(TKP2021-NKTA-21) Támogató: Nemzeti Kutatási, Fejlesztési és Innovációs Hivatal
The increasing demand for nanofiltration processes in drinking water treatment, industrial
separation and wastewater treatment processes has highlighted several shortcomings
of current state-of-the-art thin film composite (TFC NF) membranes, including limitations
in chemical resistance, fouling resistance and selectivity. Polyelectrolyte multilayer
(PEM) membranes provide a viable, industrially applicable alternative, providing significant
improvements in these limitations. Laboratory experiments using artificial feedwaters
have demonstrated selectivity an order of magnitude higher than polyamide NF, significantly
higher fouling resistance and excellent chemical resistance (e.g., 200,000 ppmh chlorine
resistance and stability over the 0–14 pH range). This review provides a brief overview
of the various parameters that can be modified during the layer-by-layer procedure
to determine and fine-tune the properties of the resulting NF membrane. The different
parameters that can be adjusted during the layer-by-layer process are presented, which
are used to optimize the properties of the resulting nanofiltration membrane. Substantial
progress in PEM membrane development is presented, particularly selectivity improvements,
of which the most promising route seems to be asymmetric PEM NF membranes, offering
a breakthrough in active layer thickness and organic/salt selectivity: an average
of 98% micropollutant rejection coupled with a NaCl rejection below 15%. Advantages
for wastewater treatment are highlighted, including high selectivity, fouling resistance,
chemical stability and a wide range of cleaning methods. Additionally, disadvantages
of the current PEM NF membranes are also outlined; while these may impede their use
in some industrial wastewater applications, they are largely not restrictive. The
effect of realistic feeds (wastewaters and challenging surface waters) on PEM NF membrane
performance is also presented: pilot studies conducted for up to 12 months show stable
rejection values and no significant irreversible fouling. We close our review by identifying
research areas where further studies are needed to facilitate the adoption of this
notable technology.
