Rejection of geosmin and 2-methylisoborneol by polyamide membranes in drinking water treatment: Performance-energy efficiency evaluation and practical implications.

Polyamide nanofiltration (NF) and reverse osmosis (RO) membranes hold a great promise to address the challenge of taste and odor (T&O) compounds such as geosmin (GSM) and 2-methylisoborneol (2-MIB) in drinking water treatment. These NF/RO membranes have varied physicochemical properties that can lead to discrete separation performance accompanied by different specific energy consumption (SEC). Nevertheless, the effects of membrane properties on the trade-off between rejection of T&O compounds and SEC remain unclear. Herein, we characterized the properties of four commercial NF/RO membranes (NF270, NF90, ESNA1-K1, and XLE) and evaluated their separation performance in both synthetic and real water. The results revealed that GSM and 2-MIB rejection by all membranes is primarily governed by size exclusion. A smaller membrane pore size (e.g., XLE membrane) led to a higher rejection of the compounds but also accompanying with a higher SEC. In contrast, a large pore size (e.g., NF270 membrane) resulted in low SEC yet less effective rejection. Such severe trade-off between SEC and rejection would limit the energy-effectiveness of the membrane. A more balanced rejection-SEC is favorable, e.g., ESNA1-K1 achieved >98 % rejection for both GSM and 2-MIB with a low SEC of 0.17 kWh/m³. Further correlation analysis suggested that membrane O/N ratio and pore size had strong relevance with SEC and rejection of T&O compounds, respectively. In addition, membrane fouling resulted in reduced rejection due to the aggravated concentration polarization although that membrane water flux was mildly affected. Our findings can provide essential guidance on membrane selection and optimization to achieve energy-effective rejection of T&O compounds in membrane-based drinking water treatment.