Abstract :
A comparative study of the photocatalytic activity of two different TiO2 catalysts in solar photocatalytic oxidation, mineralization
and detoxification of waters containing herbicides 2,4-dichlorophenoxyacetic acid (2,4-D), bentazon and toxic intermediates was performed
in a pilot plant scale photoreactor. Commercial TiO2 (Degussa P25) and TiO2 synthesized by citrate sol–gel method (ECT-
1023t) were selected as photocatalysts. The optimal basic operational parameters to eliminate these herbicides and toxic intermediates
were established for both catalysts at laboratory scale. ECT-1023t showed better photocatalytic activity than the commercial Degussa
P25 at solar pilot plant scale with both herbicides in real water at natural pH (6.8–7.8) without any additive. The toxicity of the treated
solutions was evaluated using the Microtox test based on the inhibition of bioluminescence of the bacteria Vibrio fischeri. The toxic effect
of the main intermediate of 2,4-D, the 2,4-dichlorophenol (2,4-DCP), was higher than the parental herbicide. Acute toxicity of 2,4-D and
intermediates (2,4-DCP) was reduced during the photocatalytic treatment by using ECT-1023t as photocatalyst. Longer times were necessary
to obtain similar results when using P25 as photocatalyst. No inhibitory growth effect of the herbicide bentazon and its photoproducts
on Vibrio fischeri bacteria bioluminescence was observed for either photocatalyst in any of the irradiated samples collected
at predetermined times using an initial concentration of 0.1325 mM of the herbicide.
2012 Elsevier Ltd. All rights reserved.
