Reclamation of textile dyeing wastewater for process use via a highly efficient integration system

Abstract

In this study the secondary effluent after ODOBEZ system processing from a textile dyeing factory was recycledand reused in a dyeing bath. A pilot-scale combined system of a bio-activated carbon reactor (BAC) and membrane separation module (MS) was constructed and studied in detail. Through the efficacies of adsorption as well as biodegradation in BAC, the quality of secondary effluent can be improved further, and then it can be reclaimed and reused in a dyeing bath by using a membrane separation module to reduce the conductivity of the wastewater. This integrated system not only can decrease the frequencies of back washing and replacement of activated carbon via special bio-augmentation, but also alleviate the damage and fouling of membrane due to the further reductions in chemical oxygen demand (COD), suspended solids and color of influent after BAC; this lengthens the lifetime of membranes. In addition to the recycle and reuse fraction of the secondary wastewater in a dyeing bath, the final concentrated retentate after processing in this integrated system meets the stipulated regulations and can be discharged directly with no additional treatments. Once the COD of secondary inflow falls in the range of 100–200 mg/L, the COD of outflow after BAC can be reduced to the range of 50–80 mg/L with a hydraulic residence time of 4 h. In this situation the percentage of water reclamation can reach above 50%, and the final concentrated retentate can be discharged directly. The results of the dyeing tests by using recycling water showed that color deviation indexes, ΔE, were always less than 0.5, which was the criterion for laboratory-scale dyeing tests. After almost a year of operation, a detailed economics assessment was made, and it was found that a total cost 9.14 $NTD was enough to reclaim per cubic meter textile wastewater to a dyeing bath, which included costs in membrane replacement, activated carbon replacement, reagents for membrane washing and power consumption.