Effect of an acoustic field on the degradation of phenol: Ozone combined
with a low frequency acoustic field
W. Van de Moortel, 1J. De Coster, 2K. Sniegowski, 2L. Braeken, J. Degrève, 1J. Luyten
K.U.Leuven, Department of Chemical Engineering, Willem de Croylaan 46, 3001, Heverlee,
Belgium, e-mail: wim.vandemoortel@cit.kuleuven.be; 1 Associated Faculty of Industrial and
Biological Sciences, Campus De Nayer, J. De Nayerlaan 5, 2860, Sint-Katelijne-Waver,
Belgium; 2 Limburg Catholic University College, Agoralaan 2, 3590 Diepenbeek, Belgium
Phenolic compounds are commonly present contaminants in industrial wastewater, where
they appear as a result of imperfect manufacturing and/or inadequate treatment operations in
petroleum, petro-chemical, coal, and phenol producing industries (Fang et al., 1997). These
phenolic compounds can not be degraded in conventional biological wastewater treatment
plants (Badawy et al., 2009). Methods for destroying phenolic wastes and phenol residuals in
water environment have been widely investigated and advanced oxidation processes (AOPs)
have been shown as effective treatment methods (Bach et al., 2010; Turhan et al., 2008; Carr
et al., 2000). Among processes to create hydroxyl radicals, the use of an acoustic field is a
relatively novel method, by which water molecules undergo molecular fragmentation to
produce hydroxyl and hydrogen radicals (Ince et al., 2001). For appreciable radical
production, a high frequencies (600 kHz) are required (Price, 1999). Economic considerations
usually lead to the conclusion that ultrasound (US) is cost effective when used in combination
with other techniques (e.g. ozonation).
In this work, the possible synergetic effect of ultrasound on ozonation is investigated.
The application of low frequency ultrasound (20-40 kHz) is reported to enhance the mass
transfer rate of ozone from the gas phase to the liquid phase and to improve the ozone
decomposition rate into radicals. In the first part of this study, the enhancement in ozone mass
transfer rate is studied. The experiments are conducted in batch reactor systems of 2 l. Ozone
is continuously fed at a flowrate of 16 g/h. All experiments are performed at pH 3. Figure 1,
compares the build-up and decomposition of ozone when only ozonation was used, and when
ozone was combined with a low frequency acoustic field of 20 kHz and 30 W.
Figure 1: Ozoneconcentration at pH 3
The evolution of ozone concentration in the liquid is the result of ozone dissolution from the
gas into the liquid and the decomposition of ozone. For slow reactions (MH < 0.02) the net
ozone build-up can be written as:
In the presence of an acoustic field, the decomposition rate of ozone is much higher. The
value of kd changed from 0.96 hr-1 to 3.91 hr-1 Accordingly, the value of kla changes from 23
hr-1 to 38 hr-1.
In a second part, the degradation of phenol by ozone and ozone/US is investigated. Figure 2
shows the COD degradation rate when ozone was combined with an acoustic field of 30 W.
An increase in pseudo-first order constant is clearly shown (from 0.0067 to 0.0094 s-1).
Figure 2: COD-degradation of synthetic wastewater with phenol at pH 3
References
A. Bach, H. Shemer, R. Semiat, Kinetics of phenol mineralization by Fenton-like oxidation,
Desalination, 264 (2010), 188 – 192
M.I. Badawy, R.A. Wahaab, A.S. El-Kalliny, Fenton-biological treatment processes for the
removal of some pharmaceuticals from industrial wastewater, Journal of Hazardous
Materials, 167 (2009), 567 - 574
S.A. Carr, R.B. Baird, Mineralization as a mechanism for TOC removal: study of
ozone/ozone peroxide oxidation using FT-IR, Water Research, 34 (2000), 4036 – 4048
H.H.P. Fang, O.C. Chan, Toxicity of phenol towards anaerobic biogranules, Water Research,
31 (1997), 2229 – 2242
N.H. Ince, G. Tezcanli, R.K. Belen, I.G. Apikyan, Ultrasound as a catalyze of aqueous
reaction systems: the state of the art and environmental applications, Applied Catalysis B:
Environmental, 29 (2001), 167 – 176
G.J. Price, Production of free radicals in ultrasound fields, Journal of the Acoustical Society of
America, 105 (1999) 1381
K. Turhan, S. Uzman, Removal of phenol from water using ozone, Desalination, 229 (2008),
257 – 263