NAMS 2002 Workshop - ICOM 2008

Nanofiltration and Reverse Osmosis III - Applications – 3
Friday July 18, 10:45 AM-11:15 AM, Maui
Investigation of Amphoteric Polybenzimidazole (PBI) Nanofiltration Hollow
Fiber Membrane for both Cation and Anion Removal
J. Lv, National University of Singapore, Singapore
K. Yu Wang (Presenting), National University of Singapore, Singapore
T.-S. Chung, National University of Singapore, Singapore - chencts@nus.edu.sg
High levels of harmful ions in the surface and ground waters have become a
major health problem in many countries. Harmful anions removal can be
achieved by adsorption, precipitation and electrocoagulation, ion exchange and
extraction. Membrane separation processes have been proven to be a feasible
and promising option for the removal of toxic ion species. Using nanofiltration
(NF) membranes to remove toxic species of wastewater has also been carried
out. Generally, positively-charged NF membranes are only effective for cations
removal, whereas negatively- charged NF membranes are only effective for
anions removal. In this study, the removal of both anions (phosphate, arsenate,
arsenite and borate ions) and cations (copper ions) has been investigated by
employing a lab-developed amphoteric polybenzimidazole (PBI) nanofiltration
(NF) hollow fiber membrane. The amphoteric characteristics are due to the
imidazole group within PBI molecules that makes the PBI NF membrane having
an isoelectric point near pH 7.0 and shows different charge signs based on the
media pH. Investigations on the rejection capability of typical anions, e.g.
phosphate, arsenate, arsenite, borate anions and typical heavy metal cations,
e.g. copper ions, reveal that the PBI NF membrane exhibits impressive rejection
performance for various ion removals. However, their rejections are strongly
dependent on the chemical nature of electrolytes, solution pH and the feed
concentrations. The experimental results are analyzed by using the Speigler-
Kedem model with the transport parameters of the reflection coefficient and the
solute permeability (P) with the aid of molecular model and ion sizes. The PBI NF
membrane may have potential to be used in industrial removal of various
environmentally- unfriendly ion species.