Transcript
Reverse Osmosis
Dam
Pumping
Raw Water Treatment Plant
Pumping
Wastewater Treatment Plant
Collection Network
Rain
Agricultural Use Incineration
Sludge Treatment Plant
Collection
Water Cycle
Distribution Network
Boiler
Cooling Tower
Process
Discharge
Water Cycle
• Dramatic decrease in RO membrane prices (50% - 8yrs).
• Increasing costs of chemicals (esp. NaOH) for IX systems.
• Increased return on investment for reverse osmosis as pretreatment
to an ion-exchange system.
• Increased manufacturer awareness in properly designing
pretreatment systems.
• Increase in comfort level for operation of customer-owned RO
systems.
• Consistent water quality
REASONS FOR INCREASED POPULARITY WITH REVERSE OSMOSIS
RO Seminar Objectives
– Reverse Osmosis Principles and Operation (Reverse Osmotic Pressure)
– Designs and terminology
– Operating parameters, problems, troubleshooting
– Cleaning
– Products and Equipment
– Miscellaneous subjects
Reverse Osmosis
Basic Principles
Osmosis
Pure
Water
Strong
Solution
H2O
H2O
H2O
Pure Water Flow
Osmosis
Osmotic Head
Pure
Water
Strong
Solution
H2O
H2O
H2O
Pure Water Flow
Equilibrium
Equilibrium
Applied Pressure, PF
H2O
H2O
H2O
Strong
Solution
Pure
Water
= Osmotic Pressure, POF
Osmotic Pressure, PO,P
Reverse Osmosis
Applied Pressure, PF > Permeate Pressure, PP
H2O
H2O
H2O
Strong
Solution
Pure Water Flow
Pure
Water
Osmotic
Pressure, PO,F
Osmotic Pressure, PO,P
Types of Filtration
TYPICAL FILTRATION
CROSS-FLOW FILTRATION
Solids on surface quickly foul the membrane
Solids are swept away by continuous flow
Feedwater Flow Feedwater Flow
Purified water Purified water
CROSS-FLOW FILTRATION
CROSS-FLOW FILTRATION
•ONE INFLUENT
•TWO EFFLUENT STREAMS
•HIGH VELOCITY MINIMIZES MEMBRANE SCALING AND FOULING
RO Skids typically have three major
components.
TO WASTE PRODUCT FEED
CARTRIDGE
FILTER HIGH-PRESSURE
FEED PUMP
PRESSURE
VESSELS
REVERSE OSMOSIS
Cross Flow Filtration Methods
Microfiltration Ultrafiltration Nanofiltration Reverse Osmosis
Range Macro molecular Molecular Sub molecular Ionic
Particle size
1.0 - 0.1 Micron
0.1 - 0.01 Micron
0.01 - 0.001 Micron
<0.001 Micron
Removes Suspended solids, Large colloids, Bacteria
Proteins, Colloids, Organics
Pyrogens, Divalent ions
Virus
Small Organics,
Metals, Salts
Molecular Weight
>100,000 10,000 - 100,000 200 - 20,000 <300
Operating Pressure
10 psig (0.7 kg/cm2)
10 - 100 psig (0.7 kg-7.0/cm2)
150 -250 psig (14-17.5 kg/cm2)
150 - 800 psig (14- 56 kg/cm2)
Pretreatment Needs
Low Medium High High
Capital Cost Low Medium High High
The Filtration Spectrum
Thin Film Composite Polyamide Membrane
0.2 micron
40 micron
120 micron Reinforcing Fabric
Microporous Polysulfone
Polyamide Ultrathin
Barrier Layer
TFC Membrane
Membrane Comparison
Characteristic TFC CA
Operating pH 2 - 11
Salt Rejection >99% Flux Rate (GPD/Ft2) 15-20
Bacteria Resistance Excellent
Cl2 Tolerance 0.0
Physical Stability Better
Max T (0F) 113
Feed Pressure 5 - 6.5
90-96% 12-16
Poor
0.2-1.0
Good
104
> 400 PSI < 200 PSI
Membrane Comparison Cont.
CA TFC
Silica Rejection 85% 98%
Nitrate Rejection 85% 94%
Maximum SDI 5 5
3rd Year Compaction 20% 0%
Hydrolysis 2 X None
Characteristic
Typical Passage of Ions
IonIon % % SaltSalt PassagePassage % Salt Rejection% Salt RejectionAmmoniumAmmonium 55 9595SodiumSodium 22 9898PotassiumPotassium 22 9898MagnesiumMagnesium <1<1 99+99+StrontiumStrontium <1<1 99+99+CalciumCalcium <1<1 99+99+NitrateNitrate 1515 8585BisilicateBisilicate 1010 9090ChlorideChloride 22 9898FluorideFluoride 22 9898BicarbonateBicarbonate 22 9898SulfateSulfate 11 9999PhosphatePhosphate 11 9999
* TFC element rated for a 98% * TFC element rated for a 98% NaClNaCl rejectionrejection
Membrane Configurations
• Spiral Wound
• Hollow Fiber
• Tubular
Spiral Wound Membrane Elements
Flow Pattern
for a Spiral Wound Element
Spiral Wound Membrane Elements
Wound Elements
Hollow Fiber Membrane
Hollow Fiber Membrane Element
Feedwater
Permeate
Concentrate
Concentrate
Note: Only 4 hollow fibers are shown
Tubular Membrane
Reverse Osmosis
System Design & Operations
Glossary of Terms
• Concentrate
– Reject – Brine
• Permeate
– Product
Reverse Osmosis Basics
FEEDWATER
100 gpm
600 ppm TDS
PERMEATE
75 gpm
30 ppm TDS
5% Salt Passage
75% Recovery
CONCENTRATE
95% Salt Rejection
25 gpm
2310 ppm TDS
25% Concentrate
What is RO Permeate and % Recovery?
• Permeate is water recovered as product.
• % Recovery = Permeate Flow Rate x100
– % Recovery calculates percent of feedwater that
becomes product.
– % Recovery describes performance of the system
– Greater recovery=less waste=cost savings.
– Recovery typically ranges from 50% to 75% (can go as high as 85%)
– % Recovery and permeate quality are inversely related.
REVERSE OSMOSIS
Make-up Flow Rate
REVERSE OSMOSIS
RECOVERY CONCENTRATION FACTOR
50% 2
75% 4
80% 5
83% 6
87.5% 8
What is RO Concentrate and % Rejection?
• Concentrate (or Brine) is the waste from the RO.
• Reject is a calculation of the percentage of solids/solutes in feedwater rejected by the membrane.
– Typically ranges from 95% to 99+% for most ionic solutes and set by membrane manufacturer.
– Greater % reject means better permeate quality.
– Species dependant
• Multi-valent ions (Ca2+, Mg2+) higher rejection
• Monovalent ions (Na+, Cl-) lower rejection
• Gases (O2, CO2) no rejection
REVERSE OSMOSIS
RO Systems
– Reject Staging
• Multi-stages for reject
• Increased utilization of water
– Incremental increase in investment
– Minimal decrease in water quality
– Multi - Pass
• Product staging
• Improves water quality
– May eliminate the need for downstream polishing
Two-Stage RO System - Reject Staging
FEED FEED PERMEATE PERMEATE
HIGH HIGH
PRESSURE PRESSURE PUMP
TRAIN #1 TRAIN #1
TRAIN #2 TRAIN #2
ELEMENTS ELEMENTS
VESSEL VESSEL
2:1 ARRAY 2:1 ARRAY
FEED FEED REJECT REJECT
CONCENTRATE CONCENTRATE
PERMEATE PERMEATE 1st STAGE 1st STAGE
2nd STAGE 2nd STAGE
CONCENTRATE CONCENTRATE
Reject Staging
• Increased Utilization of Water
– Incremental Increase in Investment
– Minimal Degradation in Water Quality
Double Pass RO System
2nd Pass Concentrate Recycled
* pH 9.0 * pH 9.0
w/ w/ NaOH NaOH Permeate Permeate
Feed Feed 1st Pass Permeate
1 1 st st Pass Concentrate to Drain
Double Pass
• Applications:
– Seawater (High TDS)
– Ultra-high purity applications
• Benefits of interstage pH adjustment
– Improved Alkalinity Rejection
– Improved Silica Rejection
– Improved TOC Rejection
Typical RO Machine
What Are the Advantages of RO ?
• Removes nonionic impurities and dissolved solids
(i.e. organics, silica, bacteria)
• Reduction of hazardous chemical storage and
handling associated with ion exchange
• Economic advantages increase with increasing
feed TDS
What Are the Disadvantages of RO?
• Concentrate is rejected and this can be a significant volume of
water.
• RO membranes reject a fixed percentage of feedwater ions
– Further treatment is required for many applications.
• Ultimate filter which is easily fouled:
– Increasing operating costs
– Reducing membrane life
Typical Operating Cost Breakdown
Membrane Replacement
12%
Chemicals 14%
Labor 25%
Other 5%
Electrical 44%
Reverse Osmosis
Membrane Problems and Solutions
Membrane Problems
Scaling
- Mineral Salts
- Silica
Fouling
- Metal Oxides
- Colloidal Silt & Crud
- Biological & Organics
Hydrolysis & Chemical Attack
- pH, Temperature, Oxidants, Biodegradation
Compaction
REVERSE OSMOSIS
•80% to 90% of problems are related to pretreatment of RO Feedwater
•The purpose of pretreatment is to prevent
• Membrane Fouling
• Membrane Scaling
• Membrane Degradation
REVERSE OSMOSIS
Effects of Fouling, Scale, Degradation
Poor Permeate Quality
Frequent cleaning
Increased Operating Pressure
Increased O&M cost
Membrane Replacement
RO Fouling
CategoryCategory ExamplesExamples SourcesSources
Scaling SaltsScaling Salts CaCOCaCO33 FeedwaterFeedwaterCaSOCaSO44 Sulfuric AcidSulfuric AcidBaBa // SrSr -- SOSO44CaFCaF22SiOSiO22 -- ComplexesComplexes
Metal OxidesMetal Oxides IronIron FeedwaterFeedwaterManganeseManganese CorrosionCorrosionAluminumAluminum ClarifiersClarifiers
ColloidsColloids SiltSilt Surface WatersSurface WatersRustRust Corroding PipesCorroding Pipes
BiologicalBiological Organic SlimesOrganic Slimes NonNon--ClCl22 FeedFeedBacteriaBacteria OffOff--line Systemsline Systems
OrganicOrganic PolymerPolymer Coagulant OverfeedCoagulant OverfeedHydrocarbonHydrocarbon Process LeaksProcess Leaks
Scale
• Cause: – Salt exceeds solubility limits due to
concentration effects
• Prevention: – Reduce Recovery
– Acid Feed (CaCO3)
– Sodium Zeolite Softening
– Antiscalant
Concentration Polarization
Mineral Scale
Silica Fouling
Metal Oxide
Iron, Manganese and Aluminum
• Cause: – Feedwater
– Corrosion in system piping
– Clarifier carryover
• Prevention: – Oxidation & Filtration
– Greensand Filtration (Mn)
– Softening (Fe & Mn)
– Chemical Antifoulant
Iron Fouling
REVERSE OSMOSIS
•RO For:
• DOSAGE CONTROL
• LEAK ANALYSIS DIAGNOSTICS
• TRUE SYSTEM RECOVERY
• MEMBRANE INTEGRITY
• COST CONTROL
SCALE CONTROL
Components of RO TRASAR®
Trasar 8000 Handheld Fluorometer for Monitoring and Diagnostics
Trasar 3000 Fluorometer for On-line Monitor & Control
120 MW CCGT Cogeneration Plant, Florida
• Description of demineralization system
– Water source: city water
– Pre-treatment: feed water dechlorination
– Reverse osmosis: 2X100 gpm systems
– Post-treatment: mixed-bed ion exchange column
• Performance issues
– Fouling of membrane elements resulting in frequent cleanings
– Poor permeate quality resulting in frequent regeneration of polishing ion exchange bed.
Active control of scale inhibitor dosage
0
5
10
15
20
25
30
0
50
10
0
15
0
20
0
25
0Hours of Continuous Operation
PP
M a
s A
nti
sca
lan
t
Before Control After Control
Reduced membrane fouling.
0
5
10
15
20
25
30
0
20
40
60
80
100
120
140
160
180
200
Hours of Continuous Operation
pp
m a
nti
sca
lan
t
Actual Dose
Target Dose & ControlLimits
RO TRASAR® Benefits: 120 MW CCGT Cogeneration Plant
> $37,600/yr Total Savings
TBD 88% Every 800K gal Every 100K gal Polishing IX
regeneration
$6,000 50% 4 yrs life 2 yr life Membrane
replacement
$26,000 85% 4 per year 26 per year Cleaning
$5,600 25% 9 ppm 12 ppm Antiscalant
$/yr % After Before
Savings
Colloids
• Cause: – Surface water
– Corrosion in system piping - (Line all vessels)
• Prevention: – Coagulation & filtration
– Zeolite softening
– Chemical Antifoulant
Bacteria, Slime
• Cause: – Surface water – Non-Cl2 Feed – Off-Line RO System
• Prevention: – Biocide
• Cl2 residual – Dechlorination
• Non-Oxidizing Biocide • UV Sterilization
Microbiological Fouling
Organic
• Cause: – Polymer overfeed
– Surface Water
– Process Leaks
• Prevention for Polymer Overfeed: – Streaming Current Detector
– Sodium Zeolite Softener
– Inorganic Coagulant
Hydrolysis & Chemical Attack
CA MEMBRANES
• Microbio growth present • pH < 5.0 or > 6.5
• Temperatures > 104 oF (40 0C)
• Exposed to direct sunlight
TFC MEMBRANES
• Oxidants in feedwater
(i.e. Cl2, O3) • Temperatures > 112 oF (44 0C)
• Exposed to direct sunlight
Membrane Degradation
Results of Membrane Problems
• Reduced water quality
– Shorter run lengths on downstream IX
• Premature membrane replacement
• Higher operating costs
Reverse Osmosis
Monitoring
Monitoring
•Pretreatment – 90% of operational
problems are found here
•System – 10% of operational
problems are found here
RO System Monitoring
• Pretreatment monitoring
- Silt Density (SDI), Turbidity, pH,
Oxidants Particle Size and Counts
- Temperature, Pressure, TDS
- Foulants (bacteria, metals,
hardness, silica)
RO System Monitoring
• Performance monitoring
- Percent salt rejection
- Normalized permeate flowrate
- Differential pressure
Pretreatment
• Silt Density Index (SDI)
• Langlier Saturation Index (LSI)
• Stiff Davis Index (TDS >4,000 mg/L)
• Feedwater Analysis
Silt Density Index (SDI)
• Empirical indication of potential fouling
• Based on rate of plugging a 0.45m filter
• Hollow Fiber SDI < 3.0
• Spiral Wound SDI < 5.0
• Typical Well Water SDI < 3
• Typical Surface Water SDI > 6
Silt Density Index
SDI = PSDI = P30 30 // T = (1 T = (1 -- ttii // ttff) * 100) * 100
TT
SDI = PSDI = P30 30 // T = (1 T = (1 -- ttii // ttff) * 100) * 100
TT
Feed Feed SupplySupply(30(30--80 80 psig)psig)
Pressure Pressure RegulatorRegulator
Pressure Pressure GaugeGauge
ByBy--Pass to Pass to draindrain
Filter Filter HolderHolderFilter Filter HolderHolder
Langlier Saturation Index (LSI)
• Indicates the potential for CaCO3
scale
• LSI > 0 “indicates scaling”
• Calculation:
– Computer programs
– Permutit Handbook
REVERSE OSMOSIS
PERMACARE RO-12
SCALE PREDICTION SOFTWARE
Feedwater Analysis
• Minimal water test includes
– Ca, Mg, Fe, Al, Silica
– SO4, Alkalinity, pH, Conductivity
– SDI
– TOC
– Color
• Full water analysis should include analysis scaling/fouling contaminants
Additional Pretreatment
• Turbidity
• pH
• Oxidants
• Temperature
• Pressure
• TDS / Conductivity
• Foulants - bacteria, metals, hardness, silica etc.
Affect of SDI on Flux & % Recovery per Element
Feed source SDI Max. Flux
(gal/ft2/day) Max. % Recovery
RO permeate <1 25 30%
Well water <3 20 19%
Surface supply <3 17 17%
Surface/softened <5 16 15%
Seawater <5 10 13% Guidelines for 8 inch Filmtec element
Affect of SDI on Flux by System
Feed source SDI Max. Flux
(gal/ft2/day)
RO permeate <1 21 – 25
Well water <3 16 – 20
Surface supply <3 13 – 17
Surface supply <5 10 – 16
Nalco recommendations for longer membrane life
Nalco Recommendation
22
16
14
13
Effect of Temperature on Permeate Flowrate
TEMPERATURE TEMPERATURE
--1.11.1 4.44.4 10.010.0 15.615.6 21.121.1 26.726.7 32.232.2 37.837.8 43.343.3
Perm
eat
e F
low
rate
, Pe
rmeat
e F
low
rate
, %
of
Desi
gn%
of
Desi
gn
7070
8080
9090
100100
110110
60604040 5050 6060 7070 8080 9090
120120
1001003030 110110 00FF00CC
System Monitoring
The Critical 3
• Percent Salt Rejection
• Normalized Permeate Flowrate (NPF)
• Differential Pressure (ΔP)
(Use Computer and Trend Data)
Salt Rejection
% Rejection = (TDSfeed - TDSPermeate) x 100
TDSfeed
Common to use conductivity measurement as an indication of TDS
Net Differential Pressure
D P = Pf - Pc
Pf = feed pressure
Pc = concentrate pressure
D P differential pressure, “delta P” or pressure drop
Normalized Permeate Flowrate
Flownormalize : Qn = NDP(start-up) * FT * Qp
NDP(daily)
Pf = Feed Pressure
Pp = Permeate Pressure
PO,F = Osmotic Press. Feed
PO,C = Osmotic Press. Brine
FT = Temp. Correction Factor
Qp = Permeate Flowrate
NDP = Pf - Pp - PO
NDP = Pf - Pp - PO
Net Driving Pressure
Available Pressure to “Drive” the Process
• NDP = PF + PO,P - PP - PO,F
• Brackish water PO,P = 0
• Average NDP
• NDP = PF - PP - PO,F
• NDP = (PF+Pc) - (PP+PP) - (PO,F+PO,C)
2 2 2
Trending & Normalization
• Permeate Flow
• Differential Pressure
• Salt Rejection
Enter Data Using Nalco “RO Trend”
Effect of Driving Pressure on Permeate Flowrate Pe
rmeat
e F
low
rate
, %
Perm
eat
e F
low
rate
, %
Perce
nt Reje
ction, %Pe
rcent R
eje
ction, %
20%20%
40%40%
60%60%
80%80%
100%100%
0%0%20%20% 40%40% 60%60% 80%80% 100%100% 120%120%
20%20%40%40%60%60%80%80%100%100%
0%0%
DRIVING PRESSUREDRIVING PRESSURE
Feed Flow Vs. NDP
Raw Data Vs. Normalized Data
Start Up Information
• Collect Initial Data within first 24 to 72 hours
• Everything is compared to “Start up” data
Daily Operation & Performance Parameters
Date Operator’s initials Feedwater silt density index (SDI) Feedwater turbidity Feedwater temperature Feedwater temperature correction factor Feedwater pH Oxidant concentration (i.e. Cl, sanitizer) Feedwater conductivity or TDS Permeate conductivity or TDS Reject conductivity or TDS
Percent salt rejection (calculated) Feed (membrane) pressure Permeate pressure Reject pressure Net differential pressure (calculated) Net driving pressure Feedwater flowrate Permeate flowrate Reject flowrate Normalized permeate flowrate (calculated) Percent recovery (calculated)
Use Computers to Trend this Data
Trending Data
Using the Performance Variable
Feed Flow Rate (gpm)
120
110
100
90
100
90
80
100
90
80
40
30
20
Differential Pressure
Feed Flow Rate
Start-up
Membrane Elements cleaned
Leaking O-ring Replaced
Net Differential Pressure
(psig)
% Reject
Normalized Permeate Flow Rate
(gpm)
REVERSE OSMOSIS
•RO-EYE • REVERSE OSMOSIS
MONTIROING AND CONTROL SYSTEM
• Real time data monitoring
• Data normalization
• TRASAR control
T
M
Reverse Osmosis
Trouble Shooting
Product
Concentrate Feed
Brine becomes more concentrated Feed Flowrate Decreases
Flow Through a Pressure Vessel
Indications of Trouble
Change
• Salt Rejection
• Differential Pressure
• Normalized Permeate Flow
• Others
Trouble Shooting Changes
• Check Instrument Calibrations
– Compare Percent Recovery by Conductivity Vs. Flow
• Identify the Location of the Decline
– Front end Vs. Back end, Stage 1 Vs. Stage 2
• Investigate Potential Causes of the Problem
– Use both visual and analytical data
• Correct the Potential Cause of the Problem
Troubleshooting Instrument Calibration
• Compare Recovery Calculations
– Conductivity Vs. Flow
• Pressure Meter Change Out
– Quick Disconnects
• Hand Held Vs. On-line Instrumentation
• Thermometers
Trouble Shooting / Changes in Salt Rejection
• Check Individual Pressure Vessel Performance
• Probe the Pressure Vessel (Spiral Wound)
• Individual Membrane Testing – Single Element Test Skid
Identify the Location of the Decline
Check Individual Pressure Vessel Performance
First Stage Pressure Vessel Profile:
Pressure Vessel # Permeate TDS (ppm)
1 25
2 22
3 49
4 20
Second Stage Pressure Vessel Profile:
5 36
6 34
Example - 4:2 Array
When to Probe
• High salt passage
• Individual pressure vessels have high conductivity
Individual Element Performance
• Probe the Pressure Vessel (Spiral Wound)
– 1/4” Tubing into Permeate Line
– Conductivity versus Penetration
• Location of Problem
– Check front / mid / end each element
– Note direction of feed water flow
1/4” Polypropylene Tubing
RO Vessel Containing 6 Elements
Probing a Pressure Vessel
Probe every 8 inches to determine membrane or o-ring damage
Membrane Element # Permeate TDS (ppm)
1 Lead End 25
2 23
3 25
4 21
5 Tail End 54
Probing a Pressure Vessel
Remember to Note Feedwater Direction
Troubleshooting Individual Membrane Elements
• Individual Membrane Testing
– In House • Non-destructive
– Single Element Test Stand
– Autopsy • Potentially Destructive
• More detailed Information`
Problems
CauseCause General SymptomsGeneral SymptomsSalt PassageSalt Passage PermeatorPermeator DD PP Product FlowProduct Flow
ScalantsScalantsCarbonates, Sulfates,Carbonates, Sulfates,PhosphatesPhosphates
SignificantSignificantIncrease (10Increase (10--25%)25%)
Slight to ModerateSlight to ModerateIncreaseIncrease(10 (10 -- 50%)50%)
Slight DecreaseSlight Decrease(( << 10%)10%)
Metal OxidesMetal OxidesFoulantsFoulantsIron, Manganese etc.Iron, Manganese etc.
Rapid MarkedRapid MarkedIncrease (Increase ( >> 2x)2x)
Rapid MarkedRapid MarkedIncrease (Increase ( >> 2x)2x)
Rapid MarkedRapid MarkedDecrease (Decrease ( >> 50%)50%)
ColloidalColloidal Gradual Gradual Gradual Gradual Gradual Gradual
FoulantsFoulantsmostly Aluminum Silicatesmostly Aluminum Silicates
Marked IncreaseMarked Increase( ( >> 2x)2x)
Marked IncreaseMarked Increase(( >> 2x)2x)
Marked DecreaseMarked Decrease(( >> 50%)50%)
BiofilmBiofilmFoulants Foulants
Marked IncreaseMarked Increase(( >> 2x)2x)
Marked IncreaseMarked Increase(( >> 2x)2x)
Marked DecreaseMarked Decrease(( >> 50%)50%)
PluggagePluggageMacroMacro
IncreaseIncrease Rapid MarkedRapid MarkedIncrease Increase
Rapid MarkedRapid MarkedDecrease Decrease
Frequent Causes of Change
Change in Permeate TDS
Higher
“O” Ring Leakage
Membrane Damage Higher Feed TDS Low Product Flow Low Brine Flow Fouling Scaling
Lower
Lower Feedwater TDS
Initial BioFouling
Frequent Causes of Change
Change in Pressure Drop
Higher
Biofouling
Scaling
Inorganic Fouling
Higher Flow Rates
Lower Feed Temp.
Lower
Lower Flow Rates
Higher Feed Temp.
Frequent Causes of Change
Change in Feed Pressure
Higher
Scaling
Pluggage
Higher Feed TDS
Lower Feed Temp.
Improper Valving
Lower
Higher Feed Temp.
Lower Feed TDS
Membrane Damage
Frequent Causes of Change
Change in Feed Chemistry
Chemistry Change Effect on System
pH Too High Membrane Damage
pH Too Low Membrane Damage
Cl2 outside Specs. Membrane Damage
Scaling Ions above Specs. Scaling
Increased SDI / Turbidity Fouling
Reverse Osmosis
Cleaning
When do I clean?
• When any ONE of the following changes:
NPF by 10% - 15%
Differential Pressure by 10% - 15%
Salt Rejection by 10% - 15%
• Start planning your strategy at the first indication of a minimum change!
Proper Cleaning Maintenance
NormalizedNormalizedPermeatePermeateFlowrateFlowrate
TimeTime
Cleaning after 10Cleaning after 10--15% decline15% decline
NormalizedNormalizedPermeatePermeateFlowrateFlowrate
TimeTime
Improper Cleaning MaintenanceImproper Cleaning Maintenance
Cleaning after >15% declineCleaning after >15% declineCleaning after >15% declineCleaning after >15% decline
Waiting too Waiting too longlongto clean to clean reduces reduces RO RO performanceperformance
Cleaning after aCleaning after a1010--15% decline15% declinemaximizes ROmaximizes ROperformanceperformance
Cleaning Skid
5m5mCFCF
DP
SS/Plastic SS/Plastic Cleaning Cleaning PumpPump
StrainerStrainer
CleaningCleaningSolutionSolutionReturnReturnPermeate ReturnPermeate Return
Permeate Permeate
SupplySupply
T
Isolate StagesIsolate Stages
P
P
F
Sample
TC HeaterHeater
L
RecirculationRecirculation
DrainDrain
5m5mCFCF
DP
SS/Plastic SS/Plastic Cleaning Cleaning PumpPump
StrainerStrainer
CleaningCleaningSolutionSolutionReturnReturnPermeate ReturnPermeate Return
Permeate Permeate
SupplySupply
T
Isolate StagesIsolate Stages
P
P
F
Sample
TC HeaterHeater
LTCTC HeaterHeater
L
RecirculationRecirculation
DrainDrain
Cleaning
• Do Not Exceed Mftr. Specs!
– pH
– Pressure Drop
– Temperature
– Flow Rate
Cleaning
• Cleaning CF size < Operating CF size
• Use permeate as Make-up
• Mix Chemical according to instructions
• Utilize “maximum” conditions
• Dump “first system volume” (i.e., flush)
Cleaning
• Return permeate & concentrate to tank
• Make as little permeate as possible (Open concentrate valve wide open)
• Pump Size is critical
How To Choose a Chemical Cleaner
• Cleaner Selected for:
– Membrane Type
– Characteristics of Foulant
– Convenience
• Optimum Service
• Acid Cleaners First
• Followed by Caustic Cleaners
Cleaning Solutions
Things to Remember
• Start planning to clean when:
– Differential Pressure changes 10%
– NPF changes 10%
– Salt Rejection changes 10%
Things to Remember
• Order of cleaning chemicals:
– Caustic/Acid (can vary with contamination)
– Acid/Caustic (can vary with contamination)
– Sanitization
• Waiting too long will cause irreversible
damage!
Keep Good Records
Membrane Cleaning Frequency
Cleaning Frequency
Quarterly or less
Every 1-3 months
Every month or more
Adequacy Estimate
Adequate
Marginal
Not adequate
Clean Until
• pH Doesn’t Change
• Color Doesn’t Change
• Flow Doesn’t Change
• Pressure Doesn’t Change
RO Element Test & Cleaning Stand
Feed Pressure
Gauge
Permeate Flowrate
Globe Valve
Reject Flowrate
Needle
Valve
Reject Pressure
Gauge
Permeate % Salt Rejection
Monitor
Differential Pressure
Benefits of Maintaining an RO
• Reduced operating costs
• Reduced maintenance costs
• Reduced downtime
• Extended membrane life
• Improved water quality and output
Typical Treatment Scheme
MULTIMEDIA
FILTER
CHLORINE
COAGULANT
(CARBON FILTER
GREENSAND FILTER)
SODIUM
SOFTENER
ANTISCALANT
BISULFITE
ACID
CAUSTIC
TO WASTE
TREATMENT OR
COOLING TOWER
REVERSE
OSMOSIS TO ION
EXCHANGE
OR BFWFEED
WATER
Pretreatment Selection
Technique Controls
Multimedia Filters Suspended solids
Carbon Filters Suspended solids, organics, chlorine
Greensand Filters Suspended solids, iron, manganese
Sodium Softeners Hardness, scale formers, iron, manganese, some suspended solids
Chlorine Microbes, organics
Bisulfite Free chlorine
Acid / Caustic Scale formers (acid), pH
Antiscalant Scale formers, foulants
Ultrafiltration Color or Bacteria
Recovery Scale
REVERSE OSMOSIS SUMMARY
• Understanding RO terms is important for successful unit operation.
• Initial design is critical and will determine long term permeate quality.
• Data collection and normalization is vital to maintenance and trouble shooting. (RO Eye)
• Pretreatment key to keeping membranes performing well. (Permacare, RO Trasar, Permafloc and/or Ultrasoft, Ultrasand)
• Cleaning based on trends in normalized data. (Permaclean)
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