Concentration and desalination of NT dye solutions by nanofiltration were studied experimentally with a spiral-wound nanofiltration membrane element. The decrease of permeation flux and increase of the observed NaCl rejection were observed due to the formation of the gel layer and possibly the precipitate layer on the membrane surface due to the high bulk NT concentration. By analyzing concentration polarization of NaCl at the membrane-solution interface, a simple empirical correlation between the permeation flux and the interfacial mass transport coefficient was obtained and coupled with a simplified S-K model for prediction of concentration and desalination of NT solutions. The concentration polarization was investigated using the simplified model that complied with the theoretical understanding. Several operations were compared, which resulted in an optimized technology for potential field implementation.