Efficiency of nanofiltration for the elimination of steroids from water

Steroid hormones such as the synthetic 17-alpha-ethinylestradiol often persist in the sewage treatment process and metabolites of the natural steroids like estrone from estradiol accumulate resulting in relevant amounts in the aquatic environment. Since biological removal of steroids in the sewage treatment plant is not successfully complete, physical processes such as membrane filtration may become more important. We investigated the elimination of natural and synthetic steroids by nanofiltration using a laboratory membrane reactor. Chemical analysis of 17-beta-estradiol, estrone, estriol, 17-alpha-ethinylestradiol, mestranol, diethylstilbestrol, progesterone and beta-sitosterine was performed after solid phase extraction by GC-MS with standard addition. The elimination rate depended on the nanofiltration membrane material. LFC1 membrane consisting of polyamide removed the steroids over 99% whereas PES10 membrane consisting of hydrolysed polyethersulfone was less efficient, obviously caused by different pore sizes and permeability of the membrane structure.