There is growing awareness and concern about the presence of so called micro-pollutants in our surface water and drinking water. Micro-pollutants are very small organic molecules (100-1000 Dalton) and stem from industrial, medicinal and agricultural waste. They have the potential to cause long-term harm to humans and the environment, something especially true for hormones that even at very low concentrations can have a significant negative effect on health and environment.
Techniques to remove these micro-pollutants from surface and drinking water are available but are currently too costly or inconvenient for the treatment of large streams of water. An example of this is the current state of art Reverse Osmosis (RO) treatment. These membranes were designed for desalination and have significant drawbacks. For proper operation at the high pressures needed for desalination, RO membranes have a thick active separation layer, resulting in low permeabilities and high resistance and thus a high energy demand for non-desalination applications. Furthermore, current RO membranes are very susceptible to fouling and to make matters worse, they have a low chemical stability against common cleaning methods employed in drinking water industry, e.g. chlorine treatment.
In this project we propose the development of a novel RO membrane specifically designed for the removal of micro-pollutants. For this we use the self-assembly of oppositely charged polyelectrolytes at the interface of a porous support membrane. In this so-called layer-by-layer assembly, the support membrane is alternatively exposed to polycations and polyanions, to build polyelectrolyte multilayers (PEMs) of controllable thickness. The properties of the PEM, responsible for the separation properties and resistance of the membrane, can be tuned by choice of polymer and by the employed coating conditions such as pH and ionic strength. This method thus allows the design of a membrane with optimal micro-pollutant removal, by careful choice of the density, charge density and hydrophilicity of the PEM.
PEM membranes are known to be much more resistant to chemical cleaning than current RO membranes. Additionally, the versatility of the layer-by-layer assembly allows the PEMs to be grown on a multitude of substrates, thus allowing its use for the development of hollow fiber RO. In this membrane geometry the membrane is much less susceptible to fouling. In combination with its increased resistance to chemical cleaning these novel PEM based RO membranes would allow for RO treatment without expensive pre-treatment.