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

In this study the secondary effluent after ODOBEZ system processing from a textile dyeing factory was recycled and 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, )E, 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.

The reclamation of industrial textile wastewater from secondary effluent by applying the combined system of a bio-activated carbon reactor and membrane separation module has two major advantages compared to conventional activated carbon or reverse osmosis. This integrated system can not only reduce the frequency of back-washing and replacement of activated carbon through special bio-augmentation, but also can alleviate damage and fouling of membranes due to further reductions in COD, suspended solids and color by BAC, which lengthens the lifetime of membranes. In addition to recycled and reused wastewater in the dye bath, the final concentrated retentate after processing with this integrated system meets the stipulated regulations and can be discharged directly. As a result, this system can save a huge amount of water by reducing reclamation costs and offers the benefit of sustainable development for the textile dyeing industry. The cost to reclaim wastewater for processing per cubic meter was estimated to be about 9.14 $NTD/m3, which is definitely competitive as compared to the price of drinking water at 11– 13 $NTD/m3 in Taiwan.