Simultaneous effects of pH, concentration, pressure on dye removal by a polyamide nanofilter membrane; optimization through response surface methodology

In this paper, the application of a thin-film composite Nanofiltration (NF) membrane with isoelectric point (IP) of 4.5 have been applied in textile wastewater treatment. Removal of acid blue 25, disperse red 73 and methylene blue dyes under operating conditions of initial concentration (40-180 mg/l), pH (3-10) and pressure (0.5-1.1 MPa) was investigated. Response surface methodology (Box-Behnken design) was employed to design runs and analyze the effects of operating parameters. According to the results, pH had the most significant impact on the removal efficiency of disperse red73 and acid blue 25 due to the electrical repulsive force and membrane swelling,while concentration had the most impact on methylene blue removal because of screening effect. NF removal performance showed removal enhancement to 91% and 92% at pH of 10 and concentration of 180 mg/l, for disperse red73 and acid blue 25, respectively while the maximum methylene blue removal efficiency of 86% was obtained at pH of 3 and 40 mg/l. The optimum pressure was observed at 0.8 MPa for disperse red and acid blue removal, while decreasing the pressure to 0.5 MPa showed better methylene blue removal.