Nanofiltration hollow fiber development for water softening

Abstract

Polyvalent cations, probably Mg2+ and Ca2+ are the main predominant contributors in hard water. They build up on contact surfaces, damage water heaters and causing high soap consumption which is bad in economic sense. Nanofiltration (NF) is a relatively new development in membrane technology and still under development. NF is created with the ability to reject macromolecules and divalent ions effectively at a relatively moderate operating pressure by combining the attributes of Reverse Osmosis (RO) and Ultrafiltration (UF). However, there is no existing membrane in the market provides efficient removal of divalent ions while producing high water permeation flux. Therefore, it is needed to develop NF membranes for water softening. The author was involved in assisting in the development of high performance of NF hollow fiber membranes suitable for water softening. Membrane separation tends to offer lower operating and by-product disposal costs, consuming relatively low energy consumption compared to conventional methods. Dual layer nanofiltration hollow fibers were produced, modified by cross-linking to increase its density and selectivity. Different cross-linking conditions were modified to evaluate the effects caused on the dual layer NF HFs. The optimum conditions to achieve best performances in this project, i.e. permeability (22.40 LMH) and rejection (91%) using 1000ppm Magnesium Chloride (MgCl2) Aqueous Solution was to cross-link with 1wt% High Molecular Weight Polyethylenimines (HMW PEI) for 1hour and followed by 1wt% Polycyclic Aromatic Hydrocarbon (PAH). The cross-linked dual layer hollow fibers has great potential for further modification to enhance membrane for more efficient for removal of hardness in water treatment.