 41 total inches

• Rough L/D calculation

• (32in X 25.4)/1mm = 813

• (6in X 25.4)/0.75 mm =

203

• (3in X 25.4)/0.5mm = 152

• L/D = 1168 adequate

particle barrier for low

NTU production

Assess Backwash Effectiveness with a Solids Retention Analysis

• Collect core samples

• Take samples at 0-2 inches, 2-6

inches,

and every 6 inches thereafter

for the entire bed depth

• Use same locations before and

after backwash

• Rinse using AWWA protocol

• Rinse 50 grams of sample

in 100mL of DI water

5 times (500 mL total) and

measure turbidity

• Multiply turbidity by

2 and plot against bed depth

• Bed depth vs. (NTU/100g

media)

Add mobile lab photo

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Assess Bed Cleanliness After Backwash

10-30 NTU: Very clean, not well

ripened. Bed is too clean,

examine wash rate and length

30-60 NTU: Clean and partially

ripened. No need for action

60-120 NTU: Reasonably clean,

well ripened. Slightly dirty,

reschedule retention analysis

soon.

120-300 NTU: Dirty media, well

ripened. Evaluate filter wash

system procedures.

300-600 NTU: Dirty media with

mudballs. Rehab bed!

Use Backwash Turbidity Profile to Determine Backwash Duration

0

50

100

150

200

250

300

350

400

0 5 10 15

Tu

rbid

ity (

NT

U)

Backwash Time (min)

AWWA Standard = 10 NTU

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Motivation







Long-Term Operation


Case Studies

Assess

Effectiveness

Implement Solutions to Improve Performance

• Add more media

• Change media type

• Pre-treatment process chemistry

• Modify backwash duration

• Implement temperature dependent high flow

backwash rate (account for water temperature to

achieve bed expansion)

• Address stratification of filter bed through staged

backwash programming

• Good operational practices

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Motivation







Long-Term Operation


Case Studies

Assess

Effectiveness

Periodic Evaluations Lead to Long-Term Success

• Once per quarter (per season)

• Adjust high flow rate for temperature

• Check media expansion – make adjustments

• Review unit filter run volume data

• Once per year

• Check media depth

• Core the filter – solids retention

• Review all filter profiles

• Every three to five years

• Send media to lab for sieve analysis

• Add media if necessary BUT – know why it’s being lost

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Case Studies

1. Catastrophic failure filter forensics

2. Commissioning a new treatment process

3. Retrofit filters for new water quality goals

4. Routine maintenance

1. Filter Forensics: Underdrain Failure

• Examining media and

backwash procedures helps

identify contributing factors

• Tools & Techniques

• Visual observation of backwash

• Visual observation of media

surface

• Media coring

• Physical characteristics

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1. Observations and Conclusions Hot-spots during backwash Uneven surface Mixed sand & anthracite

Media Anthracite Sand

Filter No. 15 16 18 15 16 18

Design Depth 20 in. 10 in.

In-place Depth 12.5 12.5 12.3 10 9.5 13

Design ES 0.45-0.55 0.9-1.1

In-place ES 0.5 0.5 0.5 1.0 1.0 1.0

Design UC <1.4 <1.4

In-place UC 1.33 1.35 1.30 1.33 1.41 1.37

• Replace underdrains

• Replace (not replenish)

media

• Change backwash

strategy to ensure

stratification

2. Commissioning a New Process

• Filter run times (terminated by

headloss) shorter than

anticipated at new WTP

• Potential factors

• Coagulation chemistry

• Abrasion concern with GAC media

• Backwash practices


• Trending runtime and headloss

• Visual observation of backwash and media surface

• Media coring and floc retention analysis

• Sieve analysis (media abrasion)

0

2

4

6

8

10

12

14

16

18

2/6 2/16 2/26 3/8 3/18

Ave

rag

e R

un

Tim

e (

hrs

)

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2. Observations and Conclusions

Clumps during & after backwash Mat on surface

• Modify coagulation chemistry

(coagulant aid, filter aid)

• Standardize backwash

protocols

• No further action required

after sieve analysis

-80

-70

-60

-50

-40

-30

-20

-10

0

0 50 100 150 200 250

Dep

th f

rom

Med

ia S

urf

ace (

in)

Turbidity of Rinse Water (NTU)

Before BW

After BW

Particles not penetrating bed

3. Retrofit Filters for New Water Quality Goals

• Dual media filters

replaced with GAC

• Filter runtimes (terminated

by turbidity breakthrough)

were shorter than

anticipated


• Trending runtime and

headloss

• Visual observation of

backwash and media

surface

• Media coring and floc

retention analysis

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Add sand to increase L/D

Pre-

Treatment

Modified

Pre-Treatment

Returned to Original

Conditions

Media ~L/D

36” GAC 760

42” GAC 1070

60” GAC 1260

36” GAC + 6”

Sand

1100

Pre-Treatment Impacted Filter Runtimes

Filt

er R

un

tim

e (h

r)

4. Routine Maintenance

• 10 year old media: Is media

replacement needed?


• Visual observation of media

surface

• Measurement of media levels

• Media coring

• Physical characteristics

• Visual observation of

backwash

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• Do not replace,

replenish to design

levels (add 4 to 6

inches of new

anthracite)

• Carefully monitor

backwash practices

SAN

D

SAN

D

ANTHRACI

TE

ANTHRACI

TE

GRAVEL GRAVEL

10”

1”

Filter Profiling Reveals All!

• Many tools are at your disposal

• Don’t wait for a failure

• Begin to establish filter baselines

now

• There’s always room for

improvement

2/18/2014

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Questions?

Laurel Passantino [email protected]

Jacqueline Rhoades [email protected]

how are my filters doing? filter profiling · after backwash •rinse using awwa protocol • rinse...

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