Kinetics of fulvic and humic acids photodegradation in water solutions

The results of the study on photodegradation of fulvic (FA) and humic (HA) acids via photolysis and photocatalysis in water environment are presented in this work. The experiments were carried out in Heraeus reactor in which simulated waters containing fulvic acids by Beijing Multigrass Formulation Co. Ltd. and humic acids by Sigma Aldrich were treated. Titanium dioxide TiO2 (P25) by Degussa was used as a catalyst. The impact of presence/absence of the catalyst (photocatalysis/photolysis), water pH (pH 3.5; 7.0 and 10), catalyst dose (from 0.025 to 0.60 gTiO2/L) and contaminants (FA, HA) concentration on the photooxidation effectiveness was checked. The change in molecular mass distribution was investigated using HP-SEC method. The rate of organic contaminants (FA, HA) oxidation was determined on the basis of values of basic water parameters i.e. DOC, UV254, color. The oxidation rate constants of fulvic and humic acids were evaluated using Langmuir–Hinshelwood (L–H) method, which enabled a detailed description of the photodegradation run. Higher reaction rates and shorter half-lives were found for fulvic acids in comparison with parameters determined for humic acids.