(454f) Natural Organic Matter Fouling Behaviors on Superwetting Nanofiltration Membranes

Authors: 
Ji, S., Beijing University of Technology
Zhang, G., Beijing University of Technology

Natural
organic matter fouling behaviors on superwetting nanofiltration
membranes

Linglong
Shan, Hongwei Fan, Hongxia Guo, Shulan Ji and Guojun Zhang

Beijing
Key Laboratory for Green Catalysis and Separation, College of Environmental and
Energy Engineering, Beijing University of Technology, Beijing, China. Email: shanlinglong@126.com

In
natural water, natural organic matter (NOM) components have been identified as precursors
of disinfection by-products. Nanofiltration has been widely recognized as a promising
technology to remove NOM from natural water. Currently, the most challenging aspect
is the often inevitable occurrence of membrane fouling, which is caused by NOM
accumulation on the membrane surface, as in NOM removal in drinking water
treatment and production. NOM fouling is considered to be governed by the
interface relationship between NOM and the membrane surface in aqueous
solution. Much work has been carried out, but the effect of hydrophilicity/-phobicity
of NOM and the membrane surface on fouling behavior is still a controversial
issue.
[1-7]

The controversy originates from the unilateral consideration of membrane
wettability or foulant hydrophilicity/-phobicity, when in fact both need to be
considered. In our study, both superhydrophilic and superhydrophobic membranes
with stable structure have been successfully obtained using two facile hybrid
approaches (see
Fig. 1).The fouling behavior of
NOM on superwetting nanofiltration membranes has been extensively investigated
using humic acid (HA: model foulant) and real natural water. The extended
Derjaguin-Landau-Verwey-Overbeek (XDLVO) approach and nanoindentor scratch
tests suggested that the superhydrophilic membrane had the strongest repulsion
force to HA due to the highest positive ¦¤GTOT value and the lowest
critical load. Excitation emission matrix analyses
of natural water also indicated that the superhydrophilic membrane showed
resistance to fouling by hydrophobic substances and therefore high removal
thereof. Conversely, the superhydrophobic membrane showed resistance to fouling
by hydrophilic substances and therefore high removal thereof (see Figs. 2 and 3). Long-term operation
suggested that the superhydrophilic membrane had high stability due to its
anti-NOM fouling capacity, which is crucial for practical
application. Based on the different anti-fouling properties of the studied
superwetting membranes, a combination of superhydrophilic and superhydrophobic
membranes was examined to further improve the removal of both hydrophobic and
hydrophilic pollutants. The RUV254 and RDOC could be
increased to 83.6% and 73.3%, respectively, by a combination of
superhydrophilic and superhydrophobic membranes. In view of the hydrophilic and
hydrophobic NOM fouling behaviors on superwetting membrane surfaces, the
superwetting strategy can be regarded as a very important approach for
obtaining a membrane with both high NOM rejection and good anti-NOM fouling
properties.  

Keywords: Superhydrophilic,
Superhydrophilic, Nanofiltration, NOM, Fouling

References

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Figure
1.
(a)
Schematic illustration of the preparation of the superhydrophilic membrane and
its surface wettability; (b) schematic illustration of the preparation of the
superhydrophobic membrane and its surface wettability.

Figure
2.
Schematic
illustration of different
anti-fouling properties of the studied superwetting membranes. Superhydrophilic
membrane showed resistance to fouling by hydrophobic substances, while the
superhydrophobic membrane showed resistance to fouling by hydrophilic
substances.

Figure
3.
EEMs
for (a) natural water; (b) natural water nanofiltrated by superhydrophilic membrane;
(c) natural water nanofiltrated by hydrophilic membrane; (d) natural water
nanofiltrated by hydrophobic membrane; (e) natural water nanofiltrated by
superhydrophobic membrane; (f) natural water nanofiltrated by superhydrophilic
membrane-superhydrophobic membrane.