Chemical Engineering Science 64 (2009) 2332 -- 2342 Contents lists available at ScienceDirect Chemical Engineering Science journal homepage: w w w . e l s e v i e r . c o m / l o c a t e / c e s Multicomponent reaction kinetics for the ozonation of p-nitrophenol and its decomposition products under acidic conditions at constant pH Markku Kuosa a,∗ , Arto Laari a , Antti Solonen b , Heikki Haario b , Juha Kallas a a Lappeenranta University of Technology, Department of ChemicalTechnology, P.O.Box 20,FIN-53851 Lappeenranta, Finland b Lappeenranta University of Technology, Department of Mathematics and Physics, P.O.Box 20,FIN-53851 Lappeenranta, Finland A R T I C L E I N F O A B S T R A C T Article history: Received 13 June 2008 Received in revised form 5 February 2009 Accepted 11 February 2009 Available online 20 February 2009 Keywords: Ozonation p-Nitrophenol Bubble column Parameter estimation Adaptive MCMC The reaction kinetics ofp-nitrophenol ozonation in a bubble column at pH 2 of water is studied. The reaction kinetic parameters, rate coefficients and stoichiometric coefficients, as well as the mass transfer coefficient are estimated by nonlinear estimation with the developed novel reaction kinetic model.The concentration of unknown intermediate compounds is presented as a residual chemical oxygen demand (COD) calculated from the measured COD and the theoretical COD for the known compounds.The de- composition rate of p-nitrophenol is almost the same on the pathway producing hydroquinone and on the pathway producing 4-nitrocathecol. Comparison of the rate coefficients with the case of initial pH 5 indicates that the p-nitrophenol degradation producing 4-nitrocathecol is more selective towards molec- ular ozone than the reaction producing hydroquinone. The identifiability and reliability of the estimated parameters,as well as the uncertainties involved in the model predictions are analyzed with the Markov chain Monte Carlo (MCMC) method.MCMC methods are Bayesian statistical methods that can be used for analyzing the distribution of parameters in nonlinear models in order to extend and supportthe information given by traditional regression analysis. © 2009 Elsevier Ltd. All rights reserved. 1. Introduction p-Nitrophenol is a commonly identified compound in waste waters of dye,textile and intermediary product industry,and be- longs to the EEC List I of hazardous pollutants and U.S.E.P.A. Prior- ity Pollutant List. Nitrophenol, and phenols in general,have been the subject of numerous studies of ozonation in recent decades (Adams et al., 1997; Masschelein and Goossens, 1984; Beltrán et al., 1992; Oturan et al.,2000; Guiza et al.,2004; Hsu et al.,2004; Shi et al., 2005 etc.), because of their toxicity and the supposed or proved carcinogenic effects on living organisms. The intermediates of the ozone–phenolreaction are quite wellknown, but the reac- tion schemes and particularly the reaction rate coefficients in the reaction schemes are poorly known. Ozone has been proven to be a very effective chemical for the degradation ofspecies that are persistent in biologicalwaste water treatment.However, the manufacturing of ozone requires large amounts of energy, which makes the optimization of ozonation processes necessary and the development of reliable hydrodynamic ∗ Corresponding author. Tel.: +358 5 621 2114; fax: +358 5 621 2199. E-mail address: markku.kuosa@lut.fi (M. Kuosa). 0009-2509/$ - see front matter © 2009 Elsevier Ltd.All rights reserved. doi:10.1016/j.ces.2009.02.014 and reaction kinetic models essential. The chemistry of ozonation in a water solution is complex.The reactions of ozonation involve di- rect molecular reactions of O 3 with dissolved compounds and trans- formation of O 3 into secondary oxidants, such as hydroxyl radicals (OH · ), hydroperoxyl radicals (HO · 2 ) and further compounds, such as · O − 3 , · HO 3 , etc. Modeling all these reactions requires large amounts of kinetic data,which is not necessarily available or applicable due to the different characteristics of waters. Therefore, the kinetic mod- elling of ozonation is usually limited to simplified models including chemicaloxygen demand (COD),BOC and TOC as lumped kinetic parameters. In an earlier study (Kuosa et al., 2007),a method was developed to estimate the reaction rate and stoichiometric coefficients ofa multicomponent reaction model in ozonation, taking also gas–liquid mass transfer and reactor hydrodynamics into consideration. How- ever,the data used in this earlier study was obtained from exper- imental runs without pH adjustment.The ozonation reactions are usually pH dependent.To remove the uncertainty concerning the effect of changing pH during the experiments, new experiments were carried out in the current study at the constant pH of 2. The devel- oped method was used to estimate the reaction kinetic parameters, rate coefficients and stoichiometric coefficients, as well as the volu- metric mass transfer coefficient. One purpose of the work was to try to find out whether pH has any effect on the reaction rates on each reaction path.