Advanced Water Production via Point of Use Super‐Ultralow‐Pressure Reverse Osmosis and Cellulose‐Polyamide Thin‐Film Nanocomposite Membranes

Abstract A novel thin‐film nanocomposite reverse osmosis (RO) membrane was developed for point‐of‐use applications (POU‐RO) at super‐ultralow pressure (0.2 MPa), incorporating carboxymethylated cellulose nanofibers (CM‐CNF). The CM‐CNF with an increased number of oxygen‐containing functional groups that positively impacts water flux, salt rejection stability, antifouling characteristics, and resistance to chlorine degradation compared to commercial RO‐PA membranes. Transmission electron microscopy (TEM), combined with geodesic and skeletonized image analysis, revealed that the average thickness of the PA/CM‐CNF membrane is 1050 nm corresponding to more than four leaf‐like layers, significantly higher than commercial membranes, which typically show fewer than two layers. Moreover, a void‐free active layer is created, providing excellent substrate coverage. Tests with CaCl₂ at 0.2 MPa showed 93.9% salt rejection and a water permeation rate of 0.93 m/d, doubling the performance of commercial membranes. Dynamic simulations confirmed the influence of CM‐CNF on enhancing water diffusion at low pressure (0.2 MPa). POU‐RO tests, conducted using a 2‐inch spiral module fabricated in the laboratory, confirmed the superior performance of the CM‐CNF membrane. Indeed, high recovery rates (>60%) and high permeation rates (close to 0.7 m/d) have been achieved by the membranes. This performance is twice than the commercial counterparts tested at 0.2 MPa.