Effect of an acoustic field on the degradation of phenol: Ozone combined with a low frequency acoustic field W.. De Nayerlaan 5, 2860, Sint-Katelijne-Waver, Belgium; 2 Limburg Catholic U
Trang 1Effect 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
Trang 2The 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 (M H < 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 k d changed from 0.96 hr-1 to 3.91 hr-1 Accordingly, the value of k l a 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
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