Membrane separation process for the treatment and reuse of bath dye effluents

Abstract

The main purpose of this work is to study the effect of sodium chloride concentration on the removal by nanofi ltration of anionic dyes in synthetic colored wastewaters and to characterise some main performances and properties of nanofi ltration membranes of different properties. Membranes Sepa DK and NF90 were used for the study and were operated at constant transmembrane pressure. The anionic dyes, Direct Red 80 (1373 g/mol) and Acid Orange G (452 g/ mol), were used at a fi xed dye concentration for different salt concentrations. Results indicated that effects of pH, concentrations of salt have a role on the permeate fl ux and dye retention for single and mixed salt dye solution. An interesting result is that retention of Orange G is enhanced and becomes high (96%) in the presence of salt. NF 90 shows a better salt rejection than Sepa DK, for the same salt and dye concentrations. The Orange G retention increases when the pH decreases from 9 to 3. For NF90, Orange G retention is about 98%, whatever the pH. NF90 achieves the higher salt retention than Sepa DK, however, a great loss in the permeate fl uxes is observed as the concentration of NaCl increased.