Title: Filtration Part II Filter Coring
1Filtration - Part IIFilter Coring
- KY Water and Wastewater Operators Conference
- March 2003
- Tim Wolfe
- Vice President
- MWH Americas
2Items Discussed - Part I
- Brief History of Water Filtration
- Todays Filters
- Filter Operating Parameters
- Particle Removal in Filters
- Headloss Development in Filters
- Unit Filter-Run Volume
- Backwashing
- Tomorrows Filter Challenges
3Items to be Discussed - Part II
- Filter Coring Method
- Physical inspection
- Core sampling, for Solids-retention profiles
(before and after backwashing) - Backwash-turbidity profile
- Backwash-expansion measurement
- Core sampling, for Sieve analysis
- Filter-effluent turbidity profile
- Solids-retention profiles
- Filter Coring Analyzing Results
4Filter CoringMethod
51. Physical Inspection
- Media Surface
- Surface variation, Cracks, Media boils
- Mudballs
- Bed depth, and Gravel migration
- Distance from top of trough to bed
- Distance between surface-wash nozzles and bed
- Backwash
- Media Loss
- Air release during backwash
- Level of backwash troughs
6Measuring Bed Depth,and Gravel Migration
72. Core Sampling
8Array of Core-Sampling Tools
9Core-Sampling Method
- Sample from three (3) bore holes for first sample
(0 - 2 in.) - Sample from two (2) bore holes for second sample
(2 - 6 in.) - Sample from one (1) bore hole for remaining
samples (6 - 12 in., etc.) - Place samples from each depth in a baggy
Core
10Collecting Core Samples, andPlacing Samples in a
Baggy
11Filter-Media Depth Profile
0 - 2
2 - 6
6 - 12
Anthracite - 24
12 - 18
36 total
18 - 24
Anthracite / Sand 21 - 27
24 - 30
Sand - 12
30 - 36
12Core-Sampling Pipe
Approximately 6 ft
Lightweight Pipe (e.g., Electrical conduit) PVC
pipe is not suitable
13Filter-Media Samples for Solids-Retention
Profiles(Before and After Backwash)
Sample No.
Sample Depth
14Dual-Media Interface Potential for Significant
Solids Storage
153. Backwash-Turbidity Profile
- Standard backwash procedure using seasonal
backwash rate - Surface wash
- Surface wash, with low-rate backwash
- High-rate backwash, without surface wash
- Collect first sample of backwash water when
filter troughs begin to overflow - 100-ml sample volume at 30 second intervals
16Backwash-Rate Relationship
- BW rate is a function of terminal velocity of
media grains - media grain size (effective size d10)
- uniformity coefficient (d60/d10)
- specific gravity
- media sphericity
- Scouring action provides effective BW of media at
10 settling velocity
17Backwash Rate Independent of Media Depth
Media scouring vs. terminal velocity of media
grains
When the expanded-bed porosity is around 0.7,
media grains are scratching against each other to
unstick the stuck solids.
18Appropriate Backwash Rate at 20c
30
25
Sand S. G. 2.65
20
15
Backwash Rate (gpm/sf)
10
Anthracite Coal S. G. 1.65
5
0
0
1
2
60 Weight grain size (ESUC)
19Temperature-Correction Factor for Backwash Rate
Multiplier for Appropriate Backwash Rate
Water Temperature (C)
204. Backwash-Expansion Measurement
21Backwash-Expansion Measurement (Cont.)
225. Core Sampling for Sieve Analysis
- Collect full-depth, filter-media core samples for
both the anthracite and the sand after backwash - Send to lab for sieve analysis of both the
anthracite and the sand samples - Effective grain size (d10), uniformity
coefficient (d60/d10) and specific gravity - ASTM methods C136 and C128
23Example of an Anthracite Core Sample for Sieve
Analysis
246. Filter-EffluentTurbidity Profile
- Perform a mini-wash of the filter following the
filter coring conducted after backwash - Bring filter back on-line
- Measure filter-effluent turbidity every 5 min for
30 minutes - Measure filter-effluent particle counts every 5
min for 30 minutes - Continue measuring if effluent turbidity is not
lt 0.1 NTU at 30 minutes
257. Solids-Retention Profiles
26Solids-Retention Lab Method
a. Remove and weigh a 50-gram sample of filter
media from a baggy b. Mix 100 ml of tap water
with media shaking for 30 sec at uniform
intensity c. Decant supernatant, and shaking
repeated with additional 100 ml water d. Final
volume of supernatant 500 ml e. Turbidity
measurement converted to NTU/100 grams of
filter media f. Develop solids-retention
profile for each sample, before and after BW
27Solids-Retention Method (cont.)
28Solids-Retention Method (cont.)
29Solids-Retention ProfileGuidelines for
Backwashed Filter
30Filter CoringAnalyzing Results
311. Physical Inspection Results
- Media Surface
- Evidence of Media Boiling, Cracks in Bed
- Presence of Mudballs
- Sloping of Filter Surface Bed Contours
- Backwash
- Air Boiling
- Vigorous Backwash on One Side
- Unequal flow of backwash in troughs - troughs may
be uneven
322. Core Samples for Solids-Retention Profile
33Lab Instruments for Developing Solids-Retention
Profiles
343. Backwash-Turbidity Samples
35Backwash-Turbidity Profile Dual-media Filters
Turbidity (NTU)
Time of Backwash (minutes)
36BW-Turbidity Profile Comparison Rapid-sand Filters
Backwash Duration (minutes)
37BW-Turbidity Profile Results Rapid-sand Filters
- Sharp Initial Backwash-Turbidity Peak
- Second Turbidity Peak after Start of Surface Wash
- Final Backwash Turbidity over Target of 20 NTU
384. Backwash ExpansionDual-Media Filter
Anthracite
( 46 in. - 36 in. ) / 36 in. x 100 28
Bed Expansion
Anthracite
29 in.
46 in.
24 in.
36 in.
Sand
Sand
17 in.
12 in.
Fixed, Filter Bed
Expanded, Filter Bed
Want the same expansion all year long - change
BW rate.
395. Sieve-Analysis Results
- Allows us to define, for both the anthracite and
the sand - d10 - 10 of the media is finer (smaller) than
that size (diameter), on a weight basis -
referred to as the effective size of the media - d60 - 60 of the media is finer (smaller) than
that size (diameter), on a weight basis - Uniformity coefficient (UC) - Ratio of d60 size
to the d10 size - Specific gravity ( i.e., weight of media / weight
of water )
40Sieve-Analysis Results (Cont.)
- Also allows us to define, for the anthracite
- d90 - 90 of the anthracite is finer (smaller)
than that size (diameter), on a weight basis - Important because we want a ratio for the d90
coal size to the d10 sand size of approx. 3
(i.e., 3 - 6 in. of intermixing at interface) - Ratio significantly bigger than 3 ( i.e., too
much intermixing at interface ) - Ratio significantly smaller than 3 ( i.e., no
intermixing at interface )
416. Filter-Effluent Turbidity Profile Results
427. Solids-Retention Profiles
43Ideal FilterSolids-Retention Profile
0
5
10
15
Media depth (in)
Before Backwash
20
After Backwash
25
30
Turbidity (NTU/100 g of Media)
44Poorly Backwashed Filter(No Surface Wash)
Media Depth (inches)
Before Backwash
After Backwash
Turbidity (NTU/100 g of Media)
45Poorly Backwashed Filter(With Surface Wash)
Before Backwash
Media Depth (in)
After Backwash
Turbidity (NTU/100 g of Media)
46Poorly Matched Media (Sand is not Fluidized)
0
5 0
100
150
200
250
300
0
5
Before Wash
Anthracite Coal
10
Dual Media Filter
Depth From Top of Bed (in)
15
Sand
20
Coal Mixed
25
Sand
After Wash
30
Floc Deposition on Filter Media
Turbidity (NTU/100 g of Media)
47Core-Sampling Outcomes
- Actual depth of filter media L/d ratios
- Backwash-turbidity profile
- Effectiveness of backwash
- Grain-size distribution media size and
uniformity coefficient - Filter-effluent turbidity profile
- Solids-retention profiles
48Filter-Coring Conclusions
- Effective Tool for Diagnosis of Filter-Media
- Condition, and
- Backwash Effectiveness
- Provides Specific Recommendations
- for Change in
- Filter Operation
49Items Discussed - Part II
- Filter Coring Method
- Physical inspection
- Core sampling, for Solids-retention profiles
(before and after backwashing) - Backwash-turbidity profile
- Backwash-expansion measurement
- Core sampling, for Sieve analysis
- Filter-effluent turbidity profile
- Solids-retention profiles
- Filter Coring Analyzing Results