Comparison of caffeine oxidation by Fenton reagent in combination with UV light and ultrasound waves

The oxidation of aqueous caffeine solutions ([Ca]0=100.0 mg L-1) was analysed, operating at pH=3.0 and 25ºC using different AOPs, which combine the Fenton reagent ([H2O2]0=15.0 mM and [Fe2+]0=20.0 mg L-1) with low power UV light (15W,), medium (150W), and high (720 W). The Fenton reagent, combined with 150W UV light, was the most energetic treatment, proving that at 20 min it completely degrades caffeine and 80% of the water aromaticity. This hard oxidative process is accompanied by a high oxygen consumption, up to concentrations of [DO]=0.9 mg L-1 at the time when the caffeine contained in the water is completely degraded. On the other hand, 150W UV light is the only treatment capable of decreasing the concentration of total solids dissolved in water, according to a ratio of 0.0035 min-1. US waves allow degrading caffeine by 35%. This treatment leads to the emission of high oxygen concentrations ([DO]=20.0 mg L-1), which subsequently decreases along time. The UV lamp of 15W allows degrading caffeine by 12%, but does not affect the rest of the parameters analysed.