Impacts of membrane properties on reactive dye removal from dye/salt mixtures by asymmetric cellulose acetate and composite polyamide nanofiltration membranes

Abstract

This paper aims to study fundamentally the impacts of membrane properties on the reactive dye removal from dye/salt mixtures by nanofiltration membranes. To begin with, two types of nanofiltration membranes of similar pore size, namely asymmetric cellulose acetate membrane and thin-film composite polyamide membrane were fabricated, and their key physical, chemical and performance properties were characterized. After that, these resultant membranes were employed to perform dye removal experiments with aqueous solutions of reactive black 5 and NaCl under different operational parameters. The dye removal rate and steady permeate flux were determined and correlated with the measured membrane properties. It was found that there were significant differences between the dye removal performances of the two membranes, and that the membrane properties played an important role in dye removal rate, stable permeate flux and their change behaviors under operational conditions. Surface charge was the most influential property for dye removal efficiency at low dye and salt concentration, while surface roughness was the most influential membrane property at high dye concentration or salt concentration. Additionally, the most influential membrane property which determines the change behavior of dye removal efficiency with pressure and cross-flow velocity was pure water permeability and surface roughness, respectively.