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Separation and Purification Technology 57 (2007) 201–208

Use of an ejector for phenol containing water treatment by ozonation

Olivier Chedeville ∗, Marie Debacq, Mauro Ferrante Almanza, Catherine PorteLaboratoire de Chimie industrielle – Genie des Procedes du Conservatoire National des Arts et Metiers, Equipe EA21,

case 302, 2 rue Conte, 75003 Paris, France

Received 23 October 2006; received in revised form 26 March 2007; accepted 12 April 2007

bstract

Mass transfer of ozone in aqueous phase is a major aspect of ozonation and advanced oxidation processes. The aim of this study is to compare theerformances of an ejector with those of a more traditional gas/liquid contactor: a bubble column. The hydrodynamic study showed that the volu-etric mass transfer coefficient of the ejector (KLa = 7.2 × 10−2 to 1.35 × 10−1 s−1) was greater than that of the bubble column’s (KLa = 1.5 × 10−2

−2 −1

o 2.8 × 10 s ). Very important differences in the values of the residence time and gas retention rate were also observed. A study of phenolegradation was performed. Due to its specifications the ejector is very efficient when the kinetics of reaction is fast (diffusion-controlled regime).n both semi-batch and open circuits, the phenol was quickly eliminated and the ozone transfer was very high (up to 98%). It is to be noted thathese results were obtained for a processing time of approximately 1 s. 2007 Elsevier B.V. All rights reserved.

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eywords: Treatment process; Oxidation; Gas/liquid contactor; Ozone; Mass t

. Introduction

An increasingly strict legislation leads industrialists tomprove the treatment of their wastewaters by optimizing thexisting techniques or by using new processes. Ozonation anddvanced oxidation processes are efficient treatment methodsllowing the degradation of a great number of organic com-ounds.

Ozonation consists in molecular ozone acting directly onhe nucleophilic sites and unsaturated bonds of the organicompounds. Ozone is one of the strongest oxidants technicallypplied [1]. Its action is selective, and the kinetics of reactionepends on the nature of the organic compounds [2–4]. For dis-ociating organic compounds, second order rate constants varyrom 10−1 to 109 M−1 s−1 according to the degree of dissocia-ion of the species [5]. Advanced oxidation processes (O3/H2O2,

3/UV) make use of the indirect action of ozone. They areased on the generation of hydroxyl radicals HO• that are muchore reactive and less selective than ozone. Moreover, the kine-

ics of the reactions are faster: according to compounds, kineticonstants vary from 106 to 1010 M−1 s−1 [6,7]. Due to the fastinetics of the reactions, the treatment processes using these

∗ Corresponding author. Tel.: +33 1 40 27 22 81; fax: +33 1 40 27 20 69.E-mail address: olivier.chedeville@cnam.fr (O. Chedeville).

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383-5866/$ – see front matter © 2007 Elsevier B.V. All rights reserved.oi:10.1016/j.seppur.2007.04.004

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echniques of oxidation are often limited by the mass transferf ozone into water [8]. In the present study, two gas/liquidontactors were used: an ejector and a bubble column.

An ejector is a gas/liquid contactor with interesting perfor-ances but still little used in industry. It ensures an intimate

ontact between the two phases and allows a very fast transferf the ozone into the water. This kind of contactor is based on theonversion of the potential energy of a fluid into kinetic energyhere, the fluid is the liquid to be treated). This transformations accompanied by a depression used to draw up a second fluidhere the oxidizing gas) and create an intimate contact betweenhe two fluids. According to flow rates of the fluids, the contact is

ore or less intense [9]. The bubble column is a more traditionalontactor. A porous diffuser was used to introduce the gas at theottom of the column, for a counter-current flow. The size of theubbles depends on the type of diffuser used and the propertiesf the liquid [10].

Phenol and its derivatives (cresol, xylenol) are compoundsargely used in textile, petrochemical and agrochemical indus-ries. Phenol stands out by its organoleptic and bactericidalroperties, making it difficult to treat by traditional ways. Theecomposition of this compound by ozone has already been stu-

ied. The kinetics of the reaction between ozone and phenols fast: according to Hoigne and Bader [5], the rate of phenolegradation observes a pseudo-first order kinetics with regardo phenol concentration, and the kinetic constant varies from

2 urification Technology 57 (2007) 201–208

1sedatpi

oscooo

2

2

orarlcv

2

2

Vtccop(l

ttc

2

1could contain a volume of liquid of VT,C = 2.5 × 10−3 m3. Aperistaltic pump ensured the circulation of the liquid, introdu-ced at the head of the column. A maximum liquid flow rate

02 O. Chedeville et al. / Separation and P

.3 × 103 to 109 M−1 s−1 according to the pH, the deprotonatedhape of phenol (pKa = 9.9) being much more reactive. Esplugast al. [7] compared different processes of oxidation for phenolegradation; the latter was not always complete (between 56nd 100% of pollutant abatement) in spite of relatively impor-ant durations of treatment (30–80 min). It appeared that sucharameters as pH or reagents concentration have an importantmpact on the treatment efficiency.

The objective of this study was to compare the performancesf the two gas/liquid contactors. Initially, a hydrodynamictudy was performed to estimate the volumetric mass transferoefficient KLa and to observe its variations according to theperational parameters. Then, a phenol solution was treated inrder to observe the efficiency of the treatment method in termsf pollutant abatement and mass transfer.

. Materials and methods

.1. Gas circuit

Ozone was produced from pure oxygen in a LABO LOXzonator, provided by the Trailigaz company. This type of appa-atus guarantees an average ozone production of 16 g h−1 forconcentration of 5% in weight. The gas flow rate G could be

egulated from 0.1 to 0.8 Nm−3 h−1. The unconverted ozone wased to a thermal destructor. For the two installations, the gas cir-uit were made of Teflon. The valves, flowmeters and non-returnalves, provided by company EM-Technik, were made of PFA.

.2. Description of oxidation pilots

.2.1. Case of the ejectorThe polluted liquid contained in a tank, whose volume was

T,E = 3 × 10−2 m3 (Fig. 1), was first led to the heat exchanger,hen to the ejector (Fig. 2). The temperature T of the liquidould be held at between 20 and 35 ◦C. The liquid flow rate Lould be controlled between 0.5 and 1 m3 h−1. A phenomenon

f aspiration of the ozone occurred within the ejector. The twohases, intensely mixed, were then led into the mixture tubeheight: 1.04 m; diameter: 2 × 10−2 m), allowing a return of theiquid in the tank. The latter was surmounted by a cyclone used

Fig. 1. Schematic of the pilot.

Fig. 2. Ejector.

o separate the droplets of water from the gas. This gas was led tohe ozone analyzer and to the thermal destructor. With an openircuit set up, the liquid was initially contained in another tank.

.2.2. The bubble columnThe bubble column (Fig. 3) had a cylindrical body (length:

.4 m; diameter: 0.05 m) and a spherical head. The column

Fig. 3. Schematic of the bubble column.

Purifi

otamrd

2

2

tcpcfcmn

dcl

ctpwSt

φ

wVotoe(b

tcV

t

2ds

k

T2

2sn

Tkc

2

mawtta

H

wcic

(

2

wbuc

t

w(

sa quasi-plug flow reactor, tr is rather close to the transit time ttdefined by:

tt = VC

L + G(6)

Table 1Hatta number

Ha Regime Place of the reaction G/L contactorcharacteristic

O. Chedeville et al. / Separation and

f 0.16 m3 h−1 could be obtained. The porous diffuser (diame-er of the pores ranging between 41 and 100 �m) was placedt the bottom of the column. The gas could be introduced at aaximum flow rate of 0.2 Nm3 h−1. The unconverted ozone was

ecovered at the head of the column and was led to the thermalestructor.

.3. Hydrodynamic calculations

.3.1. Volumetric mass transfer coefficient KLaThe volumetric mass transfer coefficient KLa is a key parame-

er for the description of a gas/liquid contactor. The mass transferoefficient KL (m s−1) is a function of the physicochemical pro-erties of the liquid, the bubbles size and the hydrodynamiconditions [11]. The specific area a (m2 m−3) is the ratio of inter-acial area and the volume of the reactor. The latter parameteran be obtained by several methods (chemical or photographicethods). It is a function of the size of the bubbles and their

umber [10].According to the model suggested by Gao et al. [12],

ecomposition of ozone is supposed to be proportional to theoncentration of the ozone dissolved in water. The proportiona-ity factor is the constant of decomposition kD (s−1).

It is assumed that the dissolved ozone concentration in theontactors is uniform. This is an approximation in the case ofhe bubble column, in which the ozone dissolved concentrationrobably changes along the height, but not for the ejector inhich agitation is very strong and contact time very short (seeection 3.1). According to the diffusional double film theory,

he mass balance of ozone in the liquid phase is:

= VCKLa([O3]eq − [O3]0) − VTkD[O3]0 (1)

ith φ the molar flow of ozone in the liquid phase (mol s−1),C the volume of the gas/liquid contactor (m3), VT the volumef liquid (m3), KLa the volumetric mass transfer coefficient ofhe gas/liquid contactor (s−1), kD the decomposition constantf ozone (s−1), [O3]eq the dissolved ozone concentration inquilibrium with the partial pressure of ozone in the gas phasemol m−3) and [O3]0 is the dissolved ozone concentration in theulk liquid (mol m−3).

In the case of the ejector VC corresponds to the volume ofhe mixing tube (VC = 3.3 × 10−4 m3). In the case of the bubbleolumn, VC is supposed to be identical to the volume of liquidT,C.

A method in two stages was used to determine the values ofhe two coefficients.

.3.1.1. Stage 1: steady state. After the ozonation started, theissolved ozone concentration did not vary any more: the steadytate (SS) was obtained: φ = 0; then, according to (1):

D = k′ Vc

VTKLa with k′ = [O3]eq

SS − [O3]0SS

[O3]0SS

(2)

he value of [O3]eqSS was estimated using Henry’s law [13]. At

0 ◦C, [O3]eqSS = 0.22 g m−3/g Nm−3 in the gas phase.

<

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cation Technology 57 (2007) 201–208 203

.3.1.2. Stage 2: stopping ozonation. Ozone production wastopped once steady state was reached. The gas introduced didot contain ozone: [O3]eq = 0. Then, according to (1) and (2):

d[O3]0

[O3]0 = −(k′ + 1)VC

VTKLa dt (3)

he term −(k′ + 1)(VC/VT)KLa is the slope, α, of ln([O3]0) = f(t).′ having been previously estimated, kD and KLa could be cal-ulated.

.3.2. The Hatta numberThe Hatta number is a very important criterion giving infor-

ation on the competition between the kinetics of the reactionnd the diffusion inside the liquid film (Table 1). It indicateshere the chemical reaction takes place (in the bulk liquid or in

he film) and allows to choose the appropriate gas/liquid contac-or [10]. In the case of a first order reaction in regards to ozonend compound A, the Hatta number is given by [14]:

a =√

k[A]0DO3

kL(4)

ith k the kinetic constant of the reaction between ozone andompound A (M−1 s−1), [A]0 the concentration of compound An the bulk liquid (mol−1 m3) and DO3 is the diffusivity coeffi-ient of ozone into water (m2 s−1).

The value of k has been estimated by Hoigne and Bader [5]Table 5).

.3.3. Mean residence time trThis parameter allows to determine the average time during

hich the liquid is in contact with the gas. Working with theubble column, a sodium chloride solution (100 g L−1) wassed as a tracer, by carrying out a pulse injection. The outletoncentration was measured by conductivity:

r =∑t∞

t0 t[NaCl]�t∑t∞t0 [NaCl]�t

(5)

ith [NaCl] the NaCl outlet concentration measured at tmol m−3). At t∞, [NaCl]t∞ = [NaCl]t0.

In the case of the ejector, the mean residence time was toohort to be measured by this method. Nevertheless, when using

0.3 Kinetic Bulk liquid Liquid volume0.3–3 Transition Partially in film Interfacial area

and liquidvolume

3 Diffusion Entirely in film Interfacial area

2 urific

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ε

wv

p

2

2

t

r

wt

2

t

w(l

t

w[

2

oc

n

w

2

2

lwd

2

bist

2

tr

3

3

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3

ai2ttttuottis

The ozone decomposition coefficient had a similar evolution:it rose from 4.6 × 10−4 to 1.15 × 10−3 s−1: this could be explai-ned by a local temperature rise in the ejector when gas flow rateis higher, which lead to a decrease of ozone solubility.

04 O. Chedeville et al. / Separation and P

.3.4. Gas retention rate εg

εg corresponds to the ratio of the gas volume on the totalolume. For the bubble column, this parameter was estimatedy first measuring the mass of liquid corresponding to VT,C, thenhe mass of liquid in the gas/liquid mixture corresponding to theame volume:

g = Vg

Vg + VL(7)

ith Vg the gas phase volume of (m3) and VL is the liquid phaseolume (m3).

For the ejector, εg was determined by Merrouche [9] with ahotographic method.

.4. Phenol degradation calculations

.4.1. Ozone transferThe efficiency of the mass transfer is given by the ozone

ransfer ratio rO3 :

O3 = CO3,i − CO3,o

CO3,i× 100 (8)

ith CO3,i the ozone concentration in the inlet gas and CO3,o ishe ozone concentration in the outlet gas (g Nm−3).

.4.2. Phenol abatementThe phenol abatement in an open circuit is given by:

a = ([phenol]i − [phenol]o) × 100

[phenol]i(9)

ith [phenol]i the phenol concentration in the inlet liquidmol L−1) and [phenol]o is the phenol concentration in the outletiquid (mol L−1).

The phenol abatement in a semi-batch circuit is given by:

a = ([phenol]t=0 − [phenol]t) × 100

[phenol]t=0

ith [phenol]t=0 the initial phenol concentration (mol L−1) andphenol]t is the phenol concentration at t (mol L−1).

.4.3. Stoichiometric ratioThe number of moles of ozone transferred (nO3,t) per mole

f phenol consumed (nphen,c) was also determined. In an openircuit, this ratio is given by:

O3,t/nphen,c = GCO3,irO3

L[phenol]itaMO3

(10)

ith MO3 the molar mass of ozone (g mol−1).

.5. Analyzes

.5.1. HPLC

Phenol concentration was monitored by HPLC, C18

ichrospher column. The mobile phase used was a mixtureater/acetonitrile: 50/50 at a flow rate of 0.7 mL min−1. An UVetector (210 nm) was used.

FL

ation Technology 57 (2007) 201–208

.5.2. Dissolved ozoneThe ozone dissolved in the aqueous phase was measured

y the carmin indigo method: the attack of trisulfonate carminndigo by O3 in an acid medium leads to a discoloration of theolution, followed by spectrophotometry at 600 nm (spectropho-ometer DR2100, HACH).

.5.3. Ozone in gas phaseThe ozone in the gas phase was monitored with a UV spec-

rophotometer (BMT 961, Messtechnik). This analyzer emits aadiation at 254 nm (ozone absorption wavelength).

. Results and discussion

.1. Determination of hydrodynamic characteristics

The KLa and kD coefficients were estimated for differentxperimental conditions, in order to test the influence of theas flow rate and liquid flow rate on the transfer capacity of theontactors. Experimental conditions and results are presented inable 2. Carrying out a series of the same experiment enabled

o estimate the experimental uncertainty �KLa = 6 × 10−3 s−1

nd �kD = 6 × 10−5 s−1.

.1.1. Case of the ejectorAll the experiments presented in Table 2 were performed

t pH 5.5, with distilled water and ozone concentration in thenlet gas CO3,i = 20 g Nm−3. The results of the experiments 1,

and 3, presented in Fig. 4, showed that the volumetric massransfer coefficient is an increasing function of G: the value ofhe volumetric mass transfer coefficient rose from 7.2 × 10−2

o 1.35 × 10−1 s−1 when G rose from 0.25 to 0.45 Nm3 h−1,hese differences being significant with regard to experimentalncertainty. This phenomenon can be explained by a decreasef the transfer resistance in more turbulent conditions and byhe increase of the specific area of the contactor. The results ofhe experiments 3, 4 and 5 showed that liquid flow rate has nonfluence on the value of KLa: the differences observed are notignificant with regard to experimental uncertainty.

ig. 4. Influence of G (ejector). T = 20 ◦C, CO3,i = 20 g Nm−3, pH 5.5,= 0.9 m3 h−1.

O. Chedeville et al. / Separation and Purification Technology 57 (2007) 201–208 205

Table 2Experimental conditions and results—effect of liquid and gas flow rates

Exp. L (m3 h−1) G (Nm3 h−1) k′ α (10−3 s−1) kD (10−4 s−1) KLa (10−2 s−1)

Ejector1 0.9 0.25 0.59 −1.23 4.6 7.22 0.9 0.35 0.77 −2.06 9 113 0.9 0.45 0.079 −1.58 11.5 13.54 0.8 0.45 0.201 −1.75 10 13.25 1.0 0.45 0.113 −1.75 11.6 14.2

Bubble column6 0.12 0.06 0.085 −16.7 13 1.57 0.12 0.08 0.09 −23.0 20 2.1

3

ti5tta1rro

bc

wtwncdcT

3

mfiI

FL

tceatrcItib

nupvtmtfccis

3

8 0.12 0.1 0.0869 0.1 0.1 0.093

10 0.15 0.1 0.093

.1.2. Case of the bubble columnThe experiments presented in Table 2 were performed with

ap water (pH 7.5), at 20 ◦C and with an ozone concentrationn the gas phase of 20 g Nm−3. The results of experiments 4,

and 6, presented in Fig. 5, showed that the more importanthe gas flow rate was (from 0.25 to 0.45 Nm3 h−1), the higherhe volumetric mass transfer coefficient (from 0.9 to 1.7 min−1)nd the ozone decomposition coefficient (from 8 × 10−2 to5 × 10−2 min−1) were, the variations being significant withegard to the experimental uncertainty. As for the ejector, expe-iments 8, 9 and 10 showed that liquid flow rate has no influencen the value of the volumetric gas transfer.

These results showed that KLa is higher in the ejector. It cane explained by a more important specific area and better mixingonditions.

For the ozone decomposition coefficient, it appeared that kDas higher in the case of the bubble column than in the case of

he ejector. This can be explained by the matrix used: tap wateras used in the bubble column in order to obtain an homoge-eous regime (homogeneous bubble size) for the experimentalonditions chosen. This tap water was more basic pH 7.5 thanistilled water used in the ejector pH 5.5. Moreover the tap waterontains more competing materials which reacted with ozone.hese reactions lead to ozone decomposition and increase of kD.

.1.3. Discussion

Table 3 presents the synthesis of the results of the hydrodyna-

ic study of the two gas/liquid contactors, and the experimentalelds (values of G and L) for which these results were obtained.n both cases, the liquid flow rate has an important impact on

ig. 5. Influence of G (bubble column). T = 20 ◦C, CO3,i = 20 g Nm−3, pH 7.5,= 0.12 m3 h−1.

3

a

TS

VLGtε

K

−30.8 25 2.8−28.3 23 2.6−28.3 23 2.6

r and εg values, but not on the volumetric mass transfer coeffi-ient. The gas flow rate has an important influence on KLa. Thisffect can be explained by the rise in the values of the specificrea when G increases. It appears that the ejector is more suitablehan the bubble column in the case of a diffusion-controlledegime (Ha > 3) as the value of its volumetric mass transferoefficient is higher and its gas retention rate is more important.t is important to notice that the residence time in the mixtureube located under the ejector is very short (≈1 s), whereas its about 150 s in the bubble column. The characteristics of theubble column recommend it for a kinetic-controlled regime.

In its study, Gao et al. [12] listed results from literature obtai-ed for contactors which dimensions are rather close to thosesed in his reactor (Karman reactor) and to those used in theresent study (Table 4). The results presented show that thealues of the volumetric mass transfer coefficient obtained forhe column are in conformity with those estimated by different

ethods in other studies. It appears that the performances ofhe ejector are higher than those of the gases/liquid contactorsrequently used. Moreover, the experimental results show that itould be interesting to increase G in order to improve the effi-iency of the mass transfer when the kinetics of the reactions fast. However, it is necessary to insure that contact time isufficiently long.

.2. Degradation of phenol

.2.1. Semi-batch circuit experiments

These experiments were performed in order to observe the

dvisability of using an ejector according to the kinetic regime.

able 3ynthesis of the hydrodynamic study

Bubble column Ejector

(m3) 2.5 × 10−3 30 × 10−3

(m3 h−1) 0–0.16 0.5–1(Nm3 h−1) 0–0.16 0–0.5

r (s) 60–150 ≈1

g 0.02–0.07 0.2–0.46

La (s−1) 1.5 × 10−2 to 2.8 × 10−2 7.2 × 10−2 to 1.35 × 10−1

206 O. Chedeville et al. / Separation and Purification Technology 57 (2007) 201–208

Table 4Comparison of the coefficients of transfers of different processes [12]

Contactor Operating conditions KLa (s−1)

Bubble column (H = 5.5 m) CO3,i = 8–60 g −3, G = 0.3–1.2 Nm3 h−1, L = 0.1–0.45 m3 h−1 3 × 10−3 to 2 × 10−2

Fixed bed column CO3,i = 30 g m−3, G = 5–10 Nm3 h−1 6.3 × 10−3 to 1.4 × 10−2

Electrostatic spray CO3,i = 10 g m−3, G = 0.12 × 10−1 −1 −2

Bubble column CO3,i = 10 g m−3, G = 0.12 × 10−Karman reactor CO3,i = 10 g m−3, G = 60–240 NL

Table 5Experimental conditions

pH kO3/phenol [5] (M−1 s−1) Ha Regime

2.7 103 7 × 10−2 Kinetic controlled7 106 2 Transition

1

3dtdL[a

3apthtttae

F[

adta

TiSobt

3

pc

3rct

• The solutions treated were identical (same pollutant concen-

9 108 21 Diffusion controlled1.3 >109 >67 Diffusion controlled

.2.1.1. Experimental conditions. The kinetics of reactionepends strongly on the pH value [5]. Four experiments, presen-ed in Table 5, were performed at different pH levels, involvingifferent Hatta number values [5]. The other conditions were= 0.8 m3 h−1, G = 0.5 Nm3 h−1, T = 20 ◦C, [O3]i = 12 g Nm−3,

phenol]t=0 = 6 × 10−2 g m−3. The pH was initially adjusted byddition of NaOH or H2SO4.

.2.1.2. Results and discussion. The evolutions of the pollutantbatement (Fig. 6) and ozone mass transfer (Fig. 7) indicate thathenol was degraded in a first stage. During this degradation,he higher the pH was, the faster the phenol degradation and theigher the ozone transfer ratio were. At pH 11.3, phenol wasotally degraded in 30 min, whereas the treatment time was up

o 75 min at pH 2.7. In a diffusion-controlled regime, the ejec-or appeared to be very efficient: phenol was quickly degradednd the ozone mass transfer was maximal (rO3 = 100%). For thexperiments at pH 11.3 and 9, the results were rather close during

ig. 6. Phenol abatement evolution. L = 0.8 m3 h−1, G = 0.5 Nm3 h−1, T = 20 ◦C,O3]i = 12 g Nm−3, [phenol]t=0 = 6 × 10−2 g m−3. Ejector, semi-batch.

F[

NL h <2.5 × 101 NL h−1 9 × 10−3

h−1, L = 0.66–0.84 m3 h−1 8.3 × 10−3 to 2.5 × 10−3

bout 20 min: all the ozone introduced was used for the phenolegradation and the reaction was limited by the ozone concen-ration in the inlet gas. At a lower pH, the reaction was slowernd the ejector was not the most appropriate gas/liquid contactor.

The second stage corresponds to a by-products oxidation.hese by-products (oxalic, glyxalic, maleic, fumaric acids)

nduce a decrease in pH and were less reactive with the ozone.o, the transfer ratio decreased. Nevertheless, the degradationf these carboxylic acids could be easily realized with a classiciological treatment, and it did not seem worthwhile to continuehe treatment after the phenol degradation.

.2.2. Open circuit experimentsIn order to compare the performances of the two installations,

henol degradation experiments were carried out in an openircuit.

.2.2.1. Experimental conditions. For the two couples of expe-iments (one with the ejector and the other with the bubbleolumn), the experimental conditions were selected accordingo several criteria:

tration and pH, solutions prepared with tap water). So, Hattanumber was the same for each couple of experiments.

ig. 7. rO3 = f(t). L = 0.8 m3 h−1, G = 0.5 Nm3 h−1, T = 20 ◦C,O3]i = 12 g Nm−3, [phenol]t=0 = 6 × 10−2 g m−3. Ejector, semi-batch.

O. Chedeville et al. / Separation and Purification Technology 57 (2007) 201–208 207

Table 6Experimental conditions and results

L (m3 h−1) G (Nm3 h−1) CO3,i (g Nm−3) Ha ta (%) rO3 (%) nO3,t/nphen,c

AColumn 0.1 0.1 13 1.9 85.4 93.1 2.8Ejector 0.8 0.35 30 1.9 76.2 81 2.8

BColumn 0.1 0.1 13 8.6 52 95 2.6

A regim

•

•

TtrTH

3rtmtrhe

cabpTav(pt

ftroI[ipuvttat

4

chrrtff(saw

A

ta

R

Ejector 0.8 0.35 30

—transition regime: pH 7.5; [phenol]i = 10−2 g L−1; B—diffusion-controlled

The ratio of the quantity of ozone introduced (nO3,i) on thequantity of pollutant (nphen,i) was identical.All the experiments were carried out at 20 ◦C.

The other experimental conditions are presented in Table 6.he modification of the kinetic of the reaction by varying

he pH enabled to carry out experiments in transitionegime (0.3 < Ha < 3) and diffusion-controlled regime (Ha > 3).he pH was initially adjusted by addition of NaOH or2SO4.

.2.2.2. Results and discussion. At pH 7.5 (Ha = 1.9), theesults presented in Table 6 show that the bubble column seemso be the most efficient gas/liquid contactor: the phenol abate-

ent rate and the ozone transfer ratio were about 10% higherhan those obtained with the ejector. When the reaction occur-ed in the bulk liquid and in the film, due to its high liquidold-up and residence time, the bubble column is the mostfficient.

At pH 8.5 (Ha = 8.6), the results presented in Table 6 indi-ate that the ejector presents better performances: the phenolbatement rate was higher than the one obtained with theubble column, the quantity of ozone consumed per mole ofhenol was smaller and the ozone transfer ratio was higher.hese results can be explained by the importance of the contactrea between the two phases generated by the ejector. Moreo-er, an increase in the ozone concentration in the gas phasetechnically not feasible here) could allow to obtain a com-lete and fast phenol elimination with a very efficient massransfer.

To conclude, the results showed that in the case of aast kinetics of reaction, the ejector, which has an impor-ant volumetric mass transfer coefficient and gas retentionate, is the more efficient gas/liquid contactor: high levels ofzone mass transfer and pollutant abatement were obtained.n comparison with the results obtained in different studies6,7,15,16], the use of the ejector allows a significant decreasen ozone consumption: during the experiments carried out atH 8.5: rO3 was very high (>98%) and the quantity of ozonesed per mole of phenol was small (nO3 /nphen = 1.9). Moreo-er, all these results were obtained for very short contact

imes (about 1 s). For a space requirement similar to that ofhe bubble column, the ejector allowed to treat flow ratespproximately 10 times higher in a hundredth of the contactime.

8.6 74 98 1.9

e: pH 8.5; [phenol]i = 2 × 10−2 g L−1.

. Conclusion

In a first stage, the hydrodynamic properties of the twoontactors were estimated. It appeared that the ejector hadigher volumetric mass transfer coefficient and gas retentionate, making it an ideal processing device when the chemicaleaction occurs in the bulk liquid. By raising the pH, it appearedhat the ejector gave better results for the treatment of phenol:or a contact time of about 1 s between the two phases, a largeraction of ozone introduced was transferred in liquid phaserO3 > 98%). So, for diffusion-controlled regime (ozonation atufficiently high pH or advanced oxidation process), the ejectorllows a treatment of important flow rate, in a very short time,ith a very efficient mass transfer.

cknowledgments

The authors wish to thank Caroline Wisniewski (Sanofi Aven-is), Marielle Coste and Florencio Martin (Anjou Recherche),nd ANVAR for supporting this investigation.

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