1. 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

4. REAL BIG PIPE REAL BIG PUMPS HEAD WATERS OF COLORADO RIVER
CONFLUENCE OF OHIO AND MISSISSIPPI RIVERS

6. 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)

7. 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

8. 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

9. 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

10. 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

11. Cost Comparison Evaporation 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

12. 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

13. 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)

15. Solar Gradient Ponds Evolved From Conceptual Zero-Discharge RO Plant
Product
Water RO
Evaporator
Concentrator

16. 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

17. 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

18. 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

19. 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

20. Lime Softening Pretreatment / RO Process

21. 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

22. X-Ray Analysis of NF Membrane

23. NF Pretreatment / RO Process

24. Summary of Costs