Micropollutant Sorption to Membrane Polymers: A Review of Mechanisms for Estrogens
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Date
2011Author
Schäfer, Andrea
Akanyeti, Ime
Semião, Andrea J.C.
Metadata
Abstract
Organic micropollutants such as estrogens occur in water in increasing quantities from
predominantly anthropogenic sources. In water such micropollutants partition to surfaces such as
membrane polymers but also any other natural or treatment related surfaces. Such interactions are
often observed as sorption in treatment processes and this phenomenon is exploited in activated
carbon filtration, for example. Sorption is important for polymeric materials and this is used for the
concentration of such micropollutants for analytical purposes in solid phase extraction. In
membrane filtration the mechanism of micropollutant sorption is a relative new discovery that was
facilitated through new analytical techniques. This sorption plays an important role in
micropollutant retention by membranes although mechanisms of interaction are to date not
understood. This review is focused on sorption of estrogens on polymeric surfaces, specifically
membrane polymers. Such sorption has been observed to a large extent with values of up to 1.2
ng/cm2 measured. Sorption is dependent on the type of polymer, micropollutant characteristics,
solution chemistry, membrane operating conditions as well as membrane morphology. Likely
contributors to sorption are the surface roughness as well as the microporosity of such polymers.
While retention – or and reflection coefficient as well as solute to effective pore size ratio – control
the access of such micropollutants to the inner surface, pore size, porosity and thickness as well as
morphology or shape of inner voids determines the available area for sorption. The interaction
mechanisms are governed, most likely, by hydrophobic as well as solvation effects and interplay of
molecular and supramolecular interactions such as hydrogen bonding, π-cation/anion interactions,
π-π stacking, ion-dipole and dipole-dipole interactions, the extent of which is naturally dependent
on micropollutant and polymer characteristics. Systematic investigations are required to identify
and quantify both relative contributions and strength of such interactions and develop suitable
surface characterisation tools. This is a difficult endeavour given the complexity of systems, the
possibility of several interactions taking place simultaneously and the generally weaker forces
involved.