Comparative analysis of reverse osmosis and nanofiltration for the removal of dissolved contaminants in water reuse applications

The increasing demand for drinking water has led to the adoption of unconventional water sources, such as water reuse. Reverse osmosis (RO) and nanofiltration (NF) membranes are effective barriers against trace organic contaminants in potable water reuse applications. However, the use of RO is being challenged by NF, primarily due to NF's potential to achieve similar contaminant removal as RO but with higher productivity and lower energy requirements. This study compares NF and RO membranes in terms of contaminant removal and energy consumption for potable water reuse applications. RO (BW30XFR) and dense and loose NF (NF90 and NF270) membranes were tested in bench-scale systems, and RO (TW30) and NF (NF9) membrane elements were tested in an engineering scale system utilizing UF-filtered reclaimed wastewater. The highest solute passage was observed using NF270 membrane. There was no difference between NF90 and BW30XFR in terms of divalent ion passage, but NF90's total organic carbon and monovalent ion passages were higher. Both NF90 and BW30XFR highly rejected negatively charged trace organic contaminants (TOrCs), though rejections were lower for neutral and positively charged compounds. Furthermore, all compounds were highly rejected in the engineering-scale system by NF9 and TW30. These results highlight the potential of dense NF membranes as an energy-efficient barrier for contaminant removal.