Transcript Insert Client Name/ or Name of Presentation

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
CONFLUENCE OF
OHIO AND
MISSISSIPPI
RIVERS
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 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
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 Ponds
Evolved From Conceptual Zero-Discharge RO Plant
Product
Water
Product
~96% of feed
Permeate and Distillate
Water
~75% of feed
~20% of feed
~1% of feed
Raw
Water
Thermal
Desalination
Evaporator
Membrane
RO
Filtration
~25%
of feed
Brine
Concentrator
Concentrator
Product Salt
~5%
of feed
Saturated Brine
Slurry
Salinity Gradient Solar Pond
Heat
Upper Convective Zone
Non-Convective Zone
Lower Convective Zone
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
Lime
MgO
Polymer
CO2
Microfiltration
98% Recovery
Reverse Osmosis
62% Recovery
Solids Contact Basin
1.76 MGD
Brackish RO Reject
1.79 MGD
1.72 MGD
Recarbonation
Reject
40,000 gpd
Filtrate and Thickener Overflow
35,000 gpd
Total wastewater to storage = 728,000 gpd
Filter Press
Dewatering
Reject
653,000 gpd
To storage for
final disposal
Lime Sludge To On-site Dewatering
28,800 lbs/d - 69,000 gpd @ 5% solids
50% sludge cake
to landfill
1.07 MGD
RO Permeate
Recycle
to Product
Water
Thickener
Figure 8-1 Lime Softening/RO Option
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
Sulfuric Acid to pH 5.8
Antiscalant
Nanofiltration Membrane Softening
95% Recovery
Brackish RO Reject
1.79 MGD
pH adjustment tanks to
off-gas CO2 and
equalize RO reject flow
Reverse Osmosis
95% Recovery
1.7 MGD
Nanofilter Permeate
1.62 MGD
RO Permeate
89,500 gpd Reject
To Evaporation Ponds
85,000 gpd
To Evaporation Ponds
Total Reject to Evaporation Ponds = 174,500 MGD
Figure 8-4 NF Softening/RO Option
Recycle
to Product
Water
Summary of Costs
Disposal Option
Capital
Cost
Deep Well Disposal
Evaporation Ponds Alone
Lime Softening/RO/Evap
NF/RO/Evap
$9,696,200
$40,668,300
$21,864,800
$13,564,000
Annual
Total Present
O&M
Worth
85% Recovery
750,000
$995,000
$1,777,200
$1,160,200
20 Year Water
Production (AF)
PW$/AF
27,696,200
$71,011,000
$61,432,000
$39,869,900
617680
617680
662160
682380
$45
$115
$93
$55
$42,179,400
$43,260,800
$26,032,900
617680
641720
645080
$68
$67
$40
90% Recovery
Evaporation Ponds Alone
Lime Softening/RO/Evap
NF/RO/Evap
Costs include 15% engineering
$23,132,400
$16,201,900
$8,636,579
$657,000
$1,152,011
$837,400