Reuse of textile wastewater for dyeing cotton knitted fabric with hybrid treatment: Coagulation/sand filtration/UF/NF-RO.

The aim of this study was to investigate the usefulness of a membrane hybrid process for the treatment of real textile wastewater (TWW) and its potential reuse in the dyeing of cotton knitted fabric (DCF) process. To determine a suitable pretreatment, sand filtration, coagulation, and UF hollow fiber (UF-HF) were compared on a laboratory scale in terms of turbidity, color, and total organic carbon (TOC). Here, UF-HF provided the best removal results of 93.6%, 99.0%, and 29.0%, respectively. The second stage involves the study of UF flat sheet membranes (5, 10, 20, and 50 kDa). The 5 kDa membrane provided the best permeate quality according to the chemical oxygen demand (COD), turbidity, TOC, conductivity, and color by 54.5%, 83.9%, 94.2%, and 45.7-83.3%, respectively. The final step was treatment with nanofiltration (NF) and reverse osmosis (RO) and these effluents were reused for dyeing. Finally, the effluents from UF-HF/5 kDa UF/RO (Scenario 1) and UF-HF/5 kDa UF/NF (Scenario 2) were analyzed for turbidity, COD, TOC, biological oxygen demand, conductivity, hardness, anions and cations, and color. Both scenarios provided high removal results of 76.3-83.5%, 94.6-97.7%, 88.5-99%, 95.4-98.0%, 59.2-99.0%, 88.7-98.7%, 60.7-99.1%, and 80.0-100%, respectively. They also satisfied the DCF tests compared to the standard DCF samples. The innovative aspect of this research is as follows: 1) the complete analysis of hybrid membrane separation processes for the purpose of reuse of treated textile wastewater and 2) the proposal of a new criterion for reuse for DCF.