Fouling behavior and performance of a submerged flat-sheet nanofiltration membrane system for direct treatment of secondary wastewater effluent

Direct nanofiltration (NF) of secondary treated effluent can significantly simplify water recycling, especially for small scale operations. This study evaluated the performance of a novel flat-sheet submerged NF membrane module at low water flux to minimize membrane fouling. The separation performance of the NF system was assessed by periodically measuring the color, turbidity, pH, UV light absorbance at the wavelength of 254 nm, and total organic carbon concentrations of the NF feed water and permeate. During the 48-d test, negligible membrane fouling was found when direct NF treatment of secondary wastewater effluent was conducted at a water flux of 3 L/m2h. The trans-membrane pressure increased by less than 0.072 kPa/d. The foulant layer on the membrane surface was readily removed by simple physical cleaning, which suggests that the reversible fouling was the major fouling mechanism. Direct NF treatment achieved high and stable removal of organics (total organic carbon removal of >80 %) during the operation period. This study demonstrated the efficacy of the direct NF treatment using a submerged NF module for achieving stable operations and producing high-quality recycled water