Transcript Osmonics Operation and Maintenance Seminar

Michael Bourke – Wigen Water Technologies
www.wigen.com
Potable Applications of NF/RO
 Aesthetic
 Regulatory
 TDS
 Nitrate
 Hardness
 Arsenic
 Sulfate
 Radionuclides
 Color
 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%
>90%
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.
Pressure
Membrane
Feed Water
Permeate
Concentrate
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
Spacer Material
Permeate
Carrier
Material
Permeate
Membrane
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
Case Studies
 City of Wellman, IA

New RO System for Radium & Ammonia Removal and General
Water Quality Improvement.
 City of Creighton, NE

Upgraded RO System to Improve Nitrate Removal.
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Background
Trial Objectives
Pilot Plant Selection
Results
Full-scale System Design
Wellman, Iowa
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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
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
Concentrate
S2 Feed
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
Trial Results
System Flows vs. Time
18.00
Potential Membrane
Damage
13.00
Flow (gpm)
No decrease = minimal fouling
8.00
3.00
26-Jun-09
06-Jul-09
16-Jul-09
26-Jul-09
05-Aug-09
15-Aug-09
25-Aug-09
04-Sep-09
14-Sep-09
24-Sep-09
04-Oct-09
Date
Normalized Permeate Flow
Permeate Flow
Concentrate Flow
Linear (Normalized Permeate Flow)
Trial Results
Normalized Permeate Conductivity vs. Time
Normalized Permeate Conductivity (uS/cm)
40.00
CIP Performed
35.00
30.00
25.00
20.00
15.00
10.00
5.00
0.00
26-Jun-09
06-Jul-09
16-Jul-09
26-Jul-09
05-Aug-09
15-Aug-09
25-Aug-09
04-Sep-09
Date
Normalized Permeate Conductivity (uS/cm)
Linear (Normalized Permeate Conductivity (uS/cm))
Permeate Conductivity
14-Sep-09
24-Sep-09
04-Oct-09
Trial Results
TDS vs. Time
• 98.9% TDS Reduction
• 16-28 mg/L
2000
1000
500
Hardness vs. Time
5
2
9
9/1
9/2
9/2
1000
900
Date
600
500
400
300
200
100
9/ 2
9
9/ 2
2
9/ 1
5
9/ 8
9/ 1
8/ 2
5
8/ 1
8
8/ 1
1
8/ 4
0
7/ 2
8
• 99.9% Hardness Reduction
• 0.9-2.0 mg/L as CaCO3
(slight increase in last week)
700
7/ 2
1
Permeate TDS
Hardness
(mg/las CaCO3 )
800
Feed TDS
7/ 1
4
9/8
9/1
5
8
8/1
8/2
1
8
7/2
8/1
1
7/2
8/4
4
0
7/1
TDS
(mg/l)
1500
Date
Feed Hardness
Permeate Hardness
Trial Results
4.5
Sulfate vs. Time
4
• 99.94% Sulfate Reduction
• 0.9-4.2 mg/L (slight increase
in last week)
1400
3.5
3
1000
(mg/l)
SulfateSulfate
- mg/L
1200
2.5800
2600
400
1.5
Ammonia vs. Time
200
4.5
9/ 2
9
9/ 2
2
9/ 1
5
9/ 8
9/ 1
8/ 2
5
8/ 1
8
8/ 1
1
8/ 4
7/ 2
8
7/ 2
1
4
Date
0
1
2
3
4
3.5
5
6
7
Feed Sulfate
8
9
Permeate Sulfate
Ammonia
(mg/l as N)
0.5
5
0
7/ 1
4
1
10
3
2.5
2
1.5
1
0.5
9/ 2
9
9/ 2
2
9/ 1
5
9/ 8
9/ 1
8/ 2
5
8/ 1
8
8/ 1
1
8/ 4
7/ 2
8
7/ 2
1
0
7/ 1
4
• Below detection (<0.09 mg/L)
Date
Feed Ammonia
Permeate Ammonia
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 46 months.
Full-Scale Design
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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
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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
RO Train 2
Well Pumps
Finished Water
525 gpm
Greensand
Filters
RO Train 3
RO Train 4
RO Concentrate
120 gpm
Permeate 400 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%
>90%
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:
Power
Chemicals# & cartridge filters
Membrane replacement (5 years)
Total*
#Bisulfite,
c/1000 gal
10.4
14.9
16.5
41.8
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!
Questions?
www.wigen.com