DESALINATION Desalination 177 (2005) 121-132
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Application of a metal membrane for rainwater utilization: filtration characteristics and membrane fouling R e e - H o K i m a*, S a n g h o L e e a, J o n g - O h K i m b "Korea Institute of Construction Technology, 2311 Daehwa-Dong, llsan-Gu, Goyang-Si, Gyeonggi-Do, 411-712, South Korea Tel. +82 (31) 910-0304; Fax +82 (31) 910-291; email:
[email protected] hDepartment of Civil Engineering, Kangnung National Universi04, 120 Gangneung Deahangno, Gangneung-Si, Gangwon-Do. 210-702, South Korea Received 26 April 2004; accepted 3 December 2004
Abstract
Growing interests in society for saving water resources have led to different attempts to use rainwater. Rainwater utilization provides a sustainable water supply in urban areas and buffers extreme runoffsituations in the watercourses. However, rainwater in the urban area contains substantial amounts of contaminants including particles, microorganisms, heavy metals, and organics and cannot be used without proper treatment. In this work, a filtration technique using a metal membrane was designed and developed for efficient and safe use of rainwater. The treatment system consists of a feed tank containing rainwater and a metal membrane submerged into the tank. Experiments were performed to compare filtration characteristics of rainwater in a storage tank, roof runoff, and roof garden runoff. Ozone bubbling as well as aeration in the feed side was considered to reduce membrane fouling and inactivate microorganisms. Metal membranes appear to be suitable to clarify rainwater because of their high treatment efficiency of microorganisms and particulates. However, the filterability highly depended on the rainwater sources, nominal pore size of filter, filtration conditions, and operation mode. The major fouling mechanism for the metal membrane filtration was pore blockage.
Keywords: Rainwater; Metal membrane; Water reuse; Ozone; Submerged filtration; Fouling mechanism
1. Introduction Continued urban growth together with increasing requirements for the preservation of environment around cities have placed conflicting de*Corresponding author.
mands on water systems [ i ]. Increases in population and water use are resulting in increased pressures on water resources and quality [2,3] but traditional planning concepts for water supply and management in the urban area have already shown a limit. Moreover, urbanization has increased
0011-9164/05/$- See front matter © 2005 Elsevier B.V. All rights reserved doi: 10.1016/j. desal.2004.12.004
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R.-H. Kim et al. / Desa#nation 177 (2005) 121-132
impermeable areas that have lost functions of stormwater storage and infiltration, leading to water-related disasters including urban floods and droughts [4,5]. Recently, rainwater utilization that provides an ongoing water supply in urban areas has drawn attention as one of the best available ways for sustainable urban development. Rainwater utilization involves all the activities such as collection of rainwater from roofs and other surfaces, its storage, infiltration into the ground, and subsequent use. Rainwater utilizations systems a~'e considered as a less resource intensive and more ecologically benign form of water supply. They also reduce reliance on other water sources, and, in many contexts, are cost-effective [6,7]. Moreover, rainwater utilization not only allows an effective control of stormwater runoff by storing and infiltrating rainwater but also aids the restoration of the hydrological cycle in urban areas. However, an increasing concern in rainwater utilization is the level of contamination in rainwater runoff [8,9]. Contaminated rainwater may result in human infection and chemical intoxication although rainwater is mainly for non-potable use. Ionic and organic pollutants in rainwater runoff may deteriorate water environment in an urban area [10]. There are several sources of pollutants in rainwater runoff: atmospheric pollutants including particles, colloids, microorganisms, heavy metals and organics, accumulate on the roofs and other surfaces as dry deposition as well as being washed out of the atmosphere in rain, resulting in a deterioration of rainwater quality. In addition, the catchment surface materials themselves may be a source of some metals including copper, aluminum, iron and lead. Thus, an efficient and economical method to clarify rainwater is of great concern in rainwater storage and utilization. A novel technology that has a potential to clarify rainwater is metal membrane filtration [ i 1]. Metal membrane technology holds a great promise for rainwater treatment because it has unique
advantages over polymeric microfilters [12]: a metal membrane is durable to high pressure up to 1 MPa, high temperature up to 350°C, outer shock power, and chemical oxidation such as ozonation. Unlike polymeric microfiiters, lifetime of metal membranes is long enough to minimize the maintenance cost. Metal membranes can be stored in dry forms, which makes it more attractive than polymeric membranes because rainwater filtration may operate intermittently. This work focuses on the development of a novel technology to treat contaminated rainwater using metal membranes. A submerged type of the metal membrane system was introduced to remove contaminants effectively while maintaining high flux and low transmembrane pressure. In situ injection of ozone was also attempted to minimize membrane fouling and to improve filterability of rainwater [11]. The filtration characteristics as well as treated water quality were monitored to provide insight into the design and operation of the system.
2. Experiments Rainwater collected from different locations was used in this study as illustrated in Fig. 1. These include stored rainwater in a tank; runoff from a roof of the building; and runofffrom a roof garden. In this building, only the runoff from a roof was collected and then transferred into the storage tank whereas the runoff from the roof garden was drained. Commercially available MMFs (metal membrane filters), supplied by a manufacturing company (FiberTech, Korea), were used for filtration tests. The dimensions and basic characteristics of MMFs are provided in Table i. To compare MMFs with conventional PMF (polymeric membrane filter), a mini membrane module with a membrane area of 9.3 x 10-3 m2was prepared using hydropbilic hollow fibers (Mitsubish Rayon) with a pore size of 0.1 gin. The experiments using the metal membrane were performed in two different modes: total
123
R.-1f. Kim et al. / Desalination 177 (2005) 121-132 Building "GreenRoof"
(a)
Runofffrom~
Pump
RoofRunoff
I ImDDDDDI ~H []D[3D~ml /
PressureGauge 9 ~ t a l t i c
......................
tl ti ,
/
1
/
o
GraduatedCylinder
Metal
Membrane o
Fig. 1. Threetypes of rainwaterfrom buildings:roof runoff, runoff from "green roof", and rainwater in storage tank. recycle and continuous operation. In total recycle operation, both the concentrate from the membrane filtration loop and permeate were recycled into the tank while keeping the tank volume constant during the operation time. A schematic diagram of a submerged metal membrane system used for the total recycle operation is shown in Fig. 2a. A metal membrane module made of stainless steel was immersed and suspended vertically in the reactor. Permeate from the membrane module was pulled by a peristaltic pump. To examine the effect of chemical cleaning, a laboratory ozone generator (Trigen Ozonia) was used to produce ozone bubles in the feed tank. In continous operation mode, the permeate was continuously taken out of the filtration loop as shown in Fig. 2b. The membrane module was directly submerged into the rainwater storage tank (40 m 3) and the filtration was conducted using the Siphon effect. In both cases, the flux was monitored by collecting the permeate on a graduated cylinder. The transmembrane pressure was continuously measured using a pressure transducer (ZSE40F-01-22, SMC, Japan). Metal membranes with 1 ~tm and 5 ~tm were compared and the characteristics of the membranes are summarized in Table 1. Spectrophotometric methods of Hach [13] using DR-4000 spectrophotometer were adapted to measure the ionic concentrations and turbidity.
~
o
o
~o~_~ - Ozone FeedTank
(b)
Air Blower or OzoneGenerator
PressureGauge 9
Metal Membrane
~-] GraduatedCylinder
RainwaterStorageTank
Fig. 2. Schematicsof metal membranefiltration system: (a) total recyclesystem(b) continuousoperation system.
Conductivity and pH were also measured and automatically corrected for temperature influence. The size distribution of particles in rainwater and treated water were analyzed using a particle size analyzer (Malvern Mastersizer/E, UK) and a particle counter (Met One, USA). The Compact Dry Kit (Nissui, Japan) and Colilert Kit (IDEXX, USA) were used to quantify total viable microorganisms (TC) and total coliform includingE, coli. The required volumes for measuring TC and coliform (and also E. coli) were I mL and 50 mL,
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Table I Summary of metal membrane filters Parameter Outer radius (r,), m Nominal pore radius (r;), ~tm filter area length (L), m Membrane area (A,,), × 10-3 m2 Membrane resistance (R,,), xl0 I° m-1
5 lam metal membrane filter 0.014 5 0.222 9.76 1.01
respectively. The analytical results for microbial contaminants were expressed as the number per unit volume instead o f log removal because the primary focus was to meet the greywater regulations.
3. Results and discussion
3.1. Rainwater quality and treatment efficiency by MMFs (metal membrane filters) First, the rainwater quality was monitored over the five rain events as summarized in Table 2. The runoff from roofs has the best water quality and the stored rainwater in the tank showed similar quality except for conductivity and color. This suggests that extra amounts of pollutant were dissolved into the rainwater during transport or storage. The runoff from roof garden contains
! !am metal membrane filter 0.014 1 0.222 9.76 1.04
many more pollutants including ions (conductivity), organics (color), nutrients (nitrogen and phosphate), and heavy metals (Fe, Cu, and zinc). These additional amounts of pollutants appear to come from the soil layer, which originally contains fertilizers and soil humics, in the roof garden system. Table 3 compares the rainwater quality from various sources with the regulations for drinking water and greywater in Korea to see the potential for using rainwater as an alternative water source. The rainwater samples satisfy the greywater standards except for microbial pollutants (total viable bacterial count and total coliform) and particulates (turbidity). As for heavy metals, rainwaters even meet the quality regulations for drinking water. Although microbial contaminants were primary targets, particulate and other pollutants were also concerned in this application. This
Table 2 Composition of rainwaters in different sources (total sample number = 5)
Turbidity, NTU pH Conductivity, laS/cm Total phosphate, mg/L Total nitrogen, mg/L Iron, mg/L Copper, mg/L Zinc, mg/L Total viable bacteria count, ml-~ Suspended solids, mg/L Color
Rainwater in storage t~zlk
Runoff from roof
Runofffrom roof garden
2.0 7.5 123.7 0.20 1.0 0.033 0.054 0.15 303 5.4 22
1.0 6.9 28.5 0.21 0.8 0.02 0.04 0.08 351 5.2 8
1.3 7.8 167.5 1.18 1.6 0.06 0.17 0.14 341 4.0 250
R.-H. Kim et al. /Desalination 177 (2005) 121-132
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R.-H. Kim et al. / Desalination 177 (2005) 121-132
126
is because these pollutants may cause technical problems such as the quality deterioration of water for toilet flushing/cleaning as well as psychological barriers against the treated water. Moreover, turbidity may be used as a surrogate for microbial contaminants that is usually hard to measure continuously. Thus, it appears that additional treatments such as disinfection and membrane filtration are required for reducing mainly microbial and particulate pollutants to allow the use o f rainwater as greywater. Fig. 3 illustrates the inactivation of total coliforms by various treatment options including UV
(ultraviolet light), ozone, PMF (polymeric membrane filter) and MMFs (metal membrane filters). UV treatment seems to be less effective than ozone because the intensity of the UV used here was low (Itjr~ = 5.4 W/m2). No coliform was detected after 10 min treatment with ozone. Membrane filtration also showed capability to reduce total coilforms in the product water by rejecting them. 0.1 lxm PMF and 1 ~tm MMF showed similar high removals (> 98%) whereas 5 ~tm MMF resulted in about 78% of removal efficiency. Combinations of ozone treatment for 1 min and MMF membranes lead to almost complete inactivation of
250
250
(a) UV and ozone treatments
(b) Metal membrane treatments
200
200 o o
o~
is0
150 ,9o 100
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8
8 T
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UV UV UV Ozone Ozone Ozone (5 min) (30 min) (60 min) (1 rain) (5 min) (lOmin)
Feed
0.2 um PMF
5 um MMF 1 um MMF Ozone + Ozone + 5urn MMF lum MMF
Fig. 3. Inactivation efficiency ofcoliforms by UV, ozone, and membranes. Conditions: flux for PMF = 70 L/mLh; flux for MMFs = 2000 L/m2-h;/uz A, 5.4 W/m~; ozone dosage, 2.58 g/h.
1
(b) 1/am MMF
(a) 5 ~tm MMF 0.8
0.8 e--
co
o 0.6
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o~ 0.6
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~
!:?i!i-~ii:::
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,
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0.2
~ii
10
15
Particle Size (urn)
25
50
2
5
10
15
25
50
Particle size (urn)
Fig. 4. Number rejection of particles by MMFs (metal membrane filters). Conditions: flux for MMF = 2000 L/mLh; aeration rate -- 50 mL/min.
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R.-14. Kim et al. / Desalination 177 (2005) 121-132
coliforms. These results suggest that metal membrane filtration has the potential to control microbial contaminations in rainwater. Fig. 4 shows the rejection of particles by MMFs with different pore sizes. The results were obtained using the particle counter (Met One, USA) and expressed as number rejection. Clearly, 1 lam MMF removes more particles than 5 p,m MMF and the volume-based particle rejections for I lam and 5 ~tm MMF were 0.95 and 0.80, respective!y. Although the data is not shown here, 0.1 ktm PMF shows the volume-based particle rejection of 0.97. However, the rejection did not exactly match the nominal pore size for MMFs. For example, the rejections for 5 mm particles were the smallest for both membranes and some of the particles larger than 15 !am were still found in the permeate. This is attributed to the broad distribution of pores in the metal membrane filter. Since the metal membranes used here were made of metal fibers with the diameter of about 6 !am, they should have a wide range of pore sizes. 3.2. Filtration characteristics o f rainwater from different sources
Fig. 5 shows the transmembrane pressure profiles for PMF and MMFs during the filtration of rainwater samples stored in the tank. The filtration tests were conducted in a total recycle mode under constant flux using the total feed volume of 3 L. The flux for PMF was 70 L/m2-h and the fluxes for MMFs were 800 L/m2-h. Air bubbling at 50 mL/min was carried out during the filtration to minimize fouling. Although the flux for PMF was less than 9% of the flux for MMFs, the transmembrane pressure increased much faster. This indicates that the PMF membrane was rapidly fouled because of its smaller pore size. Considering the fact that the PMF does not have clear benefits in terms of treatment efficiency of microorganisms and particles, it appears that MMFs are better treatment options for rainwater treatment due to their higher flux and slower fouling [1 !]. Moreover, cleaning of MMF membranes is easier
0.20 ©
0.1 i.tm PMF
[]
5 p,m MMF
1 lain MMF
(-i
0.15
13..
o.lo
E
o
E 0,05 c m I.-
0.00
10
20
30
40
50
60
Time(min)
Fig. 5. Comparison of transmembrane pressure profiles for PMF (polymeric membrane filter) and MMFs (metal membrane filters). Conditions: operation mode, total recycle; flux for PMF = 70 L/m2-h; flux for MMF = 800 L/m2-h; aeration rate = 50 mL/min; temperature = 25°C.
than PMF membranes because MMF can be used with strong cleaning agents including chlorine, ozone, H:O2, and strong acids/bases. Fig. 6 compares the filtration characteristics of three rainwaters using MMFs. The operation conditions were the same as in the previous tests except that the permeate flux was 2000 L/m2-h. Transmembrane pressure did not increase much for filtration of stored rainwater for both membranes. However, a rapid increase in the transmembrane pressure with filtration time was observed when filtering runoff rainwaters using the 1 p,m membrane,e while no increase in the transmembrane pressure was shown for the 5 ~tm membrane. This is because most foulants that block the 1 Ixm membrane are small enough to pass through the 5 ~m membrane in case of roof and roof garden runoffs. Moreover, humic substances in roof garden runoff together with other particulate foulants seem to cause serious fouling. Although membranes with smaller pores such as UF sometimes result in less severe fouling than membranes with larger pores such as MF due to a reduced potential of pore blocking, the 5 p,m MMF has better filterability than 1 p.m MMF in this
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R.-H. Kim et al. / Desalination 177 (2005) 121-132
0.30
0.30
(b) 1 pm MMF
(a) 5 ~,m MMF 0.25
~" 0.25
© stored rainwater roof runoff [] roof garden runoff
0.20 o
0.15
to
P,
/
0.15
' ~ ~ o
stored rainwater
r°°ff;~;d°effnrunoff
j:~"
~[] roo
E 0.10
0.10
I-
~
0.20
0.05
t--
0.05
0.00
0.00
0
'5
10
15 Time (rain)
20
25
30
0
5
10
15
20
25
30
Time (rain)
Fig. 6. Effect of input rainwater characteristics on transmembrane pressure for metal membranes. Conditions: operation mode, total recycle; flux = 2000 L/mLh; aeration rate = 50 mL/min; temperature = 25°C.
study. This is because the fouling mechanisms for both MMFs were the same while the foulant loading on 1 I,tm MMF was larger. Details on the fouling mechanisms will be discussed later with Fig. 9. Here, ozone bubbling was introduced to minimize rapid fouling during metal membrane filtration of roof garden runoff. The metal membrane is suitable to be used with ozone because o f its excellent chemical stability and is reported to be effective to prevent fouling [14]. The transmembrane pressure with ozone bubbling was compared with that with aeration (without ozone) in Fig. 7. The increasing rate of the transmembrane pressure with ozone bubbling was much smaller than that with air bubbling. This is probably because ozo,~e in water destructs organic matters and destabilizes colloids. These effects have occasionally been referred to as microflocculation/ozone-induced particle destabilization/coagulation effects [ 15]. Similar reduction in ultrafiltration membrane fouling with pre-ozonation due to ozone-induced particle destabilization was reported by other researchers [16]. In summary, metal membrane filtration appears to be suitable for treating stored rainwater and roof runoff. When treating roof garden runoff, however, the metal membrane with
0.30 •
0.25.
=~ o.2o.
filtration with air bubbling filtration with ozone bubbling
CL
t~ 0.15. t~ 0.10'
~ 0.05 1
='-'-V
";'--'---
0.00 10
20
30
40
50
60
Time (rain)
Fig. 7. Effect of ozonation on filtration characteristics for roof garden runoffusing I IxmMMF. Conditions: operation mode- total recycle; flux = 2000 L/mLh; aeration rate = 50 mL/min; ozone dose = 50 mg/h; temperature = 25°C. ozone bubbling seems to be better in terms of flux improvement. 3.3. Continuous operation
In continuous operation, filtration was performed using the Siphon effect at the transmembrane pressure of 0.06 bar. The experiments were conducted using the two MMFs. No aeration or
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R.-H. Kim et aL / Desalination 177 (2005) 12 I-132
ozonation was performed in these tests since the purpose o f the tests was to d e t e r m i n e the possibility of operation with minimum operating cost. In practical operation, regular backwashing or cleaning seems to be more economical than continuous aeration. Permeate flux decreased faster with a 1 !am filter than with a 5 ~tm filter as shown in Fig. 8. The rapid fouling in a continuous operation mode is attributed to the difference in the feed volume. In the total recycle mode, the feed volume was only 3 L so the total amount o f foulants was much smaller than in the continuous operation mode. Moreover, no aeration was employed in continuous operation, which may accelerate fouling.
2000
~:~
© 5 p_m MMF
In this study, we only examined the possibility to use metal membranes without ozone because ozonation is more expensive than the conventional chlorine process. However, it appeared that using ozone is much more effective than without using ozone in terms of disinfection and fouling control, as shown in Fig. 8. Based on the results in this paper, researches are ongoing to combine a continuous membrane system combined with ozone in a pilot-plant scale. Table 4 summarizes the productivity of the permeate water and the price of the metal membranes based on the filtration data in Fig. 8. Backwashing at 60 min interval was assumed for the calculation of the average flux. Due to superior filterability, 5 !am MMF shows more than 4 times higher productivity per membrane cost than 1 ~tm MMF. 3. 4. Fouling mechanisms
1500 'c" 1000
50O
0 0
50
100
150
200
Time (min)
Fig. 8. Flux decline in metal membrane filtration of stored rainwater. Conditions: operation mode - continuous; transmembrane pressure = 0.06 bar; aeration rate = 0 mL/ rain (no aeration); temperature = 18°C.
Using the results in Fig. 8, the major fouling mechanism in metal membrane filtration of rainwater was determined using the filtration models. The filtration models, originally suggested by Hermia [17], include three fouling mechanisms such as pore constriction, pore blockage and cake formation. In the pore constriction mechanism, foulants are assumed to be small enough to be deposited onto the internal pore walls of the membrane, leading to a decrease in the effective pore size and the permeability. In this case, the reduction in membrane permeability is expressed as a decrease in the total pore volume. In the pore
Table 4 Estimated productivity of permeate per cost of metal membrane lam metal membrane Full scale module size, mm Membrane area, m 2 Price, US$ Average flux, L/m2-h Permeate flow rate per membrane cost, L/h-US$
~b65 × L 500 0.204 250 1380 1,12
1 p,m metal membrane d~65 × L 500 0.204 416 508 0.25
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R.-H. Kim et al. / Desalination 177 (2005) 121-132
b l o c k a g e mechanism, the foulant size is assumed to be similar to the pore size of the membrane. This allows each particle arriving in the membrane to block pores easily with no superposition o f particles. In the c a k e f i l t r a t i o n mechanisms, particles that deposit on the membrane surface form cake layers which cause an additional hydraulic resistance because their size is assumed to be larger than the pore size. These three filtration models provide different equations for flux decline as summarized in Table 5 [18].
Fig. 9 compares the experimental data from Fig. 8 with model fit results using equations in Table 4. The experimental results were expressed in the form of reduced flux defined as the permeate flux divided by the initial flux. In both cases, the pore blockage model and pore constriction provided the closest fit to experimental data, indicating they are the major fouling mechanisms rather than cake formation in metal membrane filtration o f rainwater. Although the data is not shown here, the model fit under different transmembrane
Table 5 Summary of equations for filtration models Equation
Fitting parameter
J
-2
Pore constriction
T=O + ,ojoAc,j)
Pore blockage
J=exp(- JoAC,j) do
= i+~o~doAcj.ee t
Cake formation J -do - A --
Pore constriction constant, g-J Pore blocking constant, g-~
)'
z
f3~
permeate flux at time t, m/s initial permeate flux, m/s membrane area, m 2
Cake formation constant, g-~
C fee d
--
t
--
1.2
foulant concentration, g/m3 filtration time, s
1.2
(a) 5 ~tmMMF 1.0'
1.0.
0.8.
O.B'
0.6.
0.6,
(b) 1 lainMMF
n ~
V
"f
V
o 0.4,
_
1~ f
~, v ~ 0.2, ~,~r. 0.0 oo
v o
.
0.4'
pore constriction
v
[] poreblockage
0.2'
.V cakeformation
nstriction
8/.,"~
[] poreblockage v cakeformation
0.0 0.2
0.4
0.6
0.8
Experimental Reduced Flux
1.0
1.2
0.0
02
0.4
0.6
0.8
1.0
Experimental Reduced Flux
Fig. 9. Comparison of experimental reduced flux (J/d) with curve fit using three filtration models listed in Table 4.
1.2
R.-H. Kim et al. / Desalination 177 (2005) 121-132
131
Table 6 Summary of model estimations
5 ~tm MMF
13
R r, Standard error 1 }.tmMMF
13 Standard error
Pore constriction 1.39x 10-7 0.982 0.0495 1.oox 10-6 0.983 0.0346
pressure conditions showed similar results that the pore blockage and restriction are the major fouling mechanisms. This is because the metal membranes have different structures than polymeric membranes. The metal membranes consist o f one protective layer, one filtration layer, and three support layers with the total thickness of 1.5 mm [19]. This structure leads to an easy accumulation o f particles that blind and narrow the pores. Table 6 also summarizes the model fit results. The pore blockage or constriction constants are measures to express the rate of fouling per unit loading of foulants. Fore instance, the pore blockage constants for 5 lain MMF and 1 ~m MMF were 2.21 × I 0-7g -I and 1.52× 10-6g-~, respectively, indicating that the fouling rate is much faster for 1 ~tm MMF. Therefore, more frequent cleaning as well as backwashing will be required to use 1 ~tm MMF for rainwater treatment. Researches are ongoing to address fouling issues while maintaining low cost of operation to bring this technology into practice for better performance in rainwater utilization.
Pore blockage 2.21 ×10-7 0.995 0.0259 1.52x 10-6 0.984 0.0341
Cake formation 1.01 ×10-6 0.865 0.137 9.54× 10-6 0.920 0.0774
which are the major contaminants to be removed for using rainwater for toilet flushing or gardening. (2) The 1 !am MMF showed worse permeability than the 5 ~m MMF membrane because of its pore size, especially for roof and roof garden runoffs. Ozone bubbling significantly reduces the increase in the transmembrane pressure due to membrane fouling in filtering roof garden runoff. (3) Flux decline was substantial in continuous operation of the 1 p,m MMF where there was no aeration and no recycle o f permeate. The major fouling mechanisms for both MMFs were pore blockage.
Acknowledgements This work was supported by the Sustainable Water Resources Research Center, the Ministry of Science and Technology, and the Ministry of Construction and Transportation under the research grant "Technology for Rainwater Storage and Utilization".
References 4. Conclusion Metal membrane filtration combined with aeration or ozone injection was investigated as a novel method to remove contaminants from rainwater. The following conclusions can be drawn: ( 1) Metal membranes were efficient to reduce microbial and particulate pollutants in rainwater,
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[12] J.-O. Kim and 1. Somiya, Innovative fouling control by intermittent back-ozonation in metal membrane micro filtration system. 3rd World Water Congress, Melbourne, 2002. [13] Hach, Hach Water Analysis Handbook. 2nd ed., Hach Company, Colorado, USA, 1992. [14] J.-O. Kim, E.-B. Shin, W. Bae, S.-K. Kim and R.H. Kim, Effect of intermittent back ozonation for membrane fouling reduction in microflltration using a metal membrane. Desalination, 143 (2002) 285294. [15] D.A. Rekhow, P.C. Singer and R.R. Trusell. Ozone as a coagulant aid. in Annual AWWA Conference Proc., AWWA, Denver, Colorado, 1986. [16] H. Hyung, S. Lee, J. Yoon and C.-H. Lee, Effect of preozonation on flux and water quality in ozonationuitrafiltration hybrid system for water treatment. Ozone Sci. Technol., 22 (2000) 637-652. [ 17] J. Herima, Constant pressure blocking filtration laws application to power law non-Newtonian fluids. Trans. IChE, 60 (1982) 183-187. [18] L.J. Zeman and A.L. Zydney, Microfiltration and UItrafiltration: Principles and Applications. Marcel Dekker, Inc., New York, 1996. [19] S.-H. Min, Manufacturing process of metal membrane, in Workshop on Water Treatment Using Metal Membrane Process and Advanced Oxidation Technology. Kangwon University, Korea, 2004. -
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