Michael Bourke – Wigen Water Technologies Case Studies of Two Small Systems Using NF/RO to Improve Drinking Water Quality Michael Bourke – Wigen Water Technologies www.wigen.com

Potable Applications of NF/RO Aesthetic TDS Hardness Sulfate Color Regulatory Nitrate Arsenic Radionuclides Fluoride Selenium Pesticides Heavy Metals

Contaminant Removal Rates using RO & NF Comparative Removal Rates NF RO Monovalent Ions (Sodium, Potassium, Chloride, Nitrate, etc) <50% >98% Divalent Ions (Calcium, Magnesium, Sulfate, Carbonate, Iron, etc) >90% >99% Microsolutes (<100 Mw) 0-50% 0-99% Microsolutes (>100 Mw) >50%

Pressure Membrane Feed Water Permeate Concentrate Membrane separation is a process in which properly pretreated source water is delivered at moderate pressures against a semipermeable membrane. The membrane rejects most solute ions and molecules, while allowing water of very low mineral content to pass through. Feed Water Membrane Permeate Concentrate Pressure

Permeate Carrier Material The most common RO membrane material today is aromatic polyamide, typically in the form of thin-film composites. They consist of a thin film of membrane bonded to layers of other porous materials that are tightly wound to support and strengthen the membrane. Feed Water Concentrate Permeate Membrane Material Spacer Material Permeate Carrier Material

NF/RO Membrane Operation

NF/RO System Components

1. Feed water characteristics - Cations - Anions - Silt Density Index (SDI) - Temperature - Oxidants 2. Pre-treatment requirements - Mechanical and/or chemical - Solids removal (turbidity < 1 NTU) - Fe/Mn removal - Anti-scalant and sodium bisulfite dosing 3. Determine desired permeate quality & flow - Membrane selection - Recovery achievable/waste volume - Amount of bypass 4. O&M Requirements - Power & Pretreatment chemicals - Cartridge filter replacement - CIP Chemicals - Membrane Replacement

Cleaning Frequency? 10-15% increase in normalized differential pressure 10-15% decrease in normalized permeate flow 10-15% decrease in permeate quality Prior to sanitization Regular Maintenance Schedule Every 3 to 12 months 12

Case Studies City of Wellman, IA City of Creighton, NE New RO System for Radium & Ammonia Removal and General Water Quality Improvement. City of Creighton, NE Upgraded RO System to Improve Nitrate Removal.

Case Study #1: RO Pilot Study Evaluates Removal of TDS, Sulfate, Ammonia and Radionuclides at Wellman IA Background Trial Objectives Pilot Plant Selection Results Full-scale System Design

Wellman, Iowa Population ~1400 Groundwater supply Greensand Filters DW violations for: Nitrite Combined radium

Raw Water Characteristics Parameter Range (Ave) TDS, mg/L 1600 – 3620 (1914) Ammonia, mg/L as N 0.2-4.2 (3.8) Total Hardness, mg/L as CaCO3 780-1070 Sulfate, mg/L 91- 2230 (1219) Combined Radium, pCi/L 2.0 – 21.3 (6.5) Fluoride, mg/L 0.6 – 1.1 Silica, mg/L as SiO2 13 – 14 Iron, mg/L < 0.03 mg/L Manganese, mg/L 0.006 – 0.055 Chloride, mg/L 6.5 – 85.6 Sodium, mg/L 150 - 764 TOC, mg/L 1.3 – 1.8

Trial Objectives Three month trial required by IA DNR. Parameter (actual) Target Combined Radium (2.0-21.3) < 5.0 pCi/L* Sulfate (910-2230) < 250 mg/L# TDS (1600-3620) < 500 mg/L# Hardness (780-1070) < 250 mg/L as CaCO3 Ammonia (0.2-4.2) As low as possible *EPA Primary DW Regulation #EPA Secondary DW Regulation Three month trial required by IA DNR. Demonstrate RO system performance on a pilot plant representative of a full-scale system.

Pilot Criteria Representative of Full-scale Design Average flux rates Array Length (6L) – representative flux per element Membrane element diameter/type Representative Pre-treatment Filtration Fe/Mn Removal Chemical Dosing Representative Feed Water

Pilot Plant Set-up S2 Feed Concentrate S1 Feed (elements 4-6) S1 Feed (elements 1-3) 2-2:1-1, 3-Long Pilot Plant, Simulates 2:1, 6-Long System

Pilot Plant Set-up

Trial Design Duration – cover minimum CIP frequency Data Collection Automatic (pressure, flows, conductivity, temperature) Normalized data to monitor system performance, early signs of fouling or membrane damage. Manual (feed, permeate & concentrate samples) Membrane Autopsy Detect/identify cause of fouling (lead and end elements)

Data Normalization Takes changes in pressure and temperature and then normalizes, or adjusts, the recorded permeate flow rate accordingly. Graphically shows the permeate flow rate without the effects temperature Indicates the need for cleaning Helps troubleshoot system 4

Trial Results Potential Membrane Damage No decrease = minimal fouling

Trial Results CIP Performed

Trial Results 98.9% TDS Reduction 16-28 mg/L 99.9% Hardness Reduction 0.9-2.0 mg/L as CaCO3 (slight increase in last week)

Trial Results 99.94% Sulfate Reduction 0.9-4.2 mg/L (slight increase in last week) Below detection (<0.09 mg/L)

Membrane Autopsies First membrane in bank 1 and last in bank 2 No visible signs of fouling. ∆P and Flowrate within acceptable ranges Conductivity rejections of 97.3% & 97.1% below spec of 99.5% - possible chlorine damage. Fujiwara test was positive for halogen on membranes indicating oxidative attack.

Results Summary TDS, sulfate, hardness & ammonia reduced to well below targets. Combined radium (226/228) reduced to below detection <1.0 pCi/L (feed levels only ~2.0 pCi/L during trial). Increase in permeate flow and some salts determined to be due to chlorine oxidation. Possible chlorine peaks in feed or loss of sodium bisulfite dosing. No fouling experienced over trial period with 2.3 mg/L dose of Vitec 3000, and CIP frequency likely to be every 4- 6 months.

Full-Scale Design Two x 100 gpm RO skids 20% Bypass stream Design flux of 14.4 GFD & 75% recovery Array: 3:1, 6-Long Toray TMG20-400 membranes ORP meter on feed to shut down RO on detection of Cl2 residual. Waste to sewer.

Full-Scale Installation July 2011

Case Study #2: Upgrade of Creighton’s RO System brings City back in to Compliance with Nitrate MCL Background RO System Capabilities for NO3 Removal & Factors Impacting Performance Overhaul of City’s RO System System Performance – Before & After

City of Creighton Population ~1200 Groundwater supply Raw Water Nitrate 15-20 mg/L

RO System History – First in NE Installed in 1993 – first RO system in Nebraska Two skids each with two RO trains. Array per RO train: 3:2, 6-long Feed: 130 gpm per train Permeate: 100 gpm per train (76% recovery)

Water Treatment Plant Bypass – 125 gpm RO Train 1 Well Pumps Finished Water 525 gpm Greensand Filters RO Train 3 Permeate 400 gpm RO Train 4 RO Concentrate 120 gpm

RO System History Bypass: 50% reduced to 25% with increasing raw water nitrate levels to stay in compliance. Trains 1 & 2 historically had significantly more use: Membranes replaced most recently in 1 & 2 due to greater TDS and nitrate leakage. No improvement in Train 1 and 2 performance after membrane replacement. System placed on compliance order in early 2011 – given 90 days to get in compliance.

WWT Investigation Projection conducted for Toray TMG20N-400C low energy RO membranes. With 20 mg/L NO3-N in feed, theoretical permeate level was 1.67 mg/L. Nitrate from trains 1 & 2 was >5.0 mg/L. Determined that reconditioned RO membranes had been recently installed in trains 1 and 2. Typically used for hardness removal Not suitable for nitrate removal

Projection Results Parameter Raw Feed Permeate Nitrate, mg/L as N 20 1.67 (actual ~5.5) Hardness, mg/L as CaCO3 223 2.5 Sulfate, mg/L 22 0.05 Calcium, mg/L 77 0.66 Magnesium, mg/L 12.9 0.11 Silica, mg/L as SiO2 13 0.21 Chloride, mg/L 10 0.04 Sodium, mg/L 15.3 0.17 TDS, mg/L 11.0 (actual ~140)

Contaminant Removal Rates using RO & NF Comparative Removal Rates NF RO Monovalent Ions (Sodium, Potassium, Chloride, Nitrate, etc) <50% >98% Divalent Ions (Calcium, Magnesium, Sulfate, Carbonate, Iron, etc) >90% >99% Microsolutes (<100 Mw) 0-50% 0-99% Microsolutes (>100 Mw) >50%

Recommendations Install Toray Low Energy Membranes (TMG20N-400C) in worst performing trains (1 & 2). Fastest and lowest cost to get system back in compliance. Future: Replace existing pumps with more efficient low energy pumps. Replace membranes in trains 3 & 4.

Individual Train Performance Trains 1 & 2 Membranes Replaced

Overall Nitrate Removal Data Trains 1 & 2 Membranes Replaced

Individual Train Performance Trains 1 & 2 Membranes Replaced

Low Energy Membrane Savings Previous RO Membranes: Operating Pressure: 150 psi Pump Power: 20 HP per train Annual Power Cost*: $7,840 per train @ 10c/kWh Low Energy RO Membranes: Operating Pressure: 110 psi Pump Power: 15 HP per train Annual Power Cost*: $5,880 per train @ 10c/kWh Annual Power Savings: $7,840 (25% reduction) *Assuming 60% plant utilization

Process Economics Operating Costs: c/1000 gal Power 10.4 Chemicals# & cartridge filters 14.9 Membrane replacement (5 years) 16.5 Total* 41.8 #Bisulfite, antiscalant, CIP chemicals *Assuming 60% plant utilization, 75% recovery & 20% bypass.

Results Summary Determined that reconditioned membranes were not effectively removing nitrate and resulting in MCL violations. Replacement of train 1& 2 membranes immediately brought system back in to compliance. Low energy membranes will save City ~$8000 per year in pumping power. Don’t assume any RO membrane can remove >90% nitrate!

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