Degradation of naphthalene-1,5-disulphonate in a flow reactor.: Modelling via reduced dimensionless centered variables

Abstract

This paper reports on a cylindrical concentric photochemical immersion-type reactor capable of degrading naphthalene 1,5-disulphonate, a non-biodegradable pollutant in the Rhine river. This study reports on the influence of the chemical parameters affecting the degradation, mixing conditions and processes taking place in the liquid being continuously replaced near the light source. A process mediated by Cu 2+ / Fe 2+ ions analogous to the Haber–Weiss cycle was found to be the system of choice for the substrate degradation. The optical absorption of the iron chromophore and not the intensity of the applied light was observed to be the most important factor determining the kinetics and efficiency during the degradation of the substrate. The degradation of the pollutant was studied in the 20–200 TOC (mg C l −1) range. The photon flux of the actinic sources used varied between 0.8 and 3.1×10 16 photons s −1 cm −2. Experimental evidence is provided to the effect that no saturation effects were observed during reactor operation taking into account the concentration of the absorbing chromophore and photon flux in the reactor during the degradation experiments. The reactor volume of the mixing flask unit used was 2.33. The solution parameters used during flow mode operation made use of the experimental data found during the optimization of reactor batch mode operation. A single exponential function was constructed for the treatment of the experimental data to optimize the most economical use of chemicals, electrical energy and time to degrade a given amount of pollutant. This function allowed to predict the TOC values taking into consideration five of the chemical parameters affecting the degradation by way of reduced centered dimensionless variables. These variables significantly contributing to substrate degradation have been identified and modeled through contour plots and surfaces in two and three dimensions (2D, 3D). The abatement of the pollutant up to almost complete disappearance of the substrate was susceptible to modelization. The correlation factor between experimental and values predicted by the exponential function was better than 95% as computed by the appropriate analytical function. The sulfo-groups play an important role in the recalcitrance of naphthalene 1,5-disulphonate. These sulfo-groups are seen to be rapidly removed by the pretreatment used allowing the substrate to reach biocompatibility in a few minutes.