Photodegradation of steroid-hormone micropollutants in a flow-through membrane reactor coated with Pd(II)-porphyrin

Abstract

The efficient degradation of steroid-hormone micropollutants is demonstrated in a single-pass, continuous operation of the photocatalytic membrane reactor (PMR) holding a visible-light excited Pd(II)-porphyrin-coated poly(vinylidene fluoride) microfiltration membrane. The PMR operated at a water flux of 600 L m−2 h−1 exhibited a residence time of 0.6 s and significant removal of 17ß-estradiol and estrone at environmentally relevant (ng L−1) concentrations, when treated either individually (R = 85 ± 5 %) or as a mixture of estrone, 17ß-estradiol, testosterone and progesterone. The highest 17ß-estradiol removal achieved at a water flux 60 L m−2 h−1ensured the concentration in the permeate of 2 ng L−1. At alkaline pH, the photodegradation process was inhibited by the repulsion between the ionized 17ß-estradiol molecules and the membrane surface. An increase in a water flux through the PMR decreased the removal, but favoured the rate of disappearance. The rate constant for reactions of singlet oxygen with 17ß-estradiol (7·108 M−1 s−1) at ng L−1 concentrations was close to the diffusion limit. This study provides the new insights into solar-driven photocatalytic water treatment technologies for effective removal of micropollutants.