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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 Rick Arber, Ben Johnson Richard P. Arber Associates Pat Mulhern MRE
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
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.
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
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