Evaluation of Caffeine Degradation by Sequential Coupling of TiO2/O3/H2O2/UV Processes

This study provides new insight into the implementation and synergy effect of coupling in sequences of the photocatalysis ([TiO 2 -UVC]), ozone (O 3 ) and hydrogen peroxide (H 2 O 2 ) applied to degradation and mineralization of a model compound such as caffeine (in synthetic solution and industrial wastewater). The system consists of an annular photoreactor coupled to two venturi valves with a continuous dosage of O 3 and H 2 O 2 , the combination of binary processes such as O 3 /H 2 O 2 , TiO 2 /O 3 and UVC/H 2 O 2 was evaluated, as well as the coupling of TiO 2 /O 3 /H 2 O 2 /UVC in order to estimate all the possible synergy effects. It was found that the coupling between photocatalysis and hydrogen peroxide shows a negligible performance of caffeine treatment in both synthetic and real wastewater because the reaction rate, degradation and mineralization of caffeine does not improve considerably compared to the photocatalysis process alone. Meanwhile, the coupling between photocatalysis and ozonation shows the highest synergy effect. The coupling of all the processes evaluated TiO 2 /O 3 /H 2 O 2 /UVC achieved 100% degradation of caffeine, but the mineralization was lower than photocatalysis coupled with ozonation. This could be due to the peroxide and ozone compete by active sites of the catalyst and can also act as scavengers of oxidizing species, hindering the caffeine mineralization. The results show that the combination of photocatalysis with ozone and peroxide can make a synergy effect for industrial wastewater treatment.