de Grooth, Dr.Ir. J. (Joris)

Novel Polymeric Membranes for Water Purification

There is a growing need for novel water purification concepts based upon membrane filtration. Emerging pollutants such as hormones, antibiotics, bisphenol A etc., may over time cause severe health problems [1]. Current water purification concepts, based upon e.g. ultrafiltration hollow fibre membranes, are not designed to remove these so-called endocrine disrupting chemicals (EDCs). This problem is however not limited to UF only, even nanofiltration membranes with a molecular weight cut-off of 200 and reverse osmosis have a low rejection to some of these EDCs [2]. The main reason for this is that retention is not based solely on molecular weight, but on a combination of size, hydrophilicity and charge.

In addition, most of the existing nanofiltration membranes are based on either poly amides or cellulose acetate. Major drawback of these membrane materials is their low chlorine stability. This severely reduces the possibilities for disinfection, and subsequently their application for potable water production.

These new demands however require a novel membrane concept, be it UF, NF or RO, that can cope with these challenges while keeping a relatively high output.

The membranes will have a hollow fiber geometry (see Figure 1 for a example) and need to be chlorine stable. Hollow fiber geometries are desired as compared to spiral wound modules, hollow fibers will be less susceptible to (bio)fouling and need less (or no) pre-treatment.

Title: Figure 1 - Description: Cross section of a hollow fiber NF membrane

Figure 1: Cross section of a hollow fiber NF membrane.

When reducing the pore size of a membrane (from UF to NF to RO), separation will shift from (pore)size driven towards a solution diffusion type of process. This transition partly overlaps with the area of application of NF. This grey transition area is the focus of the project and will be further investigated in order to get a better understanding of the molecular dynamics during membrane synthesis and operation. It also aids in getting insight in, predict and improve the retention of differently charged contaminants, which is another issue that will be addressed. Hollow fiber membranes with different charges and variable charge densities will be prepared starting from commodity polymers (such as PEEK or PES). Next to this, novel polymers will be synthesized as well.

References:

  1. De Voogt, P., et al., Development of a common priority list of pharmaceuticals relevant for the water cycle. Water Science and Technology, 2009. 59(1): p. 39-46.
  2. Yangali-Quintanilla, V., et al., Proposing nanofiltration as acceptable barrier for organic contaminants in water reuse. Journal of Membrane Science, 2010. 362(1-2): p. 334-345.