Treatment of waste brine from a brackish reverse osmosis plant
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Treatment of Waste Brine from a Brackish Reverse Osmosis Plant. El Paso Water Utilities and Fort Bliss Eastside Brackish Groundwater Desalination Facility Joel C. Rife, P.E., DEE September 16, 2002. HEAD WATERS OF COLORADO RIVER. REAL BIG PIPE. REAL BIG PUMPS.

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Treatment of Waste Brine from a Brackish Reverse Osmosis Plant

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Treatment of Waste Brine from a Brackish Reverse Osmosis Plant

El Paso Water Utilities and Fort Bliss

Eastside Brackish Groundwater Desalination Facility

Joel C. Rife, P.E., DEE

September 16, 2002





Brackish Water Treatment Becoming Feasible

  • Membrane Technologies More Affordable

  • Problem is What to do with the Waste Reject Water

    • Direct Discharge Not An Option

    • Activated Sludge Microbes Have No Interest In TDS

    • Historically Hasn’t Been a Problem with Desalination Plants (Dump in Ocean)

Brackish RO Facility Design Criteria

Permeate Flow (Drinking Water to Storage) 18 MGD

Evaporation/Concentration Options

  • RO Plant Recovery 90 Percent

  • TDS in Reject 11,000 mg/L

  • Reject Flow 1.8 MGD

    Deep Well Disposal Option

  • Recovery 85 percent (permitting constraints – max. allowable TDS)

  • TDS in reject 8,000 mg/L

  • Reject flow 3.2 MGD

Evaporation Options

  • Full-Scale Evaporation Ponds

  • Turbo-Mist Evaporator and Pond System

  • TNRCC Pond Liner Requirements

    -Clay w/permeability <1 x 107 cm/sec

    -Plastic liner with leak detection

Full-Scale Evaporation Ponds

  • Designed for 5 Consecutive “Critical” Years Storage per TNRCC Requirements

  • 5-Foot Depth

  • 431 Acres

  • Compared Single Pond vs. 4-cell vs. 15-cell

  • Recommendation – 4-cell

  • 60-mil HDPE Liner

Turbo-Mist Evaporator and Pond

  • Proprietary Machine by Slimline Mfg. LTD

  • Nozzles in Ring at End of 100 MPH Wind

  • Pilot Test Found 15-20% Water Evaporated Through Turbo-Mist Units

  • Wind Must Remain Below 10 MPH to Prevent Excessive Drift

  • 3000 Connected HP

Cost ComparisonEvaporation Options

Full-Scale Evaporation Pond

  • Capital Cost $25.42 Million

  • 20-yr Present Worth $44.36 Million

    Turbo-Mist and Pond

  • Capital Cost $13.8 Million

  • 20-yr Present Worth $56.74 Million

Deep Well Disposal

Evaluation Criteria

  • Depth

  • Confining Zone

  • Simplicity of Geological Structure

  • Risk of Inducing Seismicity

  • Injection Zone TDS

  • One-Hour Pressure Buildup

  • Distance Traveled After 30 Years

Deep Well Disposal

  • Capital Cost $9.69 Million

  • 20-yr Present Worth $27.69 Million

  • Cost Significantly Less Than Evaporation

    Regulatory Requirements Are a Concern:

  • Well Classification Delay Until Hydrogeology and Water Chemistry are Characterized

  • Permit (Extensive Public Participation)

  • Authorization by Rule (Less of a Delay)

Solar Gradient PondsEvolved From Conceptual Zero-Discharge RO Plant






Solar Gradient Ponds

  • Effective for Seawater RO Brine Disposal – 60 Installations World-Wide

  • Thermal Energy Can Be Used For Heating or To Produce Electricity

  • Capital Cost $35.2 Million

    Cost Comparison per 1000 Gallons Delivered

    RO With Full-Scale Evaporation$1.95

    RO With Deep Well Disposal$1.46

    RO With Solar Gradient Ponds$2.04

Membrane Concentrator System

  • Goal: Decrease Reject Volume While Deep Well Permitting Process is Completed

  • Challenge: “Treat the Untreatable”

  • Solution: Pretreatment Prior to Further Concentration by Reverse Osmosis

    Pretreatment Options Investigated:

  • Lime Softening

  • High-Rate Nanofiltration

Lime Softening Pretreatment

  • Objective is to Reduce Silica and Carbonate Hardness Back to Original Brackish Reject Water Concentrations

  • Use of Magnesium Salts for Silica Removal Common Practice for Boiler Feed Water

  • Lack of Data for Treatment of High Silica Concentrations

  • Jar Testing Required to Prove Out Silica Removal and Determine Dosage Requirements

Results of Lime Treatment Jar Testing

  • Silica and Hardness Removal Goals Achieved with Lime Only

  • Recirculated Lime Floc Critical

  • Further Reductions of Silica with Magnesium Salt Addition

  • Polymer Required to Achieve Acceptable Silt Density Index (<3)

  • Barium Still a Problem – Final RO Recovery of 60% Due to High Barium

Lime Softening Pretreatment / RO Process

High-Rate NF Softening Option

  • Suggested by Osmonics Based on Successful Oil Field Experiments

  • Concept is to Remove Cations (Ca, Mg, Fe, Ba) That Act as Nucleating Sites for Silica, While Passing Silica

  • “Slick” Single Pass Membrane is Key to Prevent Silica Buildup On Membrane

  • Successful Bench Scale Experiment Conducted on Simulated Reject

X-Ray Analysis of NF Membrane

NF Pretreatment / RO Process

Summary of Costs

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