(380a) Zwitterionic Nanofiltration Membranes for the Removal of Harmful Algal Toxins from Lake Water

Microcystin toxins such as Microcystin-LR (MCLR) pose a significant threat to human health due to their high toxicity levels. These toxins have become increasing in various bodies of water, including Lake Fayetteville. The state of Arkansas follows the EPA regulations that state swimming advisories should be issued if Microcystin-LR (MCLR) can be detected at levels greater than 8 μg/L. According to Arkansas Department of Environmental Quality, MCLR has been detected at levels up to 50 μg/L in Arkansas water bodies. Nanofiltration (NF) is a practical treatment strategy for this toxin based on size, however NF is known to be susceptible to fouling, particularly when used in practical settings with complex fouling profiles. To address these issues this study evaluates the efficacy of a zwitterionic modified nanofiltration membrane. The primary objective is to determine the membrane's capability to selectively reject MCLR molecules from both synthetic water and real lake water samples.

The zwitterionic polymer polyetheleneimine- sulfobetaine methacrylate (PEI-SBMA) was synthesized through a Michael addition reaction. The resultant product was purified by 1 kDa dialysis tube for 2 days and further purification carried out with freeze-drying. Membrane modification was done through N-ethyl-N′-(3-(dimethylamino) propyl) carbodiimide/N-hydroxysuccinimide (EDC/NHS) process activation and followed by 1% PEI-SBMA grafting on the activated membrane. The resulting membrane was characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), contact angle analysis and X-ray photoelectron spectroscopy (XPS) to confirm the zwitterionic addition.

Modified and unmodified nanofiltration membranes were tested using a dead-end filtration cell (Sterlitech, Auburn, WA, USA) with a model solution containing 10-100 ppb MCLR. The MCLR rejection of zwitterionic nanofiltration membrane and fouling were compared with two NF membranes BW 30 and NF 270 (Dow Chemical, Midland, MI, USA). The lake water collected from the Fayetteville Lake, Arkansas studied with both modified and unmodified membranes. Fouling was assessed by monitoring membrane flux throughout the experiment. To study the antifouling properties of the modified membranes, the natural organic matter (NOM) model foulants such as bovine serum albumin and alginate were studied in a crossflow filtration cell for long-time run. Membrane performance experiments were repeated with the modified membrane and compared to the bare membrane’s performance for both synthetic and real water solutions.

Significantly, the rejection of microcystin LR experiences a substantial increase for the modified membranes in comparison to pristine NF 270. The rejection values increased from 71% to 95%.

Additionally, a notable significant flux decline was observed in both the unmodified NF 270 and BW 30 membranes, where the flux nearly dropped to 30% within a 30-minute timeframe using NF 270 (Figure 8a), and to less than 1 mL/min consistently with BW 30. In contrast, the modified membranes (NF M1 and NF M2) exhibited a comparatively moderate decline, ranging from 15% to 18%. This relatively lower flux decline in the developed membranes is a positive indication of their robust performance. The modified membrane demonstrates a superior fouling resistance when subjected to testing with NOM’s.

This project focused on the development of fouling-resistant membranes utilizing zwitterionic polymers. The efficacy of these modified membranes was investigated for both synthetic microcystin removal and use with real lake water containing microcystin. The results demonstrated that the zwitterionic polymer-modified membrane (NF M1) exhibited good fouling resistance and microcystin removal efficiency compared to the commercial membranes. This enhancement in performance suggests the potential of these developed membranes for real lake water purification particularly in addressing challenges related to fouling and microcystin removal.