Reclamation of printing effluents of a carpet manufacturing industry by membrane processes

The effluent from the print dying process of a carpet manufacturing industry was subjected to nanofiltration (NF) and ultrafiltration (UF) processes aiming at water reuse. Three alternatives were adopted; (i) NF, (ii) loose UF (MWCO 20,000 Da) followed by NF and (iii) tight UF (MWCO 1000 Da) followed by NF. The separation performances and flux decline levels were compared for the detemination of the best process. Printing effluent was chemically precipitated using alum and fed to a lab-scale plate-and-frame membrane module under a trans-membrane pressure of 1.75 × 105 and 5.90 × 105 Pa (1.75 and 5.90 bar) for UF and NF processes, respectively. All the alternatives were tested in concentration mode of filtration where a volume reduction factor of up to 28.5 was achieved. The NF process provided very high separation performance for COD, color, turbidity, total solids and total hardness. The flux decline started at 16% and reached up to 31% at a volume reduction factor of 11.8. The loose and tight UF processes applied before NF to reduce this flux decline were not effective with a very severe flux decline of about 60% in both processes. The comparison resulted in a recommendation with single stage NF with adequate effluent characteristics.