Pre-ozonation for high recovery of nanofiltration (NF) membrane system: Membrane fouling reduction and trace organic compound attenuation

This study demonstrated the use of nanofiltration (NF) membrane with pre-ozonation for surface water brine treatment. Pre-ozonation, used for fouling control, with relatively low ozone doses (0.1-0.4 mg O-3/mg DOC ratios) significantly reduced organic fouling potential. A classical pore blocking model revealed that the dominant fouling mechanism was cake filtration. Based on a statistical correlation test, macromolecules (apparent molecular weight > 10 k Da) of typtophan-like aromatic protein and soluble microbial-like matter exhibited strong correlation to fouling potential. Small molecules (< 1600 Da) of UV-absorbing matter were also correlated with fouling potential whereas bulk parameters such as SUVA displayed relatively lower correlation with fouling potential. Trace organic compound (TOrC) attenuation by ozone, membranes, and combination of ozone and membranes were also examined. Greater than 70% removal of the 17 TOrCs was achieved at 0.4 mg O-3/mg DOC ratio. The NF membrane (NF90) alone also could remove more than 90% of TOrCs. When pre-ozonation was performed with the NF membrane, all TOrCs tested were removed to less than the limits of detection. In conclusion, the application of pre-ozonation to NF membrane not only can alleviate organic fouling potential, but also can function as a dual barrier for ensuring removal of TOrCs for water treatment.