Reuse of reverse osmosis concentrate in textile and dyeing industry by combined process of persulfate oxidation and lime-soda softening

Abstract

The advanced oxidation technology dominated the disposal of reverse osmosis concentrate in textile and dyeing industry due to its extremely low biodegradability. For resource conservation and sustainable development, the reverse osmosis concentrate was reused in dyeing procedure after being treated properly with combining method of persulfate oxidation and lime-soda softening. Firstly, the refractory organics was oxidized by persulfate thermal activation and the results indicated that the most efficient and economical reaction happened with initial pH = 5.0, 1000 mg/L initial persulfate concentration and 75 °C. In this process, chemical oxygen demand degradation fitted the pseudo-first-order model well and the sodium sulfate concentration increased from 9600 to about 10,350 mg/L. Then, the hardness of reverse osmosis concentrate including Ca2+ and Mg2+ hardness was softened efficiently by lime-soda softening technology and appropriate lime and soda concentration was determined to be 150 mg/L and 800 mg/L, respectively. Finally, the effluent was employed as the dyeing water to test the reuse feasibility in dyeing of reactive dyes. Color strength, color difference and color fastness were all used to evaluate the dyeing performance and dyeing results showed that the effluent which was treated properly (COD ≤ 21.5 mg/L, total hardness ≤17.0 mg/L) was available for reuse in reactive dyes dyeing procedure. The study provided a novel method to treat and reuse reverse osmosis concentrate and more importantly, it promoted sodium sulfate concentration and saved its supplementation and dyeing cost in dyeing procedure.