Water Filtration technologies

Filtration Techniques

Filtration - OverviewFiltration = technique used for the separation of solids from liquids by interposing a filter, through which only the liquid can

pass, oversize solids are retained.

According to the size of contaminants to be retained, the process for separation and the filter pore size will be defined.

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Water Monovalent

Ion

Multivalent

Ion

Viruses Bacteria Suspended

solids

Microfiltration

Water Monovalent

Ion

Multivalent

Ion

Viruses Bacteria Suspended

solids

Ultrafiltration

Water Monovalent

Ion

Multivalent

Ion

Viruses Bacteria Suspended

solids

Nanofiltration

Water Monovalent

Ion

Multivalent

Ion

Viruses Bacteria Suspended

solids

Reverse

Osmosis

Filtration Techniques - Agenda

Macrofiltration or particle filtration

Microfiltration (MF)

Ultrafiltration (UF)

Reverse Osmosis (RO)

Macrofiltration

Macrofiltration

= particle filtration

Retention of particles which are of a visible size.

Filter porosity is usually > 10 µm

E.g. Backwashable Sand filters used as pretreatment

at customers’ with poor feed water quality

Microfiltration

Hepatitis

Virus

0.02 µm

Microfiltration - Definition

Microfiltration = removal of contaminants by size filtration, typically in the field

between 0.1 µm and 10 µm.

Use in lab water purification for removal of particulates & bacteria

2 types of microfilters: depth & screen filters

0.01 µm 0.1 µm 1 µm 10 µm

Blood cell

5 µmBacteria

0.22 - 2 µm

UF FiltrationMicrofiltration

Screen Filters

Typically thin, made of a solid

material pierced of similar holes

Example: a fish net

Depth Filters & Screen Filters

Depth Filters

Usually thick, made of fibers

assembled together.

Example: fibers in cotton

Microfilters – Retention Modes

Depth Filters Screen Filters

Screen Filters

Retention on filter surface

Low Capacity

100% retention (of contaminants

larger than pore size)

Use as a polisher at the end of a

purification process

Depth Filters

Retention inside filter depth

High capacity

Good retention

Use as a pre-treatment, at

the beginning of a purification

process

Depth Filters vs Screen Filters

Examples

Filter FCFGlass Fiber Filter

Depth Filters Screen Filters

Hydrophilic & Hydrophobic Membranes

Filters used to purify water “hydrophilic” filters (= they “like” water)

“Hydrophobic” membrane filters (= they “fear” water)

Usage for gas filtration.

Hydrophobic Filters

Hydrophobic screen

filter

Degasser

In-line with purified water flow and

connected to a vacuum line

Vent Filters

Connected to the tank for…

air exit during filling-up by system

air entrance &filtration while water

is being taken outHydrophobic hollow fibers

External part = water

compartment

Inside part = vacuum

compartment

Vacuum force attracts

dissolved gasses out of

water through the filter

vacuum

Degassed

Water

One more thing…

Your colleagues working with Life

Science are specialized in

filtration…

… Don’t hesitate to ask them

your “filter questions” even

you are from Waste Water

Department

Ultrafiltration

UF Principle

Definition

Ultrafiltration = similar to standard filtration technique with membrane pores

of a suitable size to remove molecules or viruses.

membranes are characterized by their Nominal Molecular

Weight Limit (NMWL) = the weight of the smallest molecules retained.

Principle

Pressure required

High molecular weight solutes retained

(based on the filter NMWL)

Lower molecular weight molecules (

Reverse Osmosis

Osmosis Phenomenon

Description: physical movement of a solvent (water) through a semi-permeable

membrane based on a difference in chemical potential.

water

Table salt

Even chemical

potentialDifferent chemical

potential Osmosis

Pressure

Water movement by diffusion of water molecules

through semi-permeable membrane

Reverse Osmosis

diffusionThe greater the

pressure the

more rapid the

diffusion of

water

Reverse Osmosis vs Filtration

Similar to filtration treatment process BUT…

Key differences:

Filtration main removal mechanism is based on size exclusion due to the pore size of the filter

Reverse osmosis involves a diffusive mechanism separation efficiency depends on:

contaminant concentration,

pressure

water flow rate.

RO requires :

a semi-permeable membrane (no visible pores)

high pressure to revert the natural osmosis flow & increase water molecule diffusion, for purification efficiency

Pressurized

Feed Water

SEM Picture of an

RO membrane cut through

Porous

Support

Active layer

(1 µm - polyamide)

Reverse Osmosis – Principle

RO membrane efficiency needs sufficient pressure (> 5 bar):

Inorganic ions rejection: 95% - 99%, if weakly ionized (e.g. Na+ ~95%) or strongly ionized

(e.g. Fe3+ ~99%)

Particles, bacteria & organic molecules (MW > 200Da): > 99%

RO membrane

Pressurized

Feed WaterPermeate

Reje

ct

Ions 95% - 99%Organic mol. +

Particulates +

Bacteria > 99%

RO cartridge

Type 3 water

Reverse Osmosis – Tangential Flow

To help limiting contaminant accumulation on RO membrane

tangential feed water flow to take contaminants away

RO membrane

Pressurized

Feed WaterPermeate

Reje

ct

RO cartridge

Type 3 water

Reverse Osmosis – Tangential Flow

Membrane

Permeate

Reject

Feed Water

Spiral RO Cartridge and Flo-Clear Filter

Membrane rinsing during 2h-4h to avoid permeate contamination

Feed Water

Inlet

Water Reject

Permeate

Outlet

Conductivity

Cell (feed)

RO Cartridge

in HousingSpiral RO

membrane

Feed Water -

tangential flow

PermeateReject

Spiral RO

Membrane

MILLIPORE

ReverseOsmosis Element

Part # PF05099Rev 1196

RO

Cartridge

MILLIPORE

ReverseOsmosis Element

Part # PF05099Rev 1196

Sanitization Port

MILLIPORE

ReverseOsmosis Element

Part # PF05099Rev 1196

RO cartridge

RO Efficiency – Ionic Rejection

RO efficiency is estimated by tracking its efficiency in rejecting ions :

Conductivity measured upstream and downstream of the RO (at 25°C)

Calculation of % of feed (-) permeate conductivities = “% ionic rejection”

Ionic rejection increases with feed pressure increase, up to ~5 bar max ion rejection

Clean Water

P= min 5 barPermeate

Reje

ct

Ions 95% - 99%

Cleaned standard

water

RO Permeate Flow

Permeate flow F proportional to feed pressure P: if P1 > P2 F1 > F2

Permeate flow F increases with feed temperature T: if T1 > T2 F1 > F2

Pressurized

Feed Water

Reje

ct

RO cartridge

F1 > F2P1 > P2

T1 > T2

Flow restriction

Permeate

Flowwaterdiffusion

Note: Salt diffusion ↑ with temperature % ion rejection↓ when temp↑

F1 > F2

42 L/h

RO RecoveryRO recovery

Amount of feed water required to produce a volume of purified water

Recovery = 100 x (permeate flow / feed water flow )

Pressurized

Feed WaterPermeate

Reje

ct

RO cartridge

RO Recovery = 100 x (3) = 6.6 %

(45)

RO RecoveryOptimized RO recovery by addition of a” recovery loop” part of RO reject is

diverted and reused to feed the RO membrane

lower feed water quality = more challenging conditions

Pressurized

Feed Water

Reje

ct

Permeate

Recovery Loop

RO cartridge

Water Waste – Improving Recovery

2,400 galons/h 400 galons/h

2,000 galons/h

If no recirculation System Recovery = Membrane recovery

(for 1 membrane)

System Recovery 10.6 %

Membrane recovery 10.6 %

RO RecoveryOptimized RO recovery by addition of a” recovery loop” part of RO reject is

diverted and reused to feed the RO membrane

Benefits: Water savings, Reduction on running costs

Lower cleaned water quality = more challenging conditions

Pressurized

partial

cleaned

Water

Reje

ct

Permeate

Recovery Loop

RO cartridge

RO & Storage

Still, RO purification is a slow process

permeate storage (for enough water available in one go)

Pressurized

Feed Water

Reje

ct

Permeate

Recovery Loop

Storage

TankRO cartridge

Reverse Osmosis Life Time

RO Membrane Life Time

RO membrane life time decreases…

with time % ionic rejection slowly goes down.

with the impact of feed water quality :

Hardness scale deposit on its surface

Chlorine chemical attack piercing holes

Organic Molecules fouling by accumulation on its surface

Particulates (& Colloids) fouling and scratches

ionic rejection reduction -/+ flow variations

Feed Water Quality Impact

Feed Water Contaminants Effect on RO membrane Specification Prevention / Solution

Particles

Colloids (colloidal Silica)

Fouling - Mechanical damage (scratches if

hard)

coagulation Coating

SDI

RO Membrane Troubleshooting

Issue : RO ionic rejection and / or flow rate decrease prematurely.

If Ionic rejection is

RO Membrane ProtectionCleaning Agents

Flo-Clear

ROClean -BWarning

Flo-Clear

ROClean -AWarning

ZWACID012 ZWBASE012 ZWCL01F50Ammonium Bifluoride

RO Clean A - Acid

Trisodium Phosphate

RO Clean B - Base

Sodium Dichloroisocyanurate

Sodium Bicarbonate

Adipic Acid

Pouch (6g /unit – 12 units/ box) Pill ( 5g/unit-

45 units/ box)

Non Woven

Polyethylene

Tissue

Encapsulated

Powder

RO Clean A RO Clean B Chlorine tablets

Chlorine & Chloramines

Chlorine is the enemy of Polyamide RO membranes as chlorine oxidizes the polyamide structure creating “holes

“in the membrane. This is an irreversible procedure, affecting the performance of the RO cartridge in terms of rejection.

Effect of chlorine in water:

Chlorine reacts with water to for hypochlorous acid

CL2 + H20 HOCl- + H+ +Cl-

Formation of Hypochlorous acid (H2OCl) is favored by low pH. The hypochlorous acid dissociates into hypochlorite ion at a higher

pH.

HOCl- OCl- +H+

Hypochlorous acid has very strong bactericidal properties. It can penetrate the cell walls of bacteria and disrupt the cell.

Hypochlorite ions are 100 times more oxidative than hypochlorous acid. High pH favors oxidation of RO cartridge with chlorine.

High pH is not favorable for killing bacteria. Low pH is more favorable for killing bacteria. Low pH is less favorable for oxidization

of RO cartridges.

Chlorine is introduced into water as Sodium hypochlorite. (NaOCl)

NaOCl + H20 - NaOH + HOCl

As the pH increases, more and more hypochlorite ions are formed. At pH 7.5 the amount of hypochlorous acid and hypochlorite

ions are equal. At a pH of 10, hypochlorite ions are most abundant.

Hence it is advised to sanitize the RO membrane at a pH around 7. This ensures enough hypochlorous acid for disinfection, but

not too much hypochlorite ions, which are destructive to the Polyamide membrane.

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RO Membrane Protection

To save RO membrane life time, protection is added into our systems:

System Flush

= High flow of feed water going over RO membrane surface

to take contaminants away and limit fouling

Sanitization

= to degrade the biofilm growing & gradually fouling RO surface

Flo-Clear pre-treatment pack upstream the RO membrane

= combination of 3 purification technologies

to remove chlorine & organics

to prevent scaling

to remove particulates & colloids

RO : Flush vs Rinse

Flush

RO : Flush vs Rinse

Rinse

RO : Flush vs Rinse

Process

EDI or Tank

Reverse Osmosis Summary

Benefits

Up to 99% of water contaminants removed in single pass through the RO cartridge

Easy tracking of efficiency by % ionic rejection monitoring

Minimum maintenance

Limitations

Type 3 water produce

RO membrane ages and is sensitive to main

water contaminants *(1) it is a consumable

Water waste * (2)

Functioning dependent on feed temperature

and pressure * (3)

Storage required due to slow purification

process * (4)

* Limitations minimized thanks to our system improved design :

RO (1) + recovery loop (2) + booster pump (3)

+ optimized tanks (4)

Conclusion

Filtration techniques:

Microfiltration (depth & screen filtrations particulates & bacteria)

Ultrafiltration (Filter Package pyrogen-free & nuclease-free water)

Reverse Osmosis (complete technology removing up to 99% of all

contaminants)

Ion exchange

Agenda

Ion-exchange theory

Definitions

Bead structure

Ion-exchange operation

Binding Strength

Limitations

Ion-exchange usage

Service DI

Single use

EDI

Softening

Definitions

Ion-exchange = deionization (DI) technique

removal of charged compounds only!

performed by ion-exchange resins

Ion-exchange resin (= DI resins) = charged plastic beads

Separation based on ionic bonding (attraction of opposite charges):

Anion-exchange resins

remove anions (negatively charged)

resin is positively charged

Cation-exchange resins

remove cations (positively charged)

resin is negatively charged

Cation-Exchange Bead – Structure

Anion-exchange beads:

(+) fixed cation

(-) counter ion

Binding sites mainly inside

Porous beads

water needs to travel inside to be well-purified

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Plastic Structure

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Fixed anion (-)

Counter ion (+)

Hydrating Water

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Cation-Exchange Bead – Operation

+

-Plastic Structure

Plastic Structure

+

Fixed anion

Counter cation

Hydrating Water

+

+ Contaminating cation

Binding Strength

Calcium Ca2+

Copper Cu2+

Magnesium Mg2+

Potassium K+

Ammonia NH4+

Sodium Na+

Hydrogen H+

Sulfate SO42-

Nitrate NO3-

Chloride Cl-

Bicarbonate HCO3-

Hydroxyl OH-

Strong

Binding

Weak

Binding

• Not all ions bind to the resin

fixed ions with the same

strength.

• Their ionic strength (linked

to the number of charges)

contributes to it.

• Hydrogen & hydroxyl ions

bind with the lowest strength

So they usually are the…

Counter ions

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Cation & Anion Exchangers: Summary

Mg2+

+-

Fixed cation (+)

Counter ion (OH-)

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Fixed anion (-)Counter ion (H+)

-

CO32-

2 OH- + 2 H+ 2 H2O

Ion-Exchange Process EndExhausted resin Resin “fouling”

All binding sites occupied by

contaminating ions.

expected end of resin life

Binding sites still available inside but

surface coating by other contaminants

blocks the access.

to be avoided with good enough feed

Ion-Exchange Usage

D.I. Resin Bead Usage

Mixed bed

DI resin in a

container

Contaminated water

flow through container

Gradual ion removal by exchange vs the

counter ion: Na+ vs H+ / Cl- vs OH-

H2O

Released

H+

+ OH-

Na+Cl-

Service DI Mixed Bed Regeneration

Tap Water

DeIonized

Tap Water

Exhausted resins

collected & returned

to the plant for

regeneration

Regeneration:

1. Anionic & cationic resins separation (different

densities) in big tanks

2. Resin immersion in strong acid or strong

base solution to force counter ion back

3. Bottles are refilled with regenerated resin (-/+

fresh resin)

4. Regenerated bottles back at customers’

where exhausted ones are collected

Service DI: Benefits & Limitations

Benefits:

Low capital cost

High instant flow rate(no reservoir)

Good ionic quality:R > 10 MΩ.cm @ 25°C

Limitations:

Operating cost + transportation

Still contaminated product water:

tap water particulates, organic molecules & bacteria

Additional contaminants due to regeneration:

broken beads (fines), organic compounds & ions from other sources

Conclusion:

Process producing DI water

Process inadequate to produce water (even less

Type 1)

Service DI water still contaminated with

organics, colloids and particulates

shorten life time water system consumables.

Single Use Mixed Bed Packs

Single use mixed bed consumables

contain “virgin” mixed bed ion-

exchange resin of high quality

Resin used in

Disposable

Benefits

producing very high water quality (high resistivity)

high capacity and longer life cartridges

Single use = safety : no risk related to regeneration

Limitation:

good feed water quality required to avoid too high operating costs.

water

More cleaned water

ElectroDeIonization - EDI

EDI Technology – Principle

-+ A C A C

Allows passage of Anions

Allows passage of Cations

EDI Technology – Principle

A C A C -+

RO Feed Water

EDI Technology – Principle

A C A C

Na+

Na+

H+

H+

OH-

OH-Cl- Na+

-+

Waste Type 2 water

Na+

Cl-

Cl-

Cl-

Cl-

Na+

RO Feed Water

Cl- Na+

Conductive

Carbon

Beads

EDI Technology – Principle

A C A C

Na+

Na+

H+

H+

OH-

OH-Cl- Na+

-+

Waste Cleaned

water

Na+

Cl-

Cl-

Cl-

Cl-

Na+

RO Feed Water

Cl- Na+

Scaling due to high pH at cathode

11

10

9

8

7

surface

pH

standard flat

cathode

cathode surface

OH-

OH-

OH- Generated at Cathode

High Local Surface pH

High Scale Potential

SOFTENER NEEDED

Most Locations of Stations

Carbon Beads: less steep pH gradient

11

10

9

8

7

surface

pH

standard flat

cathode

carbon bead

cathode

cathode surface

High Surface

Area Cathode =

Generation of

hydroxyls in a

larger volume

Reduces Local Surface pH

Reduces Scale Potential

NO SOFTENER NEEDED

Activated Carbon

What is Activated Carbon ?Activated Carbon (AC) = porous material prepared from organic material heated in

specific conditions, with a high developed surface

2 types of AC:

Natural AC Synthetic AC

Polystyrene

Beads

Coconut

shell

Controlled

pyrolysis

Carbonization

Synthetic AC – Operation

Bead pores filled with water large contact surface with contaminants

Organic molecules link to binding sites by weak Van der Waals forces

UV Light

Introduction

UV light = wavelength from 100nm to 400nm

UV light properties are used to help purifying water

1. Bacteria Destruction

2. Oxidation of organic molecules

UV light produced by lamp containing small amount of mercury

Exited mercury atoms emit relevant UV wavelengths

UV – C

100 -280 nm

UV – B

280 – 315 nm

UV – A

315 -400 nm

VisibleUltraVioletX-RaysGamma

Rays

Infra

RedRadio

↑wavelength↓wavelengthUV Light

Bacteria Destruction

254nm

100%

80%

60%

40%

20%

0%240 260 280 300 320

Relative

Bactericidal

Effect

Wavelength (nm)

UV 254 nm

DNA

Photo-oxidation process using a dual wavelength UV lamp

Hydroxyl radical

Housing

Oxidized H2O

Water feed

power

supply

mercury vapor

185 / 254 nm lamp

(18 Watts)

optical quartz

sleeve

Organic carbon

Inorganic carbon

(CO2, HCO3-)

Organic Molecule Photo-Oxidation

Photo-oxidation Process:

Water irradiation with UV 185nm + 254nm free radical compounds

Free radicals attack of the organic molecules organics oxidation

Neutral

organic molecule

Short term effect:

Apparition of charges on

the organic molecule

UV 185 nm +

254 nm

Charged

organic molecule

UV 185 nm +

254 nm

CO2 H2O

+

Long term effect:

Fully degraded organic

molecule by photo-oxidation

UV Action on Organic Contaminants

3 O2

2 O3

2 O2

+2 O *

H O2

UV (185 )

UV (254)

4 OH *

UV (254)

H O2

2 O2

+

2 H O 2 2

CH OH3

+ 2 OH *

HCHO + 2 H O2

HCOOH + H O2

2 OH *

2 OH *

+CO2 2 H O2

Organic Molecule Photo-Oxidation

Long term effect: long enough contact time required between organic molecules & UV

light for full degradation

not often reached due to flow rate limiting the contact time

Short term effect: charged organics collected on ion-exchange resins downstream

from UV lamp on-line main purification way.

Mixed Bed

Ion-Exchange Resin

Neutral

Organic molecule

Charged

organic molecule

H2O

UV 185 nm +

254 nm

CO2

+

Conclusion

UV purification technology

254nm bactericidal effect

185nm + 254nm organic molecule photo-oxidation

Activated Carbon purification technology

Natural AC reduction of chlorine level

Synthetic AC adsorption of organic traces

Vacuum Degassing

Gas Content

Common Dissolved Gases in water :

Oxygen (O2) / Nitrogen (N2) / Carbon Dioxide (CO2)

Temperature Effect : dissolved gas solubility increases as temperature decreases :

Temperature Gas solubility

Pressure Effect : dissolved gas solubility increases as gas pressure increase above water.

Pressure Gas solubility

water temperature increase spontaneous degassing

vacuum (= reverse pressure) degases water

Dissolved Gas Removal

No chemical reaction with water :

Gas easy removal with physical means (eg. vacuum) – as for oxygen and nitrogen.

Chemically react with water to some extent :

Gases like CO2 , NH3 and H2S

Difficult to remove with vacuum after interaction.

Usually removed with chemical means. Example: chlorine reduction by activated carbon.

Water without dissolved gases does not stay degassed very long.

CO2 will dissolve in ultrapure water very quickly and form HCO32-

and H+ ions.

Aqueous degassing principle

Vacuum*

Degasser *generated either by a dual head pump or an reductor on the RO

reject

GENERAL CONCLUSION

Contaminants

IONS

ORGANICS

PARTICLES

& COLLOIDS

BACTERIA

& VIRUSES

GASES

DI RO UF MF AC UV

converts

organic

molecules

into CO2 or

charged

molecules

Purification Technologies

Not removed at all Totally removed

Still

Thank you!