Transcript AECOM Water Top Project Portfolio, 1 project per geography

Arsenic/Iron Co-Precipitation and
High Rate Filtration
in the City of Portage
Christopher Barnes, P.E., City of Portage
Kendra Gwin, P.E., City of Portage
Daniel Starkey, P.E., AECOM
City of Portage, Garden Lane Water Treatment Plant
City of Portage
• Population of 45,000
• Groundwater source of supply
• Water supply and distribution system operated under contract by United Water
City of Portage, Garden Lane Water Treatment Plant
Background
• Portage operates 14 well
fields located throughout
the City
• Limited treatment includes
chlorination, fluoridation
and phosphate for iron
sequestration
• Average day pumping:
5.5 MGD
• Peak day: 17.6 MG
Garden Lane
Well Field
City of Portage, Garden Lane Water Treatment Plant
Garden Lane Well Field Site
Well GL-3
Well GL-4
(New)
Well GL-2
Well GL-1
Treatment Plant Location
City of Portage, Garden Lane Water Treatment Plant
Garden Lane Well Field
• Three existing wells
• Wells contain elevated levels of iron, manganese and arsenic
• Two wells consistently above the 10 ug/L arsenic MCL
• All wells above the 0.3 mg/L iron SMCL
• Well field relegated to “stand-by” service
• This well field is in the center of the City and is a critical component of the
overall water supply and distribution system
• Shift base load capacity to a more reliable and protected aquifer
City of Portage, Garden Lane Water Treatment Plant
Feasibility Study Prepared in 2006
• Evaluated various treatment methodologies
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Coagulation/filtration
Ion exchange
Chemical oxidation/filtration
Adsorption
• Treatment iron removal alternatives were considered
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Pressure filtration
Aeration + Detention + Pressure Filtration
Aeration + Detention + Gravity Filtration
Partial Flow Treatment + Blending
• Pressure filtration was identified as the most cost-effective option
City of Portage, Garden Lane Water Treatment Plant
Co-Precipitation of Arsenic and
Iron using Pressure Filtration
• Proven technology
• Soluble iron (Fe 2+) and arsenic (As 3+) are oxidized to insoluble iron
(Fe 3+) and arsenic (AS 5+)
• Arsenic is adsorbed and enmeshed in the resulting iron floc
• Filtration removes insoluble iron/arsenic precipitate
• Iron must be present in sufficient quantity
City of Portage, Garden Lane Water Treatment Plant
Arsenic Treatment Process Selection Guide
•Iron must be present in sufficient quantity
•Ratio of iron to arsenic of 20:1 (minimum) is “rule of thumb”
•In Portage this ratio is 50+:1 with naturally occurring iron
City of Portage, Garden Lane Water Treatment Plant
Preliminary Investigation
• City investigated various pressure filtration systems
• Three systems were selected for pilot testing in 2007
• Visits made to other cities to observe and seek input from operators
• Filtronics (Anaheim, CA) was selected
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Use of proprietary media allows for higher than normal filtration rate
Short (4-min) backwash and at reduced interval (8-hour)
Backwash reclamation system was a standard offering
Significant experience in the western US where arsenic is a major problem
City of Portage, Garden Lane Water Treatment Plant
Pilot Testing
• Well GL-2 with highest levels of
arsenic was tested
• Chlorine (sodium hypochlorite) used as
oxidant
• 3-inch pilot unit
City of Portage, Garden Lane Water Treatment Plant
Pilot Testing Results
• Arsenic:
Raw Water
20 - 27 ug/L (range)
Finished Water
1.5 - 3.0 ug/L (range)
• Iron:
1.0 - 1.1 mg/L (range)
ND- 0.002 mg/L (range)
• Manganese:
0.084 - 0.086 mg/L (range)
0.018 – 0.027 mg/L (range)
• Chlorine breakpoint concentration of 19 ppm
• Excellent removals observed at chlorine feed rates of 6 to 8 ppm
City of Portage, Garden Lane Water Treatment Plant
System Design
Supply
• 3,000 GPM (4.32 MGD) firm capacity
• 4,000 GPM (5.76 MGD) total system capacity
• New 1,200 GPM supply well, GL-4
City of Portage, Garden Lane Water Treatment Plant
System Design
Filtronics Treatment and Filtration System
City of Portage, Garden Lane Water Treatment Plant
System Design
Filtration
• Reaction vessels (2)
– 3.5 minutes CT at design flow rate
• Filtration vessels (4)
– Filtration rate 10 gpm/ft2
– Backwash rate 20 gpm/ft2
– Filter area 100 ft2 per filter
• Provisions for future addition
of a 5th filter
City of Portage, Garden Lane Water Treatment Plant
Raw Water Quality
City of Portage, Garden Lane Water Treatment Plant
Finished Water Quality
City of Portage, Garden Lane Water Treatment Plant
Waste Backwash Water Management Options
• On-site management using ponds or infiltration beds
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High groundwater table
Heavy, “muck”-type soils
Limited soil permeability would result in large ponds
Well field located in a park setting
• Discharge to municipal sewer system
• Arsenic limits would likely be exceeded without pretreatment
• Prohibitively expensive
• Reclamation and re-use
• Separate solids and reuse backwash water
• Dewater and dispose iron/arsenic solids in a Type II landfill
City of Portage, Garden Lane Water Treatment Plant
Filter Backwash
City of Portage, Garden Lane Water Treatment Plant
Filter Backwash
• Backwash interval:
8 hours
• Backwash duration: 4 minutes
• Rinse duration:
1 minute
• Backwash rate:
20 gpm/ft2
• Rinse rate:
10 gpm/ft2
City of Portage, Garden Lane Water Treatment Plant
Filter Backwash
• Waste backwash volume: 9,000 gallons per backwash
• Tank sized to accommodate 16 filter backwashes
• 150,000 gallon total capacity
• Iron/arsenic precipitate settles in the
conical tank bottom
City of Portage, Garden Lane Water Treatment Plant
Backwash Reclamation
• Decanter collects supernatant, which
is pumped to the head of the plant for
filtration and reuse
• Backwash recycle rate is limited to
<10% of the forward flow
City of Portage, Garden Lane Water Treatment Plant
Backwash Reclamation
• Solids accumulate in the
waste backwash tank
• Estimated that solids will
be removed 2x year
• Plate and frame filter press
is provided to dewater
precipitate
• Solids were tested during
pilot study and are nonhazardous
City of Portage, Garden Lane Water Treatment Plant
City of Portage, Garden Lane Water Treatment Plant
City of Portage, Garden Lane Water Treatment Plant
City of Portage, Garden Lane Water Treatment Plant
City of Portage, Garden Lane Water Treatment Plant
New Well House, GL-4
City of Portage, Garden Lane Water Treatment Plant
New Well, GL-4
City of Portage, Garden Lane Water Treatment Plant
Sustainability Features
• Natural Lighting
• Pervious Pavement (Parking Area)
• Natural Prairie Site Restoration
• Stormwater “Rain Garden”
City of Portage, Garden Lane Water Treatment Plant
Current Status
• System was started in June 2010
• Arsenic and iron removals have been consistent with results of pilot work
• Finished water quality:
• Arsenic
• Iron
2-3 ug/L
<0.01 mg/L
• Waste backwash sludge dewatering not performed to date
• Resolving communication issues between the local filter control panel and the
central SCADA system
• Developing a level of comfort with operating the City of Portage’s first fullscale treatment system
City of Portage, Garden Lane Water Treatment Plant
Ribbon Cutting Ceremony August 2, 2010