CT4471 Drinking water I Micro- and ultrafiltrationCT4471 Drinking water I Dr.ir. S.G.J. Heijman...
Transcript of CT4471 Drinking water I Micro- and ultrafiltrationCT4471 Drinking water I Dr.ir. S.G.J. Heijman...
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
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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