Membrane

Technology: From

Manufacture to

ProductionMay 2018

Osmosis

Graphic pulled from https://earthobservatory.nasa.gov/Features/Water/page2.php

• Surface Waters

• Ground Water

• Seawater

• Lakes

• Reclaimed water

• Others

Water Sources

• Salts

• Gases

• Chemicals

• Silica

• Organics/Tannins/Humic Acids

• Algae, etc

• Particulate-suspended

Constituents found in Water

Common Methods of

Pretreatment

5

Booster

Pump

Dual-Media

Filter

Cartridge

Filter

RO

Pressure

Pump

RO Membrane

100 gpm

3:2 Array

Chlorine

Injection

SBS

Injection

Ferric

Chloride

Cationic

Polymer

Acid

Injection

Antiscalant

Injection

Coagulation Tank

Lime

Sulfuric

Acid

Injection Cartridge

Filter

UV Light

Particulate

6

• Target Quality for RO Membrane

• Turbidity < 0.2 NTU

• SDI < 3 (ideal)

• Particle Counts <100 per 1ml (2-50 micron)

• Cations

– Calcium - Ca

– Magnesium - Mg

– Sodium - Na

– Potassium - K

– Iron - Fe

– Manganese - Mn

– Aluminum - Al

– Barium - Ba

– Strontium - Sr

• Anions

– Alkalinity - HCO3

– Sulfate - SO4

– Chloride - Cl

– Fluoride - F

– Nitrate - NO3

– Sulfate - SO4

– Phosphate - PO4

– Silica - SiO2

Complete Water Analysis

The Filtration Spectrum

Membrane Construction

Graphic pulled from https://membranes.com

Composite Membrane

Polyamide membrane layer0.2 to 5.0 micron thick

Permeate carriernonwoven polyester500 micron thick

Polysulphone support layer50 micron thick

Crossflow Filtration

Feed Water Concentrate

Permeate

Performance

12

-70 MGD; Municipal Wastewater Recycle

13

Crossflow

• Salt Rejection:

– the ability of the membrane to hinder certain elements from passing through.

– Calculation:

% rejection =

{1 - (permeate TDS/feed TDS)} 100

– Example: {1- (20/1000)} 100 = 98%

Terms

d TDS)} 100

– Example: {1- (20/1000)} 100 = 98%

Expectations

• Percent Recovery

– The percent of permeate water that is recovered from the feed water

– Calculation:

• (Permeate GPM/Feed GPM) (100) = % Recovery

– Example:

• (75 GPM/100 GPM) (100) = 75% Recovery

Terms

Concentration Factor

50% Recovery2x Concentration

75% Recovery4x Concentration

90% Recovery10x Concentration

Feed Water

Product Water

Concentrate Water

1000 PPM

2000 PPM4000 PPM10000 PPM

Terms

Concentration Factor @ Feed Water TDS of 150

% Recovery Concentration Factor Concentrate TDS

50 2.0 300

55 2.2 330

60 2.5 375

65 2.9 435

70 3.3 495

75 4.0 600

80 5.0 750

85 6.7 1005

90 10.0 1500

95 20.0 3000

Concentration Factor = 1/(1-Recovery)

Terms

Keys to Membrane Operation

• Pretreatment, pretreatment, pretreatment

• System Design

• Properly Clean Membranes

• Record Keeping

d TDS)} 100

– Example: {1- (20/1000)} 100 = 98%

Expectations

Expectations

Damage by Oxidizers

Cause

• Chlorine

• Peroxide

• Permanganate

• pH hydrolysis

Symptoms

• Loss of rejection in the first stage (array)

• Can be slow or instantaneous loss of rejection depending on the concentration

Dyed membrane surface showing chlorine damage

Chlorine Damage

• Chlorine Damage is irreversible

• Indications of chlorine damage (after normalized)

– High permeate flow at lower pressure

– High permeate conductivity/low rejection

24

Chlorine Damage

• Two ways to verify chlorine on site

– Wet test method

• Strips

• Hach DPD method

– ORP

• Establish baseline and then adjust chemicals for baseline +10%

25

Causes of Fouling

• Colloidal Fouling

• Scale

• Chemical Fouling

• Biological Fouling

• Inadequate Membrane Cleaning

– Procedures or chemistry selection or both

Feed WaterConcentrate

Product

Colloidal Fouling

Colloidal and silt

particles are termed

“particulates” (e.g.

clays, colloidal silica,

rust particles and

bacteria) and are

present in virtually

all feedwaters.

Indicators of colloidal

fouling would be:

•High pressure differential

on first array.

•Membrane telescoping.

•High turbidity in feedwater.

•Surface water supply.

Causes – Colloidal

• Media filters not working properly

• Turbid surface waters

• High suspended solids

• Inadequate pretreatment

Symptoms - Colloidal

Fouling• High pressure differential on elements

• Rapid fouling of the first stage

Options for Scale Control

• Acid Injection

• Antiscalant Injection

• Ion Exchange Softener

• Reduce Recovery Rate

• Sometimes Nothing

Scale Formation

Scale will often

be seen on the

downstream end

of the last

membrane in the

system or on the

inside of the last

pressure vessel.

Scale can be abrasive

and scratch the

membrane surface

causing permanent

damage.

Feed WaterConcentrate

Product

• Scaling occurs when soluble minerals become concentrated in the RO and exceed saturation limits.

– Gather a complete water analysis

– Evaluate the scaling potential of the feedwater

– Ensure that the scaling potential is or can be brought under control

Scale Formation

Most Common Scales Effecting RO

• Calcium Carbonate - CaCO3

• Calcium Sulfate - CaSO4

• Barium Sulfate - BaSO4

• Iron - Fe+2

• Silica - SiO2

• Calcium Phosphate - Ca3(PO4)2????

Calcium Carbonate

34

Calcium Phosphate

35

36

CaPO4 & CaCO3

37

Calcium Carbonate

Calcium Carbonate Scale

Ca CO3

Ca CO3

CO3

CO3

CO3

CO3

CaCa

CaCa

Ca

Common Scale Control Methods

• Antiscalant Addition

– Antiscalants work through threshold inhibition, crystal modification, and dispersion to keep supersaturated minerals from scaling the membranes.

– Dispersion capability further reduces colloidal fouling tendencies.

Mechanisms of Antiscalants

• Threshold Inhibition

– The ability of an antiscalant to keep supersaturated solutions of sparingly soluble salts in solution.

– When crystals begin to form, negative charges on the antiscalant molecule attack the positive charges on the scale, interrupting the growth of the crystal.

Antiscalant Notes

• Typical antiscalant dosages are 1-4 ppm

• Antiscalants only delay scale formation

• Because of this, Post Flushing an RO after shutdown is essential

• Inject antiscalant/dispersant after pretreatment equipment and before cartridge filter housing.

Feed WaterConcentrate

Product

Chemical Fouling

When incompatible

chemistries are

mixed together

there will be a

measurable

increase in

turbidity.

Incompatible

chemistry can

cause a sticky

foulant and

plug front end

membranes.

Feed WaterConcentrate

Product

Biological Fouling

Slime in Vessels

or Pipe.

Noticeable odor.

High Pressure

Differential in

1st Array

What is Data Normalization?

Normalization is a comparison of the actual performance to a given reference performance while the influences of

operating parameters are taken into account. The reference performance may be the designed performance or the

measured initial performance.

Plant performance normalization is strongly recommended, because it allows an early identification of potential

problems (e.g. scaling or fouling) when the normalized data are recorded daily. Corrective measures are much more

effective when taken early.

• Note: Reference from Dow Technical Manual

Minimum Data Required for Normalization:

Pressures (psig)Feed

Concentrate

Permeate

Flows (gpm)Permeate

Concentrate

Conductivity/TDSFeed

Permeate

Temperature

Technical Support

46

Data Logging

Is the RO Fouling?

What happens to Normalized flow when the pressure goes up and the temperature goes down?

What does the data tell me?What happens to Normalized flow when the pressure goes

up and the temperature goes down?

Is the RO Fouling?What happens to normalized flow when the temperature goes up and the pressure stays the same?

What does it tell me?What happens to normalized flow when the temperature goes

up and the pressure stays the same?

Clean in Time

Clean When Needed

Membrane Cleaning

CleaningTank

200 gall min.

5u Cartridge Filter

36 gallons

36 gallons

36 gallons

36 gallons

36 gallons

36 gallons

144 gallonsFirst Array

72 gallonsSecond Array

ConcentrateConcentrate

Vessel Flow Rate

Clean Each vessel at the proper flow rate no matter how many membrane elements are in the vessel

Feed WaterConcentrate

Product1

2

3

5

4

Cleaning Flow - 40 gpm x 3 = 120 gpm

Cleaning Flow - 40 gpm x 2 = 80 gpm

Membrane Cleaning

A good membrane clean involves selecting the proper chemistry and using the proper mechanical approach.

Saving Membranes

NormalizedPermeateFlow Rate

Time

Cleaning after 10-15% decline

NormalizedPermeateFlow Rate

Time

Improper Cleaning Maintenance

Cleaning after > 15% decline

Cleaning after a10-15% declinemaximizes ROperformance

Waiting too longto clean reduces RO performance

Proper Cleaning Maintenance

O&M Costs

57

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