Testing of Drinking Water Treatment Co–Polymers for Compatibility with Polyamide Reverse Osmosis Membranes

摘要

Cationic polymers used in traditional drinking water treatment, in theory, will bind to the partially negatively charged polyamide membrane during reverse osmosis (RO) treatment. This paper tested a variety of cationic, anionic, and non-ionic polymers in terms of (1) aiding in turbidity removal when used in conjunction with alum coagulation (10 mg/L as Al_2(SO_4)_3•14 H_2O), sedimentation, and dual-media filtration, and (2) their binding affinity towards a polyamide membrane. Binding affinity was tested by exposing polyamide RO membranes to 50 mg/L of each polymer for 48 hrs and then conducting attenuated total reflectance Fourier-transform infrared (FT-IR) spectroscopy on the membrane samples and principal component analysis (PCA) of the FT-IR spectra. Results from the turbidity removal tests showed that cationic polymers provided the lowest median effluent turbidity (0.03 – 0.11 NTU), followed by anionic polymers (0.06 –0.08 NTU), and finally non-ionic polymers (0.11 – 0.17 NTU). While PCA of the FT-IR spectra did detect differences in polymer-exposed membranes versus a control, no discernable difference in RO membrane performance was observed. Therefore, the issue of ‘membrane poisoning’ caused by organic polymer absorption onto polyamide membranes may be minimal.