Performance of Hybrid MF Membrane Systems Using
Polytetrafluoroethylene (PTFE) and Ceramic Membrane
Ikuma Hayakawa*, Hiroyuki Nishimura*, Masayuki Hara*, Yoshimitsu Komatsu*,
Iwao Tsuda**, Masami Oya**
* Osaka Municipal Waterworks Bureau Kunijima purification plant 1-3-14 Kunijima Higashi-Yodogawa-ku Osaka city
(E-mail: [email protected])
** Hanshin Water Supply Authority 3-20-1 Nishi-Okamoto Higashi-Nada-ku Kobe city
(E-mail: [email protected])
Abstract
This study seeks to examine the applicability of Hybrid MF Membrane Systems to surface water of the
Yodo river, which has high pollution level and has its source in Lake Biwa, in place of the treatment method
featuring chemical oxidation that generates by-products. Hybrid MF Membrane Systems (submerged type
with PTFE membranes and casing type with ceramic membranes) are new water treatment systems that
combine adsorption using activated carbon and biological oxidation with membrane separation. The testing
units for these systems started operation in September 2009. Conditions for stable operation were examined
for both systems, using trans-membrane pressure (TMP) as an index. Performance of each system was also
studied. In the case of the Submerged Type MF Membrane System, certain findings were obtained
concerning the relationship of the coagulant and powdered activated carbon (PAC) feeding rate with TMP.
Favorable performance was also obtained through biological oxidation over nine detention hours during the
low temperature period, with ammonia nitrogen and manganese ions respectively at below 0.02 mg/L and
below 0.001 mg/L. On the other hand, a problem remained with the total organic carbon (TOC), which
stood higher than the existing advanced water treatment system (AWTS) at 1.1 mg/L. In the case of the
Casing Type MF Membrane System, conditions concerning stable operation were set following related
researches. Under these conditions, performance of the system during the low temperature period was
evaluated. The results indicated favorable removing rates, with turbidity at below 0.1 and TOC at 0.8 mg/L.
On the other hand, ammonia nitrogen and manganese ions stood respectively at 0.09 mg/L and 0.025 mg/L
following biological oxidation, which are levels scarcely better than the source water, suggesting the
lowered bioactivity during the low temperature period as a problem yet to be solved.
Keywords
adsorption, advanced water treatment, biological oxidation, ceramic membrane, hybrid system, PTFE
membrane
INTRODUCTION
The Osaka Municipal Waterworks Bureau (OMWB) has introduced an AWTS, which combines the
conventional coagulation-sedimentation and rapid sand filtration system with ozonation and granular
activated carbon treatment. The AWTS has enabled the degradation of trace organic substances, such as
substances with musty odor, precursor substances of disinfection by-products, agricultural chemicals etc.,
while inactivating Cryptosporidium and other pathogenic microorganisms, thus dramatically improving
the safety and reliability of tap water.
However, circumstances surrounding tap water quality are changing rapidly these days, considering the
problem of bromate ions, which are by-products of ozonation that were incorporated into the drinking
water quality standard in 2004; response to hazardous chemical substances that are yet to be regulated;
rising health awareness among citizens; increasing customer needs for tasty water and distaste for bleach
odor, and so on. In order to address such requirements, the OMWB constructed the Advanced
Technology for Optimum Treatment Experimental Station (“testing plant”) , 1 and has promoted the
optimization and upgrading of existing treatment methods, and the development of next-generation water
treatment technologies.
As a part of these efforts, the OMWB and the Hanshin Water Supply Authority (HWSA) are jointly
developing new treatment technologies, 2 which are intended to fully replace the existing methods. In
place of a method featuring chemical oxidation that generates by-products, the joint study is focused on
Hybrid MF Membrane Systems that combine adsorption using activated carbon and biological oxidation
with membrane separation, and is in progress using the testing units (two lines respectively using PTFE
membranes (submerged type) and ceramic membranes (casing type)), which are installed inside the
testing plant. These systems are expected to secure performance equivalent to the AWTS, reduce the
generation of by-products, save space required, facilitate operation and maintenance control, cut down on
chemicals cost, and make other contributions, through the biological oxidation-based treatment of various
soluble substances free from by-products, and appropriate solid-liquid separation using membranes.
This study examined conditions for the stable operation of the Hybrid MF Membrane Systems, using
TMP as an index, clarified the relationship between parameters and TMP, conducted a performance study,
and obtained findings on basic water quality items, including TOC, ammonia nitrogen and manganese
ions. The results are reported below.
This study has been adopted and subsidized as a “Innovative Technology and System for Sustainable
Water Use” under the Core Research for Evolutional Science and Technology (CREST) project, the Japan
Science and Technology Agency (JST), for from 2009 to 2014.
Coagulant
MATERIALS AND METHODS
PAC
Circulation
Acid
Overview of the Testing Units
Submerged Type MF Membrane System
Figure 1 indicates the test flow, and Table 1 shows the
Out of system
equipment specifications. In this test flow, surface water
Biological Oxidizing and
Source water
Treated water
Flush mixing
PAC Adsorption Tank
(The Yodo river )
MF membrane (submerged type)
of the Yodo river is used as source water. After adding
Figure 1. Test Flow for the Submerged Type MF Membrane System
acid agent (sulfuric acid), PAC and coagulant (aluminum
sulfate), source water is flowed into the biological Table 1. Equipment Specifications for the Submerged Type MF Membrane
oxidizing and PAC adsorption tank (“BOPA tank”), and System
Shape/type/material
Hollow fiber/MF/PTFE
filtered with PTFE membranes that are submerged in the Membrane
Nominal pore size
0.1μm
Membrane area
14m /module
BOPA tank. For physical cleaning, a combination of
Biological oxidizing and
scrubbing and counter pressure cleaning using chlorine1.1m(W) x 1.2m(L) x 2.5m(H)
PAC adsorption tank
added filtered water is used. Scrubbing is also conducted
at a set interval during filtration. Wastewater from counter pressure cleaning, during which filtration is
stopped, is returned to the BOPA tank. Desludging is conducted at a set interval from the bottom of the
BOPA tank, in accordance with the set recovery rate.
2
Casing Type MF Membrane System
Before coagulant
After coagulant
Figure 2 indicates the test flow, and Table 2 shows the
PAC
Circulation
Acid
equipment specifications. In this test flow, surface water of
the Yodo river is used as source water. After adding acid
MF membrane
Out of system
agent (sulfuric acid), PAC and coagulant (aluminum
(casing type)
Biological Oxidizing
Source water
Flush mixing
sulfate), source water is flowed into the BOPA tank, and
and
Treated water
(The Yodo river )
PAC Adsorption Tank
aerated in the BOPA tank, before flowed through the
Figure 2. Test Flow for the Casing Type MF Membrane System
upward flow setting plate and filtered with casing type
Table 2. Equipment Flow for the Casing Type MF Membrane System
ceramic membranes that are attached outside the BOPA
Shape/type/material
Monolith/MF/ceramic
tank. Cross-flow filtration is adopted as a filtration method.
Membrane
Nominal pore size
0.1μm
Membrane area
15m /module
The concentrated water is returned to the BOPA tank.
Biological oxidizing and
Physical cleaning is conducted at a set interval on the
1.1m(W) x 3.0m(L) x 1.1m(H)
PAC adsorption tank
membrane secondary side at an air pressure (approx. 0.5
MPa), stopping the filtration. Wastewater generated from cleaning is returned to the BOPA tank.
Desludging is conducted at a set interval from the bottom of the BOPA tank, in accordance with the set
recovery rate.
2
Method of Study
Submerged Type MF Membrane System
<Details of Study>
1) Examination on Conditions for Stable Operation
Conditions concerning stable operation for the Submerged Type MF Membrane System were examined
as follows, using TMP as an index.
・ Relationship between pH conditions in the BOPA tank and TMP
・ Relationship between water quality items with seasonal change (WQISC) (algae of water source and
manganese ions) and TMP
・ Relationship between the interval of physical cleaning and TMP
・ Relationship between chemical (PAC and coagulant) feeding rate and TMP
2) Study on Performance
Basic water quality items, such as TOC, ammonia nitrogen and manganese ions, were examined as
follows, using chemical feeding rate as a parameter.
・ Relationship between chlorine level in back wash water and performance
・ Relationship between PAC feeding rate and performance
<Operating Conditions>
Operating conditions for the Submerged Type MF Membrane System are indicated in Table 3.
Table 3. Operating Conditions for the Submerged Type MF Membrane System
No.
RUN1
RUN2
RUN3
RUN4
Study period
1-1
1-2
1-3
2-1
2-2
3-1
2009/9 - 10
2009/10 - 12
2009/12
2010/4
2010/4 - 5
2010/7 - 9
3-2
2010/9 - 10
4-1
4-2
2010/12
2010/12
5-1
2010/12
5-2
2010/12
5-3
2010/12 - 1
Flux
( m/d)
Detention*1
(hours)
Coagulant
feeding rate
(mg/L)
PAC feeding rate
Recovery
BOPA tank pH
(mg/L)
(%)
Approx. 7.5
(non-adjusted)
30
25
15
9
99.0
10
0.6
3
2011/1
5-5
5-6
5-7
2011/1
2011/1
2011/1 - 2
2011/2
2011/2 - 3
RUN6
7-1
RUN7
99.5
6.8 - 7.0
(acid agent fed)
3
25
Approx. 7.5
(non-adjusted)
RUN5
5-4
95 - 100
1.5
*5
4.5
0.6
9
5
99.9
Conditions for physical cleaning
(combined with scrubbing)
Once per 20 min.
Filtered water: 5.7 m/d x 30 sec.
Once per 20 min.
Chlorine-containing water:*2 5.7 m/d x
15 sec.
Filtered water: 5.7 m/d x 15 sec.
(During 8/4 - 8/19, RUN3, reverse jet
flux increased due to the failure of the
flowmeter.)
Once per 20 min.
Chlorine-containing water:*3 8.6 m/d x
15 sec.
Filtered water: 8.6 m/d x 5 sec.
Once per 10 min.
Chlorine-containing water:*3 4.3 m/d x
15 sec.
Filtered water: 4.3 m/d x 5 sec.
Once per 10 min.
Chlorine-containing water: *48.6 m/d x
15 sec.
Filtered water: 8.6 m/d x 5 sec.
Once per 10 min.
Chlorine-containing water: *38.6 m/d x
15 sec.
Filtered water: 8.6 m/d x 5 sec.
Once per 10 min.
Filtered water: 8.6 m/d x 20 sec.
*1. Detention hours are given by dividing the tank volume with the filtration flow. *2. 4mg-Cl/L *3. 2mg-Cl/L *4. 1mg-Cl/L
*5: Flux was lowered due to the progress of fouling (0.5 - 0.6 m/d).
7-2
2011/3
Casing Type MF Membrane System
<Details of Study>
1) Examination on Conditions for Stable Operation
Conditions concerning stable operation for the Casing Type MF Membrane System were examined as
follows, using TMP as an index.
・ Relationship between recovery and TMP
・ Relationship between circulating water and TMP
・ Relationship between coagulation control (feeding point and coagulation pH control) and TMP
・ Relationship between the interval of physical cleaning and TMP
2) Study on Performance
The test unit was operated under the conditions set based on the study as described in 1). The resulting
performance was evaluated, and problems to be solved were identified considering the drinking water
quality standard, target value for complementary items, and the performance of the AWTS.
<Operating Conditions>
Operating conditions for the Casing Type MF Membrane System are indicated in Table 4.
Table 4. Operating Conditions for the Casing Type MF Membrane System
No.
Study
period
RUN
1
2010/2 - 3
RUN
2
2010/4 10
Flux
( m/d)
Circulating
water ratio*
PAC
(mg/L)
Before
coagulant
(mg/L)
After
coagulant
(mg/L)
ｐH control
point
−
6.8 - 7.0
BOPA tank
BOPA tank
detention
(hours)
Conditions
for physical
cleaning
Recovery
(%)
99.5
1:1
25
Once per
30min
99
15
1.7
3
RUN
3
2010/10 2011/1
1:1
⇒
1:0
RUN
4
2011/2 - 3
1:0.3
3
12.5⇒0
12.5⇒25
6.8 - 7.0
BOPA tank
⇒
Treated water
-
25
6.5 - 6.8
Treated water
99.9
98
Once per
30min
Once per
120min
Once per
120min
* Circulating water ratio = Treated water : Circulating water
1/4
1/3
1/2
1/1
12/31
12/30
12/29
12/28
12/27
12/26
12/25
3/4
2/25
2/18
2/11
2/4
1/28
1/21
1/14
1/7
Corrected TMP kPa at 25℃
12/24
Corrected TMP kPa at 25℃
Corrected TMP kPa (at 25℃)
80
RESULTS AND DISCUSSION
Approx. pH7.5
70
Submerged Type MF Membrane System
60
50
pH6.8
Examination on Conditions for Stable Operation
40
-7.0
RUN1
Figure 3 indicates changes in TMP of the Submerged Type
30
RUN2
20
MF Membrane System. There was a large difference in
RUN3
10
changes of TMP between RUN1 and RUN2. As major causes
0
0
20
40
60
80
100
for this difference, pH conditions in the BOPA tank (“pH
Elapsed days
conditions”) and seasonal differing source water quality were
Figure 3. Behavior of TMP in the Submerged Type MF
Membrane System (RUN1 - 3)
suspected. In order to verify difference due to pH conditions,
operation was undertaken in RUN3 under two differing sets of pH Table 5. Source Water Manganese Ions, Algae of Water
conditions. This did not cause clear difference in the rising trends Source and BOPA Tank pH (RUN1 - 3)
Manganese
Algae of
BOPA tank
of TMP. With regards to seasonal differing source water quality, a
No.
ions
water source
pH
(mg/L)
(pcs/mL)
focus was placed on the relationship between TMP and source
RUN1
1300
Approx 7.5
water quality items with large seasonal changes (i.e. algae of
4
RUN2
0.022
3300
6.8-7.0
water source and manganese ions; hereafter collectively referred
to as “water quality items with seasonal change (WQISC)”). The
RUN3
0.014
820
6.8-7.0 ⇒7.5
results showed that, in RUN2, in which the values of WQISC
were relatively high, the rising trend of TMP was larger than that
RUN5-1 RUN5-2
RUN5-3
30
in other RUNs. Therefore, it is possible that WQISC have
41kPa/month
negative influence on the stable operation of membranes (see
25
47kPa/month
Figure 3 and Table 5). It will be required to promote examination
20
85kPa/month
on conditions for stable operation with a focus on the
PAC feeding rate：
15
15mg/L →1.5mg/L
relationship between WQISC and TMP.
Physical
cleaning
interval：20min→10min
10
Figure 4 indicates changes in TMP from RUN5-1 through
Back wash water ： 15m3/h → 7.5m3/h
RUN5-3. From RUN5-1 to RUN5-2, the cleaning interval was
5
shortened from 20 to 10 minutes, and the rising trends of TMP
before and after this shortening were compared (in doing so, the
Figure 4. Behavior of TMP in the Submerged Type MF
Membrane System (RUN5-1 - 5-3)
cleaning flux was lowered from 8.6 m/d to 4.3 m/d, in order to
RUN5-4 RUN5-5
RUN6
adjust the water volume used for cleaning). Consequently, the
60
rising trend of TMP was slowed down, which is considered to
50
47kPa/month
suggest that a shorter interval of physical cleaning has an effect
40
to control the rise of TMP. From RUN5-2 to RUN5-3, the PAC
30
49kPa/month
feeding rate was reduced from 15 mg/L to 1.5 mg/L, and the
20
rising trends of TMP before and after this reduction were
83kPa/month
10
compared (in doing so, the recovery rate was raised from 99.0 to
0
99.9%, in order to adjust the PAC level in the BOPA tank with
conditions before the reduction). However, the changed PAC
Figure 5. Behavior of TMP in the Submerged
feeding rate did not affect the rising trend of TMP.
Type MF Membrane System (RUN5, 6)
In RUN5-4 to RUN5-5 and RUN6, the coagulant feeding rate
was changed respectively to 25 mg/L for RUN5-4 to RUN5-5, and to 5 mg/L for RUN6. Figure 5
Increased chlorine level
in back wash water
RUN5-4
Manganese ions (mg/L) (
indicates the resulting changes in TMP. Immediately
following the reduction of coagulant feeding rate from 25
mg/L to 5 mg/L, the rising rate of TMP became larger as
had been expected. However, the rising rate subsequently
returned to the same level as before the reduction.
Continued research is considered necessary.
Stopped the chlorine addition
RUN7-2
RUN5-5∼7-1
0.070
0.060
0.050
0.040
0.030
0.020
0.010
0.000
Source water
Treated water
1/6
1/26
2/15
3/7
3/27
Figure 6. Changes of Manganese Ions in the Submerged
Type MF Membrane System（RUN5-4 - RUN7）
Reduced PAC feeding
5.0
4.0
TOC(mg/L)
Study on Performance
1) Relationship between Performance and Chlorine Level
in Back Wash Water
Figure 6 indicates changes in the level of manganese ions in
treated water in RUN5-4 through RUN7-2.Performance of
manganese ions improved around the increase of chlorine level in
back wash water. However, the performance was retained after the
stop of chlorine addition. Continued research is considered
necessary.
Source water
Treated water
3.0
2.0
1.0
0.0
12/17
12/24
12/31
1/7
1/14
1/21
Figure 7. Changes of TOC in the Submerged
2) Relationship between Performance and PAC Feeding Rate
Type MF Membrane System (RUN4 - RUN5)
Figure 7 indicates changes in the level of TOC in treated water in
RUN4 to RUN5. The PAC feeding rate was reduced from 15 mg/L to 1.5 mg/L (in doing so, the recovery
rate was raised from 99.0 to 99.9%, in order to Table 6. Average Values of TOC, Ammonia Nitrogen and Manganese Ions (2010)
(mg/L)
retain the PAC level in the tank). This resulted in
Source
Treated
Removal
Item
a lowered TOC removal trend. This suggests that
water
water
rate
TOC (n=106)
2.2
0.8
59％
the PAC feeding rate affects the TOC
0.08
0.07
 10℃ (n=89)
−2％
Ammonia nitrogen
performance substantially.
0.08
0.06
< 10℃ (n=25)
14％
Manganese ions
 10℃ (n=83)
< 10℃ (n=25)
0.015
0.024
0.008
0.014
43％
41％
3) Summary
Table 6 shows the average values of TOC, Table 7. Average Values of TOC, Ammonia Nitrogen and Manganese Ions (RUN7-2)
(mg/L)
ammonia nitrogen and manganese ions in treated
Source
Treated
Removal
Item
water
water
rate
water in 2010. Table 7 lists the average values in
TOC (n=9)
1.9
1.1
34％
treated water for RUN7-2 only, in which the stop
0.06
0.02
 10℃ (n=6)
70％
Ammonia nitrogen
of chlorine addition and reduction of PAC feeding
0.06
0.02
< 10℃ (n=4)
70％
0.018
0.001
 10℃ (n=6)
93％
rate were undertaken. Partly because retention
Manganese ions
0.019
0.001
< 10℃ (n=25)
93％
time in the BOPA tank was nine hours, which was
longer than in the previous RUNs, the performances of ammonia nitrogen and manganese ions were
improved in RUN7-2. On the other hand, the TOC performance was lowered. An action is considered
necessary to improve the TOC performance.
Corrected TMP kPa at25℃
Casing Type MF Membrane System
160
Examination on Conditions for Stable Operation
RUN1
RUN2
Figure 8 indicates changes in corrected TMP (at 25C)
120
RUN3
from RUN1 through RUN3. The recovery rate was lowered
80
from 99.5 to 99.0% from RUN1 to RUN2, thereby reducing
the SS level in the BOPA tank from approx. 3,000 mg/L to
40
1,500 mg/L, and relieving the turbidity load on membranes.
0
However, the rising trend of TMP did not change.
0
15
30
45
60
75
90
Therefore, the turbidity-removing effect of the flow setting
Elapsed days
Figure 8. Changes of TMP in the Casing Type MF
plate, which was attached to the BOPA tank, was verified.
Membrane System (RUN1 - 3)
In the meantime, pressure rise in the first half was reduced
in RUN3, compared to RUN1 and 2. Figure 9 shows changes in corrected TMP in RUN3 and their
relationship with pH values.
During Period 1 in this figure, coagulant was fed 12.5 mg/L respectively into the point before and after
the BOPA tank. During Period 2, coagulant was fed 25 mg/L only into the point after the tank,
immediately before the filtration. Except during Period 3, TMP did not rise substantially. This is
considered to suggest that coagulation immediately before
filtration has an effect to control the rise of TMP. While the
②
③
circulation water ratio was set at 1:0 during Period 2, TMP
did not rise substantially except during Period 3. Thus it was
verified that circulation water ratio was not a governing
factor for the rise of TMP. Therefore, the shearing force due
①
to parallel flow on the membrane surface is not considered to
Coagulant
wasn’t fed
contribute substantially to the control of rise in TMP.
In the early stage, the coagulation pH was controlled by
adjusting pH in the BOPA tank at around 6.8. Because the
Figure 9. Changes in Corrected TMP and their
BOPA tank pH rose during Period 3, additional acid was fed
Relationship with pH Values in the Casing Type
MF Membrane System (RUN3)
into the tank. This lowered the pH of treated water to below
6.5, causing a considerable deviation of coagulation pH from the appropriate pH zone. This is considered
to be the cause of the rapid rise in TMP during Period 3.5, 6
Based on the above results, conditions for stable operation were arranged as follows. The feeding point
for coagulant is limited to the point after the tank. Acid is adjusted in order to control coagulation pH at
approx. 6.5 - 6.8. Circulation water ratio is set at 1:0.3, and the small flow is secured, in order to prevent
the clogging of flow channels of membrane elements (φ2.5 mm) due to turbidity, even though the effect
of cross-flow to control TMP is minimal. The interval of physical cleaning is set at 120 minutes, based on
the general cleaning interval for ceramic membranes, and considering the viewpoint of utility cost
reduction.
180
7.8
Corrected T MP
T reated water pH
BOPA tank pH
7.6
140
7.4
120
7.2
100
7
pH
Corrected TMP kPa at 25 ℃
160
80
6.8
60
6.6
40
6.4
20
6.2
12/28
12/18
12/8
11/28
11/18
11/8
10/29
10/19
10/9
6
9/29
0
Removal rate
Removal rate
Mn ions（μg/L）
NH4-N（mg/L）
Table 8. Comparison of Performance with the AWTS (average of Feb. 2011, average
Study on Performance
temperature 8°C)
Under the conditions set as described above,
AWTS*
Casing Type MF
RUN4 was operated. Its performance results are
Item
Source water
Evaluation
(reference)
Membrane System
indicated in Table 8. For reference, this table
also shows quality before adding chlorine to
Turbidity (mg/L)
6.3
<0.1
○
<0.1
water treated by the AWTS. With regards to
Manganese ions (mg/L)
0.028
0.025
×
0.002
turbidity, stable removal was achieved by the
Ammonia nitrogen (mg/L)
0.09
0.09
△
0.08
membrane separation. Bromic acids also stood
TOC (mg/L)
1.9
0.8
○
0.8
below the detection limit, because there is no
UV absorbance (260nm)
0.033
0.010
△
0.008
process that generates them. On the other hand,
Fluorescence intensity
216
54
△
20
ammonia nitrogen and manganese ions were not
Bromic acids (mg/L)
<0.0005
<0.0005
○
0.0018
removed favorably, even though their removal
○:
favorably
removed,
△:
slightly
inferior
to
the
AWTS,
×:
fundamental
action
required
was expected through biological oxidation in the
BOPA tank. This is considered to be because * Water immediately before chlorine addition at the Kunijima Treatment Plant, OMWB, average of Feb. 2009
the bioactivity was lowered
Source water
T reated water
Source water
T reated water
Removal rate
Removal rat e
during the low temperature
0.10
100%
25
100%
period. Among items related to
0.08
80%
20
80%
organic substances, TOC not
0.06
60%
15
60%
only satisfied the drinking water
0.04
40%
10
40%
quality standard (≦ 3 mg/L), but
0.02
20%
20%
5
also
showed
performance
0.00
0%
0
0%
equivalent to water treated by the
10 ℃≦
10 ℃＞
10 ℃≦
10 ℃＞
10. Removal Rate of Ammonia Nitrogen in RUN3 of Figure 11. Removal Rate of Manganese Ions in RUN3 of
AWTS. This was enabled by the Figure
the Casing Type MF Membrane System(average value)
the Casing Type MF Membrane System (average value)
combination of coagulation and
membrane separation, coupled with the adsorption effect of PAC. On the other hand, the UV absorbance
(260 nm) and fluorescence intensity values lagged slightly behind those of water treated by the AWTS.
It was considered that increased organisms would be effective to improve the performances of ammonia
nitrogen and manganese ions during the low temperature period. Therefore, RUN3 was adjusted to a high
recovery rate of 99.9%. The performances are shown in Figures 10 and 11. Both the figures use average
values. The performance of manganese ions in treated water is not considered favorable, because they
were not controlled below the target value (0.01 mg/L) not only below 10C, but also at or above 10C.
With regards to ammonia nitrogen, there was hardly any difference in the removal rate from that in the
RUN with the recovery of 99.5% (58% at or above 10C, and 21% below 10C), even though the
organism level in the BOPA tank was theoretically five times as high. This suggests that, during a short
detention time as in this testing unit (approx. three hours), improvement in biological oxidation
performance cannot be expected through increasing organisms (SS level) in the BOPA tank.
Table 9 indicates the relationship of PAC feeding rate and Table 9. Relationship of PAC Feeding Rate and Recovery Rate with
TOC (average value)
(mg/L)
recovery rate with TOC. It can be suggested from this table that
Source
Treated Removal
Operating Conditions
the performance of organic substances can be improved
water
water
rate
through changing PAC feeding rate and recovery rate.
PAC 15mg/L
2.0
0.64
67%
Removal rate 99%
According to the table, PAC feeding rate had been fixed at 15
PAC 15mg/L
2.1
0.57
72%
mg/L up to RUN3, while the recovery was changed. The
Removal rate 99.5%
PAC
15mg/L
resulting performance was high above that of water treated by
2.2
0.55
74%
Removal rate 99.9%
the AWTS in each cycle. By changing recovery rate from 99.0
AWTS GAC treated water
1.7
0.8
53%
to 99.9%, SS level in the BOPA tank differs by approx.
(average value of 2009)
1,000%. Change in the TOC reduction rate is small compared
to this percentage. Based on these, it is suggested that the excellence of TOC performance over that of the
AWTS depends largely on PAC feeding rate, rather than on recovery rate. Therefore, the required
removal performance is likely to be achieved for organic substances other than TOC, through using PAC
feeding rate as a key parameter (it has been verified that the reduction rates of UV absorbance (260 nm)
and fluorescence intensity vary by changes in PAC feeding rate). In RUN4, however, the PAC feeding
rate and recovery rate were set respectively at 3 mg/L and 98.0%, aiming at achieving reduced chemicals
cost and TOC performance equivalent to that of the AWTS treatment. It is considered necessary to
examine how to set an appropriate feeding rate and recovery, considering the cost of PAC feeding.
CONCLUSIONS
Submerged Type MF Membrane System
Summary
1) Examination on Conditions for Stable Operation
・ Research on the influence of pH adjustment on TMP indicated that there was no clear difference in
the rising trend of TMP at pH 6.8 - 7.5.
・ Research on the relationship between source water WQISC (algae of water source and manganese
ions) and TMP suggested a possibility that these items affect TMP.
・ Research on the behavior of TMP following the shortening of physical cleaning interval from 20 to 10
minutes indicated a slower rising trend of TMP, suggesting that a shorter interval of physical cleaning
has an effect to control the rise of TMP.
・ The influence of reduction in PAC feeding rate and coagulant feeding rate on TMP is not clear at this
point. Continued research is considered necessary.
2) Study on Performance
・ Research on the influence of chlorine level in back wash water on performance indicated that the
performance of manganese ions improved around the increase of chlorine level. However, the
performance was retained after the stop of chlorine addition. Continued research is considered
necessary.
・ When the PAC feeding rate was reduced from 15 mg/L to 1.5 mg/L, a lowered TOC removal trend
resulted. Because other conditions were also changed in this process, continued research is considered
necessary.
・ Following the above actions (i.e. stop of chlorine addition to cleaning water, and reduction in PAC feeding
rate), improved performances of ammonia nitrogen and manganese ions have been retained, though the TOC
performance has declined. Therefore, actions should be examined to improve the TOC performance.
Future Requirement
・ First, in the Submerged Type MF Membrane System only, verification should be continued on
conditions for stable operation and on performance, using TMP as an index, under the conditions that
the PAC and coagulant feeding rates are reduced and chlorine is not added to back wash water.
Casing Type MF Membrane System
Summary
1) Examination on Conditions for Stable Operation
・ From the viewpoint of controlling TMP, conditions for the stable operation of this system were
examined with filtration flux of 1.7 m/d. Based on this examination, the feeding of coagulant is
limited to the point after the tank at the feeding rate of 25 mg/L. Acid is adjusted in order to control
coagulation pH at approx. 6.5 - 6.8. Circulation water ratio is set at 1:0.3. The interval of physical
cleaning should be set at 120 minutes. The PAC feeding rate and recovery rate will be set as
appropriate based on future study, as parameters mainly concerning performance.
2) Study on Performance
・ Research was conducted on performance of this system during the low temperature period, under the
operating conditions set as described in 1). The results showed favorable turbidity performance below
0.1, owing to removal by membrane separation. At the same time, the TOC performance was
equivalent to that of the AWTS at 0.8 mg/L on the average. This was enabled by the combination of
coagulation and membrane separation, coupled with the adsorption effect of PAC. On the other hand,
ammonia nitrogen and manganese ions stood respectively at 0.09 mg/L and 0.025 mg/L, which are
levels scarcely better than the source water, despite the expectations for removal by biological
oxidation in the BOPA tank. While the TOC performance was found favorable, the UV absorbance
(260 nm) and fluorescence intensity values stood respectively at 0.010 and 54 on the average, which
managed to reach certain performance levels but lagged slightly behind those of the AWTS.
・ As an action to improve the performances of ammonia nitrogen and manganese ions, it was examined
the possibility of upgrading the recovery rate and concentrating the organism level. Unfortunately,
fundamental improvement turned out to be difficult with a short detention time (approx. three hours)
in the BOPA tank.
Future Requirement
・ The performance data of this system that are reported herein only cover a short term of approximately
one month. It will be required to identify performance on a year-round basis, and examine how to
achieve the targeted water quality.
・ During a low temperature period, in which bioactivity slows down, the performance of manganese
ions declines particularly remarkably. Because treatment with only the Casing Type MF Membrane
System seems difficult, it should be examined how to combine it with other pre-treatment methods,
such as Biological Roughing Filter (BRF), ozonation or feeding of chlorine or other oxidizing agents
using a method that would not increase by-products (e.g. bromic acids), and so on.
REFERENCES
1) I. Tsuda, M. Oya, K. Michishita, E.Karatani, M.Hara (2010) , “Joint Research on Water Treatment Technologies by the
Osaka Municipal Waterworks Bureau and the Hanshin Water Supply Authority”, The 61st National Waterworks Research
Presentations, P.242-243
2) Y. Komatsu, M. Hara, T. Hirabayashi, T. Ishimoto, E. Karatani, A. Kimura (2010) , “An Initiative for Technological
Development toward the Establishment of a Next-Generation Water Treatment System in Osaka City”, The 61st National
Waterworks Research Presentations, P.108-109
3) Y. Watanabe(2006) ,Water Metabolic System and Membrane Technology, MEMBRANE, 31(4) , P.180-187
4) Lake Biwa Environmental Research Institute (2009-2010), Water Quality Database and Research Results on Planktons in
the Seta River, http://www.lberi.jp/root/jp/24pl/bkjhplankton_setagawa.htm (viewed on April 21, 2011)
5) T. Maeda, K. Kimura, Y. Watanabe (2005) , “Influence of Coagulation Conditions on Membrane Fouling in PreCoagulation/MF Membrane Treatment”, Sanitary Engineering Symposium Papers No.13, P.235-238
6) R. Bian, Y. Watanabe, G. Ozawa, N. Tambo (1998) , “Membrane Fouling in UF Membrane Treatment (Second Report) Evaluation of Pre-Treatment in Batch Filtration Tests”, Japan Water Works Journal, Vol. 762, P.11-19