Treatment of effluents from textile-rinsing operations by thermally stable nanofiltration membranes

Thermally stable nanofiltration membranes were used to recover hot water from rinsing effluents from acid and reactive dyeing operations. Two types of flat-sheet membranes, MPF-34 (MWCO 200) and MPF-36 (MWCO 1000), were tested at 60°C and 10 bar. Experiments carried out with the made-up feeds containing acid dye and acetic acid showed that both membranes were able to retain more than 99% of dye. MPF-36 suffered from substantial flux decline due to the dye and acid in the feeds but still provided higher fluxes than MPF-34. Furthermore, reactive dye rejection of MPF-36 was acceptable, ranging from 97 to 99.5%, while the fluxes, 105–140 l/m2.h, were exceptionally high. MPF-36 was then further tested with the wastewater from industrial processes. The membrane could recover hot water by removing more than 98% of acid dye and 90% of reactive dyes. Despite severe fouling by acid dye, the membrane was still able to provide 40–50 l/m2.h of permeate fluxes. For the reactive dye rinsing effluents, remarkably high fluxes of 120–150 l/m2.h were obtained. Chemical cleaning of the used membrane with 0.2% wt. HNO3 and subsequently 0.5% wt. NaOH recovered 80–100% of the flux.

The capability of thermally stable NF membranes, MPF-36 (MWCO 1000) and MPF-34 (MWCO 200), to treat wastewater from washing operation in textile dyeing was evaluated. MPF-36 had a remarkably high water flux of 212.4 l/m2.h, while the flux of MPF-34, 27.9 l/m2.h, was notably lower. Results obtained from the feeds prepared in laboratory revealed that MPF-36 significantly suffered from flux decline due to the presence of 0.1 %wt. acetic acid in the feed. Even so, its flux was still higher than that of MPF-34. Both membranes efficiently retained acid and reactive dyes. However, the treated water from MPF-36 contained a significant amount of NaCl and acetic acid and likely required another treatment to recover these compounds. Since MPF-36 provided higher fluxes, it was further tested with industrial effluents. The membranes continued to show exceptionally high fluxes because wastewater from actual rinsing operation was dilute. More than 98% of acid colors and 90% of reactive dyes were removed from the treated water, accompanied with the reduction of SS and COD. Based on the experiments, both membranes are capable of producing permeate of reusable quality. The ability of MPF-36 to provide very high flux and acceptable rejection at high operating temperature made it more attractive to the recovery of energy from the wastewater. However, as characteristics of effluents vary greatly because dyeing processes use a wide range of dye classes, techniques and equipment, the use MPF-36 is specific to type of the effluent.