The aim of this work is to study the degradation kinetics of the endocrine disruptor benzyl butyl phthalate using ozone and UV radiation. The model comprises four parallel subsystems that are identified and isolated: (1) direct photolysis, (2) direct ozonation in the absence of hydroxyl radicals, (3) complete ozonation (direct + indirect oxidation), and (4) ozone + UV. To determine the nature of ozone attacks and the influence of ·OH radicals on O3 activity, two sets of experiments were performed: (i) conventional ozonation and (ii) the same ozonation experiments in the presence of tert-butanol as radical scavenger, where only the reactions involving molecular ozone are present. The explored variables were (i) ozone concentration, (ii) incident radiation rate at the reactor windows, (iii) reaction pH, and (iv) the presence of radical scavengers. Major intermediates of BBP degradation were identified. Degradation kinetics was correctly modeled by a pseudo-second-order kinetic model based on the sum of all the effects occurring during the treatment. The corresponding kinetic constants were obtained, and the relative contributions of each of the considered subsystems were evaluated.

This report presents a comprehensive study of the degradation kinetics of herbicide 2,4-D using ozone with and without intensification with UVC radiation. The by-products cause several seriesparallel reactions that compete with the process of photon absorption when radiation is applied.Five processes were analyzed separately: (i) the direct photolysis of 2,4-D and its main byproducts, (ii) direct ozonation in the absence of hydroxyl radicals using tert-butanol as radical scavenger, (iii) the oxidation when ozone reacts in parallel with hydroxyl radicals, (iv) the reaction enhanced with UVC radiation and (v) the oxidation improved by pH modifications.A kinetic model was developed based on the main reaction by-products. The corresponding parameters of the reacting system were determined (9 of its 29 kinetic constants were previously unknown).Simulation results, including a rigorous description of the reacting system and the radiation field (having dark and illuminated volumes) agree very well with the experimental data.

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This work presents a study focused on the development of a simple useful tool to predict the generation of trihalomethanes in drinking water purification systems, using two precursors and trichloromethane as model compounds through a simple chlorine decay model. This work proposed a semiempirical model without adjustable power parameters where fast and slow stages and the effect of pH were included. Despite that the model is not based in a complete kinetic scheme, using the proposed equations it is possible to predict the simultaneous evolution of chlorine and TCM with a set of linear kinetics parameters which characterize the system and will be obtained using simple routine laboratory measurements. The results show that both TCM formation and chlorine decay are strongly dependent on the chemical nature of the model precursor. Although resorcinol and phenol have different reactivity with chlorine and represent different functional groups which are present in natural compounds, the TCM generation appears to be properly described in both cases by the total chlorine consumption. Considering that during the potabilization processes the pH changes, the study of the effects of this variable is very important to achieve the minimization of THMs generation. The pH has a significant effect on the time evolution of chlorine-substituted hydroxybenzene intermediates and therefore on the TCM formation, since the properties of the reacting species are directly affected by the reaction medium for their participation in the different reaction paths. The study of the distribution and selectivity of the intermediate species allowed explaining the results obtained for the kinetics of formation of TCM. The results suggest that in order to understand the effect of pH, the nature of oxidation of HOCl and ClO‒, should be considered simultaneously with the electronegative nature of the precursor compounds. Finally, in terms of minimizing the generation of THM it is important to consider the potential impact of pH changes within the water treatment process and supply and the stages where chlorination may be carried out.