Membranes for Posting

8/20/2019 Membranes for Posting

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Physical, chemical,

and/or electrical

driving force

Permeate

Solute or particle

rejection

Feed or concentrate

Semi-permeable (selective) membrane

Accumulated, rejected material,

migrating back to bulk solution



c c ( x )

c p( x )Feed

(Qf , c f )

Permeate

(Q p, c p,out )

Concentrate (Qc , c c ,out ),

Retentate, Rejectate



Membrane

Applications in

Drinking Water

Treatment



Pressure-Driven Membrane

Processes

• Separate by size and chemistry

• Concentration, Porosity Effects



OTHE D!"!#$ %OCES

• Carge !radient ("lectrodial#sis)

• Concentration !radient (Dial#sis)

• Temperat$re !radient (Termoosmosis)



PRESSUREGRADIENT

POREDIAMETER

MEM&'#E

DES!$#'T!O#

REMOVALEFFICIENCY



RelativeSizes

SeparationProcess

Molecular Weight(approx..)

Size, MicronsIonic Range

0.001

(nanometer)

Molecular Range

0.01

Macro

Molecular Range

0.1 1.0

Micro

Particle Range

10 100

Macro Particle Range

1000

100 1,000 100,000 00,000

!acteriaVirusesDissolved Salts

(ions)"lgae

#la$s Silt

"s%estos

&i%ers

Cysts San'

#onventional &iltration

(granular me'ia)

Organics (e.g., Color , NOM, SOCs)

Microiltration

ltrailtration

*ano

iltration

Reverse

+smosis

Membrane %eparations &or Application to Drinking

Water Treatment



Membrane

cross section

(%)



The Two Meanings of Filtration:

2. Porous Membrane Filtration

(µ

m



1 µm

PM"-M"%P&+M" la$er

Microporous Pol$sulone Support

' PDMA"MA*+ PFMA Tin*&ilm Composite

-F Membrane (Pol#s$l&one %$pport .a#er)



Membrane !eometr#

Spiral Woun'

*&/R+

ollo &i%ers

M&/&





Tubu)ar E)ements



Spira) E)ements

(a)





!#O$'#!C S*#THET!CS

Ceramics

$)ass

Meta))ic

• Excellent thermal stability

• Withstands chemical attack



P+'TE '#D %'ME



T/o MF01F Con&ig$rations

• "ncased

membrane

s#stem

• %$bmergedmembrane

s#stem

Pump supp)ies positive pressure to PSH ater

throu.h membrane media/

%eed

0ater

%i)trate

Pump

Pressure

"esse)1s2

Membrane

Pump suction P++S ater

throu.h membrane media/

%eed

0ater

%i)trate

Pump

Open

Tan3

Membrane



Permeate

2F

Air

Ra/ Water P$mp

3*43 psi

Wasting

!mmersed Membranes ith

$ent)e Crossf)o





-F 5 R %cottsdale

Water Camp$s



CA%CAD" %6%T"M

RETENTATE

PERMEATE

FEED



PERMEATEFEED

RETENTATE

Qf

Cf

A

QP

CPQR

CR

TMP = “Transmembrane pressure (difference)”

Flux (“LMH” or “GFD”) = QQ p p / A / A

(Conaminan) !e"ecion (#) = 1 − C C p p /C /C f f

!eco$er% (#) = Q p /Qf



Membrane

Geometry

Aro!imate "ac#ing

Density (m$%m&)

#apillar$ 0002000

Spiral oun' 3004000

ollo i%er 10004000

&lat (plate an'rame)

40000

5u%ular 100600

Membrane Process Transmembrane Pressure, ∆P

tot (kPa)

System Recovery (7)(a)

Microiltration 10 to 100 80 to 889

ltrailtration 0 to 600 2 to 89

*anoiltration 400 to 100 3 to 809

Reverse +smosis 00 to 2000 :0 to 80

(a) De&ined as te ratio o& ermeate &lo/ rate to &eed &lo/ rate



L P gh ρ =

( )

4

M&

6 4

;g ms1,000 Pa 1.0

Pa1.6 m

;g m1000 8.21

m s L

P h

g ρ

÷ = = = ÷ ÷

( )4

:

R+

6 4

;g ms<.x10 Pa 1.0

Pa<8 m

;g m1000 8.21

m s L

P h

g ρ

÷ = = =

÷ ÷

E4amp)e/ Wat eigt /o$ld a col$mn o& /ater a7e to be to e8ert a

press$re e9$al to 4: kPa; ': kPa;

So)ution/ From &l$id mecanics<

Tere&ore<



E4amp)e/ Wat is te a7erage 7elocit# o& sol$tion to/ard a

membrane, i& te &l$8 is : .M2;

6

4

= 1 m cm cm

0 100 .0m h 1000 = m hV J

= = ÷ ÷



%)o Throu.h Porous Membranes

4

4 f

L vh f

D g =

%or +aminar %)o<

:</Re f =

f P gh ρ ∆ =

Darcy-0eisbach E5n<

%or Steady %)o

Throu.h a Pore<Ha.en-Poiseui))e E5n<

4

2

pore

pore

r P J

L µ

∆=

4

2

pores pore

mem

mem mem

A r P J

A µξδ

∆=




,riving &orce

&lux

P

J ∆= =Resistance 13.6m7-s2<

P

J µ µ ∆= =R

RMembrane esistance 1m−1

<

Process Typical Volumetric

Flux , ('%m$)

Typical Membrane

Resistance, Rm (m−*)

Micro+iltration *$- *!*** *!**$

/ltra+iltration &*- *!**$ *!**&

Nano+iltration $- *!**& *!**0

1everse osmosis -0 -!**& *!**-




/ mem

mem

P

J

δ δ

∆=Resistivity8

1

Resistivit$ /

V

V

mem

J

k P δ = = ∆Permeabi)ity for overa)) f)o<

/

i

i

mem

J

k P δ = ∆Permeabi)ity for individua)species<



(µ

m

Contaminant e9ection by Open

Pores 1C)ean Membrane2



A

Mem%rane

Pore

Contaminant e9ection by Open

Pores 1C)ean Membrane2

(=(

(=4

(=3

(=>

(='

(=:

(=+

(=?

(=@

(=A

4=(

(=( (=4 (=3 (=> (=' (=: (=+ (=? (=@ (=A 4=(

Partic)e-to-Pore Diameter atio, i

P a r t i c ) e e 9 e c t i o

n ,

R i

%)at

Parabo)ic

Modified

parabo)ic

e)ocity Profi)e at Entrance

!ncreasin. drivin. force increases f)u4 of both ater and

contaminants/ So, re9ection of a .iven type of partic)e by a

c)ean membrane is predicted to be independent of ∆P or J.



Membrane Fouling



Problems Caused by NOM

MembraneFouling

+

++

++# #++

+

+

+

#++

#+++

+

++#

++

+

+

+

+

+

DBPs+Cl2

Interferencew/ActivatedCarbon



-M Fo$ling o& an MF Membrane

Note: <3% Removal of NOM fromFeed

Gel Surface

Membrane

Gel Cross-Section

Membranesupport





2eated Al$min$m 8ide Particles (2APs)

')71SO:2;<#aOH pH =/>((>((> ooC, 7: hrsC, 7: hrs

Particle %iBe Range:

1.5∼20 µ.5∼20 µm, mean ?@m, mean ?@ µmmPoint o& ero Carge< pH =/=pH =/=

"T %$r&ace Area< ((A m((A m77 6. 6.

Al$min$m Content< ?7@B 1')1OH2?7@B 1')1OH2;;

•HH77O2O2



Transmembrane press$re /it 7ar#ing 2APs

s$r&ace loadings



DC Concentrations in Permeate



Progressi7e -M Deposition on te 2APs .a#er

"sp8 > +6m7 (,7>> +6m7 ;,A>> +6m7

:,=>> +6m7 =,>>> +6m7 =,>>> +6m7



%$mmar#< Per&ormance and Modeling

o& Poro$s Membranes

• %ol$tion &l$8 proportional to ∆P , in7ersel# proportional to resistance

• Resistance o& clean membrane can be estimated &rom basic &l$id

mecanics

• E& contaminant rejection is primaril# d$e to geometrical &actors, it is

e8pected to be insensiti7e to applied press$re and &l$8

• En practice, resistance o& acc$m$lated rejected species 9$ickl#

o7er/elms tat o& membrane (&o$ling)

• Fre9$ent back/asing red$ces, b$t does not eliminate &o$ling

• En drinking /ater s#stems treating s$r&ace /ater, -M is o&ten amajor &o$ling species, e7en to$g onl# a small &raction o& te -M

is rejected

• Approaces to red$ce &o$ling b# -M and oter species are te

&oc$s o& acti7e researc



Transport Throu.h 0ater-Se)ective,

Dense 1#on-Porous2 Membranes

0ith no∆

P , the concentration .radients drive ater toard the

feed and contaminants toard the permeate/

c w ,f ::=

=:::

::=:

=:: %ol$te, rejection

smosis o& /ater

Press$re pro&ile &or P e7er#/ere

c w , p

c s,f

c s, p



!ncreasin. pressure increases the effective concentration of any

species/ %or an increase of∆

P , the effective concentration is8

, exp ieff i i

V P c c

RT ∆= ÷

12 g/mol =0.012

1000 g/= mol!V = =

: 13.<x10 ;Pa!V

RT

− −=

't∆

P ;>>> 3Pa8 , exp 1.046ieff ! ! !V P c c c

RT ∆= = ÷

%or ater8

't 7@oC8

esu)t8 Even a )ar.e ∆P increases effective concentrations by

on)y a fe percent/



The pressure re5uired to brin. the effective concentration of

ater up to the concentration of pure ater 1and thereby stop

diffusion2 is the osmotic pressure, / Permeate is often

appro4imated as pure ater/ !n this e4amp)e, is a pressure that

increases c eff by ?(B/ #ote that c eff of the so)ute a)so increases by

?(B/

c w ,f

::=

=:::

::=:

=::

c w , p

%ol$te, rejection

smosis eliminated

c w,eff ,f

::=:

P

P π

=:+c s,f

c s, p

c s,eff ,f



'pp)yin. a ∆P F

causes ater to move in the opposite direction

from passive osmosis, hence is ca))ed reverse osmosis/ %or P

?;>>> 3Pa, c eff increases by ?;B, so8

c w ,f

::=

=:::

::=:

=::

c w , p

%ol$te, rejection

Re7erse osmosis

c w,eff ,f

:+=:

P

P G π

=:?

')thou.h increasin. ∆P causes the same percenta.e increase in

c eff for ater and so)ute, it has a much bi..er effect on∆

c eff for

ater than for so)ute/

c s,f

c s, p

c s,eff ,f



Permeate

Concentration increase due to solute rejection

and slow diffusion back to bulk solution

Concentration increase in bulk concentratedue to selective water removal



Permeate

Highest salt concentrations occur right next to

membrane, where precipitation (‘scaling’) ismost likely



Per&ormance and Modeling o& Dense

Membranes

• Water &l$8 occ$rs b# di&&$sion, and is Hproportional to ∆P −∆π ,beca$se canging ∆P as big e&&ect on ∆c w ,eff

• %ol$te &l$8 occ$rs b# di&&$sion, and is Hproportional to ∆c i , beca$se

canging ∆P as small e&&ect on ∆c i ,eff • Concl$sion< canging ∆P increases /ater transport more tan

sol$te transport, and so increases rejection (di&&erent &rom poro$s

membranes)

• Fo$ling also occ$rs on dense membranes, mostl# b# -M and

precipitation (scaling)I red$ced b# Janti*scalantsK

• Dense membranes canLt be back/ased, beca$se re9$ired

press$res /o$ld be too igI tere&ore, major e&&ort is $s$all#

de7oted to pre*treatment to remo7e &o$lants

• Approaces to red$ce &o$ling are te &oc$s o& acti7e researc

Documents

Membranes for Posting