Poly(vinylidene fluoride) membrane with immobilized TiO2 for degradation of steroid hormone micropollutants in a photocatalytic membrane reactor.

The lack of effective technologies to remove steroid hormones (SHs) from aquatic systems is a critical issue for both environment and public health. The performance of a flow-through photocatalytic membrane reactor (PMR) with TiO2 immobilized on a photostable poly(vinylidene fluoride) membrane (PVDF-TiO2) was evaluated in the context of SHs degradation at concentrations from 0.05 to 1000 µg/L under UV exposure (365 nm). A comprehensive investigation into the membrane preparation approach, including varying the surface Ti content and distribution, and membrane pore size, was conducted to gain insights on the rate-limiting steps for the SHs degradation. Increasing surface Ti content from 4 % to 6.5 % enhanced the 17ß-estradiol (E2) degradation from 46 ± 12-81 ± 6 %. Apparent degradation kinetics were independent of both TiO2 homogeneity and membrane pore size (0.1-0.45 µm). With optimized conditions, E2 removal was higher than 96 % at environmentally relevant feed concentration (100 ng/L), a flux of 60 L/m2h, 25 mW/cm2, and 6.5 % Ti. These results indicated that the E2 degradation on the PVDF-TiO2 membrane was limited by the catalyst content and light penetration depth. Further exploration of novel TiO2 immobilization approach that can offer a larger catalyst content and light penetration is required to improve the micropollutant removal efficiency in PMR.

Photocatalytic degradation of steroid hormone micropollutants by TiO2-coated polyethersulfone membranes in a continuous flow-through process.

Micropollutants in the aquatic environment pose a high risk to both environmental and human health. The photocatalytic degradation of steroid hormones in a flow-through photocatalytic membrane reactor under UV light (365 nm) at environmentally relevant concentrations (50 ng l-1 to 1 mg l-1) was examined using a polyethersulfone-titanium dioxide (PES-TiO2) membrane. The TiO2 nanoparticles (10-30 nm) were immobilized both on the surface and in the nanopores (220 nm) of the membrane. Water quality and operational parameters were evaluated to elucidate the limiting factors in the degradation of steroid hormones. Flow through the photocatalytic membrane increased contact between the micropollutants and ·OH in the pores. Notably, 80% of both oestradiol and oestrone was removed from a 200 ng l-1 feed (at 25 mW cm-2 and 300 l m-2 h-1). Progesterone and testosterone removal was lower at 44% and 33%, respectively. Increasing the oestradiol concentration to 1 mg l-1 resulted in 20% removal, whereas with a 100 ng l-1 solution, a maximum removal of 94% was achieved at 44 mW cm-2 and 60 l m-2 h-1. The effectiveness of the relatively well-known PES-TiO2 membrane for micropollutant removal has been demonstrated; this effectiveness is due to the nanoscale size of the membrane, which provides a high surface area and facilitates close contact of the radicals with the very small (0.8 nm) micropollutant at an extremely low, environmentally relevant concentration (100 ng l-1).