HGVIK ♦ AKTUALNA PROBLEMATIKA U VODOOPSKRBI I ODVODNJI ♦ BOL 2012
FRESHWATER MEMBRANE FILTRATION INTERNATIONAL CASE STUDIES
Josef Lahnsteiner, Arnold Gmuender, Christoph Maer, Yagna Prasad,
Reinhard Nowotny
SAŽETAK
Najsuvremenija postrojenja za pitku vodu najčešće uključuju jedinicu za membransku filtraciju,
zbog njihovog učinkovitog uklanjanja česca kao i dezinfekcionog svojstva. Ovaj članak opisuje
aplikaciju membranske filtracije slatkih voda u različim regijama. U Švicarskoj je tretman voda
iz kraških vodnosnih sustava jedna od glavnih tema vodosnabdijevanja. U tom kontekstu pojašnjeno je, pročišćavanje kraške i izvorske vode tlačnom membranskom ultrafiltracijom (UF) koja
pruža visok stupanj sigurnos. Nadalje, opisana je u svijetu jedinstvena tehnologija proizvodnje
pitke vode iz procesa prečišćavanja otpadnih voda u Namibiji (Windhuk). Nakon sekundarnog
taložnika se prečišćena otpadna voda ulijeva u gore pomenuto postrojenje pitke vode, gdje je
impleneran napredni višeslojni ultrafiltracioni sistem kao konačna barijera. Treća tema ovog
članka je tretman podzemih voda za vodoopskrbu sportskog sela (Igre Commonwealtha) u Indiji
(Delhi). Ovaj presžni projekt je prvi slučaj primjene ultrafiltracije za vodosnabdijevanje u Indiji.
Na kraju, ali ne i manje važno, pomenut je i tretman vode zirškog jezera pomoću tlačne membranske filtracije.
ABSTRACT Due to their efficient parcle removal and disinfecon properes, increasing numbers of membrane filtraon units are being incorporated into state-of-the-art drinking water treatment
plants. This paper describes freshwater membrane applicaons in different regions, as for example in Switzerland where karst water treatment is a major topic. Within this context, the purificaon of karsc spring water by submerged and pressure-driven ultrafiltraon (UF) membranes,
which provide a high degree of safety, is discussed. Furthermore, the globally unique potable
reuse pracce in Windhoek/Namibia is described. In this case, drinking water is reclaimed from
secondary domesc effluent by an advanced mul-barrier system with UF as a final barrier. The
third topic is groundwater treatment for the Commonwealth Games Village in Delhi/India. This
presgious project showcases the first drinking water UF applicaon in India. Last, but not least,
water treatment with mul-barrier systems employing submerged and pressure-driven membranes on Lake Zurich in Switzerland is discussed.
1 Introduction
Due to their efficient parcle removal and disinfecon properes, increasing numbers of membrane
filtraon units (submerged or pressure driven ultrafiltraon) are being incorporated into state-of-theart drinking water treatment plants (mul-barrier systems and single stage plants). Moreover, owing
to the reducon of the fouling potenal of downstream reverse osmosis membranes (reducon of
turbidity, SDI and colloids, etc) such units are also used in the industrial recycling field and as a result
of these benefits, the number of installaons is steadily growing (15% per year since 2000). Membrane
* Dipl.-Ing. Dr. Josef Lahnsteiner, VA TECH WABAG GmbH, Dresdner Strasse 87-91, 1120 Vienna, Austria, [email protected]
* Dipl.-Ing. Reinhard Nowotny, VA TECH WABAG GmbH, Dresdner Strasse 87-91, 1120 Vienna, Austria, [email protected]
** Mr. Arnold Gmuender, WABAG Wassertechnik AG, Bürglistrasse 31, 8401 Winterthur, Switzerland, [email protected]
** Dipl.-Ing. Christoph Maer, WABAG Wassertechnik AG, Bürglistrasse 31, 8401 Winterthur, Switzerland, [email protected]
*** Yagna Prasad, VATECH WABAG Ltd, 11, Murrays Gate Road, Alwarpet, Chennai 600018, India, [email protected]
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Josef Lahnsteiner, Arnold Gmuender, Christoph Maer, Yagna Prasad, Reinhard Nowotny
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separaon is the most sophiscated filtraon process, membranes represenng very fine filters through which water is either pressed or sucked. Ultrafiltraon is a membrane process that employs very
fine pores with sizes of approximately 0.01 - 0.05 μm. Accordingly, any parcles that are larger than
this cut-off are removed, while dissolved ions and molecules with low molecular weights are allowed
to pass. Therefore, ultrafiltraon forms a complete barrier against turbidity and microbiological contaminants such as bacteria, viruses and protozoa, and a paral barrier against organic material (rejecon
of high molecular DOC). The membranes have to be cleaned periodically by back-flushing with water
and chemicals. During backwashing, the flow direcon inside the membranes is reversed and all of the
non-absorbed fouling is flushed out of the system. In order to increase the recovery rate and to save
energy, the used back-flush water is frequently treated by separate membrane units and recycled to
the inlet of the mul-barrier system (drinking water treatment plant).
Some of the major fresh water membrane projects completed by WABAG in recent years in differing
regions are subsequently highlighted. These include the treatment of karst water in Switzerland
using submerged and pressure-driven membranes; potable reuse in Windhoek/Namibia by means
of an advanced mul-barrier system with ultrafiltraon as a final barrier; groundwater treatment for
the Commonwealth Games Village in Delhi/India and water treatment on Lake Zurich in Switzerland,
employing mul-barrier systems with submerged and pressure-driven membranes.
2 Case studies
2.1 Karst water treatment in Switzerland
Karsc spring waters are regularly subject to high levels of turbidity, which also includes a large number of bacteria. Membrane filtraon represents a technology that copes ideally with these fluctuang
condions. In the last ten years, WABAG has completed more than ten membrane filtraon projects
for the treatment of karst water. The first of these was the installaon of a submerged ultrafiltraon
plant (outside-in hollow fibre) as a single treatment stage for the district of Tavannes in Switzerland.
This two-line system (2,400 m3/day) safely treats raw water with heavily fluctuang turbidity (including
a high number of bacteria). Figure 1 shows the UF process units (ZEEWEED 1000; 1,680 m2 membrane
area each; polyvinylidene fluoride [PVDF]; nominal membrane pore size 0.02 μm).
Figure 1. Tavannes submerged ultrafiltraon units
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Josef Lahnsteiner, Arnold Gmuender, Christoph Maer, Yagna Prasad, Reinhard Nowotny
The plant was started up in November 2002. In Figure 2 the permeability in the first four months
of operaon is shown. In the first month an irreversible permeabilty loss of approximately 30 L/
m2*h*bar ocurred (from 170 to 140 L/m2*h*bar). This inial loss is a normal occurrence (loss of porosity), which is caused mainly by the internal adsopron of humic acids by the membrane (Jermann
2007). Further permeability losses (10 to 15 L/m2*h*bar caused by pore blocking, cake and gel layer
formaon) can be recovered by chemical-enhanced (causc and acid) backwashes.
Figure 2. Tavannes karst water UF – permeability in the first four months of operaon
Figure 3 shows the permeability and raw water turbidity (which had values of up to 15 NTU), in the
same period (first four months of operaon). The clean water quality constanly met Swiss drinking
water standards (e.g. E. coli 0/100 mL, fecal coliforms 0/100 mL, turbidity <0.2NTU).
Figure 3. Tavannes karst water UF - permeabilty and turbidity November 2002 to March 2003
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Figure 4 shows permeability behaviour since July 2004. Permeability has remained at the same level
since the beginning of 2007, while maintenance cleaning has only been performed once a year.
Figure 4. Tavannes karst water UF – effect of maintenance cleaning on permeabilty
The largest karst/spring water project (21,600 m3/day) is currently under compleon for the city of
Lausanne in western Switzerland. In the past, Lausanne (populaon: 120,000) ulised 15% untreated
water from the Sonzier Spring. However, the use of this source was limited to mes of good water quality (turbidity < 0.5 NTU). In periods of poor water quality, especially from April to June when glacier
meltdown caused the standard to deteriorate, the spring water had to be substuted by lake water,
which involved high energy consumpon for pumping. Therefore, it was decided to build a treatment
plant in order to raise the usage rao of the cheaper spring water. Pressure-driven Inge Dizzer XL 0.9
MB 60 membrane modules (inside-out, mulbore hollow fibre; 0.9 mm inner diameter; polyether
sulfone modified [PES-M]; Inge GmbH T-rack, Figure 5) are to be employed as a single treatment step.
A 300 μm jet filter will be used for pre-filtraon. The plant consists of five lines with a total of 170 modules (5x34; total membrane area: 10,200 m2). The design flux is 88 L/m2*h. The turbidity peaks in the
raw water are up to 3 NTU. As compared to the aforemenoned Tavannes project (up to 15 NTU), this
is relavely low and explains why a pressure-driven membrane (with higher flux rates as compared to
submerged systems) can be operated in Sonzier. The plant will be started up at the end of 2012.
Figure 5. Ultrafiltraon unit - Inge T-rack configuraon
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HGVIK ♦ Bol 2012
Josef Lahnsteiner, Arnold Gmuender, Christoph Maer, Yagna Prasad, Reinhard Nowotny
Figure 6 shows some results from pilot tesng in June 2009. As can be seen in this diagram, fluctuang raw water qualies (turbidity and SAC peaks) could be dealt with relavely easily. For although
permeability was reduced by these poor raw water condions, it recovered soon aerwards without
operang parameter adjustment, i.e. the relave high flux (103 L/m2*h) was maintained and the
cleaning frequency did not need alteraon (increase). In the unlikely event of even worse condions
occurring (higher and more frequent turbidity peaks), this possibility (increase of backwash frequency) would constute a control opon (Hartmann 2010).
Figure 6. Pilot test results – Sonzier spring water
2.2 Potable reuse in Windhoek, Namibia
At the New Goreangab Water Reclamaon Plant (NGWRP) in Windhoek, an advanced mul- barrier
system with ultra-filtraon as a final treatment step has been in successful operaon since 2002. In
this facility, secondary domesc effluent is converted into high-quality potable water, which is directly reused by the populaon of Windhoek (Lahnsteiner, 2007). This represents a globally unique
water reuse pracce (direct potable reuse).
The treatment train (Figure 7) includes treatment barriers consisng of powdered acvated carbon
(PAC) dosing (oponal), pre-ozonaon, enhanced coagulaon and flocculaon, dissolved air flotaon (DAF), dual media filtraon, main ozonaon, biological acvated carbon (BAC) filtraon, granular
acvated carbon (GAC) adsorpon, ultrafiltraon (UF), disinfecon with chlorine and stabilizaon
with causc soda (NaOH).
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Figure 7. NGWRP process flow diagram
In this system, a pressure-driven, hollow fibre membrane (inner diameter 0.8 mm, inside-out,
polyether sulfone [PES], X-Flow) is operated as a final barrier for the removal of bacteria, viruses and
other pathogenic micro-organisms such as cryptosporidium and giardia. All the parcles larger than
0.04 μm are removed. The ultrafiltraon system (Figure 8) is designed for a net output of 21,000
m3/d.
Figure 8 NGWRP - ultrafiltraon unit
The design parameters (raw water and treated water) and the excellent water quality accomplished
during the performance test can be seen in Table 1.
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Table 1. NGWRP - water quality
Major Parameters
Units
Raw water
(design values)
Treated water
(guarantee values)
Performance test
results
Turbidity
NTU
53
0.1
0.08
DOC
mg/l
15
5
1.0
THM
μg/l
169
20
11
Giardia
per 100 ml
214
0 or log 6 removal
0
Cryptosporidium
per 100 ml
334
0 or log 6 removal
0
E. Coli
per 100 ml
20,347
0
0
Physical & chemical
Microbiological
The membranes are cleaned using both back-flushing with permeate (every 40 minutes) and chemical enhanced backwashes (CEB; CEB 1 with HCl and CEB 2 with causc NaOCl). Table 2 summarises
the membrane cleaning procedure, as well as the consumpon of backwash water and chemicals.
In order to increase the recovery rate of the reclamaon plant, the used water from permeate backwashing is recycled to the plant inlet. The used water from the CEBs is discharged into the sewerage
system in order to avoid any risk of chlorinated hydrocarbon recycling. The average membrane life is
9 years, which is four years longer than that guaranteed by the membrane supplier.
Table 2. NGWRP - typical membrane cleaning procedure
Normal backwashes with permeate
Racks in operaon
Hours of operaon
Duraon before backflush (min.)
Duraon of backflush (sec.)
Flow rate during backflush (m3/h)
4
18
40
40
490
Daily avg. total water consumpon for backflushes (m3)
588
Used backwash water is recycled to the plant inlet
Chemical-enhanced backwash (CEB)
CEB2 with NaOCl + NaOH aer 8-9 permeate backflushes
CEB1 with HCl follows aer 4 x CEB2
Typical chemical-enhanced backwash consumpon
Total daily avg. consumpon of HCl [35%] (L)
20
Total daily avg. consumpon of NaOCl [12-14%] (L)
Total daily avg. consumpon of NaOH [47%] (L)
Used backwash water is discharged into the sewerage system
40
130
Table 3 provides a comparison of the NGWRP UF with the UF units employed in other reuse/recycling
applicaons, i.e. in the recycling of refinery effluents (Panipat Refinery, India) and the industrial
reuse of secondary municipal effluent (Chennai Petrol Corporaon Ltd. Refinery, India). The same
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membrane is used (pressure-driven, hollow fibre polyether sulfone membranes) in all three UF process steps, but as can be seen in the table, the design fluxes of the UF units (Windhoek: 102 L/m2*h
gross flux, Panipat: 54 L/m2*h gross flux and Chennai: 66 L/m2*h gross flux) are quite different. This
is due to the fact that the Windhoek raw water (secondary domesc effluent) is subject to far more
extensive pre-treatment (polishing in maturaon ponds, ozone and acvated carbon addionally in
the reclamaon plant upstream to UF) than that from the other two raw water sources. This shows
that the design of UF processes depends very much on pre-treatment and the resultant UF feed
water quality. The reason for the difference in the Panipat and Chennai UF fluxes (54 L/m2*h vs. 66
L/m2*h) is that secondary refinery effluents basically contain more “difficult” organic compounds
(e.g. petrochemical macromolecules) than secondary municipal effluents. Another factor is that at
the me of process design, more experience was available for the treatment of the laer raw water
source (Lahnsteiner 2010).
Table 3. Comparison of UF for different reuse/recycling applicaons
Design parameters
Windhoek
Panipat
Chennai
Raw water (UF feed)
Pre-treated secondary Pre-treated secondary
domesc effluent - po- refinery effluent - indutable reuse
strial recycling
Membrane material
Hollow fibre polyether - Hollow fibre polyether - Hollow fibre polyether sulfone
sulfone
sulfone
3
Design feed flow [m /h]
Pre-treated secondary
municipal effluent industrial reuse
1000
894
475
102
54
66
850
760
428
Design net flux [l/m *h]
87
46
59
Recovery [%]
85
85
90
5 (+1 standby)
6 (+1 standby)
3 (+1 standby)
Pressure vessels/skid
15
18
15
Vessels total
70
108
45
Elements/vessel
4
4
4
280
432
180
35
38
40
9,800
16,416
7,200
2
Design gross flux [l/m /h]
3
Design permeate flow [m /h]
2
Skids
Elements total
2
Membrane area/element [m ]
2
Membrane area [m ]
2.3 Ground water treatment at the Commonwealth Games Village, New Delhi/India
Within the framework of the 19th Commonwealth Games, which were hosted by the Indian capital
city of Delhi, a mul-barrier system (including ultrafiltraon) for groundwater purificaon was started-up in 2010 at the Games Village in order to provide the 8,000 athletes and officials with safe
drinking water (4,600 m3/day). This project was highly presgious and represented the first Indian
drinking water treatment plant to employ ultrafiltraon. Since the end of the Games, the plant has
been serving the drinking water requirements of the populaon in the surrounding area.
The raw water is drawn from three bore wells and a Ranney well. The bore wells are located near
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Josef Lahnsteiner, Arnold Gmuender, Christoph Maer, Yagna Prasad, Reinhard Nowotny
the arficial embankment built in the flood plain of the Yamuna River. The major aims are soening
for the removal of temporary hardness and membrane filtraon for both turbidity removal and disinfecon. The main design parameters (inlet and clean water target values) can be seen in Table 4.
Table 4. Main design parameters
Parameter
Unit
pH
Turbidity
Colour
Total hardness as CaCO3
Iron as Fe
Taste and odour
Total coliforms
Fecal coliforms
NTU
Hz Units
mg/L
mg/L
MPN
MPN
Raw water
7.2 -8.6
50
500
0.85
Clean water
7.5 – 8.5
< 0.5
< 0.5
< 200
<0.3
unobjeconable
2.3/100 mL
0.23/100 mL
The process comprises aeraon, lime soening and coagulaon with polyaluminium chloride (PACl),
flocculaon and sedimentaon in a high-rate, solid contact clarifier, neutralisaon and pH adjustment of the “so water” in a re-carbonizaon tank, clarificaon in tube selers, ultrafiltraon,
disinfecon by ultraviolet light and chlorinaon of the filtered water, and sludge thickening and
dewatering of the thickened sludge (Figure 9). VA TECH WABAG India Ltd was commissioned with
the construcon and operaon of the plant (design, built, operate [DBO] contract).
Figure 9. Process Flow Diagram of the Commonwealth Games Village Water Treatment Plant
The pressure-driven ultrafiltraon unit consists of three skids with 32 pressure vessels each, which
contain hollow fibre membranes (X-Flow, Aquaflex; 0.8mm inner diameter; polyether sulfone [PES];
nominal pore size 25 nm; Figure 10). The gross flux has been designed for 53.5 L/m2*h (with a flow
of 192 m3/h and a total membrane area of 3,840m2). The design recovery rate is 92.4% which results
in a design net flux of 49.4 L/m2*h. The membranes are cleaned by permeate backwash and acid and
alkaline chemical-enhanced backwashes (HCl and causc NaOCl respecvely).
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Figure 10. Membrane skid (le), membrane module (top right) and a secon of the 25nm pore size PES
membrane (boom right)
As can be seen in Figure 9, this procedure is praccally a zero liquid discharge process. Consequently,
all the process liquids (including the used CEB water) are recycled to the plant inlet. This is because in water-stressed Delhi, the recovery rate has a higher priority than the avoidance of the risk of
chlorinated hydrocarbon recycling (which could be the case due to the NaOCl CEB). However, such a
risk is low, as the used NaOCl backwash water is substanally diluted and if formed in relevant concentraons, to a certain extent the chlorinated hydrocarbons would be discharged in the dewatered
sludge (dissolved in the residual liquid and adsorbed on the sludge solids).
2.4 Water treatment on Lake Zurich, Switzerland
Lake Zurich is a very important source of drinking water, not only for the city of Zurich with a populaon of some 400,000, but also for a number of smaller communies along the lakeside. However,
the lake water treatment plants built in the early sixes require upgrading or replacement by new
capacity. Therefore, extensive pilot trials, involving industry, technical instutes and water supply
companies have been conducted over many years and have resulted in the evaluaon of the mulbarrier systems shown in Figure 11.
Figure 11. Modern mul-barrier systems for lake water treatment (doed stages oponal)
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Josef Lahnsteiner, Arnold Gmuender, Christoph Maer, Yagna Prasad, Reinhard Nowotny
Both types of membranes, submerged and pressure-driven, were successfully tested in the treatment systems (Helbling 2012). The first full-scale plant of its kind is the Maennedorf three-stage,
mul-barrier system (15,000 m³/d) on Lake Zurich, which has been in successful operaon since
2005. It includes pre-ozonaon, acvated carbon filtraon and pressure-driven ultrafiltraon (Figure
12). The results have been excellent, e.g. turbidity < 0.02 NTU, AOC < 30 μg/l and the final water is
biologically stable, which even allows the abandonment of chlorine dosing for network protecon.
The used backwash water is treated by submerged membranes, which allows the permeate to be
recycled. The discharge to the STP amounts to less than 1.5% of drinking water output.
Figure 12. Membrane skid (le) with 44 mulbore type ultrafiltraon modules
At Horgen, which is also situated on Lake Zurich, a further mul-barrier system plant with a maximum daily capacity of 25,000 m3 will commence operaon in September 2012. The plant consists of
submerged ultrafiltraon membranes as a first stage, followed by ozonaon and acvated carbon
filtraon. The pilot trials demonstrated that both pressure-driven and submerged membranes are
suitable for this kind of lake water and the operaonal experience to be gained in the coming years
will be very valuable for a detailed comparison of both membrane types.
3 Future developments
Ultrafiltraon as a single stage, or employed in mul-barrier systems, is a proven technology. Nonetheless, issues such as fouling control and reducons in energy consumpon (“lower carbon soluons”) and the chemicals requirement, as well as new membrane materials (polymeric and inorganic with or without nanoparcles), represent long-term topics in membrane science, research and
development. The major innovaons that are likely to be implemented in the near future would
seem to be ceramic membranes, the removal of micro-pollutants by powered acvated carbon (PAC)
and the subsequent separaon of the PAC by ultrafiltraon. The major advantages of ceramic membranes are their extended lifeme and higher chemical resistance (can be combined with oxidaon
processes). Trace organics are praccally impossible to remove by ultrafiltraon. Therefore, combinaons such as the aforemenoned use of PAC and UF, or advanced oxidaon upstream of ceramic
membranes, have to be employed.
4 Conclusions
The major benefits of ultrafiltraon are a high degree parcle removal and disinfecon. The quality of the clean water (potable as well as process water) is substanally improved. Due to these
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properes, the number of installaons is steadily increasing. As can be seen in this review, which
addresses a variety of applicaons in different regions, freshwater membrane filtraon is state-ofthe-art. Nevertheless, most treatment plants are tailor made for specific requirements. This means
that correct design, which in many cases is based on pilot tests, is crucial. In this context, adequate
pre-treatment (removal of turbidity, NOM, etc.) and the selecon of the appropriate membrane
system (submerged or pressure driven, etc.) are of primary importance. In order to accomplish the
lowest total cost (OPEX + CAPEX), the “economic opmum flux”, which provides stable operaon
and minimum chemical-enhanced cleaning, has to be idenfied and implemented. Backwash water recycling can further improve the economic performance (increase of recovery rate and energy
savings) and last, but not least, it must be said that proper process surveillance and the correct
subsequent conclusions and O&M measures are also essenal for the successful employment of
ultrafiltraon (as a single stage or in mul-barrier systems).
References
Gmuender, A. & Vescoli, D. (2009) Pressure and Submerged Membranes in Mul-barrier Systems for the
Treatment of Surface Water. Proceedings of the 5th IWA Specialised Membrane Technology Conference
held at Beijing September 1-3, 2009
Hartmann, P. & Gmuender, A. (2010) Membrantechnologie - Erfahrungen schweiz- und weltweit. gwa 1/2010
pp 11-17
Helbling, J. & Bosshart, U. (2012) UF-Membranen in Mul Barrieren Systemen – Auswirkungen auf einzelne
Verfahrensstufen. Aqua & Gas No 3 2012, pp 34-38
Jermann, D., Pronk W., Meylan, S. & Boller, M. (2007) Interplay of different NOM fouling mechanisms during
ultrafiltraon for drinking water producon. Water Research Vol 41, Issue 8, pp 1713-1722
Lahnsteiner, J. & Mial, R. D. (2010) Reuse and recycling of secondary effluents in refineries employing advanced mul-barrier systems. Water Science & Technology Vol 62 No 8 pp 1813-1820
Lahnsteiner, J. & Lempert, G. (2007) Water management in Windhoek, Namibia. Water Science & Technology
Vol 55 No 1-2 pp 441-448
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