Mechanism and role of partitioning in removal of organics by RO and NF composite membranes

Strong partitioning in polyamide negatively affects the rejection of organic contaminants in RO and NF filtration. The effect may be significant for larger contaminants having low solubility in water. In extreme cases this may counterbalance the sieving effect and limit the applicability of RO/NF to removal of moderately hydrophobic substances (e.g., hormones, nonyl phenol, etc). The hydrophobicity of polyamides is good for salt rejection, yet it may be unfavorable in removal of organics. To date, the main effort has been directed towards optimal membranes for desalination, but a larger diversity of membranes (e.g., in terms of polarity) might be necessary to achieve optimal rejection for different classes of organics.