Desalination 229 (2008) 257–263

*Corresponding author.

Removal of phenol from water using ozone

Kadir Turhana, Suheyla Uzmanb

aYildiz Technical University, Chemistry Department,34220 Esenler, Istanbul, TurkeyTel. +90 (212) 4491642; Fax +90 (212) 4491514; email: turhankadir@yahoo.com

bYeditepe University, Chemical Engineering Department, 34755 Kayisdagi, Istanbul, Turkey

Received 15 December 2006; accepted revised 25 September 2007

Abstract

Aromatic compounds are extensively used in several of industries and can cause pollution in water sources.This study aims to examine the degradability of phenol by ring cleavage in aqueous solutions using ozone and todetermine the kinetics. A semi-batch process was employed in this study. Samples from the reaction medium weretaken at certain time intervals, and concentrations of phenol were determined using a UV/VIS spectrophotometer.The samples were also subjected to total organic carbon (TOC) analysis to monitor concentration changes ofphenol. The intermediate products formed during ozonization were determined GC/MS.

Keywords: Ozone; Phenol; Aromatic pollutants; Advanced oxidation process (AOPs); Kinetic

1. Introduction

Many industries use phenolic materials in theirmanufacturing processes. Phenol is also used inthe production of drugs, weed killers, and syn-thetic resins. Phenol and its derivatives are presentin the wastewaters of industries such as coking,pulp mills, paint and dyes, wine distilleries, oiland gasoline, synthetic rubber, textiles, pharma-ceuticals, solvent, manufacture of pesticides, pa-per, and wood, etc. [1–3]. Occupational exposureto phenol has been reported during its productionand use, as well as in the use of phenolic resins in

the wood products industry. It has also been de-tected in automotive exhaust and tobacco smoke[4]. Toxic organic contaminants, such as hetero-cyclic and phenolic compounds, present seriousenvironmental risks and should be eliminated be-fore discharge into natural water bodies. Concen-trations of phenol and its products in municipalwastewaters vary from trace quantities up to 1000μg/L. There have been reports of toxic organiccompounds remaining in trace quantities (μg/L)in the treated effluent of many wastewater treat-ment plants. It should be noted that the contami-nation of drinking water by phenolics at even aconcentration of 1 μg/L could cause significant

doi:10.1016/j.desal.2007.09.0120011-9164/08/$– See front matter © 2008 Published by Elsevier B.V.

258 K. Turhan, S. Uzman / Desalination 229 (2008) 257–263

taste and odor problems making it unfit for use.Human consumption of phenol-contaminated

water can result in severe pain leading to damageof the capillaries ultimately causing death [5].With the rapid increase in the number of chemi-cal industries, a great deal of wastewater is pro-duced, which causes pollution and degrades theenvironment. Many of these industrial wastewa-ters, particularly the ones containing phenoliccompounds are well known to be characterizedby higher salinity, acidity, chemical oxygen de-mand (COD) value and low biodegradability,which means that the effluent cannot be treatedby the conventional process [6,7]. An alternativemethod of treating such wastewater is advancedoxidation processes (AOPs), where highly reac-tive free radicals, especially hydroxyl radicals, aremostly utilized to destroy the pollutants in waste-water. These processes involve the following mainsub-processes: direct ozonization, wet air oxida-tion (WAO), hydrogen peroxide oxidation, UVphotolysis, etc. [7–9].

Ozonation is widely employed in water treat-ment for disinfection. Decomposition of the phe-nolic substances in tap water is responsible formusty taste and odors. Hoigné and his co-work-ers have revealed that ozonation produces hy-droxyl (OH) radical through the decompositionof ozone (O3) with OH– and proposed Staehelin,Buhler and Hoigné model (SBH) for the complexreaction cascade during ozonation [10]. They alsoreported that OH radical is one of the most reac-tive species in ozonation of water and the amountof OH radical determines the efficiency ofozonation [11]. Recently, some kinetic modelswere provided to explain the efficiency of OHradicals in advanced oxidation processes using OHradical scavengers [12]. However, there have beenvery few papers which determined the amount andthe dynamics of OH radical directly. There is agrowing public concern about the widespreadcontamination of surface and groundwaters byvarious organic compounds over the past severaldecades. Especially, like many phenolic com-

pounds, chlorophenols have been used widely inthe manufacturing pesticides and other industrialchemicals [13–15]. In this study, synthetic aque-ous solutions of phenol were treated with ozone.The reaction of ozone with phenol was investi-gated at different conditions, such as phenol con-centration, ozone concentration and contact time.Total organic carbon and UV analysis of the aro-matic by-products formed during and after theozonation reaction were employed. The resultsfrom TOC analysis, reaction rate were investi-gated. GC/MS and HPLC were also used to studyreaction’s intermediates and final products.

2. Materials and methods

Phenol solution was prepared from pure stan-dard (Merck, 99.9% of purity) with distilled wa-ter. The concentrations of phenol solutions were25, 50, 75 and 100 mg/L, respectively. The ozo-nization reaction was carried out in the systemwhich was shown in Fig. 1. The reactor capacitywas 3,000 mL. Ozonation experiments were per-formed in a 2,000 mL capacity ozone bubble col-umn between 0 and 2 h in semi-batch suppliedwith counter current recirculation of the liquid tothe gas flow. Fischer 502 model ozone generatorwas used for the production of ozone from dryoxygen (99.9% of purity). The oxygen flow rateto the generator was adjusted at 120 L/h and moni-tored with a rotameter incorporated into the ozonegenerator. The ozone stream was continuouslyintroduced in the sample through a porous spargeras microbubbles at the bottom of the ozonecontactor. The diffusion rates of the ozone/oxy-gen mixture, introduced from the bottom of thereactor through a sintered glass diffusing plate,were 2, 4 and 6 g/Lh. Excess ozone was passedinto gas absorption bottle containing KI solution(2% wt). The excess amount of ozone was deter-mined by titration of the solutions in the bubblersusing sodium thiosulphate and starch as indica-tor, and calibration curve was established [16].All tubing and the fittings from the ozone genera-

K. Turhan, S. Uzman / Desalination 229 (2008) 257–263 259

O2 Ozone

Generator

Trap

ReactionColumn

Exit

Valve

Sample

Pump

Mechanic stirrer

Reactor

Temperature Control

Pump

Base

Otomatic dosimat

Transformer

Temp.Cont.SensorpH electrode

ooo

o

Fig. 1. Scheme of ozonization.

tor to the reactor and the gas absorption bottleswere made of glass and Teflon. The dosages ofozone consumed in medium were calculated forall the experiments, which were performed atambient temperature at 20±1°C. Rate of mechani-cal stirrer was adjusted to 2100 rpm, and circula-tion rate of pump between reactor and reactioncolumn adjusted 1875 mL/min.

75 mL samples were collected from reactioncolumn upper end at different time intervals dur-ing the ozonation reaction for the determinationof the by products. Ozonation of phenol was car-ried out at four different initial concentrations, 25,50, 75 and 100 mg/L, with three different ozoneconcentrations 2, 4 and 6 g/Lh.

The aromatic compounds were determined bymeans of a liquid–liquid extraction of the aque-ous samples with methylene chloride. During theexperiments the water samples were withdrawnregularly from the reactor. The control of decom-position dynamics of the studied compounds aswell as the intermediate and final product analy-ses were realized by UV absorbency, HPLC(Perkin Elmer) equipped with UV-Vis detector

Philips PU 8700 model. A reverse phase columnof XDB-C18, Agilent 5μ was 250 mm in lengthand 4.6 mm in diameter. The isocratic method witha solvent mixture of methanol–water (40:60) as amobile phase with the flow rate of 1mL/min. wasapplied and GC/MS a HP5890 Plus II gas chro-matograph equipped with a flame ionization de-tector (FID) was used for quantifying the repre-sentative phenol intermediate and final productsof reaction. The chromatographic conditions werethe following: column DB-WAX (30 m × 0.25mm, 0.25 μm); injection volume: 3 μL in splitless(0.8 min); injection temperature: 300°C; carriergas: helium (30 cm/s); auxiliary gas: nitrogen andtemperature programme: 40(1)-25-120(3)-4-240.

3. Results and discussion

In this study, the degradability of phenol inaqueous solutions was investigated using ozone.Additionally, decomposition kinetic of phenol inthe presence of ozone was calculated using maxi-

260 K. Turhan, S. Uzman / Desalination 229 (2008) 257–263

mum rate constants, from the plots of concentra-tion vs. time.

The UV absorbency is used for the prelimi-nary control of the degree of decomposition. TheGC/MS and HPLC analysis are used to identifyintermediate and final products formed duringozonation. It was found that reaction of ozone withphenol at pH 9, in addition to catechol (C) andhydroquinone (HQ) are likely primary oxidationproducts, p-benzoquinone (PBQ) and o-benzo-quinone (OBQ), the others are more oxidized spe-cies, and CO2 and water the final oxidation prod-ucts. The detected degradation products are shownin Fig. 2.

This initial attack of the ozone molecule leadsfirst to the formation of ortho- and para-hydroxy-lated by-products. These hydroxylated com-pounds are highly susceptible to further ozonation.The compounds lead to the formation of quinoidand, due to the opening of the aromatic cycle, tothe formation of aliphatic products with carbonyland carboxyl functions. The nucleophilic reactionis found locally on molecular sites showing anelectronic deficit and, more frequently, on carbonscarrying electron acceptor groups. In summary,the molecular ozone reactions are extremely se-

O H

( P )

O H O H

O H

O H

( C )

( H Q )

O

O

( P B Q )

O

O

( O B Q )

C O 2 H

C O 2 H

( M A ) C O 2 + H 2 O

O H

H O O

O

( O A )

Fig. 2. Reaction pathway in the phenol degradation.

lective and limited to unsaturated aromatic andaliphatic compounds as well as to specific func-tional groups.

Fig. 3 shows the evolution in phenol concen-tration during ozonation reaction. Ozone is un-stable in water. The decay of ozone in naturalwaters is characterized by a fast initial decreaseof ozone, followed by second phase in whichozone decreases with first-order kinetics. Themechanism and the kinetics of the elementary re-actions involved in ozone decomposition havebeen investigated in studies [17–19].

The trend of decrease of TOC and phenol con-centration was found to be same and by-productformed was determined by a mass spectrometer.It was shown that by-product formed was notstable, it immediately decomposed to differentproducts as shown in Fig. 2. It was also foundthat the amounts of ozone were sufficient for phe-nol decomposition. As a result of kinetic investi-gation, the decomposition reaction of phenol wasfound to be of the first order with almost constantk values (Fig. 4).

As expected that, Rmax values increased withthe increasing O3 concentration especially for twophenol concentrations (50 mg/L and 75 mg/L).

K. Turhan, S. Uzman / Desalination 229 (2008) 257–263 261

0

10

20

30

40

50

0 10 20 30 40 50

Time (min)

Con

cent

ratio

n (m

g/L)

2 g/hL O3

4 g/hL O3

6 g/hL O3

(b)

0

15

30

45

60

75

0 10 20 30 40 50

Time (min)

Con

cent

ratio

n (m

g/L)

2 g/hL O3

4 g/hL O3

6 g/hL O3

(c)

0

20

40

60

80

100

0 10 20 30 40 50

Time (min)

Con

cent

ratio

n (m

g/L)

2 g/hL O3

4 g/hL O3

6 g/hL O3

(d)

Fig. 3. Change in phenol concentration after reaction with ozone at different initial phenol: (a) 25 mg/L, (b) 50 mg/L,(c) 75 mg/L and (d) 100 mg/L, and ozone concentrations.

Decomposition kinetics of phenol in the presenceof ozone was calculated using maximum rate con-stants, from graphics of concentration vs. time.Maximum R value was found as 409.55 mg/Lhfor phenol. According to all obtained results, itwas found that phenol decomposition occurs inthe using of enough ozone, and the decomposi-tion reaction follows first order reaction kinetics[20].

4. Conclusions

As a result of present study the all results weresummarized as follows;• The system can get free of phenol to part it

with ozonization process.• Degradation is computable with first degree

kinetic.

• Catechol, hydroquinone, p-benzoquinone ando-benzoquinone, maleic acid and oxalic acidintermediate products can occur at the end ofozonization.

• It was seen that some organic compounds suchas, catechol, hydroquinone, p-benzoquinonecan be oxidized completely with ozone to CO2and H2O, but destruction of some organic com-pounds requires a long ozonation time and highozone dosages.

• The principal final products are CO2 and H2Oover oxalic acid in alkaline media.

Acknowledgement

Financial support of this research byTUBITAK (The Scientific and Technical Research

0

5

10

15

20

25

0 10 20 30 40 50

Time (min)

Con

cent

ratio

n (m

g/L)

2 g/hL O3

4 g/hL O3

6 g/hL O3

(a)

262 K. Turhan, S. Uzman / Desalination 229 (2008) 257–263

Fig. 4. Changing ofphenol concentration (A) with ozone concentration (O) vs. time. C0: initial concentration of phenol,C: concentration of phenol at time. A: 50 mg/L, O: 2 g/hL (a.), O: 4 g/hL (b.), O: 6 g/hL (c.), respectively. A: 75 mg/L,O: 2 g/hL (a.), O: 4 g/hL (b.), O: 6 g/hL (c.), respectively.

Council of Turkey) [Project Number: KTCAG-71] is gratefully acknowledged.

References[1] M.S.E. Abdo, S.A.Nosier, Y.A.El-Tawil, S.M. Fadi

and M.I. El-Khairy, J. Environ. Sci. Health A, 32(4)(1997) 1159–1169.

[2] B. Seredynska-Sobecka, M. Tomaszewska and A.W.Morawski, Desalination, 182 (2005) 151–157.

[3] W. Kujawski, A. Warszawski, W. Ratajczak, T.Porebski, W. Capala and I. Ostrowska, Desalination,163 (2004) 287–296.

[4] B. Bae, R.L. Autenrieth and J.S. Bonner, WaterEnviron. Res., (1995) 67(2), 215–223.

[5] P.L. McCarty, P.V. Roberts and E.J. Bouver, Trans-port and fate of organic contaminants in soil. Proc.Speciality Conference Water Forum, San Francisco,1981, pp. 606–615.

[6] J.S. Miller, D. Olejnik, Ozone Sci. Eng., 26(5)

K. Turhan, S. Uzman / Desalination 229 (2008) 257–263 263

(2004) 453–464.[7] T. Poznyak and B.G. Arazia, Ozone Sci. Eng., 27(6)

(2005) 351–357.[8] S. Esplugas, J. Gimenez, S. Contreras, E. Pascual

and M. Rodrguez, Water Res., 36(4) (2002) 1034–1042.

[9] N.H. Salah, M. Bouhelassa, S. Bekkouche and A.Boultif, Desalination, 166 (2004) 347–354.

[10] J. Staehelin, R.E. Buhler and J. Hoigné, J. Phys.Chem., 88(24) (1984) 5999–6004.

[11] J. Hoigné, The Chemistry of Ozone in Water. Pro-cess Technologies for Water Treatment. New York,Plenum Press, 1988, pp. 121–143.

[12] R. Andreozzi, V. Caprio, A. Insola and R. Marotta,Catal Today, 52 (1999) 51–59.

[13] P.K. Hong, Y. Zeng, Water Res., 36(17) (2002)4243–4254.

[14] T. Poznyak and J. Vivero, Ozone Sci. Eng., 27(6)(2005) 447–458.

[15] N.C. Shang, Y.H. Yu and H.W. Ma, J. Environ. Sci.Health: A. Toxicol. Hazard Substance Environ. Eng.,37(2) (2002) 261–271.

[16] APHA–AWWA–WPCF Standard Methods for theExamination of Water and Wastewater. 19th ed.,A.D. Eaton, L.S. Clesceri and A.E. Greenberg, eds.,Washington DC, 1995.

[17] L. Forni, D. Bahnemann and E.J. Hart, J. Phys.Chem., 86 (1982) 255–259.

[18] J. Hoigné, H. Bader, W.R. Haag and J. Staehelin,Water Res., 19 (1985) 993–1004.

[19] H. Tomiyasu, H. Fukutomi and G. Gordon, InorganicChem., 24 (1985) 2962–2966.

[20] K. Turhan, PhD thesis, Yildiz Technical University,Istanbul, 2001.