Microfiltration/ultrafiltration as pretreatment for reclamation of rinsing waters of indigo dyeing

This paper focuses on the applicability of microfiltration (MF)/ultrafiltration (UF) as a pretreatment to nanofiltration (NF) for the reclamation of rinsing waters of indigo dyeing process. Two different MF alternatives, single 5 mm MF and sequential 5 mm'/0.45 mm MF, were evaluated as prefiltration to improve the performance of the proceeding UF stage. UF tests performed after 5 mm MF using 100 kDa, 50 kDa, 20 kDa, 2 kDa and 1 kDa membranes have indicated that all the UF membranes provided the same cumulative color retention of 98 Á 99%. However, in terms of COD retention, UF membranes presented different performances and the highest retentions were by both 50 kDa (56%) and 100 kDa (59%) membranes. As regards permeation rate, 100 kDa and 50 kDa UF membranes appeared to have the highest flux decline due to fouling. When sequential MF (5 mm'/0.45 mm) was adopted to decrease this fouling, 0.45 mm MF before UF was found not to provide any significant improvement. Thus, single stage 5 mm MF followed by 100 kDa UF was selected as the best prefiltration train to NF that permits the textile producer to reclaim indigo dyeing wastewater.

This paper presents a comparative study of MF/UF as prefiltration to NF in the reclamation of indigo dyeing rinsing waters. On the basis of the permeate flux and permeate quality, the best prefiltration scheme was selected. Results reported here indicate that all UF membranes tested having pore sizes ranging from 1 kDa to 100 kDa provided a high color retention (98 Á 99%) and the membrane having 100 kDa MWCO was found to be the most suitable UF membrane, for prefiltration to NF considering its high flux, and COD and conductivity retentions. 5 mm MF prefiltration showed the best performance as a prefiltration alternative for the UF of rinsing waters of indigo dyeing process. No improvement in wastewater fluxes and COD, color and conductivity retentions were obtained for second prefiltration alternative (5 mm' 0.45 mm MF) when compared to the first one (5 mm MF). /