reverse osmosis module

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



•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 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


Change in Pressure Drop

Higher

Biofouling

Scaling

Inorganic Fouling

Higher Flow Rates

Lower Feed Temp.

Lower

Lower Flow Rates

Higher Feed Temp.


Change in Feed Pressure

Higher

Scaling

Pluggage

Higher Feed TDS

Lower Feed Temp.

Improper Valving

Lower

Higher Feed Temp.

Lower Feed TDS

Membrane Damage


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)

reverse osmosis module

Engineering