Treatment of Waste Brine from a Treatment of Waste Brine from a Brackish Reverse Osmosis PlantBrackish Reverse Osmosis Plant

El Paso Water Utilities and Fort BlissEl Paso Water Utilities and Fort Bliss

Eastside Brackish Groundwater Eastside Brackish Groundwater Desalination FacilityDesalination Facility

Joel C. Rife, P.E., DEEJoel C. Rife, P.E., DEE

September 16, 2002September 16, 2002

CONFLUENCE OF CONFLUENCE OF OHIO AND OHIO AND MISSISSIPPI MISSISSIPPI RIVERSRIVERS

REAL BIG PIPEREAL BIG PIPE

HEAD WATERS OF COLORADO RIVERHEAD WATERS OF COLORADO RIVER

REAL BIG PUMPSREAL BIG PUMPS

Brackish Water Treatment Becoming FeasibleBrackish 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 CriteriaBrackish 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 OptionsEvaporation 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 PondsFull-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 Turbo-Mist Evaporator and Pondand 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 ComparisonCost ComparisonEvaporation OptionsEvaporation 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 DisposalDeep 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 DisposalDeep 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 PondsSolar Gradient PondsEvolved From Conceptual Zero-Discharge RO Plant Evolved From Conceptual Zero-Discharge RO Plant

Membrane Filtration

Product Water~96% of feed

ThermalDesalination

BrineConcentrator

~1% of feed

Permeate and Distillate

~20% of feed~75% of feed

Saturated Brine Slurry

Raw Water

Salinity Gradient Solar Pond

~5%of feed

Upper Convective Zone

Non-Convective Zone

Lower Convective Zone

Product Salt

Heat

~25%of feed

Membrane Filtration

Product Water~96% of feed

ThermalDesalination

BrineConcentrator

~1% of feed

Permeate and Distillate

~20% of feed~75% of feed

Saturated Brine Slurry

Raw Water

Salinity Gradient Solar Pond

~5%of feed

Upper Convective Zone

Non-Convective Zone

Lower Convective Zone

Product Salt

Heat

~25%of feed

RO Evaporator Concentrator

Product

Water

Solar Gradient PondsSolar 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 SystemMembrane 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 PretreatmentLime 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 TestingResults 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 ProcessLime Softening Pretreatment / RO Process

Lime MgO Polymer CO2

Microfiltration Reverse Osmosis98% Recovery 62% Recovery

Solids Contact Basin1.76 MGD 1.72 MGD 1.07 MGD

Brackish RO Reject RO Permeate1.79 MGD Recarbonation Recycle

to ProductWater

Reject Reject40,000 gpd 653,000 gpd

Filtrate and Thickener Overflow 35,000 gpd To storage forfinal disposal

Total wastewater to storage = 728,000 gpd Lime Sludge To On-site Dewatering 28,800 lbs/d - 69,000 gpd @ 5% solids

50% sludge cake Filter Press to landfill Dewatering Thickener

High-Rate NF Softening OptionHigh-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 MembraneX-Ray Analysis of NF Membrane

NF Pretreatment / RO ProcessNF Pretreatment / RO Process

Sulfuric Acid to pH 5.8 AntiscalantNanofiltration Membrane Softening Reverse Osmosis95% Recovery 95% Recovery

Brackish RO Reject pH adjustment tanks to 1.7 MGD 1.62 MGD Recycle1.79 MGD off-gas CO2 and Nanofilter Permeate RO Permeate to Product

equalize RO reject flow Water

89,500 gpd Reject 85,000 gpd

To Evaporation Ponds To Evaporation Ponds

Total Reject to Evaporation Ponds = 174,500 MGD

Summary of CostsSummary of Costs

Disposal Option Capital

Cost Annual O&M

Total Present Worth

20 Year Water Production (AF)

PW$/AF

85% Recovery

Deep Well Disposal $9,696,200 750,000 27,696,200 617680 $45

Evaporation Ponds Alone $40,668,300 $995,000 $71,011,000 617680 $115

Lime Softening/RO/Evap $21,864,800 $1,777,200 $61,432,000 662160 $93

NF/RO/Evap $13,564,000 $1,160,200 $39,869,900 682380 $55

90% Recovery

Evaporation Ponds Alone $23,132,400 $657,000 $42,179,400 617680 $68

Lime Softening/RO/Evap $16,201,900 $1,152,011 $43,260,800 641720 $67

NF/RO/Evap $8,636,579 $837,400 $26,032,900 645080 $40

Costs include 15% engineering