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Application of New Generation Ceramic Membranes for
Challenging Waters
S.G. Lehman, L. Liu*, * and S. Adham*
* Applied Research Department, MWH Americas, Inc., 618 Michillinda Avenue, Suite 200, Arcadia, CA, 91007,
United States
(E-mail: geno.lehman@mwhglobal.com; li.liu@mwhglobal.com; samer.adham@mwhglobal.com)
Abstract
Historically, the use of MF/UF for drinking water and wastewater treatment has been almost
exclusively focused on polymeric membranes. New generation ceramic membranes have been
recently introduced in the market, which possess unique advantages over currently available
polymeric membranes. Ceramic membranes are mechanically superior to polymeric membranes
and are more resistant to severe environments (chemical, thermal). And as a result, ceramic
membranes can perform more efficiently than existing polymeric membranes under more rigorous
operation conditions. Ceramic membranes are able to operate at higher filtration flux, higher
feedwater recoveries, have more efficient backwash using high pressures, operate at extended
backwash intervals and have low chemical cleaning requirements, while experiencing long
membrane life without breakage. This paper presents results of a pilot study designed to
investigate the application of new generation ceramic membranes for water and wastewater
treatment. Ozonation and coagulation pretreatment were evaluated to optimize the operation of
ceramic membrane. Few pilot studies with ceramic membranes have been performed - most of
which have occurred outside of the U.S. The study is one of the first pilot studies performed in the
U.S. to evaluate using ceramic membranes to treat surface water and wastewater effluent using
full-scale ceramic membrane modules.
Keywords
microfiltraion; ceramic membrane; pretreatment; ozonation; coagulation; surface water; WWTP
effluent
INTRODUCTION
The installation of microfiltration (MF) and ultrafiltration (UF) facilities for municipal water and
wastewater treatment has dramatically increased over the past decade (Adham et al., 2005). This
growth has been primarily spurred by the increasing demand for reliable fresh water, a demand
created by a rapidly growing population and a warming global climate. Public concerns over the
ability of conventional treatment to produce safe water have created a market for applying
membrane-based treatment processes to alleviate water scarcity and ensure high quality water. In
pursuit of these goals, continued innovation and development has been performed to improve the
effectiveness and lower the cost of membrane-based treatment methods.
Historically, the use of MF/UF for water and wastewater treatment has been almost exclusively
focused on polymeric membranes (Van der Bruggen et al., 2003). Polymeric membranes have been
known to often have integrity problems regarding the module assembly (potting) or material
stability. Most polymeric membrane systems operate well within a fairly neutral to slightly acidic
pH range, with prolonged extreme acidic or alkaline conditions posing potential problems
(Farahbakhsh et al., 2004). Furthermore, exposure to extreme oxidant conditions created by
chlorine and ozone can cause degradation of polymeric membranes (Castro and Zander, 1993). As
a result, innovative MF/UF membranes are currently being developed to improve pore distribution,
mechanical stability, and chemical stability, using optimized polymeric formulations or alternative
materials (i.e., ceramics, steel, polytetrafluoroethylene, etc.). Once such unique material that shows
promise in addressing the current challenges of conventional polymeric membranes is ceramics.
Ceramic membranes are mechanically and thermally superior to polymeric membranes and are
more resistant to severe chemical environments (Shanbhag et al., 1998; Lee and Cho, 2004; Karnik
2004). With ceramic membranes, a filtration at high temperature (up to 500 °C) and extreme pH
values (pH 1-14) is possible (Benfer et al., 2001). The pore-size can be easily controlled by the
sintering and the sol/gel process used to prepare ceramic membranes (Van der Bruggen et al.,
2003). The ceramic membrane provides excellent backwash efficiency as the material itself can
withstand high backwash pressure. The fouling cake, which may clog membrane pores can be
effectively removed during intensive backwash. Additionally, chemical cleaning efficiency is often
enhanced, since more aggressive acidic and oxidant conditions can be applied to ceramic
membranes.
This paper discusses results of pilot studies designed to investigate the application of new
generation ceramic membranes for water and wastewater treatment, focusing on specific properties
described above. This study aims to demonstrate the robust nature of the ceramic membrane
process operating on challenging source waters and to investigate ozonation as a pretreatment
process. Few pilot studies with ceramic membranes have been performed - most of which have
occurred outside of the U.S. To the authors’ knowledge, this study is the first pilot study performed
in the U.S. to evaluate ceramic membranes using full-scale membrane modules to treat surface
water and wastewater treatment plant (WWTP) effluent.
METHODS
Pilot System
A schematic diagram of the pilot system is shown in Figure 1. The system consists of two parts: the
ozone unit (Pacific Ozone, Benicia, CA) and the ceramic microfiltration unit (NGK Insulators, Ltd.,
Japan). For the pilot study on surface water, the membrane unit was operated with in-line
coagulation; for the pilot study on wastewater effluent, ozonation and coagulation pretreatment
were performed in series prior to the membrane process.
Compressed Air
Filtrate
Ozone
Generator
BW
Water
Backwash
Water Tank
Ozone
Contactor
Coagulant
Break Tank
Feed Water
Chemicals
for CEB
Ceramic
Membrane
Module
Backwash Waste Water
Ozonated
Water
Feed Pump
Ozone
Feed Pump
Membrane
Figure 1.
Schematic of the Ceramic Membrane Pilot Unit
2
Full-scale monolith ceramic membrane elements were used in this study, having dimensions of 59.1
in. (1.5 m) in length and 7.1 in. (0.18 m) in diameter as shown in Figure 2. The active membrane
surface area for a single pressure-driven element is 269 ft2 (25 m2). The ceramic membrane
operates as a pressurized membrane configuration in a direct filtration (dead-end) mode. Each
ceramic membrane element utilizes 2,000 inside/out channels (filtration cells), in which raw water
is filtered through a thin ceramic membrane separation layer (0.1 µm nominal pore size). The
filtrate outflows from the element through water collection slits, via internal water collection cells.
At the completion of each filtration phase, the membrane is backwashed with pressure up to 73 psi.
The membrane is chlorine resistant and could be operated at pH ranged from 2 to 12. The ceramic
membrane surface is hydrophilic and has a slightly negative surface charge.
Figure 2.
Full-scale ceramic membrane element (courtesy of NGK Insulators, Ltd.)
Water quality
California State Project Water (SPW) was used as the source water for the pilot study on surface
water. Raw SPW was supplied by the Agua de Lejos Water Treatment Plant (WTP), operated by
the City of Upland’s Water Facilities Authority (Upland, CA). The source water is characterized by
moderate hardness and alkalinity, moderate total organic carbon (TOC) and low turbidity. The raw
water alkalinity was approximately 75 mg/L as CaCO3. Turbidity varied from 0.9 NTU to 20 NTU
while the TOC values were observed between 2.8 to 5.4 mg/L. Raw water pH was consistently 7.5
and temperature varied between 11C and 26C through the study.
Secondary effluent from a conventional activated sludge process was used as the source water for
the pilot study on wastewater effluent. The pilot is located at the Inland Empire Utilities Agency
(IEUA) Recycling Plant No. 5 (RP-5) in Chino, California. The pH of the secondary effluent was
consistently near 6.8 and temperature varied between 21 °C to 25 °C through the study. Turbidity
varied from 0.6 NTU to 1.8 NTU while the TOC values were observed between 3.8 to 6.0 mg/L.
The alkalinity was approximately 140 mg/L as CaCO3 throughout the testing. Full nitrification has
been consistently achieved in the secondary effluent, indicated by the low concentrations of nitrite
(NO2-N < 0.03 mg/L) in the feedwater to the membrane.
3
RESULTS AND DISCUSSION
Extensive pilot studies on surface water and WWTP effluent were conducted with to demonstrate
the performance of ceramic membranes with respect to pretreatment condition, operating flux,
backwash efficiency, and long term fouling trends. Selected results are presented below.
Treatment of Surface Water
For treating surface water 2 mg/L-Al of in-line coagulation was chosen as the optimal condition,
under which a 2-week run at 100 gfd was conducted with Acid CEB (Chemical Enhanced
Backwash) to demonstrate long term performance. As shown in Figure 3, the NGK ceramic
membrane operated under the aforementioned condition was able to maintain a stable performance
over the 2-week period. The specific flux declined to 61% of the initial value after 140 hours
operation. However, the flux was completely restored after each Acid CEB.
Normalized Specific Flux @20°C
1.0
0.8
0.6
CEB
0.4
CEB
0.2
Initial Specific Flux
@20°C = 40 gfd/psi
0.0
0
70
140
210
280
350
420
Time (hours)
Figure 3.
Long-term operation with 2mg/L-Al in-line coagulation and Acid CEB
Treatment of WWTP Secondary Effluent
The optimal coagulant dose for wastewater operation in this study was determined to be 3.5 mg/LAl (data not shown in this paper). Figure 4 summarizes the long-term performance data of the NGK
ceramic membrane treating WWTP secondary effluent under three different flux conditions. The
membrane was continuously operated for 950 hours. An increase of transmembrane pressure (TMP)
was recorded over time, which yielded the specific flux decline indicating the membrane fouling.
As shown in Figure 4, the pilot testing began at a flux of 50 gfd to establish the baseline comparison
with polymeric membranes that typically operate at a similar flux and recovery for water reuse
applications. Utilizing one Cl2 CEB every two days, no fouling was observed over the 200 hours of
operation (approximately 9 days). Both the TMP and the specific flux remained constant at this
4
condition, demonstrating the improved performance of ceramic membrane when treating secondary
wastewater at fluxes typical to commercial polymeric membranes.
25
50 gfd
100 gfd
20
24
15
18
CEB
10
CIP
12
5
TMP
Temp
0
45 0
Specific Flux at 20 °C
(gfd/psi)
30
150 gfd
6
200
400
600
800
0
1000
Specific Flux
at 20 °C
200
400
600
800
1000
36
Temperature (°C)
Trans-membrane Pressure
(psi)
After 200 hours, the flux was promoted to 100 gfd while the CEB frequency was maintained at once
every two days. As shown in Figure 4, initial fouling was observed in the first 48 hours after
changing the condition; however, CEB was able to recover most of the specific flux except for the
first cycle. From hr 250 to 650, the TMP was maintained between 4.1 psi to 5.4 psi with no
significant irreversible fouling. For the 450 hours of operation (approximately 18 days), the
ceramic membrane demonstrated stable performance at 100 gfd, as the Cl2 CEB every two days
fully controlled the fouling tendency with TMP below 8 psi.
27
18
9
0
0
Time of Operation (hour)
Figure 4.
Long-term Operation on Secondary Effluent in Phase I Testing
At hour 660, a full cleaning in-place (CIP) was performed to restore the initial permeability of the
membrane. Specific flux increased to 44.6 gfd/psi after the cleaning. Flux was promoted to 150 gfd
and the CEB frequency was maintained at once every two days. As expected, the membrane
experienced more fouling at higher flux. Moreover, fouling significantly increased once TMP
exceeded 7.5 psi at 150 gfd. The CEB at 2-day frequency was insufficient to stabilize the
membrane performance at this high flux and irreversible fouling was observed.
5
Treatment of Secondary Effluent with Pre-ozonation
The objective of this testing was to optimize the membrane treatment by adding a pre-ozonation
step to the overall coagulation/MF process. With ozone pretreatment, it was expected that the
membrane performance could be stabilized at an optimal coagulant dose lower than what was
established in the previous section. The ceramic membrane was operated at 100 gfd (corrected to
20°C) with 120-min hydraulic backwash interval and no CEB, when ozone was incorporated into
the pretreatment train.
Optimization of Ozone Doses. A series of ozone doses were investigated and the optimal ozone and
coagulant combination was selected for the long-term performance evaluation. Figure 5 shows that
different trends of specific flux decline were developed when the ozone dose was decreased
stepwise from 6 mg/L to 2.7 mg/L. As shown in this figure, the membrane experienced increased
fouling with decreased pre-ozonation, when the PACl dose was maintained at 1 mg/L-Al. Results
showed that and the membrane operation could be stabilized at an ozone dose as low as 3.5 mg/L.
With 6 mg/L ozone and 1 mg/L PACl, almost no fouling was observed after 5 days of operation.
With 5 mg/L ozone, the membrane specific flux decreased to about 84% of the initial specific flux
after 2 days of operation, and stabilized at 82% to 88% of the initial specific flux (i.e., 43 to 46
gfd/psi adjusted to 20°C) in the next 3 days. With 3.5 mg/L ozone, the membrane specific flux
further decreased to 76 % of the initial specific flux after 2 days, and stabilized at 70% to 82% of
the initial specific flux (i.e., 36 to 43 gfd/psi adjusted to 20°C) in the next 3 days. When the ozone
dose was further decreased to 2.7 mg/L, however, the membrane started to foul rapidly. The
membrane specific flux decreased to 42% of the initial specific flux after 3 days, and to 36% after 5
days. No significant improvement of the membrane operation was observed compared to the
baseline condition of 3.5 mg/L PACl and no ozone. Therefore, the ozone dose was backed to 3.5
mg/L, since it appeared to be a critical dose above which a stable membrane operation could be
maintained.
Normalized Specific Flux at 20 °C
(Jsp/Jsp,0)
1.0
0.8
0.6
0.4
6 O3 - 1 Al
5 O3 - 1 Al
0.2
Jsp,0 =52 gfd/psi
3.5 O3 - 1 Al
2.7 O3 - 1 Al
0.0
0
24
48
72
96
120
144
Time of Operation (hour)
Figure 5.
Fouling of NGK Membrane with 1 mg/L PACl and Decreasing Ozone (6 to 2.7 mg/L)
6
Table 1 summarizes the ozone residual in the contactor effluent measured for each ozone dose. The
residual data shows that the ozone demand of the feed water during optimization study was
approximately 3.3 mg/L. This was close to the critical ozone dose of 3.5 mg/L as identified in the
above section. Therefore, an interesting observation was made when relating the ozone residual to
the membrane performance. It appears that the membrane operation could be stabilized for long
term operation when ozone was applied above the demand.
It is also important to note that the critical ozone dose for membrane operation is related to not only
the coagulation condition but also the feed water quality. Future study needs to be conducted to
investigate the mechanism of ozonation and coagulation synergy in order to further understand their
effects on the operation of NGK ceramic membrane.
Table 1. Ozone Residual and Membrane Performance in Optimization Study
Ozone Dose
(mg/L)
6
5
3.5
2.7
Ozone Residual
(mg/L)
0.89
0.61
0.15
<0.05
Jsp/Jsp,0
@ Day 3
0.98
0.88
0.72
0.42
Jsp/Jsp,0
@ Day 5
0.98
0.82
0.70
0.36
Four-week Long Term Pilot Operation. Based on the optimization results discussed in the previous
section, a combination of 4 mg/L ozone and 1 mg/L PACl was selected as the pretreatment dosing
condition, under which membrane operation was stabilized for long-term evaluation. The ozone
dose was slightly higher than the aforementioned critical ozone dose of 3.5 mg/L to provide a
targeted ozone residual of 0.4-0.6 mg/L.
Figure 6 summarizes the long-term performance data of the NGK ceramic membrane filtering
secondary effluent with optimized pretreatment conditions. The membrane unit had been
continuously operated for 680 hours, with a pretreatment dosing of 4 mg/L ozone and 1 mg/L PACl.
The operational condition of the membrane was kept at a flux of 100 gfd@20°C, 2-hour backwash
interval and no CEB. An increase of TMP was recorded over time, which yielded the specific flux
decline indicating the membrane fouling.
As shown in Figure 6, the ceramic membrane demonstrated stable performance through the first
400 hours of operation, as the TMP was well controlled in the range of 1.9 to 2.5 psi and the
specific flux between 40 and 55 gfd/psi@20°C. The break of data at the 400 hour (numbered as 
in Figure 6) was caused by the temporary loss of data logging since the laptop rebooted in the
midnight. This data loss did not interrupt any membrane operation and data logging was resumed
next morning.
After 550 hours of operation, a TMP spike and sudden specific flux drop was observed (numbered
as  in Figure 6) when a strong rain storm occurred at the testing site. It was discovered that the
cover of the coagulant tank was blown away in the storm and the coagulant in the tank was diluted
by the rain. As a result, the membrane rapidly fouled to 20 psi in 24 hours when running with
diluted coagulant. The next day, the operator restored the coagulant feed and resumed the
membrane operation without any cleaning. Interestingly, the membrane “self-recovered” with the
restoration of 1 mg/L PACl in the feed line. The TMP quickly recovered to 4 psi in 8 hours and
further to 2.5 psi by the end of Week 4. Accordingly, the specific flux gradually restored to 40
7
gfd/psi@20°C by the closure of the testing at the end of 680 hours of operation.
20
24
15
18
2
10
5
12
6
1
0
75 0
Specific Flux at 20 °C
(gfd/psi)
30
TMP
Temp
100
200
300
400
500
600
Temperature (°C)
25
0
700125
60
100
45
75
30
50
15
25
Specific Flux at 20°C
Flux at 20°C
0
0
100
200
300
400
500
600
Flux at 20 °C (gfd)
Trans-membrane Pressure
(psi)
Overall the membrane was able to show a stable performance through the long-term operation with
4 mg/L ozone and 1 mg/L PACl. Although testing was interrupted due to the loss of the coagulant,
the membrane quickly recovered itself without any cleaning after the restoration of coagulant feed.
0
700
Time of Operation (hour)
Figure 6.
Long-term Operation of NGK Ceramic Membrane with 4 mg/LOzone and 1 mg/L PACl
Table 2 summarizes the weekly water quality data that was collected during the long-term
performance evaluation. As shown in this table, the following observations were made:
o The ozone residual remained at around 0.45 mg/L in the contactor effluent and not detected
before the membrane.
o The pH of the water remained at 6.8 and temperature at 22-23°C.
o 9-20% of the TOC in feed water was removed through the process, leaving the finished
water of 3.2 - 4.7 mg/L TOC.
o The reduction of UV absorbance was substantial: over 50% of UV absorbance was removed
through the ozone/coagulation/MF process.
o The bromide levels in the feed, ozonated and filtrate waters remained at 120 µg/L, indicating
little bromate formation. This was further verified by the lab analysis that had shown less
than 5 µg/L bromate in all the samples.
o 17-25% of the phosphate reduction was achieved in the long-term run, leaving the finished
water of 1.4 - 2.5 mg/L phosphate-P.
8
Table 2.Weekly Water Quality Monitored in Long-term Performance Evaluation
Parameter
Sample ID
Unit
O3 Residual
Contactor
Value
01/16
01/25
01/30
02/06
mg/L
0.46
0.48
0.38
0.45
Membrane
mg/L
<0.05
<0.05
<0.05
<0.05
Feed
-
6.8
6.8
6.8
6.8
Filtrate
-
6.8
6.9
6.8
6.8
Temperature
Feed
°C
22.5
22.3
22.4
22.3
TOC
Feed
mg/L
3.9
5.9
5.4
5.1
Ozonated
mg/L
3.7
5.5
5
4.8
Filtrate
mg/L
3.2
4.7
4.9
4.4
% Removal
%
18%
20%
9%
14%
Feed
abs
0.108
0.092
0.105
0.095
Ozonated
abs
0.062
0.049
0.054
0.048
Filtrate
abs
0.053
0.042
0.053
0.043
% Removal
%
51%
54%
50%
55%
Feed
µg/L
119
119
116
118
Ozonated
µg/L
114
122
120
119
Filt
µg/L
124
120
113
119
Feed
µg/L
<5
<5
<5
<5
Ozonated
µg/L
<5
<5
<5
<5
Filtrate
µg/L
<5
<5
<5
<5
Feed
mg/L
1.8
3.1
2.9
2.8
Ozonated
mg/L
1.8
3.1
2.9
2.7
Filtrate
mg/L
1.4
2.5
2.4
2.1
% Removal
%
22%
19%
17%
25%
pH
UV254
Bromide
Bromate
Phosphate-P
9
CONCLUSIONS
The following conclusions can be made from the pilot study:
Treating surface water
 The ceramic membrane demonstrated stable performance at 100 gfd and 100 gfd with a CEB
frequency of once every six days and coagulant dose of 2 mg/L Al.
Treating WWTP secondary effluent
 The ceramic membrane demonstrated stable performance at 50 gfd and 100 gfd with a CEB
frequency of once every two days and coagulant dose of 3.5 mg/L Al.

The membrane experienced more fouling at high flux of 150 gfd and CEB of once every two
days was insufficient to recover the membrane permeability.
Treating WWTP secondary effluent with ozonation pretreatment
 Optimization of the treatment process has shown that the membrane operation (100 gfd@20°C,
120 min backwash interval and no CEB) could be stabilized at a PACl dose of 1 mg/L and
ozone dose as low as 3.5 mg/L.

The ceramic membrane has demonstrated stable performance over the 4-week testing period
when water was pretreated with 1 mg/L PACl and 4 mg/L ozone. Reduction of UV absorbance,
TOC and phosphate was observed in the treated samples.

Loss of coagulant led to rapid fouling of the NGK ceramic membrane, even when the feed water
was still ozonated. However the ceramic membrane self recovered after the restoration of
coagulant without cleaning.
10
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