A comparison of novel ozone-based systems and photocatalysis for the removal of water pollutants

Three ozone-based systems and a photocatalytic system have been compared for the removal of a reactive dyestuff, orange RO16, and 2-chlorophenol in relation to degradation performances and ozone and energy consumptions. These systems were (1) liquid/gas–ozone (LGO): ozone was applied as it is produced in the gas phase; (2) liquid/solid–ozone (LSO): ozone was adsorbed on particulate silica-based material and then applied to water; (3) liquid/liquid–ozone (LLO): ozone was dissolved in a water-immiscible solvent and then applied to water; and (4) photocatalytic system using titanium dioxide catalyst (PHC). All four systems were capable of degrading the pollutants but presented different characteristics. The LSO system offered the possibility of using long contact times for slow ozone reactions and the LLO system is most suitable for fast ozone reactions. Both systems offer the prospect of more efficient use of ozone by extracting specific pollutants away from the water phase to the solid or the solvent phases. The PHC system presented the lowest rates and the highest energy consumptions by a factor of up to 400 times as compared to the ozone-based systems. The four systems were classified on the basis of their energy consumption as follows: for the degradation of RO16 (LLO