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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.

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Presentation on theme: "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."— Presentation transcript:

1 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

2 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

3 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 City of Portage, Garden Lane Water Treatment Plant Garden Lane Well Field

4 Garden Lane Well Field Site City of Portage, Garden Lane Water Treatment Plant Well GL-3 Well GL-2 Well GL-1 Well GL-4 (New) Treatment Plant Location

5 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

6 Feasibility Study Prepared in 2006 Evaluated various treatment methodologies Coagulation/filtration Ion exchange Chemical oxidation/filtration Adsorption Treatment iron removal alternatives were considered 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

7 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

8 Arsenic Treatment Process Selection Guide City of Portage, Garden Lane Water Treatment Plant 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

9 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 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

10 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

11 Pilot Testing Results Raw Water Finished Water Arsenic: ug/L (range) ug/L (range) Iron: mg/L (range) ND mg/L (range) Manganese: mg/L (range) – 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

12 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

13 System Design City of Portage, Garden Lane Water Treatment Plant Filtronics Treatment and Filtration System

14 System Design Filtration Reaction vessels (2) –3.5 minutes CT at design flow rate Filtration vessels (4) –Filtration rate 10 gpm/ft 2 –Backwash rate 20 gpm/ft 2 –Filter area 100 ft 2 per filter Provisions for future addition of a 5th filter City of Portage, Garden Lane Water Treatment Plant

15 Raw Water Quality City of Portage, Garden Lane Water Treatment Plant

16 Finished Water Quality City of Portage, Garden Lane Water Treatment Plant

17 Waste Backwash Water Management Options On-site management using ponds or infiltration beds 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

18 Filter Backwash City of Portage, Garden Lane Water Treatment Plant

19 Filter Backwash Backwash interval:8 hours Backwash duration:4 minutes Rinse duration:1 minute Backwash rate:20 gpm/ft 2 Rinse rate:10 gpm/ft 2 City of Portage, Garden Lane Water Treatment Plant

20 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

21 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

22 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 non- hazardous City of Portage, Garden Lane Water Treatment Plant

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27 New Well House, GL-4 City of Portage, Garden Lane Water Treatment Plant

28 New Well, GL-4 City of Portage, Garden Lane Water Treatment Plant

29 Sustainability Features Natural Lighting Pervious Pavement (Parking Area) Natural Prairie Site Restoration Stormwater Rain Garden City of Portage, Garden Lane Water Treatment Plant

30 Current Status System was started in June 2010 Arsenic and iron removals have been consistent with results of pilot work Finished water quality: Arsenic 2-3 ug/L Iron<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 Portages first full- scale treatment system City of Portage, Garden Lane Water Treatment Plant

31 Ribbon Cutting Ceremony August 2, 2010 City of Portage, Garden Lane Water Treatment Plant


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