Optimized nanofiltration for tertiary desalination

Optimized nanofiltration for tertiary desalination

jahnpng

 

In the next decades water scarcity will be a global challenge and thus purification of waste water will become more relevant. Membrane separation processes are already well established in the drinking water industry, but for some water sources (e.g. waste water) the selectivity still needs to be improved. Nanofiltration (NF) membranes have a pore size of ~1 nm which corresponds to a molecular weight cut-off of 300-500 g/mol. The selectivity of a NF membrane can be described by the SEDE (steric, electric and dielectric exclusion) model [1]. Yet for charged species the Donnan effect can have the biggest influence and is mainly dependent on the surface charge, which has impact on the rejection behavior. For example, a negatively charged membrane surface results in a low rejection of divalent cations such as Ca2+ and Mg2+, what can be beneficial when treated saline waste water shall be used for irrigation [2].

In this work we aim to fabricate high flux membranes with an as low as possible rejection for highly charged species (e.g. Mg2+, Ca2+), but keep the rejection for monovalent (Na+) ones at least 50 %. The potential of a rather easy approach toward such nanofiltration membranes via grafting strong cation-exchange polymer layers with high charge density on suited ultrafiltration membranes [3] will be explored first. More promising, but also more challenging is the preparation of charge mosaic membranes, which consist of positively and negatively charged domains in the membrane’s barrier layer. To obtain such charge mosaic membranes, polymeric nanogels with a high charge density are prepared and subsequently be embedded in a polyelectrolyte layer on a suited porous support membrane.

References

  1. S. Bason, Y. Kaufman, V. Freger, J. Phys. Chem. B 2010, 114, 3510
  2. S. Levchenko, V. Freger, Envir. Sci. Techn. Lett. 2016, 3, 339
  3. R. Bernstein, E. Antón, M. Ulbricht, ACS Appl. Mater. Interf. 2012, 4, 3438

Funding

This work is supported by the German Ministry of Education and Research within the “German-Israel Water Technology Cooperation” (project number 02WIL1488).

Contact:
Philipp Jahn