Nanofiltration of contaminated water and wastewater using membrane modules reconfigured from commercial spiral-wound elements

Abstract

Submerged nanofiltration (NF) membrane treatment can be an attractive approach for water purification because advanced drinking water treatment can be performed at a low energy consumption without pre-treatment. This pilot-scale study aimed to evaluate the feasibility of employing flat-sheet NF membrane modules, adapted from commercial 4-inch spiral-wound elements, to scale up the direct NF treatment of polluted water for the first time. The pilot-scale submerged NF systems operated at a transmembrane pressure of approximately 50 kPa, directly filtering municipal secondary-treated wastewater and zoo pond water as feed sources for over 46 and 99 days, respectively. The initial permeate flux for the secondary-treated wastewater effluent was 1.1 L/m²h, which was half of the 2.0 L/m²h flux for the zoo pond water. This discrepancy is attributed to the high salinity (e.g., high osmotic pressure difference) of the secondary-treated wastewater effluent. Over time, the permeate flux gradually declined due to membrane fouling but eventually stabilized for both feed waters. Despite variations in the quality of the feed water during the experiments, the permeate quality met high water quality standards. This study highlights the potential of direct NF treatment using reconfigured commercial NF membrane modules for sustainable urban water cycle management.