Background, aim, and scope: The optimal conditions of o-toluidine degradation by fluidized-bed Fenton process were determined using Box-Behnken designs (BBD). The BBD can be used to find the optimal conditions in multivariable systems. The optimal conditions obtained by the design were further applied in the kinetic analysis of o-toluidine oxidation in fluidized-bed Fenton process.
Materials and methods: The 1.35-L fluidized-bed reactor used in all experiments was a cylindrical vessel with an inlet, outlet, and recirculation pump. The o-toluidine was determined by high-performance liquid chromatography.
Results and discussion: Analytical results indicated that pH, Fe(2+), and H(2)O(2) were significant factors in o-toluidine and chemical oxygen demand (COD) removal, but loading carrier was not. The pH significantly affected not only o-toluidine degradation, but also total iron removal. The predicted conditions for optimal removal of 1 mM of o-toluidine using 100 g of carriers were pH 3 ± 0.5, 1 mM of Fe(2+), and 17 mM of H(2)O(2). Removal of o-toluidine and COD in the actual experiment was higher than predicted, whereas removal of total iron was slightly lower. The kinetic study showed that the initial rate and rate constant (k) of o-toluidine degradation in the fluidized-bed Fenton process correlated Fe(2+) concentration. In the Fe(2+)/H(2)O(2) stage, high concentration of H(2)O(2) produced a scavenging effect.
Conclusions: The predicted removal efficiencies of o-toluidine and COD were 90.2% and 41.4%, respectively. Moreover, the removals of o-toluidine and COD in the actual experiment were 99.8% and 61.8%, respectively.