Removal of natural hormone estrone from secondary effluents using nanofiltration and reverse osmosis

Abstract

The rejection of steroid hormone estrone by nanofiltration (NF) and reverse osmosis (RO) membranes in treated sewage effluent was investigated. Four NF/RO membranes with different materials and interfacial characteristics were utilized. To better understand hormone removal mechanisms in treated effluent, effluent organic matters (EfOM) were fractionated using column chromatographic method with resins XAD-8, AG MP-50 and IRA-96. The results indicate that the presence of EfOM in feed solution could enhance estrone rejection significantly. Hydrophobic acid (HpoA) organic fraction made a crucial contribution to this “enhancement effect”. Hydrophobic base (HpoB) could also improve estrone rejection while hydrophobic neutral (HpoN) and hydrophilic acid (HpiA) with low aromaticity had little effects. The increment in estrone rejection was predominantly attributed to the binding of estrone by EfOM in feed solutions, which led to an increase in molecular weight and appearance of negative charge (for the HpoA case) and thus an increased level of estrone rejection. However, the improvement of estrone rejection by HpoA decreased with increasing calcium ion concentration. The important conclusion of this study is, first, hydrophobic acid macromolecules are recommended to be added into feed water to improve the rejection of trace hormone during NF/RO membrane process, and, second, removal of calcium ions via pretreatment and application of membrane with more negative charge at its interface can greatly intensify this “enhancement effect”.