Performance evaluation of nanofiltration membranes for treatment of effluents containing reactive dye and salt

The main purpose of this work is to investigate the preliminary performance of nanofiltration membranes for treatment of effluents containing salt and reactive dye. The membranes, designated as ES20, NTR-729HF, and LES90, were kindly supplied by the Nitto Denko Corporation. ES20 and LES90 are negatively charged membranes. NTR-729HF, a substituted poly(vinyl alcohol) membrane, is neutral. Regardless of the feeds, LES90 provided the highest permeate fluxes, while ES20 gave the lowest flux. ES20 and LES90 membranes achieved the higher salt rejection than NTR-729HF. LES90, however, suffered a great loss in the salt rejection as the concentration of NaCl increased. The dye rejections of ES20 and LES90 are sufficient for the reuse of the permeate. The neutral NTR-729HF membrane exhibited lower dye retention than the charged membranes. For the feed containing salt and dye, the superposition of trans-membrane osmotic pressure and concentration polarization resulted in substantial flux decline. Nevertheless, with the presence of dye in the feed, the charged membranes were able to retain more salt. It was likely that a highly concentrated layer formed by the accumulation of dye near the membrane surface attributed to the higher salt rejection. An increase in the feed temperature contributed to a slight increase in the LES90 flux while the salt and dye rejections remained almost unchanged.