Cellulose Acetate-Based Membranes Recovered from Black-and-White Cinematographic Films for the Simultaneous Removal of Nitrate and Phosphate Anions from Water by Nanofiltration

Among the micropollutants of medium-depth waters in isolated inhabited areas, the inorganic ones deserve special attention: nitrate anion (NO₃⁻) and phosphate anions (HxPO4^⁻(3⁻x)). The individual removal of these anions from water is widely studied, with different methods being found: chemical, ion exchange or biological. This paper presents a membrane method for the simultaneous removal of nitrate anion and phosphate anions from dilute synthetic aqueous solutions. The developed method is nanofiltration using composite membranes made of cellulose acetate (CA) and silver nanoparticles (Agnp). The composite membranes were made by phase inversion of the dimethylformamide (DMF) solution containing the two components (CA–Agnp) on a polypropylene (PP) capillary fiber using deionized waster as a coagulant. The DMF solution of CA containing Agnp was obtained by dissolving black-and-white cinematographic films (exposed and unexposed to light). CA–Agnp–PP composite membranes were tested for the simultaneous removal of nitrate anion and phosphate anions from aqueous solution by nanofiltration at pressures ranging from 5 to 25 bars. A removal of over 98% of phosphate anions and more than 95% of nitrate anion was achieved. Fluxes of 10 L·m^⁻2·h^⁻1 were obtained for the working pressure of 15 atm, depending on the pH, flow rate and concentration of the feed water (feed solution). Variable parameters studied were also the concentration of CA and Agnp.