Performances of NF and RO applied in combined system and separately for the treatment and recycling of biologically pretreated real textile wastewater

In this study, integrated membrane systems represented by Ultrafiltration/Nanofiltration (UF/NF), Ultrafiltration/Reverse Osmosis (UF/RO) and direct Nanofiltration (D/NF) and Reverse Osmosis (D/RO) applied separately at a semi pilot scale were investigated for the treatment and reuse of biologically pretreated real textile wastewater. The separation performances taking into account the operating pressure (TMP) and flux recovery ratio (FRR) was extensively investigated. Long-term performance of the membrane systems separation was analyzed as well.Accordingly NF and RO can achieve high separation performances with good permeate. The fouling study shows that the FRR at the optimal pressures of 8 bar for NF and 10 bar for RO was higher than 90%.

When using UF as pre-treatment under optimal TMP of 3bar, the application of the hybrid UF/NF and UF/RO systems allows a decrease of the TMP from 8 bar to 6 bar for NF and from 14 bar to 12 bar for RO. An enhancement of the permeate flux respectively of 36% and 29% has been also achieved.Both hybrid processes showed good antifouling characteristics with a permeate flux maintained at almost constant value since the first minutes of filtration of 44 L/h.m² at 6bar for UF/NF and 42 L/hm² at 10 bar for UF/RO.

Taking into account the water process quality usually used in the company in terms of chemical oxygen demand (COD), chloride and Total Dissolved Solids (TDS) content, the UF/NF process is effective enough to provide water of reuse quality for dyeing using reactive dyes with the protocol usually used by the company.