dissolved air flotation (daf)...dissolved air flotation (daf): commissioning and operations at the...
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Dissolved Air Flotation (DAF): Commissioning and Operations at the
White Tanks Regional Water Treatment Plant
Jeremiah Mecham, Agua Fria District Operations Superintendent
Timothy J. White, P.E., Project Engineer
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Agenda Plant Background Dissolved Air Flotation
Process Overview White Tanks Design
Operational Experience Q&A
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Background Overuse of groundwater in Agua Fria district
Declining water levels, ground subsidence Water quality issues
Surface Water Plant recommended by WESTCAPS AAW takes lead for WTRWTP
Planning 2001 Advertise Design Concept / RFP 2003 Design 2003 through 2005 Groundbreaking 2007 Startup 2009
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White Tanks Regional Water Treatment Plant
Treats CAP water from Beardsley Canal in Surprise, AZ
Capacity 13.4 MGD initial 80 MGD ultimate
Major Treatment:
DAF GAC filtration UV Cl2 Disinfection
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Clarification Options Conventional Sedimentation
Plate and Tube Settlers
Solids Contact / Solids Blanket Clarifiers
Dissolved Air Flotation (DAF) Ballasted Flocculation (Actiflo)
Direct Filtration
Raw Water Pump Station
Flocculation
Settle / Flotation
GAC/Sand Filtration
UV Light Disinfection
Clearwell Storage
Clarification
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DAF Selection Overview Based upon raw water quality and overall treatment
goals, process selection recommended using Dissolved Air Flotation
Fundamentals of DAF treatment similar to conventional treatment (coag/floc/sed)
Small footprint / high loading rates
Effective on low turbidity water, highly efficient at removing algae
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What is Dissolved Air Flotation? Why chose it? Separation process similar to gravity sedimentation
Target is Small, Uniform Floc That Readily Floats Uses thousands of microbubbles to attach and lift particles / floc Chemistry critical to maximize particle attachment to bubbles More Concentrated Solids with DAF
Clarified Water Turbidity Often Lower than Conventional/ Filtered Water Turbidity Typically Similar
Treatment of <1 NTU, 99% algae count reduction, and 15% TOC removal Flexibility to Improve Performance by Adjusting Recycle
Lower Capital Cost for DAF/Higher Power Cost
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Process Coagulant Usage
0
10
20
30
40
50
0 15 25 50 75 100 125 150
Turbidity, NTU
Coa
gula
nt D
ose,
mg/
l
DAF
Gravity Clarification
Direct Filt.
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DAF Components Saturator tanks – air and water are
combined under pressure to super saturate the water with air
Recycle pumps – uses clarified water to generate super saturated stream
Nozzles – create pressure drop to release supersaturated air as microbubbles. Pressure drop critical in providing correct size bubble
False floor – promotes hydraulics Sludge removal – sludge floats and
collects at top of basin – basins are periodically flooded hydraulically to remove solids
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White Tanks DAF Schematic
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AquaDAF Flow Diagram
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White Tanks DAF Flow Limits
Plant Flow Two in Service Three in Service Four in Service
Q total, mgd
Q mgd
Loading Rate,
gpm/ft2 Q
mgd
Loading Rate,
gpm/ft2 Q
mgd
Loading Rate,
gpm/ft2
5.0 2.5 3.0 1.7 2.0 1.3 1.5
10.0 5.0 6.0 3.3 4.0 2.5 3.0
13.4 6.7 8.0 4.5 5.3 3.4 4.0
20.0 - - 6.7 8.0 5.0 6.0
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Operational Experience Background Experience
Plant Supervisor experienced with DAF
Well Field Operators Plant Maintenance
Training Lab Classroom Field Other Facilities
Operations Results
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Facility Layout
Intake
Screening Structure
Raw Reservoirs
Raw PS
DAF/ Filters
WW Basins
Chemical Storage
UV Finished Water Basin
Admin Building
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Training
Lab Training/Testing Team Management/Vendors
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Training
Classroom Training Provided by vendors
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Training
Field Training Provided by vendors/Project
management team
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Training
Field Training Provided by vendors/Project
management team
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Site Visit Site Visits to Operating American Water Facilities
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Operations
Challenges Staffing Nozzles Training
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Raw & Settled Water Turbidities
0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
4.00
11/5/2009 0:00 11/5/2009 12:00 11/6/2009 0:00 11/6/2009 12:00 11/7/2009 0:00 11/7/2009 12:00
Date
Turb
idity
(NTU
)
WT_AIT_21001 WT_AIT_22010 WT_AIT_31101 WT_AIT_31201 WT_AIT_31301
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Operations CHEMICAL USAGE DURING VALIDATION TESTING
CHEMICAL[1
]
11/05/09 11/06/09 11/07/09 Dose (mg/L) Gallons Dose
(mg/L) Gallons Dose (mg/L) Gallons
Ferric Chloride 18.0 125.7
18.0 141.3 15.0 42.7
13:00 = 15
Sodium Hydroxide
08:00= 10.0
17.1 0.0 (offline) 0 0.0
(offline) 0 10:30= 8.0
13:00= 0.0 (offline)
Sodium Hypochlorite 0.70 20.8 0.70 25.4 0.70 8.5
[1] FeCl3 at 41% strength, S.G. 1.43. NaOH at 33% strength, S.G. 1.36. NaOCl at 12.5% strength, S.G. 1.10
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Results Analyte
11/5/2009 11/6/2009 11/7/2009
Raw Finished Raw Finished Raw Finished
OPERATOR MEASUREMENTS
Turbidity (NTU)[1] 0.40 0.13 0.42 0.13 0.36 0.17
Chlorine, Free (mg/L) N/A Inf: 0.44
Eff: 0.38 N/A Inf: 0.46 Eff: 0.36 N/A Inf: 0.58
Eff: 0.46
Alkalinity (mg/L as CaCO3)
123 N/A 114 111 118 109
TDS (mg/L) 169 N/A 161 160 161 159
GRAB SAMPLES
E. Coli N/A Negative N/A Negative N/A Negative[2]
Total Coliform N/A Negative N/A Negative N/A Negative2
TOC (mg/L) 2.94 (RW)[3] 2.52 (SW)[4] 0.90 2.88 (RW)
2.50 (SW) 0.67 2.89 (RW) 2.53 (SW) 0.70
TOC Removal N/A 69% N/A 77% N/A 76%
[1] Finished Water turbidity samples were taken from Combined Filter Effluent Sample measurements [2] Samples were only required for 2 days of testing. Additionally, 11/7/09 was a Saturday when the laboratory was closed, meaning analysis of this sample would have been delayed until outside of the allowable hold time. [3] RW = Raw Water as collected from the Screening Structure Sample tap. [4] SW = Settled Water as collected from the DAF Effluent Sample tap.