Photocatalytic decomposition of estrogens in aquatic environment by reciprocating immersion of TiO2-modified polytetrafluoroethylene mesh sheets

Photocatalytic decomposition of 17β-estradiol (E2) and estron (E1) in aqueous solutions was carried out by use of TiO2 photocatalysts immobilized on polytetrafluoroethylene (PTFE) mesh sheets and irradiated with black fluorescent lamps. The TiO2-modified PTFE mesh sheets were stacked in a 0.5 l (1 l=1 dm3) or 5 l beaker and were reciprocatively immersed in the range of 2–4 cm at the rate of 5–120 rpm. The first-order rate constant of E2 decomposition (initial concentration, 250 μg l−1) was proportional to the ratio of the surface area of the TiO2-modified PTFE mesh sheets to the volume of the treated water. It was also proportional to the square root of the reciprocation rate of the TiO2-modified PTFE mesh sheets, which was mainly due to mass-transfer limited condition. In addition, it was increased with increasing temperature, which was explained by the change of diffusion rate of E2 in water. About 90% of E1 in a practical discharged water was decomposed by using the 5 l reactor in 4 min with good reproducibility. Based on the results, application of this system to purification of discharged water at a sewage treatment plant could be expected.