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Indirect Potable Reuse at Cottonwood Water and Sanitation District. Rick Arber, Ben Johnson Richard P. Arber Associates Pat Mulhern MRE. Types of Reuse. Agricultural & Industrial. Exchanges Recycle-process, cooling. Municipal. Urban Landscape Irrigation Indirect Potable Use

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Indirect Potable Reuse at Cottonwood Water and Sanitation District

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Indirect Potable Reuse at Cottonwood Water and Sanitation District

Rick Arber, Ben Johnson

Richard P. Arber Associates

Pat Mulhern

MRE


Types of Reuse


Agricultural & Industrial

  • Exchanges

  • Recycle-process, cooling


Municipal

  • Urban Landscape Irrigation

  • Indirect Potable Use

  • Direct Potable Reuse


WTP

WWTP

AWT

Non-Potable Reuse


WTP

WWTP

WTP

WWTP

Unplanned Indirect Potable Reuse


Aquifer

WTP

WWTP

AWT

Planned Indirect Potable Reuse


WTP

WWTP

Direct Potable Reuse

AWT


Cottonwood Water and Sanitation District


CWSD….

  • Formed in 1981

  • 1200 Acres of residential and commercial development

  • Slow development in 1980s

  • Rapid development in 1990s


  • Water Supplies

    • Deep wells (Dawson, Denver, Arapahoe, Laramie Fox Hills)

    • Cherry Creek alluvium

  • Wastewater

    • ACWWA Lone Tree Creek WWTP


    • Deep Wells

      • 995 acre Feet

      • Fe, Mn, H2S

    • Alluvial Water

      • 141 acre feet senior rights

      • 585 acre feet junior rights

      • Upstream discharges (Pinery, Parker, Stonegate)


    • Deep Wells

      • non-renewing

      • draw down/capacities

      • require treatment

    • Alluvial Wells

      • renewable

      • high capacity

      • require treatment


    Alternatives

    • Deep Wells

      • Non-renewing; eventual depletion

      • Additional wells need with draw down

      • Limited production

      • Treatment required


    Alternatives

    • Dual Distribution $$$

    • Import Groundwater $$$


    Alternatives

    • Reuse

      Renewable supply

      Extend deep groundwater

      Greater production


    Centralized vs. Decentralized Treatment

    • Capital cost 10% less for centralized treatment.

    • O&M cost similar for centralized treatment and decentralized.

    • Centralized treatment easier to operate.


    The Plan


    • Average daily demand 2 mgd

    • Maximum daily demand 6 mgd


    Treatment

    • Cartridge Filters

    • UV?

    • Anti-scalant

    • Nanofiltration

    • Degassifier

    • pH adjust

    • Alkalinity

    • Chlorine


    Indirect Potable Reuse

    • Multiple Barriers

      • WWTP/AWT

      • Alluvium (3000 ft.,~ 1.5 years travel)

      • Membrane water treatment (100%)

      • Final disinfection


    Concentrate Disposal

    • Cherry Creek Basin

      • PO4

    • Split Flow

      • ACWWA WWTP (base flow)

      • Irrigation


    Pilot Testing


    Objectives

    • Evaluate effectiveness of NF on raw water

    • Determine design criteria

    • Evaluate fouling potential

    • Evaluate feed, permeate, and concentrate water quality

    • Select appropriate membrane


    Pilot Testing Plan

    • Three month duration

      • Test different membranes

    • Sample water quality 6 times

      • At beginning and end of each membrane test

    • Operate at 83% recovery

      • 2.0 gpm permeate

      • 0.5 gpm concentrate


    Performance

    • Tested two membranes

      • Osmonics

      • Filmtec (2 month test)

    • Added anti-scalant chemical(Pro Treat)

      • Potential for sulfate precipitation reduced

    • No significant fouling was observed


    Results

    • Both membranes performed well

      • Osmonics tighter - higher driving pressure

      • Filmtec looser - lower contaminant rejection

    • Average Rejection

      • TDS

        • Osmonics 68%Filmtec 62%

      • Hardness

        • Osmonics 84%Filmtec 69%

      • TOC successfully rejected by both membranes (BDL)


    Project Costs

    • Treatment

      • $9.3 million

    • Ancillary facilities

      • $2.3 million


    Public Education Program

    • Consultant

    • Literature

    • CDPHE involvement

    • Public meetings


    Schedule

    • Predesign underway

    • Design 2003

    • Construct 2004

    • Start up 2005


    Conclusions

    • NF effective in removing TOC

    • Multiple barriers provide public health protection

    • Indirect potable reuse is viable, cost effective water supply for CWSD

    • Public support is needed


    • Questions?


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