Photocatalytic Oxidation of Toluene in Water From an Algae Pond With High Dissolved Oxygen Content

Water in well-mixed ponds containing photosynthetic algae has been observed to have an extremely high Dissolved Oxygen (DO) content. Up to four times saturation levels of DO have been recorded. Since DO is known to have an important role in the photocatalytic oxidation of organic contaminants in water, it was hypothesized that a faster rate of contaminant destruction would be observed in water drawn from algae ponds supersaturated with DO. In order to verify this hypothesis a bench scale, batch type photoreactor was constructed. Some baseline tests were performed to investigate the influence of UV intensity, water pH and DO content on the photocatalytic destruction of toluene in water. An array of ultraviolet “blacklight” lamps in a lamp box was used to simulate solar ultraviolet radiation. First-order reaction rate constants were calculated from the destruction data, using a kinetic model proposed earlier. The reaction was found to proceed forward equally fast at pH 4 and 10. A power law relation was derived for the reaction rate dependence on UV intensity. Presence of DO in the water was found to be required for the reaction to go forward. Water from an algae pond, supersaturated with dissolved oxygen was spiked with toluene and destruction tests were then conducted in the same reactor. These tests did not show the expected improvement in destruction rates.