Carbonaceous decomposition of a recalcitrant effluent treated by the photo-Fenton process: a kinetic approach

Natural effluents with marked variation in their chemical composition over decomposition time in the matrix from which they are generated have a complex composition and are not totally known in most cases. Landfill leachate can be considered an effluent with complex composition, requiring imminent and more comprehensive studies on organic load degradation. Such complexity of numerous organic compounds (most of them recalcitrant humic and fulvic substances) demands a large number of kinetic equations to satisfactorily describe the temporal evolution of such conversion. Thereby, this work aims to study a kinetic approach grounded on previously consolidated chemical reactions of radical generation through the photo-Fenton mechanism. A molar balance was developed for each species in a batch photo-Fenton process and the resulting ordinary differential equations were numerically solved in MATLAB(TM). The kinetic model satisfactorily described an organic load conversion of the effluent under the various experimental conditions studied herein. Experimental trends could be represented by a free-radical mechanism and a degradation rate equation of first order for organic carbon, hydroxyl radical and H+. The model fittings revealed a hydroxyl radical/organic carbon stoichiometric ratio of 2:1. The kinetic study has confirmed the importance of pH levels for the reaction medium, and indicated that degradation rate depends on the medium organic composition, which provided an exponential function of conversion for the degradation rate coefficient. The model simulations corroborated the positive effect of sunlight on the radical generation through decomposition reaction with a rate coefficient in the range 4 x 10(-3)-2 x 10(-1) s(-1). [GRAPHICS] .