Removal of antibiotics and estrogens by nanofiltration and reverse osmosis membranes

The separation behavior of a variety of emerging contaminants, including nine antibiotics and six estrogens commonly reported in natural environment, by four commercial nanofiltration and reverse osmosis (NF/RO) membranes at various water conditions (pH, concentration) was investigated. The contaminant rejection at pH 6.0 followed a decreasing trend of XLE (94%-100%) approximate to NF90 (88%-100%) > NF270 (25%-85%) > DL (16%-75%). The dense structures of NF90 and XLE reflected by their small effective pore radii (0.30-0.31 nm) contributed mainly to their high rejection, demonstrating the important role of size exclusion. For the negatively charged loose NF270 and DL membranes (0.40-0.45 nm), charge repulsion made additional contribution, which is markedly reflected by their greater rejection to charged antibiotics than neutral estrogens (45%-85% vs. 25%-60% by NF270). The correlation between rejection data and normalized molecular sizes at pH 4.0 and 9.0 intuitively demonstrated the individual role of size exclusion and charge repulsion. The adsorption by membranes was mainly responsible for the initial compound reduction in feedwater by 6%-25% within 3 h, while only 0.3%-5.6% was attributed to self-degradation. The adsorption capacity was determined, which might be mainly governed by hydrophobic interaction. The resolved controlling factors and mechanisms will contribute to the accurate prediction and membrane selection for trace contaminant removal by membrane process.

Automated summary

The separation behavior of emerging contaminants using commercial nanofiltration and reverse osmosis membranes was investigated. The study found that the physical structure and charge characteristics of the membranes played a crucial role in contaminant rejection, and adsorption was an important mechanism for contaminant removal.