Experiment and modeling of advanced ozone membrane reactor for treatment of organic endocrine disrupting pollutants in water

Catalysis Today 193 (2012) 120–127

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Experiment and modeling of advanced ozone membrane reactor for treatment of organic endocrine disrupting pollutants in water Hung Lai Ho a , Wai Kit Chan a , Angelique Blondy a , King Lun Yeung a,b,∗ , Jean-Christophe Schrotter c a b c

Department of Chemical and Biomolecular Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong Division of Environment, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong Water Research Center of Veolia, Anjou Recherche, Chemin de la Digue, BP 76. 78603, Maisons Laffitte, Cedex, France

a r t i c l e

i n f o

Article history: Received 19 October 2011 Received in revised form 15 February 2012 Accepted 28 March 2012 Available online 12 May 2012 Keywords: Water and wastewater treatment Ozonation reaction Phthalate Nanofiltration membrane Zeolite membrane

a b s t r a c t An advanced ozone membrane reactor that uses membranes for ozone distribution, reaction contact and selective water separation was used for ozone treatment of a recalcitrant endocrine disrupting compound in water. Experiments and model calculation were employed to examine the ozonation of phthalate in the new reactor. Experimental results showed that fast ozone mass transfer rate is responsible for membrane reactor’s superb performance compared with a semibatch reactor. Selective water removal further enhanced phthalate conversion and TOC removal by concentrating the pollutants in the reaction zone. Clean water was produced by membrane separation. Mathematical model was used to investigate the effect of membranes, reactor design and reaction operation on pollutant conversion and removal. © 2012 Elsevier B.V. All rights reserved.

1. Introduction There is growing evidence that a large number of chemical compounds found in common household products ranging from medicines, cosmetics and personal care products, and household cleansers, can survive state-of-the-art wastewater treatment processes to contaminate surface and ground waters [1–10]. Many of these compounds are endocrine disruptors and studies carried out in 2001 [11] and 2003 [12] showed that a large numbers of endocrine disrupting chemicals (EDCs) survive conventional drinking water treatment processes to persist in finished, potable water. Several of the compounds were even found in samples of human blood, milk and urine [13]. Although health risk from chronic exposure to EDCs in humans has not been adequately addressed, their effects on normal hormonal processes is well documented and there is extensive evidence of their adverse effects in wildlife [14]. It is particularly disturbing that most studies in animal models [15] showed that early life stages are the most vulnerable to the actions of EDCs, putting pregnant women and children at greater risk [16].

∗ Corresponding author at: Department of Chemical and Biomolecular Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong. Tel.: +852 23587123; fax: +852 23580054. E-mail address: [email protected] (K.L. Yeung). 0920-5861/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cattod.2012.03.059

Ozone and membrane processes are technologies that showed the best promise for treatment of EDCs in water [17,18]. However, ozone treatment alone suffered from slow mineralization rates [19] and the UV/O3 and O3 /H2 O2 used by various authors [20–22] to remedy this shortcoming are often expensive and complex. Nanofiltration and reverse osmosis membrane can remove most EDCs [23,24], but the separated EDCs require further treatment. In addition, membrane fouling is a concern [25]. Ozone has been used in membrane to alleviate membrane fouling by organic matters [26,27] and improves membrane filtration processes [28]. Shanbhag et al. [29] explored in their early work the use of a silicone capillary membrane for ozone distributor for treatment of chemical micropollutants in water. More recently Karnik et al. [30] employed a catalytic membrane based on ultrafiltration and ozonation for drinking water treatment. This work examines an advanced ozone membrane reactor for treatment of recalcitrant organic EDCs in water. The membrane reactor uses membranes for ozone distribution, reaction contactor and water separation in a compact unit that synergistically combines ozone oxidation and membrane separation to achieve greater treatment efficiency. The use of multi-functional membrane reactor was shown to benefit gas-phase and liquid phase reactions [31–38]. Indeed, prior works showed the new membrane reactor increased mineralization rate, improved ozone utilization, reduced membrane fouling and enhanced clean water production [39,40]. This study investigates the design of the reactor and membranes using a mathematical model to guide the optimization and scale-up the process

H.L. Ho et al. / Catalysis Today 193 (2012) 120–127

Nomenclature Ac Ag Am C Co Cv D De Di En Ni No Nw P P Pe Q˙ R Rm Rcp X K ab kDd kDi kH kL p q˙ r rin rout r t

v v¯ x y z

cross-sectional area (m2 ) surface area for gas distribution (m2 ) membrane surface area (m2 ) concentration (mol m−3 ) feed concentration (mol m−3 ) convective flux (mol m−2 s−1 ) diffusivity (m2 s−1 ) depletion factor diffusive flux (mol m−2 s−1 ) enhancement factor organic compounds permeation flux (mol m−2 s−1 ) total number of species water permeation flux (m3 m−2 s−1 ) water permeance (m2 bar−1 s−1 ) EDC permeance (m−1 s−1 ) Peclet number gas feed rate (m3 s−1 ) reaction rate (mol m−3 s−1 ) membrane intrinsic resistance (bar s m−1 ) concentration polarization (bar s m−1 ) dimensionless radial location in the membrane support ozonation reaction rate constant (m3 /mol s) specific interfacial area of gas bubble (m2 m−3 ) ozone direct decomposition rate constant (s−1 ) Ozone indirect decomposition rate constant (mmol−0.5 s−1 ) Henry’s constant of ozone mass transfer coefficient of ozone from gas to water (m s−1 ) Vapor pressure (bar) gas feed flux through s.s. membrane ozone distriutor (m s−1 ) radius (m) inner radius of membrane support (m) outer radius of membrane support(m) transformed radius (m) time (s) superficial flow velocity (m s−1 ) superficial flow velocity per unit reactor height (s−1 ) mole fraction dimensionless concentration stoichiometric coefficient

Greek symbol ˛ fouling factor (m2 s bar mol−1 ) gas volume holdup ˇ ıAl alumina support thickness (m) membrane thickness (m) ım εAl porosity  dimensionless time Subscripts i different species ref reference water w A ozone B endocrine disrupting compound degradation byproducts BP Superscripts g gas

j p r Al G L Sat

121

the jth alumina support sub-model permeate retentate alumina support phase bulk gas phase bulk liquid phase saturated vapor pressure (bar)

for practical application in the treatment of EDCs-contaminated water. 2. Experiment and model 2.1. Potassium hydrogen phthalate (KHP) ozonation reaction kinetics The KHP ozonation reaction scheme in Fig. 1 was mainly based on the experimental results [39], with some of the pathways deduced from literature reports on dimethyl phthalate (DMP) [41]. The main intermediates and products include large intermediates with molecular structure similar to KHP (I1), intermediate ketones, aldehydes and carboxylic acids (I2) and simple carboxylic acids such as formic and acetic acids (I3) that have low UV detection. The reaction rate equations are fitted to a second order reaction kinetic typical for ozonation reactions [42,43]. The reaction rates were obtained from a semibatch reactor using a glass sparger for ozone distribution. Ozone was produced from pure oxygen by corona discharge in Wedeco ozone generator. The gas pressure and ozone concentration were measured by an on-line pressure gauge and ozone analyzer (BMT 964® ), respectively. The ozone gas volumetric flowrate was regulated by a Teflon flow meter (Cole Parmer® ). The 250 mL semibatch reactor was filled with 150 mL of 250 ppmC KHP solution and sparged with 200 sccm 120 ppm O3 /O2 . Samples were taken at fixed time intervals and purged with nitrogen gas. 10 mL samples were poured into a 50 mL conical flask and the dissolved ozone was measured by iodometric titration. 0.3 g KI and six drops of 0.4 M sulfuric acid were added to the solution and titrated using 0.002 M Na2 S2 O3 solution and starch indicator. The pH was measured and the organics were analyzed by Water Acquity UPLC equipped with BEH C18 column and a PDA e␭ UV–vis detector and Shimadzu total organic analyzer (TOC-V CSH). The concentrations of the intermediates and products were obtained by calculating their sensitivity factors (SFi ) from Eqs. (1) and (2). TOCCal =

N 

SFi xPAi

(1)

i=1

SSETOC =

Nrt 

(TOCMea − TOCCal )2

(2)

i=1

where PAi is the peak area of species i (AU); SFi is the sensitivity factor for species i (ppmC/AU) obtained at minimum SSETOC (i.e., squared errors of TOC); TOCCal is the calculated TOC (ppmC); TOCMea is the measured TOC (ppmC); and N is number of species. 2.2. Advanced ozone membrane reactor experiments A schematic drawing of the advanced ozone membrane reactor is shown in Fig. 2. Ozone gas bubbles were fed by a 35 mm long porous stainless steel membrane (i.e., 0.2 ␮m) welded to the stainless steel reactor shell. The stainless steel membrane was purchased from Mott Metallurgical and had inner and outer diameters of 12.5

122

H.L. Ho et al. / Catalysis Today 193 (2012) 120–127

O HO +

K O

-

KHP O

O

O

HO +

K O

-

CHO

HO

CHO

K O

+

O

O CHO OOH HC OH

-

OH

HO +

K O

-

O

O

O

O OH

HO +

K O

-

+

K O

OH O

COOH

-

Intermediate group 1 (I1)

O HO

COOH

HO

CHO O

O

OOH CHO CHO

HO

CHO

CHO

CHO

HO

COOH

HCOOH

Intermediate group 2 (I2) and Low UV-VIS absorptivity intermediates (I3)

CO2 and H2O Fig. 1. Proposed mechanism for ozonation of KHP molecules in water.

and 15.5 mm, respectively. The membrane was heat treated in air at 773 K overnight, cleaned in 0.1 N HCl solution, before rinsing with water and ethanol. This pretreatment ensures fine gas bubbles were generated uniformly over the entire membrane. Alumina membrane from Pall-Exekia with inner and outer diameters of 6.5 and 10 mm, were cut into 75 mm lengths and end-sealed with glass enamel. A thin layer of zeolite was grown on the inner tube surface for water separation, while the coarse ␣-Al2 O3 ceramic tube served as the membrane contactor. The zeolite membrane was grown by seeding and regrowth method, but unlike previous works [44–50], a template-free synthesis solution was used to grow the ZSM-5. Seeding is important for controlling the zeolite growth and membrane properties [51–55]. The membrane separator/contactor was held in place by a pair of O-rings, giving the advanced ozone membrane reactor a reactor volume of 2 cm3 , membrane distributor area of 13.7 cm2 and membrane separator/contactor area of 9.2 cm2 . Thus, the membrane area-to-reactor volume ratio for the membrane distributor was 690 m−1 , and 460 m−1 for the membrane separator. The advanced ozone membrane reactor operates in continuous mode. A 250 ppmC phthalate solution was prepared from potassium hydrogen phthalate (KHP, 99.9%, Sigma–Aldrich). The solution was fed to the membrane reactor by a Watson-Marlow peristaltic

pump. Once steady-state flow condition was reached, 130 ppm O3 /O2 gas mixture was bubbled through the membrane distributor at a flow rate of 20 sccm. The ozone gas mixture was produced by Wedeco GSO 20 ozone generator and the ozone concentration was monitored by a set of internal and external (BMT) ozone analyzers. The ozone gas flow was regulated by Teflon flow meter from ColePalmer. The gas and liquid from the retentate outlet were separated, and the disengaged ozone gas was analyzed to measure the outlet concentration. Samples of the retentate liquid were titrated for dissolved ozone, and the remaining liquid was purged with nitrogen to remove the dissolved ozone and quench the reaction. The organics in the retentate liquid were analyzed by Water Acquity UPLC and Shimadzu TOC analyzer. Reactions carried out using the membrane distributor and contactor will be referred to as membrane ozonication. Water separation and removal was accomplished by pervaporation across the zeolite membrane deposited on the inner surface of the membrane separator/contactor unit. A vacuum pressure of 60–100 Pa was maintained in the permeate-side by BOC-Edward vacuum pump. Water was selectively pervaporated across the zeolite membrane, while the organics were retained in the reaction zone for deeper oxidation. The clean permeate stream from

H.L. Ho et al. / Catalysis Today 193 (2012) 120–127

123

Fig. 2. Schematic drawing of the advanced ozone membrane reactor.

the advanced ozone membrane reactor was collected in a cooled condenser and samples were withdrawn regularly. The amount was weighed to determine the average flux. The composition and organic carbon content of the retentate and permeate samples were analyzed by UPLC and TOC to calculated the overall KHP and TOC removal efficiencies. 2.3. Advanced ozone membrane reactor modeling The advanced ozone membrane reactor consisted of three sections; the retentate, membrane and permeate. The reactor was considered to be isothermal and isobaric. A uniform ozone distribution by the membrane distributor was assumed in the model. The fluid flows in the retentate and membrane were considered along the axial and radial directions, and the diffusions of the organics in the membrane were calculated using a transient 1D convection and diffusion model. A pseudo steady-state, plug flow condition was assumed for the retentate stream and well-mixed for the permeate stream. The retentate stream and membrane separator/contactor were coupled by convective and diffusive fluxes of ozone, reactants and products across their boundaries. Water and organic flux across the ZSM-5 membrane was modeled using experimental and diffusion data, and assumed to be uniform. Thus, the composition of the permeate stream can be calculated from the component fluxes across the zeolite membrane. Ozone flux across the membrane was assumed negligible, which is consistent with experimental observation. Thus, ozone oxidation reaction can be ignored in the permeate stream. It was further assumed that the membrane was inert and do not catalyze the reaction. The material balance in the retentate section is shown in Eqs. (1)–(5) for ozone gas (Eqs. (3) and (4)), dissolve ozone in liquid (Eqs. (5) and (7)) and organic compounds (Eqs. (6) and (7)). The concentrations of ozone and organics within the porous membrane contactor are accounted for by the component material balance Eqs. (8)–(11), and their concentration profiles were calculated by finite element orthogonal collocation method. These equations along with the superficial gas velocity (Eqs. (12) and (13)) and retentate liquid velocity (Eqs. (14) and (15)) were solved using the

permeation (Eq. (19)), convective (Eq. (20)) and diffusive fluxes (Eq. (21)). Based on the concentrations at the boundary between the membrane separator and the permeate section, the permeate fluxes of water and organics were calculated and their concentrations in the permeate stream can be obtained (cf. Eqs. (16) and (20)). Material balance equations for gas phase (for hO3 f ≥ h ≥ hO3 o ): ozone gas dCAG dh

=

G − C G )V ¯ g AC − kL ab ˇ((C G /kH ) − C L ) (CoA A A A

Vg

for h ≥ hO3 o

(3)

gas phase boundary conditions: G CAG = CoA

at h = hO3 o :

(4)

Material balance equations for liquid phase (for hf ≥ h ≥ 0): dissolved ozone: dCAL dh

j

=

kL ab ˇ((CAG /kH ) − CAL ) + RAL + DifA

(5)

Vr

KHP and reaction products: dCiL dh

j

=

RiL + Difi

(6)

Vr

Liquid phase boundary conditions: L CAL = O, CBL = CoB , CjL = 0

at h = 0 :

(7)

Material balance equations in the porous membrane contactor For ozone, KHP and its degradation intermediates: Al,j

∂Ci

∂t



Al,j

j

+ Nw

∂Ci

− DiAl

∂r

Al,j

∂2 Cj

∂r 2

Al,j

1 ∂Ci + r ∂r

 Al,j

− Ri

=0

(8)

initial condition: at t = 0 :

Al,j

Ci

= 0 for

rin ≤ r ≤ rout

(9)

124

H.L. Ho et al. / Catalysis Today 193 (2012) 120–127 Table 1 Reaction rate equations.

boundary conditions:at r = rout :

 Al,j  ∂C  DiAl i  ∂r 

j

Al,j

− Nw (Ci

L,j

|r=rout − Ci ) = 0

(10)

r=rout

Species

Rate equations

Ozone

RA =

dC L

A

dt

= −zb2 kb CAL CBL − zc2 kc CAL CCL − zd2 kd CAL CDL − zu2 ku CAL CuL − 3/2

kDd CAL − kDi CAL

and at r = rin :

    ∂r 

KHP

RB =

I1

RC =

I2

RD =

I3

RU =

Al,j

∂Ci Al

Di

j

Al,j

− Nw (Ci

j

|r=rin + ni ) = 0

(11)

r=rin

˙ is calculated from: The superficial gas flow velocity (q) dvg = 0 for dh

h < hOε o and h > hOε f

˙ g qA dvg = V¯ g = LOε t Ac dh

for hO3 o ≤ h ≤ hO3 f

(12) (13)

While the retentate liquid flow velocity (v˙ r ) is obtained from: dvr = 0 for h > hmf dh

(14)

j

dvr N Am = w Lmt Ac dh

for 0 ≤ h ≤ hmf

(15)

Also, Permeate concentration (CiP ):

NoAl

CiP

=

j=1

NoAl j=1

j

ni

(16)

j

Nw

dC L

B

dt dC L

C

dt dC L

D

dt dC L

U

dt

= −kb CAL CBL = zc1 kb CAL CBL − kc CAL CCL = zd1 kb CAL CBL + zd3 kc CAL CCL − kd CAL CDL = zu3 kc CAL CCL + zu4 kd CAL CDL − ku CAL CUL

This allows the reaction to be modeled from five reaction rate equations (cf. Table 1), instead of eighteen if all reaction intermediates and products are considered. The organic molecules can react directly with the dissolve ozone, or with the hydroxyl radicals generated when ozone decomposes. The latter reaction was ignored as it is negligible at room temperature and solution pH less than 5 [56]. According to Hoigne et al. [42,43] ozone reactions with most organic compounds can be adequately described by an irreversible, second order reaction rate equation. Thus, the ozonation of KHP and organic intermediates and products (I1, I2 and I3) were described by second order rate equations shown in Table 1. Fig. 3a plots the semibatch ozonation of KHP at room temperature. The concentrations of KHP, I1, I2 and I3 are plotted in Fig. 3a along with the total organic carbon (TOC) content. The results show that in a semibatch reactor, KHP was completely reacted in 15 min of ozonation to produce the reaction intermediates I1. The I1 intermediates are more reactive than KHP (cf. Table 2) and react rapidly

Gas volume holdup (ˇ): ˇ = 8.42(vg )

(17)

˙ kL ab = 0.1995(q)

−0.246

Permeation flux

(18)

j (Nw ):

 −Nw = Pw (pSat w xw |r=rin − pw ) j

j

p

(19) j

Solute permeation flux (Ni ): −Ni = Pi (Ci j

Al,j

p

|r=rin − Ci )

Concentraon(mg/L C)

Lumped ozone mass transfer coefficient (kL ab ):

300

(20)

200 150 100 50 0

j

Convective flux (Cvi ): j

L,j

Diffusive flux



j

Difi = −DiAl

j (Difi ):

 Al,j  ∂Ck   ∂r 

0

10

20

30

40

50

60

70

Time(min) (21)

(22) r=rout

3. Results and discussion 3.1. KHP ozonation in semibatch reactor The simplified reaction mechanism between phthalate and ozone in Fig. 1, organizes the reaction products into three main groups (i.e., I1, I2 and I3). It is believed that ozone reacts with KHP according to Criegee mechanism where molecular ozone forms primary ozonide with the unsaturated bonds in the aromatic ring before decomposition into carbonyl and carboxylic compounds shown in Fig. 1. I1 consists of large intermediates deduced from the previous study on DMP ozonation. I2 are products of ozone reaction with I1 intermediates and includes citric, adipic and malonic acids, while I3 are mainly simple (C1–C4) carboxylic acids.

KHP

Calculated concentraon (mg/L C)

j

Cvi = Nw Ci

a

250

I1

I2

I3

TOC

300

b

250 200 150 100 50 0

0

50

100

150

200

250

300

Experimental concentraon(ppmC) Fig. 3. (a) Plots of KHP, intermediates, products and TOC during ozonation of 250 ppmC KHP solution at 25 ◦ C in a semibatch reactor. (b) A plot of calculated and experimental concentrations of KHP and organic carbons from semibatch reactions at 25, 40 and 60 ◦ C. Please note that symbols – experimental data and lines – model calculation ([O3 ] = 120 ppm, QO3 = 200 sccm, and Vrxtr = 150 mL).

H.L. Ho et al. / Catalysis Today 193 (2012) 120–127

100%

Ab Eab zb

I1

Ac Eac zc1 zc2

I2

Ad Ead zd1 zd2 zd3

I3

Au Eau zu2 zu3 zu4

Value at different temperature 25

40

1

3.87 12036 0.5

0.05

0.3

0.4

0.218 3111 6 0.03 0.263 11085 0.7 0.25 0.1 677 33263 0.30 0.7 1

Unit

60

0.2

m3 /(mol s) J/mol –

0.02

m3 /(mol s) J/mol – –

0.08

m3 /(mol s) J/mol – –

a

80% 60% 40% 20% 0% 0

2

4

6

8

10

12

Retenon me(min) 100%

0.08

m3 /(mol.s) J/mol – – –

with ozone to produce less toxic I2 and I3 products. The I3 products consisting of simple carboxylic acids are refractory to ozone (cf. Table 2) and are responsible for the high TOC content of the reaction mixture (Fig. 3a). They also have larger stoichiometric coefficient and consume more ozone per molecule than KHP, I1 and I2. Fig. 3a shows that there is excellent agreement between experimental data and model calculations. A semibatch reactor model based on the work of Benbelkacem and De bellefontaine [57] was used in the calculation along with the experimental rate kinetics in Tables 1 and 2. The calculated and experimental concentrations of KHP and organic carbon from experiments carried out at 25, 40 and 60 ◦ C were plotted in Fig. 3b. The plot shows that there is good agreement between experiment and model over the different temperatures and reaction conditions used in the study. 3.2. KHP ozonation in advanced ozone membrane reactor KHP ozonation was performed in the advanced ozone membrane reactor shown in Fig. 2. The reaction was carried out with and without water separation across the zeolite pervaporation membrane. The reaction at 25 and 40 ◦ C are plotted in Fig. 4 as a function of hydraulic retention time. The data show that a retention time of 6 min in the membrane reactor is sufficient to reacts all KHP in the water (Fig. 4a) and temperature affects TOC removal (Fig. 4b) more than KHP conversion during membrane ozonation. Selective water separation by zeolite membrane pervaporation during advanced ozone membrane reactor operation resulted in a significant enhancement in KHP and TOC removals. KHP was completely reacted within 3 min of ozonation (Fig. 4a) and TOC removal was doubled compared to membrane ozonation (Fig. 4b). Model calculations were conducted to investigate the membrane and advanced ozone membrane reactor performance for the KHP ozonation reaction. Rate equations from semibatch reaction experiments (Tables 1 and 2) were used along with the experimental ozone mass transfer rate (Eq. (16)), membrane permeation rates (Eq. (17)) and ozone solubility and diffusion data [58,59]. Fig. 4 shows that there is good agreement between experimental data and model calculations. The model successfully captured the behavior of the reaction in both membrane reactor configurations. Membrane ozonation gave faster KHP conversion and better TOC removal compared to the semibatch reactor equipped with a traditional glass sparger. This is mainly due to the higher ozone

TOC removal efficiency

KHP

Parameter

KHP removal efficiency

Table 2 Reaction rate constant, activation energy and stochiometry from semibatch ozonation. Species

125

b

80% 60% 40% 20% 0%

0

2

4

6

8

10

12

Retenon me(min) Fig. 4. Percent removals of (a) KHP and (b) TOC in the advanced ozone membrane reactor with (×, +) and without membrane pervaporation of water (, ). Reactions were carried out at 25 ◦ C (, ×) and 40 ◦ C (, +). Please note that symbols – experimental data and lines – model calculation ([KHP] = 250 ppmC, [O3 ] = 130 ppm, and QO3 = 20 sccm).

mass transfer rate from the fine gas bubbles produced by the stainless steel membrane distributor. The pressure drop across the membrane distributor is also small and it requires less energy to generate fine bubbles. Mathematical calculations were done to optimize ozone usage in the advanced ozone membrane reactor. Fig. 5 plots the calculated KHP and TOC removal as a function of ozone dosage (i.e., moles of ozone per mole C) for different volumetric feed flow rates of ozone. The calculations show that a complete KHP conversion can be obtained using ozone dosage as little as 2,

Fig. 5. Calculated percent removals of KHP (solid lines) and TOC (dash lines) at different ozone dosage and ozone feed flow rates (QO3 ) ([KHP] = 250 ppmC, T = 25 ◦ C, and  = 3.5 min).

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H.L. Ho et al. / Catalysis Today 193 (2012) 120–127

4. Concluding remarks This work shows that an advanced ozone membrane reactor that uses membranes for ozone distribution, reaction contactor and water separation could attain both higher EDC and TOC removals for KHP ozonation at a shorter residence time compared to a traditional semibatch reactor. A mathematical model based on experimental transport, permeation and reaction data gave an accurate description of the advanced ozone membrane reactor operation. The model was used to examine the reactor and reaction to explore membrane properties, reactor design as well as operating conditions to achieve the best pollutant removal and TOC degradation for the minimum amount of ozone use. Calculations showed that the best result could be obtained from redesigning the reactor to accommodate a larger separation membrane area. The study also showed that for ozonation of KHP, it is possible to achieve complete KHP conversion, but TOC removal approaches an asymptote at 60% at room temperature due to the refractory nature of the I3 products.

Acknowledgments The authors gratefully acknowledge funding from the Hong Kong Innovation Technology Fund (ITS/108/09FP) and financial supports of Chiaphua Industries Ltd., Anjou Recherches and Veolia Environment. We thank the Consulate General of France in Hong Kong and the Foreign Ministry of France for financial support for Ms. Angelique Blondy.

Fig. 6. Calculated percent removals of KHP (solid lines) and TOC (dash lines) as a function of (a) membrane selectivity at different membrane fluxes ( = 3.5 min), and (b) membrane areas ratio at different residence time ([KHP] = 250 ppmC, [O3 ] = 130 ppm, QO3 = 20 sccm, and T = 25 ◦ C).

when ozone is fed at high concentration but low flow rate as high ozone gas concentration and large interfacial area from small ozone gas bubbles favor fast ozone mass transfer rate and reaction. Fig. 5 shows that high TOC removal is also obtained at this ozone feed condition. The TOC removal has an asymptote of 60% at room temperature due to the refractory nature of the I3 products. However as most of the I3 products are carboxylic acids, it is possible to use biological method for their removal. The selective removal of water in the advanced ozone membrane reactor concentrates the organics in the reaction zone resulting in faster reaction and more complete degradation of organics as shown by the twofold increase in TOC removal (Fig. 4b). Model calculation was used to examine the effects of membrane selectivity and flux on KHP and TOC removal in the advanced ozone membrane reactor (Fig. 6a). The calculation shows that membrane flux is more important than membrane selectivity, and that a H2 O/organic separation of 10 is sufficient to enhance ozone degradation of the organic pollutant. Increasing the membrane selectivity from 10 to 100,000 resulted in less than 10% increase in TOC removal, while a fourfold increase in membrane flux resulted in over 20% improvement. The relative area of the membrane separator and distributor was examined in Fig. 6b. It is important to note that the calculations were based on the tube-and-shell reactor arrangement shown in Fig. 2 and therefore the membrane area ratio is constrained to values less than 0.9. The plots show that for all residence time, KHP and TOC removal increase as the area of the separation membrane increases. This suggests that it would be beneficial to consider capillary or spiral wound membranes to attain a larger separation membrane area.

References [1] G. Loraine, M. Pettigrove, Environmental Science and Technology 40 (2006) 687–695. [2] B.L. Tan, D.W. Harker, J.F. Muller, F.D. Leusch, L.A. Tremblay, H.F. Chapman, Chemosphere 69 (2007) 644–654. [3] A.J. Watkinson, E.J. Murby, S.D. Costanzo, Water Research 41 (2007) 4164–4174. [4] T. Okuda, Y. Kobayashi, R. Nagao, N. Yamashita, H. Tanaka, S. Tanaka, S. Fujii, C. Konishi, I. Houwa, Water Science and Technology 57 (2008) 65–71. [5] Y.J. Zhang, S.U. Geissen, C. Gal, Chemosphere 73 (2008) 1151–1161. [6] D. Simazaki, J. Fujiwara, S. Manabe, M. Matsuda, M. Asami, S. Kunikane, Water Science and Technology 58 (2008) 1129. [7] D. Kolpin, E. Furlong, M. Meyer, E. Thurman, S. Zaugg, L. Barber, Environmental Science and Technology 36 (2002) 1202–1211. [8] M.J. Focazio, D.W. Kolpin, K.K. Barnes, E.T. Furlong, M.T. Meyer, S.D. Zaugg, L.B. Barber, M.E. Thurman, Science of the Total Environment 402 (2008) 201–216. [9] K. Kummerer (Ed.), Pharmaceuticals in the Environment – Sources, Fate, Effects and Risks, 2nd ed., Springer, 2004. [10] S.A. Synder, P. Westerhoff, Y. Yoon, D.L. Sedlak, Environmental Engineering Science 20 (2003) 449–469. [11] P.E. Stackelberg, E. Furlong, M. Meyer, S. Zaugg, A. Henderson, D. Reissman, Science of the Total Environment 329 (2004) 99–113. [12] P.E. Stackelberg, J. Gibs, E.T. Furlong, M.T. Meyer, S.D. Zaugg, R.L. Lippincott, Science of the Total Environment 377 (2007) 255–272. [13] Center for Disease Control and Prevention, Third National Report on Human Exposure to Environmental Chemicals, National Center for Environmental Health Pub. No. 05-0570, 2005. [14] World Health Organization, Global assessment of the state-of-the-science of Endocrine Disruptors, The International Programme on Chemical Safety, WHO/PCS/EDC/03/3, 2003. [15] T.E. Stoker, L.G. Parks, L.E. Gray, R.L. Cooper, Critical Reviews in Toxicology 30 (2000) 197–252. [16] A.C. Collier, Ecohealth 4 (2007) 164–171. [17] T.A. Ternes, M. Meisenheimer, D. McDowell, F. Sacher, H.J. Brauch, B.H. Gulde, G. Preuss, U. Wilme, N.Z. Seibert, Environmental Science and Technology 36 (2002) 3855–3863. [18] P. Westerhoff, Y. Yoon, S. Snyder, E. Wert, Environmental Science and Technology 39 (2005) 6649–6663. [19] V. Camel, A. Bermond, Water Research 32 (1998) 3208–3222. [20] M.C. Huber, S. Canonica, G.Y. Park, U.V. Gunten, Environmental Science and Technology 37 (2003) 5665–5670. [21] R. Ermawati, S. Morimura, Y.Q. Tang, K. Liu, K. Kida, Journal of Bioscience and Bioengineering 103 (2007) 27–31. [22] Y.P. Zhang, J.L. Zhou, Water Research 39 (2005) 3991–4003. [23] A.M. Comerton, R.C. Andrews, D.M. Bagley, C.Y. Hao, Journal of Membrane Science 313 (2008) 323–335.

H.L. Ho et al. / Catalysis Today 193 (2012) 120–127 [24] K. Kimura, S. Toshima, G. Amy, Y. Watanabe, Journal of Membrane Science 245 (2004) 71–78. [25] S.K. Hong, M. Elimelech, Journal of Membrane Science 132 (1997) 159–181. [26] S. van Geluwe, L. Braeken, B. van der Bruggen, Water Research 45 (2011) 3551–3570. [27] B.S. Karnik, S.H.R. Davies, K.C. Chen, D.R. Jaglowski, M.J. Baumann, S.J. Masten, Water Research 39 (2004) 728–734. [28] B. Schlichter, V. Mavrov, H. Chmiel, Desalination 156 (2003) 257–265. [29] P.V. Shanbhag, A.K. Guha, K.K. Sirkar, Industrial and Engineering Chemistry Research 37 (1998) 4388–4398. [30] B.S. Karnik, S.H. Davies, M.J. Baumann, S.J. Masten, Environmental Science and Technology 39 (2005) 7656–7661. [31] K.L. Yeung, R. Aravind, J. Szegner, A. Varma, Studies in Surface Science and Catalysis 101 (1996) 1349–1358. [32] M.A. Pena, D.M. Carr, K.L. Yeung, A. Varma, Chemical Engineering Science 53 (1998) 3821–3834. [33] K.L. Yeung, R. Aravind, R.J.X. Zawada, J. Szegner, G. Cao, A. Varma, Chemical Engineering Science 49 (1994) 4823–4838. [34] Y.S. Cheng, M.A. Pena, K.L. Yeung, Journal of the Taiwan Institute of Chemical Engineers 40 (2009) 281–288. [35] Y. Guo, X.F. Zhang, H.Y. Zou, H.O. Liu, J.Q. Wang, K.L. Yeung, Chemical Communications (2009) 5898–5900. [36] A.J. Maira, W.N. Lau, C.Y. Lee, P.L. Yue, C.K. Chan, K.L. Yeung, Chemical Engineering Science 58 (2003) 959–962. [37] Y.S.S. Wan, K.L. Yeung, A. Gavriilidis, Applied Catalysis A 281 (2005) 285–293. [38] K.L. Yeung, X.F. Zhang, W.N. Lau, R. Martin-Aranda, Catalysis Today 110 (2005) 26–37. [39] S. Heng, K.L. Yeung, M. Djafer, J.C. Schrotter, Journal of Membrane Science 289 (2007) 67–75. [40] S. Heng, K.L. Yeung, A. Julbe, A. Ayral, J.C. Schrotter, Microporous and Mesoporous Materials 115 (2008) 137–146. [41] Y.H. Chen, N.C. Shang, D.C. Hsieh, Journal of Hazardous Materials 157 (2008) 260–268.

127

[42] J. Hoigne, H. Bader, Water Research 17 (1983) 173–183. [43] J. Hoigne, H. Bader, Water Research 17 (1983) 185–194. [44] L.T.Y. Au, J.L.H. Chau, C.T. Ariso, K.L. Yeung, Journal of Membrane Science 183 (2001) 269–291. [45] L.T.Y. Au, W.Y. Mui, P.S. Lau, C.T. Ariso, K.L. Yeung, Microporous and Mesoporous Materials 47 (2001) 203–216. [46] W.C. Wong, L.T.Y. Au, P.P.S. Lau, C.T. Ariso, K.L. Yeung, Journal of Membrane Science 193 (2001) 141–161. [47] Y.S. Cheng, M.A. Pena, J.L. Fierro, D.C.W. Hui, K.L. Yeung, Journal of Membrane Science 204 (2002) 329–340. [48] J.L.H. Chau, A.Y.L. Leung, K.L. Yeung, Lab-on-a-Chip 3 (2003) 53–55. [49] J.L.H. Chau, K.L. Yeung, Chemical Communications (2002) 960–961. [50] J. Motuzas, S. Heng, P.P.S.Z. Lau, K.L. Yeung, Z.J. Beresnevicius, A. Julbe, Microporous and Mesoporous Materials 99 (2007) 197–205. [51] G.H. Yang, X.F. Zhang, S.Q. Liu, K.L. Yeung, J.Q. Wang, Journal of Physics and Chemistry of Solids 68 (2007) 26–31. [52] X.F. Zhang, H.O. Liu, K.L. Yeung, Materials Chemistry and Physics 96 (2006) 42–50. [53] S.M. Lai, L.T.Y. Au, K.L. Yeung, Microporous and Mesoporous Materials 54 (2002) 63–77. [54] S.M. Kwan, K.L. Yeung, Chemical Communications (2008) 3631–3633. [55] S. Heng, P.P.S. Lau, K.L. Yeung, M. Djafer, J.C. Schrotter, Journal of Membrane Science 243 (2004) 69–78. [56] M.S. Eovitz, U. von Gunten, H.-P. Kaiser, Ozone Science and Engineering 22 (2000) 123–150. [57] H. Benbelkacem, H. De bellefontaine, Chemical Engineering and Processing 42 (2003) 723–732. [58] J.A. Roth, D.E. Sullivan, Industrial and Engineering Chemistry Fundamentals 20 (1981) 137–140. [59] P.N. Johnson, R.A. Davis, Journal of Chemical and Engineering Data 41 (1996) 1485–1487.