The influence of t-butanol on multicomponent reaction kinetics and mass transfer in p-nitrophenol ozonation is Studied at pH 2. The rate coefficients and mass transfer coefficient k(L)a are estimated with nonlinear parameter estimation. Different reaction kinetic models were used to exclude the possible effect of the model on the obtained k(L)a when using data from solutions with different t-butanol concentrations. Two of the reaction kinetic models include residual COD, which is the total COD from which the COD of the known species is subtracted. It Could be determined that the presence of t-butanol in the solution increases the hold-up and k(L)a. Evidence suggesting that radicals have a noticeable role in p-nitrophenol ozonation kinetics at low pH was found. The reliability and identifiability of the estimated parameters are Studied. (C) 2009 Elsevier B.V. All rights reserved.