Synthesis, characterization and performance assessment of thin film composite nanofiltration (TFC-NF) membranes for treating dyes wastewater

Abstract

In this study, the influence of dipping times of aqueous phase, reaction times in organic phase, and curing times on the preparation of thin film composite nanofiltration (TFC-NF) membranes were examined. Membranes were interfacially polymerized of m-phenelyne diamine and trimesoyl chloride on ultrafiltration membrane and then were characterized by means of permeability coefficient, charged solutes separation and membrane morphologies. All membranes characteristics are in the range of NF membrane. SEM micrographs show that most of the membranes have typical composite structure. The prepared membranes within 3 min dipping time (TFC-NF-D3), 30 sec reaction time (TFC-NF-R30) and curing time (TFC-NF-C15) reveal the superior charged solute separation with the trade off between permeate fluxes and rejections. These membranes were further investigated to obtain a general understanding of the possibility of membrane to separate the dye-based wastewater. Results indicate membranes have good quality of permeates (up to about 95%) and higher fluxes (1.957 to 17.977 m3/m2.s.bar) as well as to those observed with commercial membranes. Among the dominant obstacles of NF membrane process is the declination of flux over time. Therefore, the effect of dye concentration (100 mg/L, 200 mg/L, 300 mg/L and 400 mg/L) and dye - salt mixture concentration (0.1 g/L, 1.0 g/L and 10.0 g/L at fixed dye concentration of 100 mg/L) on the flux decline behavior of dye wastewater were examined. The membrane properties and the percentages of flux decline (total flux decline, irreversible and reversible fouling, and concentration polarization) were investigated to explain the flux decline behavior. The highest dye and dye -salt mixture concentration exposes that the most accelerates of flux decline, but the lowest flux recovery for all membranes. Fluxes were sharply decreased at the initial stage of filtration. It is believes that the flux decline behavior at this stage is controlled by the irreversible fouling (pore blockage and pore constriction mechanisms). When more dyes accumulated on the membrane surface, the flux decline mechanism transited to cake formation mechanism (reversible fouling). At this stage, a steady state was achieved. Thus, it is demonstrates that most of the filtration process was dominated by a reversible fouling.