Effects of the H₂O₂ concentration and spectral distribution of the UV lamp output power on the photooxidation of a water pollutant

Previous kinetics studies have been extended to analyze some practical issues concerning this process. Hence, in this work we have studied additional aspects of the H₂O₂ enhanced, UV degradation of 2,4-dichlorophenoxyacetic acid (2,4-D), namely: (i) the effect of the H₂O₂/2,4-D initial molar ratio and (ii) the effect of the irradiation power and, particularly, the characteristics of the wavelength distribution of the lamp output emission. The work was done on a well stirred, discontinuously operated tank reactor irradiated from its bottom. A UV, tubular lamp and a cylindrical reflector of parabolic cross section were used [actually, two germicidal lamps (254 nm) of different output power per unit lamp length and a medium pressure, mercury arc lamp with polychromatic emission between 220 and 760 nm]. 2,4-D concentration and TOC were the main variables used to investigate the degradation rate. There is an optimal initial concentration ratio for each 2,4-D initial concentration. It was also observed that increasing the lamp output power at 254 nm (output from 0.08 W/cm to 0.6 W/cm) favors the reaction rate. However, much more significant is the effect produced by employing a polychromatic lamp with some emission below 254 although this photonic contribution is relatively small (just 0.21 W/cm below 250 nm). A kinetic model, having parameters independent of the reactor configuration and derived from mechanistic considerations was used to analyze the experimental data.