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AWWA/AMTA© 1
Open Intake RO Pretreatment for Harmful Algal Blooms
Robert Wiley
Principal Engineer - Clarification
AWWA/AMTA© 2
Gravity Settlement
DAF
Buoyancy Flotation
Coagulant/Polymer Addition
Size: Hundreds of Microns Velocity: ~ 5-10 m/hr
Size: Tens of Microns Velocity: 20-40 m/hr
Fe(OH)3
Fe(OH)3
Fe(OH)3
Fe(OH)3 Fe(OH)3
Fe(OH)3 Fe(OH)3
Fe(OH)3
Fe(OH)3
Fe(OH)3 Fe(OH)3
Fe(OH)3
Fe(OH)3 Fe(OH)3
Fe(OH)3 Fe(OH)3
Dissolved Air Flotation (DAF)
AWWA/AMTA© 3
Dissolved Air Flotation (DAF)
Dual Stage Flocculation
Dispersion Headers
AIr Contact Zone
Air Compressor
Recirculation Pumps
(~10% Recycle)
Effluent Laterals
Effluent Channel
Sludge Channel
Reciprocating Skimmer Saturator
Recycle line (4-6 bar)
AWWA/AMTA© 4
AWWA/AMTA© 5
Sohar, Oman Pilot Study April – October 2010
FilterWorx® Pilot Unit
Clari-DAF® Pilot Unit
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Sohar, Oman Pilot Study April – October 2010
Parameter Average Min Max Turbidity (NTU) 1.40 0.28 6.93
pH 8.11 7.69 8.37
Temperature (oC) 31.4 28.4 33.8
Salinity (‰) 36.85 35.46 39.83
TSS (mg/L) UDL UDL 15
Oman Raw Water Quality Scenarios Tested and Results Parameter Avg.
SDI 1 Stage DMF (Direct Filtration)
< 4
DAF + 1 Stage DMF < 3.5
DAF + 2 Stage DMF
< 2.5
The system was optimized at a loading rate of 9 gpm/ft2 (22.5 m/hr) and flocculation times of 13 – 15 minutes.
The Clari-DAF system was operated with and without chemical feed.
It was found that using Clari-DAF system during non-algae events produced lower SDI compared to direct filtration.
AWWA/AMTA© 7
Algae Cultivation and Bench-Scale Testing Leopold teamed with Woods Hole Oceanographic Institution who cultivated Cochlodinium polykrikoides, Phaeocystis globosa, and Prorocentrum minimum for bench-scale trials.
y = 18.06xR2 = 0.83
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
0 100 200 300 400 500
Chlorophyll (mg/L)
Alg
ae (
cells
/mL
)
Correlation of algae counts and chlorophyll concentrations
-‐10.0
-‐8.0
-‐6.0
-‐4.0
-‐2.0
0.040.0 60.0 80.0 100.0 120.0 140.0
Ferric Chloride Dose (mg/L)
Zeta Poten
tial (mV)
Zeta Potential without prechlorinationZeta Potential with prechlorinationLinear (Zeta Potential without prechlorination)Linear (Zeta Potential with prechlorination)
Zeta Potential for C. polykrikoides with and without prechlorination
AWWA/AMTA© 8
US HAB Testing in 2011
Port Aransas TX
Buzzards Bay, MA
AWWA/AMTA© 9
Buzzards Bay, Massachusetts
DAF Bench Scale Jar Tester During Flotation
Naturally occurring bloom of Cochlodinium polykrikoides in August of 2011. Over 99% removal of this naturally occurring 14 million cell count per liter bloom was achievable in the DAF jar tests conducted.
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Port Aransas, Texas November 2011 Species: Karenia brevis
0.1-0.4 Million cells/L Diameter 18-45 µm
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Port Aransas, Texas November 2011
• Effect of hydraulic loading rate through the system during a naturally occurring HAB event.
• Mixing intensity & time, recycle percentage, and recycle pressure
utilized in the lab scale testing and in previous pilots proved appropriate.
• Greater than 90% removal of Karenia brevis was achieved with the DAF system under dynamic conditions.
• The algae removal in the pilot system actually exceeded the DAF jar test results which were conducted side-by-side with the pilot.
AWWA/AMTA© 12
Shuwaikh, Kuwait SWRO April 2013
94,700 m3/day Shuwaikh SWRO plant experiences “full-scale” HAB
Plant Intake
Leopold Clari-DAF System Pentair X-Flow UF
AWWA/AMTA© 13
Midway through Day 1
Day 1 of bloom
Days 3+
Shuwaikh, Kuwait SWRO April 2013
Clari-DAF at start of bloom
AWWA/AMTA© 14
Shuwaikh, Kuwait SWRO April 2013 Operational Changes
• Ferric Chloride Dose was increased from average of 4 mg/L up to 12 mg/L
• Sulfuric Acid increased from 28 mg/L to 40 mg/L
• Doubled EMF Frequency and increased the Cl2 shock dosing frequency. System Performance
• Maintained rated plant capacity
• CIP 1 month after beginning of bloom
AWWA/AMTA© 15
September 2013 – Ongoing
UAE, Gulf of Oman Pilot Study
CultivatedTetraselmis testing @ 100 million cells per Liter
AWWA/AMTA© 16
UAE, Gulf of Oman Pilot Study September 2013 – Ongoing
System Performance
• >95% removal of algae with the DAF • DAF effluent TSS <2 mg/L
• DAF effluent Turbidity avg ~0.7 ntu
• Filter Turbidity < 0.1 NTU
• Filter UFRV unaffected (actually improved) • Filter SDI decreased each day during the algae spiking
AWWA/AMTA© 17
January 2014 – Ongoing
Antofagasta, Chile Pilot Study
AWWA/AMTA© 18
January 2014 – Ongoing
Antofagasta, Chile Pilot Study Prorocentrum Micans Ehrenberg
Ceratium Fusus
Ceratium Divericatum
Pyrocystis Fusiformis
