Photocatalytic degradation kinetics of humic acid in aqueous TiO₂ dispersions: the influence of hydrogen peroxide and bicarbonate ion

The degradation of humic acid in water by means of photocatalytic method has been studied. The influence of hydrogen peroxide and bicarbonate has also been investigated. The kinetics of the photocatalytic degradation of humic acid in various concentrations (50-500 mg/L) has been followed by the determination of TOC, COD and UV-vis spectra of the reaction solution. While the pseudo first order rate constants of 50 mg/L humic acid were found 0.016, 0.03 and 0.036 for TOC, Color₄₀₀ and UV₂₅₄, the degradation rate constants for these parameters were found 0.029, 0.069 and 0.057 in the presence of 1×10⁻²M H₂O₂. The Langmuir-Hinshelwood kinetic has also been sucessfully applied to the photocatalytic degradation data. It was found that bicarbonate ions slowed down the degradation rate by scavenging the hydroxyl radicals. Low pH value has been found to be favorable for color removal in the absence of hydrogen peroxide whereas natural pH gave the best results for color removal in the presence of hydrogen peroxide.