CT4471 Drinking water I

Dr.ir. S.G.J. Heijmanmicro- and ultrafiltration

Mic

ro-a

nd u

ltraf

iltra

tion

October 16, 2007 2

Approximatemoleculairweight

Relativesize of materials in water

Treatment process

Size, µm0.001 0.01 0.1 1.0 10 100 1000

100 200 1000 10000 20000 100000 500000

Viruses Bacteria

Dissolved salt AlgeaHumic acids

Cysts Sand

Clay

ED and EDR

Reverse osmosis

Nanofiltration

UltrafiltrationMicrofiltration

Conventional filtration processes

Metal ionsArseenNitraatNitriet

Cyanide

Dissolved saltCalcium saltsSulphate salts

Maganesium saltsAluminium salts

Viruses

Hepatitis

Humic acidsTrihalomethanen

Precursors

BacteriaSalmonellaShigellaVibrio cholerae

CystenProtozoaGiardiaCryptosporidium

SiltΔP [bar]

0.01

0.05

0.1

5

30

Application area filtration processes

October 16, 2007 3

Application area filtration processes

+

+

+

-

Virusses

+

+

-

-

Multivalentsalts

++Reversed OsmosisRO

-+NanofiltrationNF

-+UltrafiltrationUF

-+Microfiltration MF

Monovalentsalts

Bacteria

Removal of bacteria and virusses is expressed as logremoval capacity90%-removal = log 199%-removal = log 299,99%-removal = log 4

Why MF/UF?

suspended solidsorganische subst.GiardiaCryptosporidiumMS2-virus

microfiltration99%50%> 4> 40

ultrafiltration99%50%> 4> 44

1.In

trodu

ctio

n

1.In

trodc

utio

n

Full scale

Module

2.C

once

pt M

F/U

F

2module

memspec

D41

LdnIAA

⋅⋅

⋅⋅⋅==

π

π

Aspec = specific membrane surface [m2/m3]Amem = membrane surface area [m2]Imodule = module volume [m3]N = number membranes in module [-]d = diameter membrane [m]L = length membrane [m]D = diameter module [m]

Dead-end Filtrationfiltration

backwash or backflush

2.C

once

pt M

F/U

F

October 16, 2007 8

3.Th

eory

Mass balans

Filtration time

Qf

QpQp = Qf

Filtration run = filtration time + back wash time

Qf = Qp + Qbw Qp = permeate flow [m3/h]Qf = feed flow [m3/h]Qbw = back wash flow [m3/h]

October 16, 2007 9

Recovery

p

rpV

VV −=γ

Recovery as high as possible (>90%):- long filtration time- short cleaning time- low cleaning flux 3.

Theo

ryγ = recovery [-]Vp = permeate production [m3]Vr = volume needed for cleaning [m3]

October 16, 2007 10

Kinetics

3.Th

eory

totmem

pR

TMPA

QJ

⋅==ν

J = flux [m3/(m2·h)]Qp = permeate flow [m3/h]Amem = membrane surface area [m2]TMP = transmembrane pessure [Pa]Rtot = totale resistanceν = dynamic viscosity [Pa/s]

time

flux

resistance

Rtot=Rmembrane+Rfouling

October 16, 2007 11

Fouling mechanisms

3.Th

eory

October 16, 2007 12

PPerm

Pfeed PConc

Trans membrane pressure

permhydr

Feed P2

PPTMP −

Δ−= ΔPHydr ≈ 0

PPerm ≈ 0

3.Th

eory

October 16, 2007 13

Cleaning

Different cleaning methods:- forward flush or cross flow- backflush or backwash- Airflush or air/water flush- Chemical enhanced flush or chemical backwash- intensive chemical cleaning or cleaning-in-place (CIP)

3.Th

eory

October 16, 2007 14

Forward flush

Flush waterFeed

Cleaning with high cross flow velocities

Re > 2300ν

ho dvRe ⋅=

3.Th

eory

d [mm] vo [m/s] drukval [Pa]

5,2 0,58 14731,5 2,01 613700,7 4,30 603850

Need cross flow for turbulent conditions

October 16, 2007 15

Back flush

3.Th

eorypermeate

Backwash water

Backwash flux = 2 tot 2,5 filtration flux

d [mm] flush time [s]

5,2 191,5 50,7 3

Time needed to flush a membrane of 1 meter with a backwash flux of 250 l/(m2·h)

October 16, 2007 16

Back flush with forward flush

October 16, 2007 17

Air flush

3.Th

eory

air

Water

Forward flush with air injectionhigher turbulence

Taylor bubbles Slug flow

October 16, 2007 18

Design concepts

4.D

esig

n co

ncep

ts

Different modules:- tubular membranes- capillary membranes1. flat sheet membranes

Different operational modes:- dead end- cross flow- under pressure- constant pressure- constant flux

Different materials:- polymer- ceramic

Different orientation:- vertical- horizontal

October 16, 2007 19

Tubular membranes

4.D

esig

n co

ncep

ts

Diameter channel = 5 – 25 mm

Easily cleaned

Low specific surface area

Low clogging potential

October 16, 2007 20

Capillary membranes

4.D

esig

n co

ncep

ts

Diameter channel = 0.5 – 5.0 mm

Well cleaned, but not as good as tubular membranes

High specific surface area

High clogging potential

October 16, 2007 21

Choosing a module

4.D

esig

n co

ncep

ts

Economical balance:

low investment costs vs low exploitation costs orhigh specific surface area vs low clogging potential

High flux >>> fast fouling

4.D

esig

n co

ncep

ts

Vertical - horizontal

October 16, 2007 23

4.D

esig

n co

ncep

ts

constant flux (ca 100 l/m2·h)

time

flux

pressure

P v, F

wconstant pressure (ca 0.5 bar)

time

flux

pressure

P v, F

w± 20 min

backwash

Dead-end vs Cross-flow filtration

4.D

esig

n co

ncep

ts

Qv

Qp

Qc

CF: Application with high suspended solid contents

CF: High cross flow velocities, high energy costs

Qf

Qp

Under pressure membrane filtration

air

membranes

Feed water

permeate

concentrate

4.D

esig

n co

ncep

ts

October 16, 2007 26

Ceramic microfiltration

October 16, 2007 27

Ceramic microfiltration

Membranelayer