-
On photocatalytic membrane reactorsin water and wastewater
treatment:
recent experiences and perspectives
2nd Summer School onEnvironmental Applications of Advanced
Oxidation Processes
Porto (Portugal), July 10-14, 2017
Sylwia Mozia
West Pomeranian University of Technology, Szczecin Institute of
Chemical Technology and Environment Engineering
ul. Puaskiego 10, 70-322 Szczecin, Polandtel. +48 91 449 48 72,
e-mail: [email protected]
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Outline1. A brief introduction to membrane processes2.
Photocatalytic membrane reactor (PMR) what is it?3. Examples of
possible applications of PMRs for treatment
of real water and wastewater:(I) Example 1: Treatment of
effluents from a municipal wastewater treatment plant (MWWTP) in a
PMR utilizing ultrafiltration (UF) application of a polymeric
membrane(II) Example 2: Treatment of lake water in a PMR and a
hybrid system coupling UVC/H2O2 and UF application of a ceramic
membrane4. Conclusions and future trends
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A brief introduction to membrane processes
-
Membrane what is it?
membrane
structure, having lateral dimensions much greater than its
thickness, through which transfer may occur under a variety of
driving forces(Terminology for membranes and membrane processes
(IUPAC Recommendations 1996)
-
Driving force
Transmembrane pressure
P Concentration (or partial pressure)
differencec, p
Electrical potential difference
E
Microfiltration (MF)
Ultrafiltration (UF)
Nanofiltration (NF)
Reverse osmosis (RO)
Dialysis
Pervaporation (PV)
Membrane distillation (MD)
Gas separation (GS)
Liquid membranes (LM)
...
Electrodialysis (ED, EDR)
Membrane electrolysis (ME)
...
Membrane processes
-
Pressure driven membrane processes
Separation process
Rejected substances
Reverse osmosis
Ultrafiltration
Nanofiltration Microfiltration
Particle filtration
Salts (aq.)
Metal ions
Synthetic dyes
Lactose (sugars)
Milk proteins
Gelatin
Endotoxin pyrogen
Viruses
Colloidal silica
E-coat pigment
Red blood cells
Bacteria
Oil emulsion Activated
carbon
Human hair Giardia cyst
Blue indigo dye
Fat
m 0,001 0,01 0,1 1,0 10 100 1000
Mol. weight 100 200 1000 20000 100000 500000 106 5x106
- MF: TMP < 0.3 MPa
- UF: TMP 0.1 1 MPa
- NF: TMP 0.5 3 MPa
- RO: TMP 1 8 (10) MPa
MF (0.1 10 um) UF (1 100 nm or 10 100 kDa)
NF (< 2nm or 250 400 Da)
RO (< 125 Da)
driving force: transmembrane pressure
(TMP)
Synthetic dyes
Mol. weight 100 200 1000 20000 100000 500000 106 5x106
(m 0,001 0,01 0,1 1,0 10 100 1000
Fat
Blue indigo dye
Giardia cyst
Human hair
Activated carbon
Oil emulsion
Bacteria
Red blood cells
E-coat pigment
Colloidal silica
Viruses
Endotoxin pyrogen
Gelatin
Milk proteins
Lactose (sugars)
Metal ions
Salts (aq.)
Particle filtration
Microfiltration
Nanofiltration
Ultrafiltration
Reverse osmosis
Rejected substances
Separation process
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Streams in membrane separation processes
feed
permeate
a portion of feed stream which passes through the membrane; in
case of water/wastewater treatment it contains mainly water and
substances that were not rejected by the membrane
retentate (concentrate)
a portion of feed stream whichdoes not pass through the
membrane; a concentrated solution containg components rejected by
the membrane
The product of a membrane process can be either permeate or
retentate, or sometimes both streams.
-
Membranes in water and wastewater treatment -problems to
solve:
Permeate flux decline due to membrane fouling deposition of
contaminants on the membrane surface or within its pores
MF/UF membranes are not efficient in separation of low molecular
organic contaminants low permeate quality
water mono- and multivalent
ions
viruses &
bacteria suspended
solids colloids
low molecular organic
substances
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Solution:
PMR
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What is a photocatalyticmembrane reactor?
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Photocatalytic Membrane Reactor (PMR)
A hybrid system in whichthe photocatalytic degradation
and membrane separation occur simultaneously
-
PHOTOCATALYSIS:- decomposition and mineralization of
contaminants- synthesis of useful organic compounds
+MEMBRANE PROCESS:
- retention of photocatalyst in the reaction environment-
possibility of recovery and reuse of the photocatalyst in further
runs- control of a residence time of reagents in the reactor-
possibility of selective separation of products- realization of a
continuous process with simultaneous separation of reagents and
photocatalyst from the solution
PMR=
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PMRs - classification
PMR
liquid phasegaseous phase
Driving force: P: microfiltration ultrafiltration
nanofiltration
Driving force: c, p: pervaporation dialysis membrane
distillation
according to the manner of photocatalyst introduction into the
reactor
according to the reaction environment
according to the membrane technique applied (liquid phase
reactions)
with a photocatalyst suspended in the reaction mixture
with a photocatalyst supported in/on the membrane
(photocatalytic membranes)
-
PMRs with photocatalytic membranes
FUNCTION OF THE MEMBRANE:
photocatalyst support
separation of the molecules present in the solution (initial
compounds and products or by-products of their decomposition)
photocatalyst
membrane
photocatalyst
membrane
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PHOTOCATALYTIC MEMBRANES
S. Mozia, Separation and Purification Technology, 73 (2010)
7191
PMRs with photocatalytic membranes
light source light source
non-photoactive support
photoactive support
photoactive separation layer
non-photoactive separation layer
a) b)
non-photoactive separation layer
non-photoactive support
photoactive support
light source
b)
a)
photoactive separation layer
light source
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separation of photocatalyst particles
separation of the molecules present in the solution (initial
compounds and products or by-products of their decomposition)
photocatalyst
membrane
PMRs with photocatalyst in a slurry
FUNCTION OF THE MEMBRANE:
membrane
photocatalyst
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A. Photocatalytic reaction conducted in a membrane module
B. Photocatalytic reaction conducted in the feed tank
C. Photocatalytic reaction conducted in an additional reservoir
(photoreactor) located between the feed tank and membrane
module
PMRs with photocatalyst in a slurry: configurations
retentate
permeate
feed
membrane
membrane module
feed tank (photocatalyst in suspension)
light source
retentate
permeate
feed
membrane
membrane module
feed tank (photocatalyst in suspension)
light source
retentate
permeate
membrane
membrane module
light source
feed tank (photocatalyst in suspension)
additional reservoir (photoreactor)
feed
S. Mozia, A.W. Morawski, R. Molinari, L. Palmisano, V. Loddo,
Chapter 6 in Handbook of membrane reactors,Volume 2: Reactor types
and industrial applications, Ed. A. Basile, Woodhead Publishing
Limited, 2013, pp. 236-295
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Example 1: Treatment of effluents from a municipal wastewater
treatment plant
(MWWTP) in a PMR utilizing ultrafiltration (UF)
application of a polymeric membrane
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Influence of photocatalyst on permeate flux
membrane: PES, UE10 (Trisep Corp.), MWCO: 10 kDa 1.5 g
TiO2P25/dm3TMP: 3 bar
membrane fouling by TiO2 particles deterioration of permeate
flux during filtration of TiO2
0
0.2
0.4
0.6
0.8
1
0 60 120 180 240 300time [min]
J/J 0
1.5g TiO2/dm3 0,4 m/s1.5g TiO2/dm3 0,6 m/s
1.5g TiO2/dm3 0,8 m/s
feed: TiO2 in distilled water
-
0
0.2
0.4
0.6
0.8
1
0 60 120 180 240 300time [min]
J/J 0 1.5gTiO2/dm
3 - 0.8m/s - 3 bar1.5g TiO2/dm3 - 0.8m/s - 2bar1.5g TiO2/dm3 -
0.8m/s - 1 bar
vN: 0.8 m/s
How to avoid membrane fouling?1. Careful selection of process
conditions:
- Transmembrane pressure (TMP)- Feed flow rate
0
100
200
300
400
500
0 1 2 3 4pressure [bar]
perm
eate
flux
[dm
3 /m2 h
]
pure waterTiO2
UE10
feed: TiO2 in distilled water
Influence of photocatalyst on permeate flux
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How to avoid membrane fouling?2. Selection of a
photocatalyst
UE10vF=0.8 m/s; TMP=3 bar0.5 gTiO2/dm3
small particles, uniform distribution
large particles, non-uniform distribution
PhotocatalystSpecific
surface area SBET [m2/g]
Anatase over rutile ratio
(A:R)
Crystallite size of
anatase [nm]
A800 6 2:98 51
P25 51 80:20 22
ST-01 252 100:0 8
0
2
4
6
8
10
12
0.1 1 10 100 1000
particle size [m]am
ount
by
volu
me
q [%
]
P25
ST01
A800
0
0.2
0.4
0.6
0.8
1
0 10 20 30
time [h]
J/J 0
ST-01
P25
A800
feed: TiO2 in distilled water
Influence of photocatalyst on permeate flux
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What is the infuence of photocatalysis on permeate flux
duringtreatment of wastewater?
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Treatment of wastewater in PMR utilizing UFMunicipal sewage
treatment plant
with a capacity of 418 000 equivalent citizens
mechanical treatment
biological treatment
secondary settling tanks
sieves, screens, grit chamber, primary
settling tanks
pre-denitrification, dephosphatation,
nitrification
sampling point PE sampling point SE
www.maps.google.pl
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Typical parameters of primary (PE) and secondary (SE) effluents
applied in the experiments
Parameters PE SETOC [mg/dm3] 70 - 80 12 - 19DOC [mg/dm3] 49 - 54
11 - 18TIC [mg/dm3] 58 - 100 42 58pH 7.5 - 8.5 7.2 -
8.5Conductivity [S/cm] 1020 - 1170 1040 - 1130TDS [ppm] 710 - 780
730 - 790Turbidity [NTU] 75 - 110 1 - 4N-NH4+ [mgN/dm3] 43 - 50 5 -
8
-
no TiO2:dense cake
layer
Increase of the permeate flux in the presence of TiO2 P25
1.5 gTiO2 P25/dm3
J 80%
J 50%
38%
0
0.2
0.4
0.6
0.8
1
0 50 100 150 200 250 300time [min]
J/J 0
PE - UFPE - PMR
in the presence of TiO2:
porous cake layer
0
0.2
0.4
0.6
0.8
1
0 50 100 150 200 250 300time [min]
J/J 0
SE - UFSE - PMR
33%
J 20%
J 60%
Influence of photocatalysis on permeate flux
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Will PMR be effectivein treatment of
wastewater?
-
0102030405060708090
UF 0.5gTiO2/dm3 1gTiO2/dm3 1.5gTiO2/dm3
C [m
g/dm
3 ]
TOC-feed
DOC-feed
DOC-permeate
Mineralization of large molecular organic contaminants proceeds
slowly.Overall treatment efficiency depends more on membrane
separation than photocatalysis.
Concentration of TOC and DOC in primary effluents (initial feed)
and in permeate after
5h of UF or PMR process
Low molecular organic contaminants and products of their
decompositionare not rejected by UF membranes.Overall treatment
efficiency depends on effectiveness of photocatalysis.
Non Steroidal Anti-Inflammatory DrugNaproxen sodium salt (MW 252
g/mol)
Feed: Naproxen in primary effluents
0
10
20
30
40
50
60
70
80
0 1 2 3 4 5 6Time [h]
Con
cent
ratio
n of
Nap
roxe
n [u
g/dm
3 ]
retentate permeate
Possible application: post-treatment (polishing) of
water/wastewater containing low concentrations of harmful or
persistent organic contaminants (tens ug/dm3 or lower), e.g.
pharmaceuticals or endocrine disrupting compounds.
Removal of organic contaminants
DOC in feed (5h): PE: ~ const.
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Stability of polymericmembranes in PMRs
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PMR with a light source located in the vicinity of membrane
surface
retentate
permeate
feed
membrane
membrane module
feed tank (photocatalyst in suspension)
light source
a danger of destruction of the polymeric membrane structure by
UV light or hydroxyl radicals
polyethersulfone (PES) polysulfone (PSU)
Resistance of membranes to UV:
-SO3-
polypropylene (PP), polyacrylonitrile (PAN) and cellulose
acetate (CA) -CH-
polytetrafluoroethylene (PTFE) and poly(vinylidene fluoride)
(PVDF)
Stability of polymeric membranes in PMRs
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PMR with a light source under or inside an additional reservoir
(photoreactor)
NO RISK OF DESTRUCTION OF POLYMERIC MEMBRANES BY UV LIGHT
retentate
permeate
membrane
membrane module
light source
feed tank (photocatalystin suspension)
additionalreservoir(photoreactor)
feed
Stability of polymeric membranes in PMRs
-
0
0,2
0,4
0,6
0,8
1
0 10 20 30 40 50 60 70
czas [h]
J/J 0
bez UV, z azydkiem sodu
z UV, bez azydku sodu
0
0,2
0,4
0,6
0,8
1
0 10 20 30 40 50 60 70
czas [h]
J/J 0
bez UV, z azydkiem sodu
z UV, bez azydku sodu
0
20
40
60
80
100
before after 70h, UV after 70h, noUV
% R
dextran 40 kDa dextran 70 kDa
photocatalysis
filtration
photocatalysis filtration
membrane: PES, UE10 (Trisep Corp.) MWCO: 10 kDa
loss of separation properties due to membrane skin layer damage,
regardless of presence or absence of UV abrasive action of TiO2
particles
photocatalyst: AEROXIDE TiO2 P25
no UV, with sodium azide (NaN3)
UV, no sodium azide (NaN3)
time [h]
Stability of polymeric membranes in PMRs
-
Example 2: Treatment of lake water in a PMR and a hybrid system
coupling
UVC/H2O2 and UF application of a ceramic
membrane
-
Treatment of surface water in PMR and UVC/H2O2UF system
Miedwie Lake - source of drinking water for Szczecin, Poland
Water Treatment Plant ZPW Miedwie:max. production: 100 000 m3 of
water per day
(at present: ca. 55 000 m3/day)
Water was collected after initial prefiltration through screens
and sieves
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Parameter Unit ValueTOC mg/dm3 8.1-8.7
Conductivity S/cm 555-573Absorbance UV254 cm-1 0.1568-0.1707
Turbidity NTU 0.54-1.66pH - 7.0-7.9Cl- mg/dm3 41.2-42.2
NO3- mg/dm3 0.8-1.7SO42- mg/dm3 85.3-86.8PO43- mg/dm3 0-0.1Na+
mg/dm3 23.4-24.0K+ mg/dm3 4.9-5.4
Ca2+ mg/dm3 63.1-67.2Mg2+ mg/dm3 16.5-17.1
Typical parameters of lake water applied in the experiments
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Influence of AOPs on permeate flux
PMR
0
0.2
0.4
0.6
0.8
1
0 50 100 150 200 250 300
J/J 0
time [min]
UVC photolysis100 mg/dm3500 mg/dm31000 mg/dm32000 mg/dm34000
mg/dm3
UVC photolysis0.03 gH2O2/dm30.15 gH2O2/dm30.3 gH2O2/dm30.6
gH2O2/dm31.2 gH2O2/dm30
0.2
0.4
0.6
0.8
1
0 50 100 150 200 250 300
J/J 0
time [min]
UVC photolysis0.5 gTiO2/dm31 gTiO2/dm31.5 gTiO2/dm32
gTiO2/dm3
UVC photolysis0.5 gTiO2/dm3
1 gTiO2/dm3
1.5 gTiO2/dm3
2 gTiO2/dm3
Both AOPs (TiO2 photocatalysis and UVC/H2O2) have
positiveinfluence on UF membrane fouling mitigation during
treatmentof lake water
BUT Increase of the permeate flux in the presence of TiO2 P25
was
slightly higher than in the presence of H2O2
UVC/H2O2UF
-
0
20
40
60
80
100
TOC
rem
oval
[%]
H2O2 concentration [g/dm3]
Rfeed RtotalRfeed Rtotal
0
20
40
60
80
100
0.5 1 1.5 2
TOC
rem
oval
[%]
TiO2 concentration [g/dm3]
Rads Rfeed RtotalRtotalRads Rfeed
Removal of organic contaminants
PMR UVC/H2O2UF
PMR: the highest TOC removal rate: 1 gTiO2/dm3. UVC/H2O2 UF:
similar efficiency at 0.15 gH2O2/dm3.
Increase of H2O2 concentration up to 0.3 g/dm3 improvementof
mineralization efficiency
Increase of TiO2 concentration up to 1.5 g/dm3 decreaseof
mineralization efficiency
58% 57%
66%
t = 5h t = 5h
-
Filtanium 5
0102030405060708090
100
0 50 70 100t [h]
R [%
]
dekstran 5 kDa
Filtanium 100
0102030405060708090
100
0 50 70 100t [h]
R [%
]
dekstran 70 kDa
membrane: TiO2 Filtanium 5kDa photocatalyst: AEROXIDE TiO2
P25
membrane: TiO2 Filtanium 100kDa
Loss of separation properties destruction of separation layer
abrasive action of TiO2 in case of skin layer built of fine
particles (fine UF membrane)
No change in separation properties no damage of separation
layer
dextran 5kDa dextran 70kDa
Stability of ceramic membranes in PMRs
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A short summary
-
Hybrid systems coupling AOPs with membrane separation, e.g. PMRs
have a great potential in water/wastewater
treatment and reuse. Application of AOPs can result in membrane
fouling mitigation and
improvement of the efficiency of organics removal.Application of
membrane separation is especially advantageous when
retention of photocatalyst in the reaction environment is
necessary. Membrane allows to realize a continuous process with
simultaneous separation of reagents (and photocatalyst) from the
solution.
However, further investigations are still needed in order to
improve the hybrid AOPs membrane systems performance.
A particular attention should be paid to the selection of
membranes for PMRs with reference to their resistance to:
damage by oxidative species abrasion by photocatalyst
particles
It is very important to investigate the real systems, which
focus on treatment of natural waters and real wastewaters. The
number of reports concerning this subject is still limited, since
most of the experiments have been conducted using model
solutions.
-
Acknowledgments
Dominika Darowna and Kacper Szymaski
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1. S. Mozia, A.W. Morawski, R. Molinari, L. Palmisano, V. Loddo,
Chapter 6: Photocatalytic membrane reactors: fundamentals, membrane
materials and operational issues, pp. 236-2952. R. Molinari, L.
Palmisano, V. Loddo, S. Mozia, A.W. Morawski, Chapter 21:
Photocatalytic membrane reactors: configurations, performance and
applications in water treatment and chemical production, pp.
808-845
Handbook of membrane reactors, Volume 2: Reactor types and
industrial applications, Ed. Angelo Basile, Woodhead Publishing
Limited, Cambridge, UK, 2013
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Thank you for your attention
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