Abstract:
Photocatalytic treatment of humic acids as model compounds representing natural organic present in drinking water sources has been studied since 1996. Considering the diverse nature of humic substances, continuous efforts should be directed to the elucidation of the photocatalytic degradation efficiency of humic substances from different origins i.e. terrestrial and aquatic humic acids. The performance of the humic photocatalytic system could be evaluated by selected parameters of UV-vis and fluorescence spectroscopic methods as well as chemical parameters as DOC measurements. The efficiency of photocatalytic treatment was presented by the application of pseudo first order and Langmuir Hinshelwood (L-H) kinetic models. Discussion was presented with reference to the previously studied model humic substances, humic and fulvic acids of various origins. The shape of UV-vis spectra of FHA and NHA obtained prior to treatment was similar to the photocatalytically oxidized humic acids’, as declining with increasing wavelength. While terrestrial humic acid had remarkably higher Color436 absorbance than the aquatic humic acid, UV254 absorbance was found to be close to each other. While 89 % of Color436 removal attained for FHA, 98 % of Color436 elimination was achieved for NHA by 60 minutes of irradiation. Additionally, UV254 observed to be reduced 73 % for FHA and 75 % for NHA. Correspondingly, DOC content of FHA and NHA were significantly removed by photocatalytic oxidation process. Moreover, fluorescence spectra of raw and oxidized humic acids were beneficial for extensive assessment of photocatalytic oxidation products. Removal rate of Color436 parameter was found to be always faster than UV254 removal as well as DOC, estimated by pseudo first order and L-H kinetic models. On the other hand, the increasing trend of the L-H rates was similar to that of first order rates, although L-H rates were approximately half the value of the pseudo first order rates of Color436, UV365, UV280 and UV254.
