Reclamation of end-of-pipe textile effluent using low energy membrane systems

Abstract

In this study, the reclamation of end-of-pipe textile effluent originating from a reactive dyeing textile mill was investigated using low energy membrane based processes. Effluent quality, salt recovery and membrane recovery were the main parameters used to evaluate the membrane process. Flat sheets of the SR90 and NF90 Dow FilmTech nanofiltration (NF) membranes were used on a pilot scale membrane system. The UF multipore membrane was used in the pretreatment runs. The quality of reclaimed water was measured against the specified water quality in terms of the internal criteria for effluent recycle (ICFER) provided by the mill. It was required to optimize the SR90 and NF90 membrane performances so as to set operating parameters for pilot study. The average critical flux for the SR90 membrane was found to be ±31 LMH at 5 bar TMP when directly feeding the effluent without any pretreatment. The average critical flux for the NF90 membrane was found to be approximately ±15 LMH at 10 bar TMP when no pretreatment was used. All rejections were found to be >90% for all specified parameters as per Table 1. The quality results from the SR90 and NF90 membranes with pretreatment showed that the permeate could be recycled and reused in the dying processes within the mill. It was however concluded that the NF90 membrane produces high quality effluent as compared to the SR90. It was of importance to determine if the SR90 and NF90 membranes could be recovered and reused after directly feeding un-pretreated feed effluent. The flux recoveries on the SR90 and NF90 membranes were 84.72% and 82.17%, respectively after chemical cleaning. It was further concluded that the salt initially fed in the dying process could be recovered from the waste stream especially when using the SR90 membrane for reuse. However, the colour parameter was found to be slightly out of specification when using the SR90 membrane. To improve the colour of effluent produced when using the SR90, it was recommended that a granular activated carbon filter needs to be employed downstream of the process to polish the effluent.