Reverse Osmosis module design and engineering emerged with membrane technology evolution. In order to understand module design, first membrane configuration needs to be explored, since the module design is always tailored according to the membrane characteristics. There is a significant difference between membrane chemistries (most important ones being cellulose acetate and thin film composite with polyamide barrier layer), and more importantly, between the different membrane configurations (hollow fine fiber and flat sheet). Therefore, before looking into detail on the module configuration, the membrane development needs to be considered.

1. Reverse Osmosis

2. Dam
Pumping
Raw Water
Treatment Plant
Pumping
Wastewater
Treatment Plant
Collection Network
Rain
Agricultural Use
IncinerationSludge Treatment
Plant
Collection
Water Cycle
Distribution
Network
Boiler
Cooling Tower
Process
Discharge
Water Cycle

3. • 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

4. RO Seminar Objectives
– Reverse Osmosis Principles and Operation
(Reverse Osmotic Pressure)
– Designs and terminology
– Operating parameters, problems, troubleshooting
– Cleaning
– Products and Equipment
– Miscellaneous subjects

5. Reverse Osmosis
Basic Principles

6. Osmosis
Pure
Water
Strong
Solution
H2O
H2O
H2O
Pure Water Flow

7. Osmosis
Osmotic Head
Pure
Water
Strong
Solution
H2O
H2O
H2O
Pure Water Flow

8. Equilibrium
Equilibrium
Applied Pressure, PF
H2O
H2O
H2O
Strong
Solution
Pure
Water
= Osmotic Pressure, POF
Osmotic Pressure, PO,P

9. 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

10. Types of Filtration
TYPICAL
FILTRATION
CROSS-FLOW
FILTRATION
Solids on surface quickly
foul the membrane
Solids are swept away
by continuous flow
Feedwater FlowFeedwater
Flow
Purified waterPurified water

11. CROSS-FLOW FILTRATION
CROSS-FLOW
FILTRATION
•ONE INFLUENT
•TWO EFFLUENT STREAMS
•HIGH VELOCITY MINIMIZES MEMBRANE
SCALING AND FOULING

12. RO Skids typically have three major
components.
TO WASTE
PRODUCTFEED
CARTRIDGE
FILTER HIGH-PRESSURE
FEED PUMP
PRESSURE
VESSELS
REVERSE OSMOSIS

13. 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

14. The Filtration Spectrum

15. Thin Film Composite Polyamide Membrane
0.2 micron
40 micron
120 micron
Reinforcing
Fabric
Microporous
Polysulfone
Polyamide
Ultrathin
Barrier Layer

16. TFC Membrane

17. Membrane Comparison
Characteristic TFCCA
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

18. 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

19. Typical Passage of Ions
IonIon %% SaltSalt PassagePassage % Salt Rejection% Salt Rejection
AmmoniumAmmonium 55 9595
SodiumSodium 22 9898
PotassiumPotassium 22 9898
MagnesiumMagnesium <1<1 99+99+
StrontiumStrontium <1<1 99+99+
CalciumCalcium <1<1 99+99+
NitrateNitrate 1515 8585
BisilicateBisilicate 1010 9090
ChlorideChloride 22 9898
FluorideFluoride 22 9898
BicarbonateBicarbonate 22 9898
SulfateSulfate 11 9999
PhosphatePhosphate 11 9999
* TFC element rated for a 98%* TFC element rated for a 98% NaClNaCl rejectionrejection

20. Membrane Configurations
• Spiral Wound
• Hollow Fiber
• Tubular

21. Spiral Wound Membrane Elements

22. Flow
Pattern
for a
Spiral
Wound
Element
Spiral Wound Membrane Elements
Wound Elements

23. Hollow Fiber Membrane

24. Hollow Fiber Membrane Element
Feedwater
P
e
r
m
e
a
t
e
Concentrate
Concentrate
Note: Only 4 hollow fibers are shown

25. Tubular Membrane

26. Reverse Osmosis
System Design & Operations

27. Glossary of Terms
• Concentrate
– Reject
– Brine
• Permeate
– Product

28. 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

29. 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

30. REVERSE OSMOSIS
RECOVERY CONCENTRATION
FACTOR
50% 2
75% 4
80% 5
83% 6
87.5% 8

31. 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

32. 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

33. Two-Stage RO System - Reject Staging
FEEDFEED PERMEATEPERMEATE
HIGHHIGH
PRESSUREPRESSURE PUMP
TRAIN #1TRAIN #1
TRAIN #2TRAIN #2
ELEMENTSELEMENTS
VESSELVESSEL
2:1 ARRAY2:1 ARRAY
FEEDFEED
REJECTREJECT
CONCENTRATECONCENTRATE
PERMEATEPERMEATE
1st STAGE1st STAGE
2nd STAGE2nd STAGE
CONCENTRATECONCENTRATE

34. Reject Staging
• Increased Utilization of
Water
– Incremental Increase in
Investment
– Minimal Degradation in
Water Quality

35. Double Pass RO System
2nd Pass Concentrate Recycled
* pH 9.0* pH 9.0
w/w/ NaOHNaOH
PermeatePermeate
FeedFeed
1st Pass Permeate
11 stst Pass Concentrate to Drain

36. Double Pass
• Applications:
– Seawater (High TDS)
– Ultra-high purity applications
• Benefits of interstage pH
adjustment
– Improved Alkalinity Rejection
– Improved Silica Rejection
– Improved TOC Rejection

37. Typical RO Machine

38. 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

39. 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

40. Typical Operating Cost Breakdown
Membrane
Replacement
12%
Chemicals
14%
Labor
25%
Other
5%
Electrical
44%

41. Reverse Osmosis
Membrane Problems and Solutions

42. Membrane Problems
 Scaling
- Mineral Salts
- Silica
 Fouling
- Metal Oxides
- Colloidal Silt & Crud
- Biological & Organics
 Hydrolysis & Chemical Attack
- pH, Temperature, Oxidants, Biodegradation
 Compaction

43. 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

44. REVERSE OSMOSIS
Effects of Fouling, Scale, Degradation
Poor Permeate Quality
Frequent cleaning
Increased Operating Pressure
Increased O&M cost
Membrane Replacement

45. RO Fouling
CategoryCategory ExamplesExamples SourcesSources
Scaling SaltsScaling Salts CaCOCaCO33 FeedwaterFeedwater
CaSOCaSO44 Sulfuric AcidSulfuric Acid
BaBa // SrSr -- SOSO44
CaFCaF22
SiOSiO22 -- ComplexesComplexes
Metal OxidesMetal Oxides IronIron FeedwaterFeedwater
ManganeseManganese CorrosionCorrosion
AluminumAluminum ClarifiersClarifiers
ColloidsColloids SiltSilt Surface WatersSurface Waters
RustRust Corroding PipesCorroding Pipes
BiologicalBiological Organic SlimesOrganic Slimes NonNon--ClCl22 FeedFeed
BacteriaBacteria OffOff--line Systemsline Systems
OrganicOrganic PolymerPolymer Coagulant OverfeedCoagulant Overfeed
HydrocarbonHydrocarbon Process LeaksProcess Leaks

46. Scale
• Cause:
– Salt exceeds solubility limits due to
concentration effects
• Prevention:
– Reduce Recovery
– Acid Feed (CaCO3)
– Sodium Zeolite Softening
– Antiscalant

47. Concentration Polarization

48. Mineral Scale

49. Silica Fouling

50. 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

51. Iron Fouling

52. REVERSE OSMOSIS
•RO
For:
• DOSAGE CONTROL
• LEAK ANALYSIS DIAGNOSTICS
• TRUE SYSTEM RECOVERY
• MEMBRANE INTEGRITY
• COST CONTROL
SCALE CONTROL

53. Components of RO TRASAR®
Trasar 8000 Handheld Fluorometer
for Monitoring and Diagnostics
Trasar 3000 Fluorometer for
On-line Monitor & Control

54. 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.

55. Active control of
scale inhibitor dosage
0
5
10
15
20
25
30
0
50
100
150
200
250
Hours of Continuous Operation
PPMasAntiscalant
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
ppmantiscalant
Actual Dose
Target Dose & Control
Limits

56. RO TRASAR® Benefits: 120 MW
CCGT Cogeneration Plant
> $37,600/yrTotal Savings
TBD88%Every 800K galEvery 100K galPolishing IX
regeneration
$6,00050%4 yrs life2 yr lifeMembrane
replacement
$26,00085%4 per year26 per yearCleaning
$5,60025%9 ppm12 ppmAntiscalant
$/yr%AfterBefore
Savings

57. Colloids
• Cause:
– Surface water
– Corrosion in system piping - (Line
all vessels)
• Prevention:
– Coagulation & filtration
– Zeolite softening
– Chemical Antifoulant

58. Bacteria, Slime
• Cause:
– Surface water
– Non-Cl2 Feed
– Off-Line RO System
• Prevention:
– Biocide
• Cl2 residual
– Dechlorination
• Non-Oxidizing Biocide
• UV Sterilization

59. Microbiological Fouling

60. Organic
• Cause:
– Polymer overfeed
– Surface Water
– Process Leaks
• Prevention for Polymer Overfeed:
– Streaming Current Detector
– Sodium Zeolite Softener
– Inorganic Coagulant

61. 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

62. Membrane Degradation

63. Results of Membrane Problems
• Reduced water quality
– Shorter run lengths on downstream IX
• Premature membrane replacement
• Higher operating costs

64. Reverse Osmosis
Monitoring

65. Monitoring
• Pretreatment
– 90% of operational
problems are found here
• System
– 10% of operational
problems are found here

66. RO System Monitoring
• Pretreatment monitoring
- Silt Density (SDI), Turbidity, pH,
Oxidants Particle Size and Counts
- Temperature, Pressure, TDS
- Foulants (bacteria, metals,
hardness, silica)

67. RO System Monitoring
• Performance monitoring
- Percent salt rejection
- Normalized permeate flowrate
- Differential pressure

68. Pretreatment
• Silt Density Index (SDI)
• Langlier Saturation Index (LSI)
• Stiff Davis Index (TDS >4,000 mg/L)
• Feedwater Analysis

69. 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

70. Silt Density Index
SDI = PSDI = P3030 // T = (1T = (1 -- ttii // ttff) * 100) * 100
TT
SDI = PSDI = P3030 // T = (1T = (1 -- ttii // ttff) * 100) * 100
TT
FeedFeed
SupplySupply
(30(30--8080
psig)psig)
PressurePressure
RegulatorRegulator
PressurePressure
GaugeGauge
ByBy--Pass toPass to
draindrain
FilterFilter
HolderHolder
FilterFilter
HolderHolder

71. Langlier Saturation Index (LSI)
• Indicates the potential for CaCO3
scale
• LSI > 0 “indicates scaling”
• Calculation:
– Computer programs
– Permutit Handbook

72. REVERSE OSMOSIS
PERMACARE RO-12
SCALE PREDICTION SOFTWARE

73. 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

74. Additional Pretreatment
• Turbidity
• pH
• Oxidants
• Temperature
• Pressure
• TDS / Conductivity
• Foulants - bacteria, metals, hardness, silica
etc.

75. 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

76. 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

77. Effect of Temperature on Permeate Flowrate
TEMPERATURETEMPERATURE
--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
PermeateFlowrate,PermeateFlowrate,
%ofDesign%ofDesign
7070
8080
9090
100100
110110
6060
4040 5050 6060 7070 8080 9090
120120
1001003030 110110 00
FF
00
CC

78. System Monitoring
The Critical 3
• Percent Salt Rejection
• Normalized Permeate Flowrate (NPF)
• Differential Pressure (ΔP)
(Use Computer and Trend Data)

79. Salt Rejection
% Rejection = (TDSfeed - TDSPermeate) x 100
TDSfeed
Common to use conductivity measurement as an
indication of TDS

80. Net Differential Pressure
DP = Pf - Pc
Pf = feed pressure
Pc = concentrate pressure
DP differential pressure, “delta P” or pressure drop

81. 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

82. 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

83. Trending & Normalization
• Permeate Flow
• Differential
Pressure
• Salt Rejection
Enter Data Using Nalco “RO Trend”

84. Effect of Driving Pressure on Permeate FlowratePermeateFlowrate,%PermeateFlowrate,%
PercentRejection,%PercentRejection,%
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

85. Feed Flow Vs. NDP

86. Raw Data Vs. Normalized Data

87. Start Up Information
• Collect Initial Data within first 24 to 72 hours
• Everything is compared to “Start up” data

88. 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

89. 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)

90. REVERSE OSMOSIS
•RO-EYE
• REVERSE OSMOSIS
MONTIROING AND
CONTROL SYSTEM
• Real time data monitoring
• Data normalization
• TRASAR control
T
M

91. Reverse Osmosis
Trouble Shooting

92. Product
ConcentrateFeed
Brine becomes more concentrated
Feed Flowrate Decreases
Flow Through a Pressure Vessel

93. Indications of Trouble
Change
• Salt Rejection
• Differential Pressure
• Normalized Permeate Flow
• Others

94. 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

95. Troubleshooting
Instrument Calibration
• Compare Recovery Calculations
– Conductivity Vs. Flow
• Pressure Meter Change Out
– Quick Disconnects
• Hand Held Vs. On-line Instrumentation
• Thermometers

96. 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

97. 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

98. When to Probe
• High salt passage
• Individual pressure vessels have
high conductivity

99. 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

100. 1/4”
Polypropylene
Tubing
RO Vessel Containing 6 Elements
Probing a Pressure Vessel
Probe every 8 inches to determine membrane or o-ring damage

101. 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

102. Troubleshooting Individual Membrane Elements
• Individual Membrane Testing
– In House
• Non-destructive
– Single Element Test Stand
– Autopsy
• Potentially Destructive
• More detailed Information`

103. Problems
CauseCause General SymptomsGeneral Symptoms
Salt PassageSalt Passage PermeatorPermeator DD PP Product FlowProduct Flow
ScalantsScalants
Carbonates, Sulfates,Carbonates, Sulfates,
PhosphatesPhosphates
SignificantSignificant
Increase (10Increase (10--25%)25%)
Slight to ModerateSlight to Moderate
IncreaseIncrease
(10(10 -- 50%)50%)
Slight DecreaseSlight Decrease
(( << 10%)10%)
Metal OxidesMetal Oxides
FoulantsFoulants
Iron, Manganese etc.Iron, Manganese etc.
Rapid MarkedRapid Marked
Increase (Increase ( >> 2x)2x)
Rapid MarkedRapid Marked
Increase (Increase ( >> 2x)2x)
Rapid MarkedRapid Marked
Decrease (Decrease ( >> 50%)50%)
ColloidalColloidal GradualGradual GradualGradual GradualGradual
FoulantsFoulants
mostly Aluminum Silicatesmostly Aluminum Silicates
Marked IncreaseMarked Increase
(( >> 2x)2x)
Marked IncreaseMarked Increase
(( >> 2x)2x)
Marked DecreaseMarked Decrease
(( >> 50%)50%)
BiofilmBiofilm
FoulantsFoulants
Marked IncreaseMarked Increase
(( >> 2x)2x)
Marked IncreaseMarked Increase
(( >> 2x)2x)
Marked DecreaseMarked Decrease
(( >> 50%)50%)
PluggagePluggage
MacroMacro
IncreaseIncrease Rapid MarkedRapid Marked
IncreaseIncrease
Rapid MarkedRapid Marked
DecreaseDecrease

104. 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

105. 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.

106. 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

111. 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

112. Reverse Osmosis
Cleaning

113. 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!

114. Proper Cleaning Maintenance
NormalizedNormalized
PermeatePermeate
FlowrateFlowrate
TimeTime
Cleaning after 10Cleaning after 10--15% decline15% decline
NormalizedNormalized
PermeatePermeate
FlowrateFlowrate
TimeTime
Improper Cleaning MaintenanceImproper Cleaning Maintenance
Cleaning after >15% declineCleaning after >15% declineCleaning after >15% declineCleaning after >15% decline
Waiting tooWaiting too
longlong
to cleanto clean
reducesreduces
RORO
performanceperformance
Cleaning after aCleaning after a
1010--15% decline15% decline
maximizes ROmaximizes RO
performanceperformance

115. Cleaning Skid
5m5m
CFCF
DP
SS/PlasticSS/Plastic
CleaningCleaning
PumpPump
StrainerStrainer
CleaningCleaning
SolutionSolution
ReturnReturnPermeate ReturnPermeate Return
PermeatePermeate
SupplySupply
T
Isolate StagesIsolate Stages
P
P
F
Sample
TC
HeaterHeater
L
RecirculationRecirculation
DrainDrain
5m5m
CFCF
DP
SS/PlasticSS/Plastic
CleaningCleaning
PumpPump
StrainerStrainer
CleaningCleaning
SolutionSolution
ReturnReturnPermeate ReturnPermeate Return
PermeatePermeate
SupplySupply
T
Isolate StagesIsolate Stages
P
P
F
Sample
TC
HeaterHeater
L
TCTC
HeaterHeater
L
RecirculationRecirculation
DrainDrain

116. Cleaning
• Do Not Exceed Mftr. Specs!
– pH
– Pressure Drop
– Temperature
– Flow Rate

117. 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)

118. Cleaning
• Return permeate & concentrate to tank
• Make as little permeate as possible
(Open concentrate valve wide open)
• Pump Size is critical

119. How To Choose a Chemical Cleaner
• Cleaner Selected for:
– Membrane Type
– Characteristics of Foulant
– Convenience
• Optimum Service
• Acid Cleaners First
• Followed by Caustic Cleaners

120. Cleaning Solutions

121. Things to Remember
• Start planning to clean when:
– Differential Pressure changes 10%
– NPF changes 10%
– Salt Rejection changes 10%

122. 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!

123. Keep Good Records

124. Membrane Cleaning Frequency
Cleaning Frequency
Quarterly or less
Every 1-3 months
Every month or more
Adequacy Estimate
Adequate
Marginal
Not adequate

125. Clean Until
• pH Doesn’t Change
• Color Doesn’t Change
• Flow Doesn’t Change
• Pressure Doesn’t Change

126. 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

127. Benefits of Maintaining an RO
• Reduced operating costs
• Reduced maintenance costs
• Reduced downtime
• Extended membrane life
• Improved water quality and output

128. 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

129. 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

130. 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)