Removal of paraquat in aqueous suspension of TiO₂ in an immersed UV photoreactor

Experiments were performed to investigate the effect of operating parameters on the photodegradation efficiency of paraquat in a TiO₂-suspended photoreactor with immersed UV lamps. TiO₂ particles were prepared by a hydrothermal method. The removal rate of paraquat in the reactor was 0.54 mg/l/h with only air-sparging. The removal rate in 24 h with both the UV radiation and air-sparging was 50% higher than that with only the UV radiation. Variations of the paraquat concentration at the UV intensities of 4 and 8 W/m² decreased slowly with time, but that at 12 W/m² decreased more rapidly. The removal efficiency at the air-sparging flow rate of 1 l/min increased as a UV light intensity increased. pH value in the reactor at the UV intensity of 12 W/m² decreased with time until 12 h and then increased with time over 12 h.