Using a Novel Hybrid NF-RO to Enhance Sodium Chloride Removal November 14, 2018 WateReuse Webcast Series 2018 by the WateReuse Association
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Today s Presenters Robert McCandless Principal Investigator Brown and Caldwell Erin Mackey Co-principal Investigator Brown and Caldwell
Hybrid NF/RO Sodium Chloride Removal Process Pilot Study A Novel Approach to Concentrate Minimization
Thank You to our Sponsors United States Bureau of Reclamation Matthew Schroll, BC, Co-author Water Research Foundation (formerly Water Environment & Research Foundation) City of Scottsdale Inland Empire Utilities Agency Tucson Water Wigen Water Technologies Dow Hydranautics Toray Industries Koch Membrane Systems Avista Technologies
Background
Impacts of Hard Water and Water Softening
Comparison of Potable and Reclaimed Water 400 Major Anions and Cations (mg/l) 350 300 WTP Finished Water WRP MF Effluent 250 200 150 100 50 0 HCO3 Cl SO4 Na Mg Ca
Pilot Process Overview Keep the Good Ions, Remove the Bad Pass 1 Pass 2 Conventional RO Monovalent Feed Ions Divalent Ions Monovalent Ions Blended Product
Pilot Process Overview Applications: Partial desalting of low to moderate TDS water Sodium chloride reduction Concentrate disposal savings Process objectives: Nanofiltration: separate monovalent and divalent ions Reverse Osmosis: remove monovalent ions Blend Stream: combine divalent ions with reverse osmosis permeate Pass 1 Divalent Ions Monovalent Feed Ions Blended Product Pass 2 Conventional RO Monovalent Ions
Process Benefits COST (-) Chemical Cost Energy Consumption Concentrate Disposal Capital Investment Conventional RO NF-RO
NF Membrane Selection Phase Abbreviated test duration 4 NF products tested for selection Cation Passage Sodium Calcium % Reduction of TDS RO Concentrate % NaCl Predicted Max RO Recovery DOW 88.5% 64% CSM 90.9% 54% Hydranautics 87.0% 60.3% KMS 82.1% 26.2% 45% 41% 46% 38% 79.2% 81.5% 79.1% 83.2% 92.7% 93.0% 93.3% 93.7% NF Membrane Selection Test Unit
Effect of Flux Rates on Salt Passage Permeate Concentration (mg/l) 250 200 150 100 50 0 HYDN Nano BW: Sodium Dow NF270: Sodium 10 11 12 13 14 15 Flux (gfd) HYDN Nano BW: Calcium Dow NF270: Calcium Within the range of flux values for this test, there is a modest change in rejection of sodium Rejection of calcium is less affected over this range of flux values. Summary of test flux rates Dow: 13.6 gfd CSM: 12.7 gfd HYD: 12.5 gfd KMS: 14.0 gfd 13
Notes on NF Membrane Selection All of the membranes tested reject TOC, sulfate and phosphate very well these are key contributors to fouling and high recovery limits. Predicted maximum recoveries were very similar Process objectives need to be considered for: TDS reduction Hardness rejection by NF Performance can be optimized via: Recovery Flux Concentrate recycle rate 14
Pilot Test Results
Pilot Test Parameters Stage A Days 63 Recovery NF 70% RO 80% Overall 86% Flux, gfd NF 14.4 RO 15.5 Anti-Scalant dose, mg/l NF 0.6 1.3 RO 1.09 Stage B Days 108 Recovery NF 74% RO 89% Overall 92% Flux, gfd NF 12.6 RO 15.1 Anti-Scalant dose, mg/l NF 1.7 7.7 RO 4.1-4.9
Water Quality Overview Sodium Chloride Average TDS reduction 32%; inline with predicted performance Good recovery of Calcium 91%, Sulfate > 99% Alkalinity 81% Salt reduction Chloride 54% Sodium 47% Blended Product Stability: LSI: - 0.20 CCPP: -7.3 mg/l CaCO3
Water Quality (TDS) Sodium Chloride Lower fraction of hardness, sulfate and alkalinity will benefit high recovery or ZLD processes Sulfate, calcium and magnesium make up 5% of RO concentrate versus 30% of feed Improvement of sodium adsorption ratio (SAR) Reclaimed water (NF feed): 8.9 NF/RO Product: 4.9
Water Quality (TOC and UV Absorbance)
Specific Flux Nanofiltration Recovery: NF 75% RO 90% Overall: 92.5% Reverse Osmosis CIP CIP CIP CIP
Normalized Permeate Conductivity Nanofiltration Reverse Osmosis Normalized conductivity Temperature
Membrane Autopsy Findings Nanofiltration Most foulants were organic Inorganic foulants mostly calcium phosphate and calcium carbonate Lesser amounts of iron, magnesium and aluminum
Nanofiltration Membrane Autopsy Foulants were mostly organic matter Foulants included bacteria, algae and particles
Membrane Autopsy Findings Membrane surface badly damaged by abrasion No evidence of oxidation by halogens (i.e., chlorine) MgSO 4 rejection slightly below manufacturers spec Water flow within spec, but at high end Brown and Caldwell 24
Membrane Autopsy Findings Reverse Osmosis No detectable foulants Undetermined mechanical failure resulted in low rejection (91% vs 99.2% spec). This seemed to have occurred very late in the test Second membrane element met manufacturer s spec
Cost Comparison with Conventional RO
Cost Comparison Design Characteristics Conventional RO NF-RO Feed capacity, gpm 700 700 Membrane area, sq ft 84,000 100,800 Operating Specific energy, kwh/kgal 0.76 1.16 1.14 1.57 Sulfuric acid, lb/mgd 74.5 0 Scale inhibitor, lb/mgd 29.2 35.9 Lime, restabilization (lb/mgd) 219 21 Membrane cleaning, #/year 5 4-6 NF 1-2 RO
Cost Comparison Water Production Conventional RO NF-RO Capital Cost $ 1,177,000 $ 1,743,000 Operating Costs (20-yr present value) $ 2,006,000 $ 2,349,000 Total Present Value $ 3,183,000 $ 4,092,000 $/kgal treated $ 0.60 $ 0.70 Recovery 85% 92.5% $/kgal produced $ 0.71 $ 0.76
Benefits for Concentrate Management
Comparison of Concentrate from Conventional RO and NF-RO Conventional RO Hybrid (NF-RO) Process Feed Flow 700 700 (gpm) Concentrate (% of feed) 15% 7.5% NF-RO concentrate flow is 50% of conventional NF-RO generates 68% less TDS for disposal Concentrate Flow 104 52 (gpm) TDS (mg/l) 8,673 5,602 TDS (tons/yr) 1,977 639
Benefit to Different Concentrate Management Strategies Disposal to Sewer or Interceptor Evaporation ponds Thermal/Mechanical Evaporation High Recovery Processes (HERO, CCRO, etc.) Brine Concentrator/ Crystallizer Reduced Salt Load Reduced Volume Reduced Chemical Consumption Reduced Energy Reduced Maintenance Salt recovery
Example 1: Disposal to Brine Interceptor Concentrate from RO Concentrate from NF-RO Overall Recovery 85% 92.5% Concentrate Management Capacity charges $1,505,000 $753,000 Annual charges (20-yr present value) $1,678,000 $839,000 All charges are based on volume No charge for TDS Total present value $3,183,000 $1,592,000 Treatment and Conc Mgmt Cost $6,343,000 $5,566,000 $/kgal produced $1.29 $1.08 32
Example 2: Volume Reduction Closed-Circuit Reverse Osmosis Treatment Concentrate from RO Concentrate from NF-RO Overall Recovery 95.5 98.5 Concentrate Management Capital Cost $434,000 $349,000 Operating Cost (20-yr present value) $1,096,000 $281,000 Present value $1,530,000 $630,000 Treatment and Conc Mgmt Cost $4,690,000 $4,604,000 $/kgal produced $0.84 $0.81 > 50% reduction in chemicals 20% lower capital cost Recovery from RO concentrate limited by scale-forming compounds. Results in 3x residual brine flow versus NF-RO.
Example 3: Evaporation Pond Conventional RO NF-RO Total Pond Area (acres) 34.4 16.8 Recovery 85% 92.5% Concentrate Management Capital Cost $34,448,000 $15,826,000 Disposal costs (20- yr present worth) $2,648,000 $932,000 Present value $37,096,000 $16,758,000 Treatment and Conc Management Cost $40,256,000 $20,732,000 $/kgal produced $8.47 $4.00 *Based on evaporation and precipitation rates for Scottsdale, Arizona; Two-stage evaporation ponds 50% pond area reduction 65% lower salt haul and landfilling cost 34
Example 4: CCRO + Evaporation Pond Conventional RO NF-RO Total Pond Area (acres) 12.4 4.9 Overall Recovery 95.5 98.5 Concentrate Management Capital Cost $21,417,000 $8,758,000 Disposal costs (20-yr present worth) $2,667,000 $821,000 Present value $24,084,000 $9,579,000 Treatment +Conc. Mgmt Cost $27,244,000 $13,553,000 $/kgal produced $5.13 $2.44 *Based on evaporation and precipitation rates for Scottsdale, Arizona; Two-stage evaporation ponds 56% pond area reduction 69% lower salt haul and landfilling cost 35
Summary A Comparison of NF/RO vs. RO only Selective removal of sodium chloride is possible; addresses problems with water softener discharges with less concentrate disposal and improved blended permeate water quality Offers significant cost savings where you only need to remove monovalent ions and easy brine disposal is off the table Reduces chemical consumption Equivalent energy consumption Significantly reduces concentrate disposal cost
Questions? Robert McCandless Principal Investigator Brown and Caldwell rmccandless@brwncald.com Erin Mackey Co-principal Investigator Brown and Caldwell Emackey@BrwnCald.com